Odin/src/check_stmt.cpp

gb_internal bool is_diverging_expr(Ast *expr) {
	expr = unparen_expr(expr);
	if (expr->kind != Ast_CallExpr) {
		return false;
	}
	if (expr->CallExpr.proc->kind == Ast_BasicDirective) {
		String name = expr->CallExpr.proc->BasicDirective.name.string;
		return name == "panic";
	}
	Ast *proc = unparen_expr(expr->CallExpr.proc);
	TypeAndValue tv = proc->tav;
	if (tv.mode == Addressing_Builtin) {
		Entity *e = entity_of_node(proc);
		BuiltinProcId id = BuiltinProc_Invalid;
		if (e != nullptr) {
			id = cast(BuiltinProcId)e->Builtin.id;
		} else {
			id = BuiltinProc_DIRECTIVE;
		}
		return builtin_procs[id].diverging;
	}
	Type *t = tv.type;
	t = base_type(t);
	return t != nullptr && t->kind == Type_Proc && t->Proc.diverging;
}
gb_internal bool is_diverging_stmt(Ast *stmt) {
	if (stmt->kind != Ast_ExprStmt) {
		return false;
	}
	return is_diverging_expr(stmt->ExprStmt.expr);
}

gb_internal bool contains_deferred_call(Ast *node) {
	if (node->viral_state_flags & ViralStateFlag_ContainsDeferredProcedure) {
		return true;
	}
	switch (node->kind) {
	case Ast_ExprStmt:
		return contains_deferred_call(node->ExprStmt.expr);
	case Ast_AssignStmt:
		for_array(i, node->AssignStmt.rhs) {
			if (contains_deferred_call(node->AssignStmt.rhs[i])) {
				return true;
			}
		}
		for_array(i, node->AssignStmt.lhs) {
			if (contains_deferred_call(node->AssignStmt.lhs[i])) {
				return true;
			}
		}
		break;
	case Ast_ValueDecl:
		for_array(i, node->ValueDecl.values) {
			if (contains_deferred_call(node->ValueDecl.values[i])) {
				return true;
			}
		}
		break;
	}

	return false;
}

gb_internal void check_stmt_list(CheckerContext *ctx, Slice<Ast *> const &stmts, u32 flags) {
	if (stmts.count == 0) {
		return;
	}

	if (flags&Stmt_CheckScopeDecls) {
		check_scope_decls(ctx, stmts, cast(isize)(1.2*stmts.count));
	}

	bool ft_ok = (flags & Stmt_FallthroughAllowed) != 0;
	flags &= ~Stmt_FallthroughAllowed;

	isize max = stmts.count;
	for (isize i = stmts.count-1; i >= 0; i--) {
		if (stmts[i]->kind != Ast_EmptyStmt) {
			break;
		}
		max--;
	}
	isize max_non_constant_declaration = stmts.count;
	for (isize i = stmts.count-1; i >= 0; i--) {
		if (stmts[i]->kind == Ast_EmptyStmt) {
			// Okay
		} else if (stmts[i]->kind == Ast_ValueDecl && !stmts[i]->ValueDecl.is_mutable) {
			// Okay
		} else {
			break;
		}
		max_non_constant_declaration--;
	}

	for (isize i = 0; i < max; i++) {
		Ast *n = stmts[i];
		if (n->kind == Ast_EmptyStmt) {
			continue;
		}
		u32 new_flags = flags;
		if (ft_ok && i+1 == max) {
			new_flags |= Stmt_FallthroughAllowed;
		}

		u32 prev_stmt_flags = ctx->stmt_flags;
		ctx->stmt_flags = new_flags;

		check_stmt(ctx, n, new_flags);

		ctx->stmt_flags = prev_stmt_flags;

		if (i+1 < max_non_constant_declaration) {
			switch (n->kind) {
			case Ast_ReturnStmt:
				error(n, "Statements after this 'return' are never executed");
				break;

			case Ast_BranchStmt:
				error(n, "Statements after this '%.*s' are never executed", LIT(n->BranchStmt.token.string));
				break;

			case Ast_ExprStmt:
				if (is_diverging_stmt(n)) {
					error(n, "Statements after a diverging procedure call are never executed");
				}
				break;
			}
		} else if (i+1 == max_non_constant_declaration) {
			if (is_diverging_stmt(n)) {
				for (isize j = 0; j < i; j++) {
					Ast *stmt = stmts[j];
					if (stmt->kind == Ast_ValueDecl && !stmt->ValueDecl.is_mutable) {

					} else if (stmt->kind == Ast_DeferStmt) {
						error(stmt, "Unreachable defer statement due to diverging procedure call at the end of the current scope");
					} else if (contains_deferred_call(stmt)) {
						error(stmt, "Unreachable deferred procedure call due to a diverging procedure call at the end of the current scope");
					}
				}
			}
		}
	}
}

gb_internal bool check_is_terminating_list(Slice<Ast *> const &stmts, String const &label) {
	// Iterate backwards
	for (isize n = stmts.count-1; n >= 0; n--) {
		Ast *stmt = stmts[n];
		if (stmt->kind == Ast_EmptyStmt) {
			// Okay
		} else if (stmt->kind == Ast_ValueDecl && !stmt->ValueDecl.is_mutable) {
			// Okay
		} else if (is_diverging_stmt(stmt)) {
			return true;
		} else {
			return check_is_terminating(stmt, label);
		}
	}

	return false;
}

gb_internal bool check_has_break_list(Slice<Ast *> const &stmts, String const &label, bool implicit) {
	for (Ast *stmt : stmts) {
		if (check_has_break(stmt, label, implicit)) {
			return true;
		}
	}
	return false;
}

gb_internal bool check_has_break_expr(Ast * expr, String const &label) {
	if (expr && expr->viral_state_flags & ViralStateFlag_ContainsOrBreak) {
		return true;
	}
	return false;
}

gb_internal bool check_has_break_expr_list(Slice<Ast *> const &exprs, String const &label) {
	for (Ast *expr : exprs) {
		if (check_has_break_expr(expr, label)) {
			return true;
		}
	}
	return false;
}

gb_internal bool check_has_break(Ast *stmt, String const &label, bool implicit) {
	switch (stmt->kind) {
	case Ast_BranchStmt:
		if (stmt->BranchStmt.token.kind == Token_break) {
			if (stmt->BranchStmt.label == nullptr) {
				return implicit;
			}
			if (stmt->BranchStmt.label->kind == Ast_Ident &&
			    stmt->BranchStmt.label->Ident.token.string == label) {
				return true;
			}
		}
		break;

	case Ast_DeferStmt:
		return check_has_break(stmt->DeferStmt.stmt, label, implicit);

	case Ast_BlockStmt:
		return check_has_break_list(stmt->BlockStmt.stmts, label, implicit);

	case Ast_IfStmt:
		if (stmt->IfStmt.init && check_has_break(stmt->IfStmt.init, label, implicit)) {
			return true;
		}
		if (stmt->IfStmt.cond && check_has_break_expr(stmt->IfStmt.cond, label)) {
			return true;
		}

		if (check_has_break(stmt->IfStmt.body, label, implicit) ||
		    (stmt->IfStmt.else_stmt != nullptr && check_has_break(stmt->IfStmt.else_stmt, label, implicit))) {
			return true;
		}
		break;

	case Ast_CaseClause:
		return check_has_break_list(stmt->CaseClause.stmts, label, implicit);

	case Ast_SwitchStmt:
		if (stmt->SwitchStmt.init && check_has_break_expr(stmt->SwitchStmt.init, label)) {
			return true;
		}
		if (label != "" && check_has_break(stmt->SwitchStmt.body, label, false)) {
			return true;
		}
		break;

	case Ast_TypeSwitchStmt:
		if (label != "" && check_has_break(stmt->TypeSwitchStmt.body, label, false)) {
			return true;
		}
		break;

	case Ast_ForStmt:
		if (stmt->ForStmt.init && check_has_break(stmt->ForStmt.init, label, implicit)) {
			return true;
		}
		if (stmt->ForStmt.cond && check_has_break_expr(stmt->ForStmt.cond, label)) {
			return true;
		}
		if (stmt->ForStmt.post && check_has_break(stmt->ForStmt.post, label, implicit)) {
			return true;
		}

		if (label != "" && check_has_break(stmt->ForStmt.body, label, false)) {
			return true;
		}
		break;

	case Ast_RangeStmt:
		if (label != "" && check_has_break(stmt->RangeStmt.body, label, false)) {
			return true;
		}
		break;

	case Ast_ExprStmt:
		if (stmt->ExprStmt.expr->viral_state_flags & ViralStateFlag_ContainsOrBreak) {
			return true;
		}
		break;

	case Ast_ValueDecl:
		if (stmt->ValueDecl.is_mutable && check_has_break_expr_list(stmt->ValueDecl.values, label)) {
			return true;
		}
		break;
	case Ast_AssignStmt:
		if (check_has_break_expr_list(stmt->AssignStmt.lhs, label)) {
			return true;
		}
		if (check_has_break_expr_list(stmt->AssignStmt.rhs, label)) {
			return true;
		}
		break;
	}

	return false;
}

String label_string(Ast *node) {
	GB_ASSERT(node != nullptr);
	if (node->kind == Ast_Ident) {
		return node->Ident.token.string;
	} else if (node->kind == Ast_Label) {
		return label_string(node->Label.name);
	}
	GB_ASSERT("INVALID LABEL");
	return {};
}

// NOTE(bill): The last expression has to be a 'return' statement
// TODO(bill): This is a mild hack and should be probably handled properly
gb_internal bool check_is_terminating(Ast *node, String const &label) {
	switch (node->kind) {
	case_ast_node(rs, ReturnStmt, node);
		return true;
	case_end;

	case_ast_node(bs, BlockStmt, node);
		if (check_is_terminating_list(bs->stmts, label)) {
			if (bs->label != nullptr) {
				return check_is_terminating_list(bs->stmts, label_string(bs->label));
			}
			return true;
		}
	case_end;

	case_ast_node(es, ExprStmt, node);
		return check_is_terminating(unparen_expr(es->expr), label);
	case_end;

	case_ast_node(vd, ValueDecl, node);
		return check_has_break_expr_list(vd->values, label);
	case_end;

	case_ast_node(as, AssignStmt, node);
		return check_has_break_expr_list(as->lhs, label) ||
		       check_has_break_expr_list(as->rhs, label);
	case_end;

	case_ast_node(bs, BranchStmt, node);
		return bs->token.kind == Token_fallthrough;
	case_end;

	case_ast_node(is, IfStmt, node);
		if (is->else_stmt != nullptr) {
			if (check_is_terminating(is->body, label) &&
			    check_is_terminating(is->else_stmt, label)) {
			    return true;
		    }
		}
	case_end;

	case_ast_node(ws, WhenStmt, node);
		// TODO(bill): Is this logic correct for when statements?
		auto const &tv = ws->cond->tav;
		if (tv.mode != Addressing_Constant) {
			// NOTE(bill): Check the things regardless as a bug occurred earlier
			if (ws->else_stmt != nullptr) {
				if (check_is_terminating(ws->body, label) &&
				    check_is_terminating(ws->else_stmt, label)) {
				    return true;
			    }
			}
			return false;
		}

		if (tv.value.kind == ExactValue_Bool) {
			if (tv.value.value_bool) {
				return check_is_terminating(ws->body, label);
			} else {
				if (ws->else_stmt == nullptr) {
					return false;
				}
				return check_is_terminating(ws->else_stmt, label);
			}
		}
	case_end;

	case_ast_node(fs, ForStmt, node);
		if (fs->cond == nullptr && !check_has_break(fs->body, label, true)) {
			if (fs->label) {
				return !check_has_break(fs->body, label_string(fs->label), false);
			}
			return true;
		}
	case_end;

	case_ast_node(rs, UnrollRangeStmt, node);
		return false;
	case_end;

	case_ast_node(rs, RangeStmt, node);
		return false;
	case_end;

	case_ast_node(ss, SwitchStmt, node);
		bool has_default = false;
		for_array(i, ss->body->BlockStmt.stmts) {
			Ast *clause = ss->body->BlockStmt.stmts[i];
			ast_node(cc, CaseClause, clause);
			if (cc->list.count == 0) {
				has_default = true;
			}
			if (!check_is_terminating_list(cc->stmts, label) ||
			    check_has_break_list(cc->stmts, label, true)) {
				return false;
			}
		}
		return has_default;
	case_end;

	case_ast_node(ss, TypeSwitchStmt, node);
		bool has_default = false;
		for_array(i, ss->body->BlockStmt.stmts) {
			Ast *clause = ss->body->BlockStmt.stmts[i];
			ast_node(cc, CaseClause, clause);
			if (cc->list.count == 0) {
				has_default = true;
			}
			if (!check_is_terminating_list(cc->stmts, label) ||
			    check_has_break_list(cc->stmts, label, true)) {
				return false;
			}
		}
		return has_default;
	case_end;
	}

	return false;
}



gb_internal Type *check_assignment_variable(CheckerContext *ctx, Operand *lhs, Operand *rhs) {
	if (rhs->mode == Addressing_Invalid) {
		return nullptr;
	}
	if (rhs->type == t_invalid &&
	    rhs->mode != Addressing_ProcGroup &&
	    rhs->mode != Addressing_Builtin) {
		return nullptr;
	}

	Ast *node = unparen_expr(lhs->expr);

	check_no_copy_assignment(*rhs, str_lit("assignment"));

	// NOTE(bill): Ignore assignments to '_'
	if (is_blank_ident(node)) {
		check_assignment(ctx, rhs, nullptr, str_lit("assignment to '_' identifier"));
		if (rhs->mode == Addressing_Invalid) {
			return nullptr;
		}
		return rhs->type;
	}

	Entity *e = nullptr;
	bool used = false;

	if (lhs->mode == Addressing_Invalid ||
	    (lhs->type == t_invalid &&
	     lhs->mode != Addressing_ProcGroup &&
	     lhs->mode != Addressing_Builtin)) {
		return nullptr;
	}

	if (rhs->mode == Addressing_ProcGroup) {
		Array<Entity *> procs = proc_group_entities(ctx, *rhs);
		GB_ASSERT(procs.count > 0);

		// NOTE(bill): These should be done
		for_array(i, procs) {
			Type *t = base_type(procs[i]->type);
			if (t == t_invalid) {
				continue;
			}
			Operand x = {};
			x.mode = Addressing_Value;
			x.type = t;
			if (check_is_assignable_to(ctx, &x, lhs->type)) {
				e = procs[i];
				add_entity_use(ctx, rhs->expr, e);
				break;
			}
		}

		if (e != nullptr) {
			rhs->mode = Addressing_Value;
			rhs->type = e->type;
			rhs->proc_group = nullptr;
		}
	} else {
		Ast *ident_node = nullptr;

		if (node->kind == Ast_Ident) {
			ident_node = node;
		} else if (node->kind == Ast_IndexExpr && node->IndexExpr.expr->kind == Ast_Ident) {
			ident_node = node->IndexExpr.expr;
		}
		if (ident_node != nullptr) {
			ast_node(i, Ident, ident_node);
			e = scope_lookup(ctx->scope, i->token.string);
			if (e != nullptr && e->kind == Entity_Variable) {
				used = (e->flags & EntityFlag_Used) != 0; // NOTE(bill): Make backup just in case
			}
		}

	}

	if (e != nullptr && used) {
		e->flags |= EntityFlag_Used;
	}

	Type *assignment_type = lhs->type;

	if (rhs->mode == Addressing_Type && is_type_polymorphic(rhs->type)) {
		gbString t = type_to_string(rhs->type);
		error(rhs->expr, "Invalid use of a non-specialized polymorphic type '%s'", t);
		gb_string_free(t);
	}

	switch (lhs->mode) {
	case Addressing_Invalid:
		return nullptr;

	case Addressing_Variable:
		if (e && e->kind == Entity_Variable && e->Variable.is_rodata) {
			error(lhs->expr, "Assignment to variable '%.*s' marked as @(rodata) is not allowed", LIT(e->token.string));
		}
		break;

	case Addressing_MapIndex: {
		Ast *ln = unparen_expr(lhs->expr);
		if (ln->kind == Ast_IndexExpr) {
			Ast *x = ln->IndexExpr.expr;
			TypeAndValue tav = x->tav;
			GB_ASSERT(tav.mode != Addressing_Invalid);
			if (tav.mode != Addressing_Variable) {
				if (!is_type_pointer(tav.type)) {
					gbString str = expr_to_string(lhs->expr);
					error(lhs->expr, "Cannot assign to the value of a map '%s'", str);
					gb_string_free(str);
					return nullptr;
				}
			}
		}

		break;
	}

	case Addressing_Context:
		break;

	case Addressing_SoaVariable:
		break;

	case Addressing_SwizzleVariable:
		break;

	default: {
		if (lhs->expr->kind == Ast_SelectorExpr) {
			// NOTE(bill): Extra error checks
			Operand op_c = {Addressing_Invalid};
			ast_node(se, SelectorExpr, lhs->expr);
			check_expr(ctx, &op_c, se->expr);
			if (op_c.mode == Addressing_MapIndex) {
				gbString str = expr_to_string(lhs->expr);
				error(lhs->expr, "Cannot assign to struct field '%s' in map", str);
				gb_string_free(str);
				return nullptr;
			}
		}

		Entity *e = entity_of_node(lhs->expr);
		Entity *original_e = e;

		Ast *name = unparen_expr(lhs->expr);
		while (name->kind == Ast_SelectorExpr) {
			name = name->SelectorExpr.expr;
			e = entity_of_node(name);
		}
		if (e == nullptr) {
			e = original_e;
		}

		gbString str = expr_to_string(lhs->expr);
		if (e != nullptr && e->flags & EntityFlag_Param) {
			ERROR_BLOCK();
			if (e->flags & EntityFlag_Using) {
				error(lhs->expr, "Cannot assign to '%s' which is from a 'using' procedure parameter", str);
			} else {
				error(lhs->expr, "Cannot assign to '%s' which is a procedure parameter", str);
			}
			if (is_type_pointer(e->type)) {
				error_line("\tSuggestion: Did you mean to shadow it? '%.*s := %.*s'?\n", LIT(e->token.string), LIT(e->token.string));
			} else {
				error_line("\tSuggestion: Did you mean to pass '%.*s' by pointer?\n", LIT(e->token.string));
			}
			show_error_on_line(e->token.pos, token_pos_end(e->token));
		} else {
			ERROR_BLOCK();
			error(lhs->expr, "Cannot assign to '%s'", str);

			if (e && e->flags & EntityFlag_ForValue) {
				isize offset = show_error_on_line(e->token.pos, token_pos_end(e->token));
				if (offset < 0) {
					if (is_type_map(e->type)) {
						error_line("\tSuggestion: Did you mean? 'for key, &%.*s in ...'\n", LIT(e->token.string));
					} else {
						error_line("\tSuggestion: Did you mean? 'for &%.*s in ...'\n", LIT(e->token.string));
					}
				} else {
					error_line("\t");
					for (isize i = 0; i < offset-1; i++) {
						error_line(" ");
					}
					error_line("'%.*s' is immutable, declare it as '&%.*s' to make it mutable\n", LIT(e->token.string), LIT(e->token.string));
				}

			} else if (e && e->flags & EntityFlag_SwitchValue) {
				isize offset = show_error_on_line(e->token.pos, token_pos_end(e->token));
				if (offset < 0) {
					error_line("\tSuggestion: Did you mean? 'switch &%.*s in ...'\n", LIT(e->token.string));
				} else {
					error_line("\t");
					for (isize i = 0; i < offset-1; i++) {
						error_line(" ");
					}
					error_line("'%.*s' is immutable, declare it as '&%.*s' to make it mutable\n", LIT(e->token.string), LIT(e->token.string));
				}
			}
		}
		gb_string_free(str);

		break;
	}
	}

	Entity *lhs_e = entity_of_node(lhs->expr);
	u8 prev_bit_field_bit_size = ctx->bit_field_bit_size;
	if (lhs_e && lhs_e->kind == Entity_Variable && lhs_e->Variable.bit_field_bit_size) {
		// HACK NOTE(bill): This is a bit of a hack, but it will work fine for this use case
		ctx->bit_field_bit_size = lhs_e->Variable.bit_field_bit_size;
	}

	check_assignment(ctx, rhs, assignment_type, str_lit("assignment"));

	ctx->bit_field_bit_size = prev_bit_field_bit_size;

	if (rhs->mode == Addressing_Invalid) {
		return nullptr;
	}

	return rhs->type;
}


gb_internal void check_stmt_internal(CheckerContext *ctx, Ast *node, u32 flags);
gb_internal void check_stmt(CheckerContext *ctx, Ast *node, u32 flags) {
	u32 prev_state_flags = ctx->state_flags;

	if (node->state_flags != 0) {
		u32 in = node->state_flags;
		u32 out = ctx->state_flags;

		if (in & StateFlag_no_bounds_check) {
			out |= StateFlag_no_bounds_check;
			out &= ~StateFlag_bounds_check;
		} else if (in & StateFlag_bounds_check) {
			out |= StateFlag_bounds_check;
			out &= ~StateFlag_no_bounds_check;
		}

		if (in & StateFlag_no_type_assert) {
			out |= StateFlag_no_type_assert;
			out &= ~StateFlag_type_assert;
		} else if (in & StateFlag_type_assert) {
			out |= StateFlag_type_assert;
			out &= ~StateFlag_no_type_assert;
		}

		ctx->state_flags = out;
	}

	check_stmt_internal(ctx, node, flags);

	ctx->state_flags = prev_state_flags;
}


gb_internal void check_when_stmt(CheckerContext *ctx, AstWhenStmt *ws, u32 flags) {
	Operand operand = {Addressing_Invalid};
	check_expr(ctx, &operand, ws->cond);
	if (operand.mode != Addressing_Constant || !is_type_boolean(operand.type)) {
		error(ws->cond, "Non-constant boolean 'when' condition");
		return;
	}
	if (ws->body == nullptr || ws->body->kind != Ast_BlockStmt) {
		error(ws->cond, "Invalid body for 'when' statement");
		return;
	}
	if (operand.value.kind == ExactValue_Bool &&
	    operand.value.value_bool) {
		check_stmt_list(ctx, ws->body->BlockStmt.stmts, flags);
	} else if (ws->else_stmt) {
		switch (ws->else_stmt->kind) {
		case Ast_BlockStmt:
			check_stmt_list(ctx, ws->else_stmt->BlockStmt.stmts, flags);
			break;
		case Ast_WhenStmt:
			check_when_stmt(ctx, &ws->else_stmt->WhenStmt, flags);
			break;
		default:
			error(ws->else_stmt, "Invalid 'else' statement in 'when' statement");
			break;
		}
	}
}

gb_internal void check_label(CheckerContext *ctx, Ast *label, Ast *parent) {
	if (label == nullptr) {
		return;
	}
	ast_node(l, Label, label);
	if (l->name->kind != Ast_Ident) {
		error(l->name, "A label's name must be an identifier");
		return;
	}
	String name = l->name->Ident.token.string;
	if (is_blank_ident(name)) {
		error(l->name, "A label's name cannot be a blank identifier");
		return;
	}


	if (ctx->curr_proc_decl == nullptr) {
		error(l->name, "A label is only allowed within a procedure");
		return;
	}
	GB_ASSERT(ctx->decl != nullptr);

	bool ok = true;
	for_array(i, ctx->decl->labels) {
		BlockLabel bl = ctx->decl->labels[i];
		if (bl.name == name) {
			error(label, "Duplicate label with the name '%.*s'", LIT(name));
			ok = false;
			break;
		}
	}

	Entity *e = alloc_entity_label(ctx->scope, l->name->Ident.token, t_invalid, label, parent);
	add_entity(ctx, ctx->scope, l->name, e);
	e->parent_proc_decl = ctx->curr_proc_decl;

	if (ok) {
		BlockLabel bl = {name, label};
		array_add(&ctx->decl->labels, bl);
	}
}

// Returns 'true' for 'continue', 'false' for 'return'
gb_internal bool check_using_stmt_entity(CheckerContext *ctx, AstUsingStmt *us, Ast *expr, bool is_selector, Entity *e) {
	if (e == nullptr) {
		if (is_blank_ident(expr)) {
			error(us->token, "'using' in a statement is not allowed with the blank identifier '_'");
		} else {
			error(us->token, "'using' applied to an unknown entity");
		}
		return true;
	}

	add_entity_use(ctx, expr, e);
	
	ERROR_BLOCK();

	switch (e->kind) {
	case Entity_TypeName: {
		Type *t = base_type(e->type);
		if (t->kind == Type_Enum) {
			for_array(i, t->Enum.fields) {
				Entity *f = t->Enum.fields[i];
				if (!is_entity_exported(f)) continue;

				Entity *found = scope_insert(ctx->scope, f);
				if (found != nullptr) {
					gbString expr_str = expr_to_string(expr);
					error(us->token, "Namespace collision while 'using' enum '%s' of: %.*s", expr_str, LIT(found->token.string));
					gb_string_free(expr_str);
					return false;
				}
				f->using_parent = e;
			}
		} else {
			error(us->token, "'using' can be only applied to enum type entities");
		}

		break;
	}

	case Entity_ImportName: {
		Scope *scope = e->ImportName.scope;
		rw_mutex_lock(&scope->mutex);
		defer (rw_mutex_unlock(&scope->mutex));

		for (auto const &entry : scope->elements) {
			String name = entry.key;
			Entity *decl = entry.value;
			if (!is_entity_exported(decl, true)) continue;

			Entity *found = scope_insert_with_name(ctx->scope, name, decl);
			if (found != nullptr) {
				gbString expr_str = expr_to_string(expr);
				error(us->token,
				      "Namespace collision while 'using' import name '%s' of: %.*s\n"
				      "\tat %s\n"
				      "\tat %s",
				      expr_str, LIT(found->token.string),
				      token_pos_to_string(found->token.pos),
				      token_pos_to_string(decl->token.pos)
				      );
				gb_string_free(expr_str);
				return false;
			}
		}

		break;
	}

	case Entity_Variable: {
		bool is_ptr = is_type_pointer(e->type);
		Type *t = base_type(type_deref(e->type));
		if (t->kind == Type_Struct) {
			wait_signal_until_available(&t->Struct.fields_wait_signal);

			Scope *found = t->Struct.scope;
			GB_ASSERT(found != nullptr);
			for (auto const &entry : found->elements) {
				Entity *f = entry.value;
				if (f->kind == Entity_Variable) {
					Entity *uvar = alloc_entity_using_variable(e, f->token, f->type, expr);
					if (!is_ptr && e->flags & EntityFlag_Value) uvar->flags |= EntityFlag_Value;
					if (e->flags & EntityFlag_Param)            uvar->flags |= EntityFlag_Param;
					if (e->flags & EntityFlag_SoaPtrField)      uvar->flags |= EntityFlag_SoaPtrField;
					Entity *prev = scope_insert(ctx->scope, uvar);
					if (prev != nullptr) {
						gbString expr_str = expr_to_string(expr);
						error(us->token, "Namespace collision while using '%s' of: '%.*s'", expr_str, LIT(prev->token.string));
						gb_string_free(expr_str);
						return false;
					}
				}
			}
		} else {
			error(us->token, "'using' can only be applied to variables of type 'struct'");
			return false;
		}

		break;
	}

	case Entity_Constant:
		error(us->token, "'using' cannot be applied to a constant");
		break;

	case Entity_Procedure:
	case Entity_ProcGroup:
	case Entity_Builtin:
		error(us->token, "'using' cannot be applied to a procedure");
		break;

	case Entity_Nil:
		error(us->token, "'using' cannot be applied to 'nil'");
		break;

	case Entity_Label:
		error(us->token, "'using' cannot be applied to a label");
		break;

	case Entity_Invalid:
		error(us->token, "'using' cannot be applied to an invalid entity");
		break;

	default:
		GB_PANIC("TODO(bill): 'using' other expressions?");
	}

	return true;
}

gb_internal void error_var_decl_identifier(Ast *name) {
	GB_ASSERT(name != nullptr);
	GB_ASSERT(name->kind != Ast_Ident);

	ERROR_BLOCK();
	gbString s = expr_to_string(name);
	defer (gb_string_free(s));

	error(name, "A variable declaration must be an identifier, got '%s'", s);
	if (name->kind == Ast_Implicit) {
		String imp = name->Implicit.string;
		if (imp == "context") {
			error_line("\tSuggestion: '%.*s' is a reserved keyword, would 'ctx' suffice?\n", LIT(imp));
		} else {
			error_line("\tNote: '%.*s' is a reserved keyword\n", LIT(imp));
		}
	}
}

gb_internal void check_unroll_range_stmt(CheckerContext *ctx, Ast *node, u32 mod_flags) {
	ast_node(irs, UnrollRangeStmt, node);
	check_open_scope(ctx, node);
	defer (check_close_scope(ctx));

	Type *val0 = nullptr;
	Type *val1 = nullptr;
	Entity *entities[2] = {};
	isize entity_count = 0;

	i64 unroll_count = -1;

	if (irs->args.count > 0) {
		if (irs->args.count > 1) {
			error(irs->args[1], "#unroll only supports a single argument for the unroll per loop amount");
		}
		Ast *arg = irs->args[0];
		if (arg->kind == Ast_FieldValue) {
			error(arg, "#unroll does not yet support named arguments");
			arg = arg->FieldValue.value;
		}

		Operand x = {};
		check_expr(ctx, &x, arg);
		if (x.mode != Addressing_Constant || !is_type_integer(x.type)) {
			gbString s = expr_to_string(x.expr);
			error(x.expr, "Expected a constant integer for #unroll, got '%s'", s);
			gb_string_free(s);
		} else {
			ExactValue value = exact_value_to_integer(x.value);
			i64 v = exact_value_to_i64(value);
			if (v < 1) {
				error(x.expr, "Expected a constant integer >= 1 for #unroll, got %lld", cast(long long)v);
			} else {
				unroll_count = v;
				if (v > 1024) {
					error(x.expr, "Too large of a value for #unroll, got %lld, expected <= 1024", cast(long long)v);
				}
			}

		}
	}

	Ast *expr = unparen_expr(irs->expr);

	ExactValue inline_for_depth = exact_value_i64(0);

	if (is_ast_range(expr)) {
		ast_node(ie, BinaryExpr, expr);
		Operand x = {};
		Operand y = {};

		bool ok = check_range(ctx, expr, true, &x, &y, &inline_for_depth);
		if (!ok) {
			goto skip_expr;
		}

		val0 = x.type;
		val1 = t_int;
	} else {
		Operand operand = {Addressing_Invalid};
		check_expr_or_type(ctx, &operand, irs->expr);

		if (operand.mode == Addressing_Type) {
			if (!is_type_enum(operand.type)) {
				gbString t = type_to_string(operand.type);
				error(operand.expr, "Cannot iterate over the type '%s'", t);
				gb_string_free(t);
				goto skip_expr;
			} else {
				val0 = operand.type;
				val1 = t_int;
				add_type_info_type(ctx, operand.type);

				Type *bt = base_type(operand.type);
				inline_for_depth = exact_value_i64(bt->Enum.fields.count);
				goto skip_expr;
			}
		} else if (operand.mode != Addressing_Invalid) {
			Type *t = base_type(operand.type);
			switch (t->kind) {
			case Type_Basic:
				if (is_type_string(t) && t->Basic.kind != Basic_cstring) {
					val0 = t_rune;
					val1 = t_int;
					inline_for_depth = exact_value_i64(operand.value.value_string.len);
					if (unroll_count > 0) {
						error(node, "#unroll(%lld) does not support strings", cast(long long)unroll_count);
					}
				}
				break;
			case Type_Array:
				val0 = t->Array.elem;
				val1 = t_int;
				inline_for_depth = unroll_count > 0 ? exact_value_i64(unroll_count) : exact_value_i64(t->Array.count);
				break;
			case Type_EnumeratedArray:
				val0 = t->EnumeratedArray.elem;
				val1 = t->EnumeratedArray.index;
				if (unroll_count > 0) {
					error(node, "#unroll(%lld) does not support enumerated arrays", cast(long long)unroll_count);
				}
				inline_for_depth = exact_value_i64(t->EnumeratedArray.count);
				break;

			case Type_Slice:
				if (unroll_count > 0) {
					val0 = t->Slice.elem;
					val1 = t_int;
					inline_for_depth = exact_value_i64(unroll_count);
				}
				break;
			case Type_DynamicArray:
				if (unroll_count > 0) {
					val0 = t->DynamicArray.elem;
					val1 = t_int;
					inline_for_depth = exact_value_i64(unroll_count);
				}
				break;
			}
		}

		if (val0 == nullptr) {
			gbString s = expr_to_string(operand.expr);
			gbString t = type_to_string(operand.type);
			error(operand.expr, "Cannot iterate over '%s' of type '%s' in an '#unroll for' statement", s, t);
			gb_string_free(t);
			gb_string_free(s);
		} else if (operand.mode != Addressing_Constant && unroll_count <= 0) {
			error(operand.expr, "An '#unroll for' expression must be known at compile time");
		}
	}

	skip_expr:; // NOTE(zhiayang): again, declaring a variable immediately after a label... weird.

	Ast * lhs[2] = {irs->val0, irs->val1};
	Type *rhs[2] = {val0, val1};

	for (isize i = 0; i < 2; i++) {
		if (lhs[i] == nullptr) {
			continue;
		}
		Ast * name = lhs[i];
		Type *type = rhs[i];

		Entity *entity = nullptr;
		if (name->kind == Ast_Ident) {
			Token token = name->Ident.token;
			String str = token.string;
			Entity *found = nullptr;

			if (!is_blank_ident(str)) {
				found = scope_lookup_current(ctx->scope, str);
			}
			if (found == nullptr) {
				entity = alloc_entity_variable(ctx->scope, token, type, EntityState_Resolved);
				entity->flags |= EntityFlag_Value;
				add_entity_definition(&ctx->checker->info, name, entity);
			} else {
				TokenPos pos = found->token.pos;
				error(token,
				      "Redeclaration of '%.*s' in this scope\n"
				      "\tat %s", LIT(str), token_pos_to_string(pos));
				entity = found;
			}
		} else {
			error_var_decl_identifier(name);
		}

		if (entity == nullptr) {
			entity = alloc_entity_dummy_variable(builtin_pkg->scope, ast_token(name));
		}

		entities[entity_count++] = entity;

		if (type == nullptr) {
			entity->type = t_invalid;
			entity->flags |= EntityFlag_Used;
		}
	}

	for (isize i = 0; i < entity_count; i++) {
		add_entity(ctx, ctx->scope, entities[i]->identifier, entities[i]);
	}


	// NOTE(bill): Minimize the amount of nesting of an '#unroll for'
	i64 prev_inline_for_depth = ctx->inline_for_depth;
	defer (ctx->inline_for_depth = prev_inline_for_depth);
	{
		i64 v = exact_value_to_i64(inline_for_depth);
		if (v <= 0) {
			// Do nothing
		} else {
			ctx->inline_for_depth = gb_max(ctx->inline_for_depth, 1) * v;
		}

		if (ctx->inline_for_depth >= MAX_INLINE_FOR_DEPTH && prev_inline_for_depth < MAX_INLINE_FOR_DEPTH) {
			ERROR_BLOCK();
			if (prev_inline_for_depth > 0) {
				error(node, "Nested '#unroll for' loop cannot be inlined as it exceeds the maximum '#unroll for' depth (%lld levels >= %lld maximum levels)", v, MAX_INLINE_FOR_DEPTH);
			} else {
				error(node, "'#unroll for' loop cannot be inlined as it exceeds the maximum '#unroll for' depth (%lld levels >= %lld maximum levels)", v, MAX_INLINE_FOR_DEPTH);
			}
			error_line("\tUse a normal 'for' loop instead by removing the 'inline' prefix\n");
			ctx->inline_for_depth = MAX_INLINE_FOR_DEPTH;
		}
	}

	check_stmt(ctx, irs->body, mod_flags);

}

gb_internal void check_switch_stmt(CheckerContext *ctx, Ast *node, u32 mod_flags) {
	ast_node(ss, SwitchStmt, node);

	Operand x = {};

	mod_flags |= Stmt_BreakAllowed | Stmt_FallthroughAllowed;
	check_open_scope(ctx, node);
	defer (check_close_scope(ctx));

	check_label(ctx, ss->label, node);

	if (ss->init != nullptr) {
		check_stmt(ctx, ss->init, 0);
	}
	if (ss->tag != nullptr) {
		check_expr(ctx, &x, ss->tag);
		check_assignment(ctx, &x, nullptr, str_lit("switch expression"));
		if (x.type == nullptr) {
			return;
		}
	} else {
		x.mode  = Addressing_Constant;
		x.type  = t_bool;
		x.value = exact_value_bool(true);

		Token token  = {};
		token.pos    = ast_token(ss->body).pos;
		token.string = str_lit("true");

		x.expr = alloc_ast_node(nullptr, Ast_Ident);
		x.expr->Ident.token = token;
	}

	// NOTE(bill): Check for multiple defaults
	Ast *first_default = nullptr;
	ast_node(bs, BlockStmt, ss->body);
	for_array(i, bs->stmts) {
		Ast *stmt = bs->stmts[i];
		Ast *default_stmt = nullptr;
		if (stmt->kind == Ast_CaseClause) {
			ast_node(cc, CaseClause, stmt);
			if (cc->list.count == 0) {
				default_stmt = stmt;
			}
		} else {
			error(stmt, "Invalid AST - expected case clause");
		}

		if (default_stmt != nullptr) {
			if (first_default != nullptr) {
				TokenPos pos = ast_token(first_default).pos;
				error(stmt,
				           "multiple default clauses\n"
				           "\tfirst at %s", token_pos_to_string(pos));
			} else {
				first_default = default_stmt;
			}
		}
	}

	bool is_partial = ss->partial;

	if (is_partial) {
		if (!is_type_enum(x.type)) {
			error(x.expr, "#partial switch statement can be only used with an enum type");
		}
	}

	SeenMap seen = {}; // NOTE(bill): Multimap, Key: ExactValue
	defer (map_destroy(&seen));

	for (Ast *stmt : bs->stmts) {
		if (stmt->kind != Ast_CaseClause) {
			// NOTE(bill): error handled by above multiple default checker
			continue;
		}
		ast_node(cc, CaseClause, stmt);

		for (Ast *expr : cc->list) {
			expr = unparen_expr(expr);

			if (is_ast_range(expr)) {
				ast_node(be, BinaryExpr, expr);
				Operand lhs = {};
				Operand rhs = {};
				check_expr_with_type_hint(ctx, &lhs, be->left, x.type);
				if (x.mode == Addressing_Invalid) {
					continue;
				}
				if (lhs.mode == Addressing_Invalid) {
					continue;
				}
				check_expr_with_type_hint(ctx, &rhs, be->right, x.type);
				if (rhs.mode == Addressing_Invalid) {
					continue;
				}

				if (!is_type_ordered(x.type)) {
					gbString str = type_to_string(x.type);
					error(expr, "Unordered type '%s', is invalid for an interval expression", str);
					gb_string_free(str);
					continue;
				}

				TokenKind upper_op = Token_Invalid;
				switch (be->op.kind) {
				case Token_Ellipsis:  upper_op = Token_LtEq; break;
				case Token_RangeFull: upper_op = Token_LtEq; break;
				case Token_RangeHalf: upper_op = Token_Lt;   break;
				default: GB_PANIC("Invalid range operator"); break;
				}


				Operand a = lhs;
				Operand b = rhs;
				check_comparison(ctx, expr, &a, &x, Token_LtEq);
				if (a.mode == Addressing_Invalid) {
					continue;
				}

				check_comparison(ctx, expr, &b, &x, upper_op);
				if (b.mode == Addressing_Invalid) {
					continue;
				}

				Operand a1 = lhs;
				Operand b1 = rhs;
				check_comparison(ctx, expr, &a1, &b1, Token_LtEq);

				add_to_seen_map(ctx, &seen, upper_op, x, lhs, rhs);

				if (is_type_string(x.type)) {
					// NOTE(bill): Force dependency for strings here
					add_package_dependency(ctx, "runtime", "string_le");
					add_package_dependency(ctx, "runtime", "string_lt");
				}

			} else {
				Operand y = {};
				if (is_type_typeid(x.type)) {
					check_expr_or_type(ctx, &y, expr, x.type);
				} else {
					check_expr_with_type_hint(ctx, &y, expr, x.type);
				}

				if (x.mode == Addressing_Invalid ||
				    y.mode == Addressing_Invalid) {
					continue;
				}

				if (y.mode == Addressing_Type) {
					Type *t = y.type;
					if (t == nullptr || t == t_invalid || is_type_polymorphic(t)) {
						error(y.expr, "Invalid type for case clause");
						continue;
					}
					t = default_type(t);
					add_type_info_type(ctx, t);
				} else {
					convert_to_typed(ctx, &y, x.type);
					if (y.mode == Addressing_Invalid) {
						continue;
					}

					// NOTE(bill): the ordering here matters
					Operand z = y;
					check_comparison(ctx, expr, &z, &x, Token_CmpEq);
					if (z.mode == Addressing_Invalid) {
						continue;
					}
					if (y.mode != Addressing_Constant) {
						continue;
					}
					update_untyped_expr_type(ctx, z.expr, x.type, !is_type_untyped(x.type));
					add_to_seen_map(ctx, &seen, y);
				}
			}
		}

		check_open_scope(ctx, stmt);
		check_stmt_list(ctx, cc->stmts, mod_flags);
		check_close_scope(ctx);
	}

	if (!is_partial && is_type_enum(x.type)) {
		TEMPORARY_ALLOCATOR_GUARD();

		Type *et = base_type(x.type);
		GB_ASSERT(is_type_enum(et));
		auto fields = et->Enum.fields;

		auto unhandled = array_make<Entity *>(temporary_allocator(), 0, fields.count);

		for (Entity *f : fields) {
			if (f->kind != Entity_Constant) {
				continue;
			}
			ExactValue v = f->Constant.value;
			auto found = map_get(&seen, hash_exact_value(v));
			if (!found) {
				array_add(&unhandled, f);
			}
		}

		if (unhandled.count > 0) {
			ERROR_BLOCK();

			if (unhandled.count == 1) {
				error_no_newline(node, "Unhandled switch case: %.*s", LIT(unhandled[0]->token.string));
			} else {
				error(node, "Unhandled switch cases:");
				for (Entity *f : unhandled) {
					error_line("\t%.*s\n", LIT(f->token.string));
				}
			}
			error_line("\tSuggestion: Was '#partial switch' wanted?\n");
		}
	}

	if (build_context.strict_style) {
		Token stok = ss->token;
		for_array(i, bs->stmts) {
			Ast *stmt = bs->stmts[i];
			if (stmt->kind != Ast_CaseClause) {
				continue;
			}
			Token ctok = stmt->CaseClause.token;
			if (ctok.pos.column > stok.pos.column) {
				error(ctok, "With '-strict-style', 'case' statements must share the same column as the 'switch' token");
			}
		}
	}
}


enum TypeSwitchKind {
	TypeSwitch_Invalid,
	TypeSwitch_Union,
	TypeSwitch_Any,
};

gb_internal TypeSwitchKind check_valid_type_switch_type(Type *type) {
	type = type_deref(type);
	if (is_type_union(type)) {
		return TypeSwitch_Union;
	}
	if (is_type_any(type)) {
		return TypeSwitch_Any;
	}
	return TypeSwitch_Invalid;
}

gb_internal void check_type_switch_stmt(CheckerContext *ctx, Ast *node, u32 mod_flags) {
	ast_node(ss, TypeSwitchStmt, node);
	Operand x = {};

	mod_flags |= Stmt_BreakAllowed | Stmt_TypeSwitch;
	check_open_scope(ctx, node);
	defer (check_close_scope(ctx));

	check_label(ctx, ss->label, node);

	if (ss->tag->kind != Ast_AssignStmt) {
		error(ss->tag, "Expected an 'in' assignment for this type switch statement");
		return;
	}

	ast_node(as, AssignStmt, ss->tag);
	Token as_token = ast_token(ss->tag);
	if (as->lhs.count != 1) {
		syntax_error(as_token, "Expected 1 name before 'in'");
		return;
	}
	if (as->rhs.count != 1) {
		syntax_error(as_token, "Expected 1 expression after 'in'");
		return;
	}
	bool is_addressed = false;

	Ast *lhs = as->lhs[0];
	Ast *rhs = as->rhs[0];
	if (lhs->kind == Ast_UnaryExpr && lhs->UnaryExpr.op.kind == Token_And) {
		is_addressed = true;
		lhs = lhs->UnaryExpr.expr;
	}

	check_expr(ctx, &x, rhs);
	check_assignment(ctx, &x, nullptr, str_lit("type switch expression"));
	add_type_info_type(ctx, x.type);

	TypeSwitchKind switch_kind = check_valid_type_switch_type(x.type);
	if (switch_kind == TypeSwitch_Invalid) {
		gbString str = type_to_string(x.type);
		error(x.expr, "Invalid type for this type switch expression, got '%s'", str);
		gb_string_free(str);
		return;
	}

	bool is_partial = ss->partial;
	if (is_partial) {
		if (switch_kind != TypeSwitch_Union) {
			error(node, "#partial switch statement may only be used with a union");
		}
	}


	// NOTE(bill): Check for multiple defaults
	Ast *first_default = nullptr;
	ast_node(bs, BlockStmt, ss->body);
	for (Ast *stmt : bs->stmts) {
		Ast *default_stmt = nullptr;
		if (stmt->kind == Ast_CaseClause) {
			ast_node(cc, CaseClause, stmt);
			if (cc->list.count == 0) {
				default_stmt = stmt;
			}
		} else {
			error(stmt, "Invalid AST - expected case clause");
		}

		if (default_stmt != nullptr) {
			if (first_default != nullptr) {
				TokenPos pos = ast_token(first_default).pos;
				error(stmt,
				      "Multiple default clauses\n"
				      "\tfirst at %s", token_pos_to_string(pos));
			} else {
				first_default = default_stmt;
			}
		}
	}

	if (lhs->kind != Ast_Ident) {
		error(rhs, "Expected an identifier, got '%.*s'", LIT(ast_strings[rhs->kind]));
		return;
	}


	Ast *nil_seen = nullptr;
	TypeSet seen = {};
	defer (type_set_destroy(&seen));

	for (Ast *stmt : bs->stmts) {
		if (stmt->kind != Ast_CaseClause) {
			// NOTE(bill): error handled by above multiple default checker
			continue;
		}
		ast_node(cc, CaseClause, stmt);

		bool saw_nil = false;
		// TODO(bill): Make robust
		Type *bt = base_type(type_deref(x.type));

		Type *case_type = nullptr;
		for (Ast *type_expr : cc->list) {
			if (type_expr != nullptr) { // Otherwise it's a default expression
				Operand y = {};
				check_expr_or_type(ctx, &y, type_expr);

				if (is_operand_nil(y)) {
					if (!type_has_nil(type_deref(x.type))) {
						error(type_expr, "'nil' case is not allowed for the type '%s'", type_to_string(type_deref(x.type)));
						continue;
					}
					saw_nil = true;

					if (nil_seen) {
						ERROR_BLOCK();
						error(type_expr, "'nil' case has already been handled previously");
						error_line("\t 'nil' was already previously seen at %s", token_pos_to_string(ast_token(nil_seen).pos));
					} else {
						nil_seen = type_expr;
					}
					case_type = y.type;
					continue;
				}

				if (y.mode != Addressing_Type) {
					gbString str = expr_to_string(type_expr);
					error(type_expr, "Expected a type as a case, got %s", str);
					gb_string_free(str);
					continue;
				}

				if (switch_kind == TypeSwitch_Union) {
					GB_ASSERT(is_type_union(bt));
					bool tag_type_found = false;
					for (Type *vt : bt->Union.variants) {
						if (are_types_identical(vt, y.type)) {
							tag_type_found = true;
							break;
						}
					}
					if (!tag_type_found) {
						gbString type_str = type_to_string(y.type);
						error(y.expr, "Unknown variant type, got '%s'", type_str);
						gb_string_free(type_str);
						continue;
					}
					case_type = y.type;
					add_type_info_type(ctx, y.type);
				} else if (switch_kind == TypeSwitch_Any) {
					case_type = y.type;
					add_type_info_type(ctx, y.type);
				} else {
					GB_PANIC("Unknown type to type switch statement");
				}

				if (type_set_update(&seen, y.type)) {
					TokenPos pos = cc->token.pos;
					gbString expr_str = expr_to_string(y.expr);
					error(y.expr,
					           "Duplicate type case '%s'\n"
					           "\tprevious type case at %s",
					           expr_str,
					           token_pos_to_string(pos));
					gb_string_free(expr_str);
					break;
				}
			}
		}

		bool is_reference = is_addressed;

		if (cc->list.count > 1 || saw_nil) {
			case_type = nullptr;
		}
		if (case_type == nullptr) {
			case_type = type_deref(x.type);
		}
		if (switch_kind == TypeSwitch_Any) {
			if (!is_type_untyped(case_type)) {
				add_type_info_type(ctx, case_type);
			}
		}

		check_open_scope(ctx, stmt);
		{
			Entity *tag_var = alloc_entity_variable(ctx->scope, lhs->Ident.token, case_type, EntityState_Resolved);
			tag_var->flags |= EntityFlag_Used;
			tag_var->flags |= EntityFlag_SwitchValue;
			if (!is_reference) {
				tag_var->flags |= EntityFlag_Value;
			}
			add_entity(ctx, ctx->scope, lhs, tag_var);
			add_entity_use(ctx, lhs, tag_var);
			add_implicit_entity(ctx, stmt, tag_var);
		}
		check_stmt_list(ctx, cc->stmts, mod_flags);
		check_close_scope(ctx);
	}

	if (!is_partial && is_type_union(type_deref(x.type))) {
		TEMPORARY_ALLOCATOR_GUARD();

		Type *ut = base_type(type_deref(x.type));
		GB_ASSERT(is_type_union(ut));
		auto variants = ut->Union.variants;

		auto unhandled = array_make<Type *>(temporary_allocator(), 0, variants.count);

		for (Type *t : variants) {
			if (!type_set_exists(&seen, t)) {
				array_add(&unhandled, t);
			}
		}

		if (unhandled.count > 0) {
			ERROR_BLOCK();

			if (unhandled.count == 1) {
				gbString s = type_to_string(unhandled[0]);
				error_no_newline(node, "Unhandled switch case: %s", s);
				gb_string_free(s);
			} else {
				error_no_newline(node, "Unhandled switch cases:\n");
				for (Type *t : unhandled) {
					gbString s = type_to_string(t);
					error_line("\t%s\n", s);
					gb_string_free(s);
				}
			}
			error_line("\n");
			error_line("\tSuggestion: Was '#partial switch' wanted?\n");
		}
	}
}

gb_internal void check_block_stmt_for_errors(CheckerContext *ctx, Ast *body)  {
	if (body->kind != Ast_BlockStmt) {
		return;
	}
	ast_node(bs, BlockStmt, body);
	// NOTE(bill, 2020-09-23): This logic is prevent common erros with block statements
	// e.g. if cond { x := 123; } // this is an error
	if (bs->scope != nullptr && bs->scope->elements.count > 0) {
		if (bs->scope->parent->node != nullptr) {
			switch (bs->scope->parent->node->kind) {
			case Ast_IfStmt:
			case Ast_ForStmt:
			case Ast_RangeStmt:
			case Ast_UnrollRangeStmt:
			case Ast_SwitchStmt:
			case Ast_TypeSwitchStmt:
				// TODO(bill): Is this a correct checking system?
				break;
			default:
				return;
			}
		}

		isize stmt_count = 0;
		Ast *the_stmt = nullptr;
		for (Ast *stmt : bs->stmts) {
			GB_ASSERT(stmt != nullptr);
			switch (stmt->kind) {
			case_ast_node(es, EmptyStmt, stmt);
			case_end;
			case_ast_node(bs, BadStmt, stmt);
			case_end;
			case_ast_node(bd, BadDecl, stmt);
			case_end;
			default:
				the_stmt = stmt;
				stmt_count += 1;
				break;
			}
		}

		if (stmt_count == 1) {
			if (the_stmt->kind == Ast_ValueDecl) {
				for (Ast *name : the_stmt->ValueDecl.names) {
					if (name->kind != Ast_Ident) {
						continue;
					}
					String n = name->Ident.token.string;
					if (n != "_") {
						error(name, "'%.*s' declared but not used", LIT(n));
					}
				}
			}
		}
	}
}

gb_internal bool all_operands_valid(Array<Operand> const &operands) {
	if (any_errors()) {
		for (Operand const &o : operands) {
			if (o.type == t_invalid) {
				return false;
			}
		}
	}
	return true;
}

gb_internal bool check_stmt_internal_builtin_proc_id(Ast *expr, BuiltinProcId *id_) {
	BuiltinProcId id = BuiltinProc_Invalid;
	Entity *e = entity_of_node(expr);
	if (e != nullptr && e->kind == Entity_Builtin) {
		if (e->Builtin.id && e->Builtin.id != BuiltinProc_DIRECTIVE) {
			id = cast(BuiltinProcId)e->Builtin.id;
		}
	}
	if (id_) *id_ = id;
	return id != BuiltinProc_Invalid;
}

gb_internal void check_range_stmt(CheckerContext *ctx, Ast *node, u32 mod_flags) {
	ast_node(rs, RangeStmt, node);

	TEMPORARY_ALLOCATOR_GUARD();

	u32 new_flags = mod_flags | Stmt_BreakAllowed | Stmt_ContinueAllowed;

	check_open_scope(ctx, node);
	check_label(ctx, rs->label, node);

	auto vals = array_make<Type *>(temporary_allocator(), 0, 2);
	auto entities = array_make<Entity *>(temporary_allocator(), 0, 2);
	bool is_map = false;
	bool is_bit_set = false;
	bool is_soa = false;
	bool is_reverse = rs->reverse;

	Ast *expr = unparen_expr(rs->expr);

	Operand rhs_operand = {};

	bool is_range = false;
	bool is_possibly_addressable = true;
	isize max_val_count = 2;
	if (is_ast_range(expr)) {
		ast_node(ie, BinaryExpr, expr);
		Operand x = {};
		Operand y = {};

		is_possibly_addressable = false;
		is_range = true;

		bool ok = check_range(ctx, expr, true, &x, &y, nullptr);
		if (!ok) {
			goto skip_expr_range_stmt;
		}
		array_add(&vals, x.type);
		array_add(&vals, t_int);

		if (is_reverse) {
			error(node, "#reverse for is not supported with ranges, prefer an explicit for loop with init, condition, and post arguments");
		}
	} else {
		Operand operand = {Addressing_Invalid};
		check_expr_base(ctx, &operand, expr, nullptr);
		error_operand_no_value(&operand);

		if (operand.mode == Addressing_Type) {
			if (!is_type_enum(operand.type)) {
				gbString t = type_to_string(operand.type);
				error(operand.expr, "Cannot iterate over the type '%s'", t);
				gb_string_free(t);
				goto skip_expr_range_stmt;
			} else {
				is_possibly_addressable = false;

				if (is_reverse) {
					error(node, "#reverse for is not supported for enum types");
				}
				array_add(&vals, operand.type);
				array_add(&vals, t_int);
				add_type_info_type(ctx, operand.type);
				if (build_context.no_rtti) {
					error(node, "Iteration over an enum type is not allowed runtime type information (RTTI) has been disallowed");
				}
				goto skip_expr_range_stmt;
			}
		} else if (operand.mode != Addressing_Invalid) {
			if (operand.mode == Addressing_OptionalOk || operand.mode == Addressing_OptionalOkPtr) {
				Ast *expr = unparen_expr(operand.expr);
				if (expr->kind != Ast_TypeAssertion) { // Only for procedure calls
					Type *end_type = nullptr;
					check_promote_optional_ok(ctx, &operand, nullptr, &end_type, false);
					if (is_type_boolean(end_type)) {
						check_promote_optional_ok(ctx, &operand, nullptr, &end_type, true);
					}
				}
			}
			bool is_ptr = is_type_pointer(operand.type);
			Type *t = base_type(type_deref(operand.type));

			switch (t->kind) {
			case Type_Basic:
				if (t->Basic.kind == Basic_string || t->Basic.kind == Basic_UntypedString) {
					is_possibly_addressable = false;
					array_add(&vals, t_rune);
					array_add(&vals, t_int);
					if (is_reverse) {
						add_package_dependency(ctx, "runtime", "string_decode_last_rune");
					} else {
						add_package_dependency(ctx, "runtime", "string_decode_rune");
					}
				}
				break;

			case Type_BitSet:
				array_add(&vals, t->BitSet.elem);
				max_val_count = 1;
				is_bit_set = true;
				is_possibly_addressable = false;
				add_type_info_type(ctx, operand.type);
				if (build_context.no_rtti && is_type_enum(t->BitSet.elem)) {
					error(node, "Iteration over a bit_set of an enum is not allowed runtime type information (RTTI) has been disallowed");
				}
				if (rs->vals.count == 1 && rs->vals[0] && rs->vals[0]->kind == Ast_Ident) {
					String name = rs->vals[0]->Ident.token.string;
					Entity *found = scope_lookup(ctx->scope, name);
					if (found && are_types_identical(found->type, t->BitSet.elem)) {
						ERROR_BLOCK();
						gbString s = expr_to_string(expr);
						error(rs->vals[0], "'%.*s' shadows a previous declaration which might be ambiguous with 'for (%.*s in %s)'", LIT(name), LIT(name), s);
						error_line("\tSuggestion: Use a different identifier if iteration is wanted, or surround in parentheses if a normal for loop is wanted\n");
						gb_string_free(s);
					}
				}
				break;

			case Type_EnumeratedArray:
				is_possibly_addressable = operand.mode == Addressing_Variable || is_ptr;
				array_add(&vals, t->EnumeratedArray.elem);
				array_add(&vals, t->EnumeratedArray.index);
				break;

			case Type_Array:
				is_possibly_addressable = operand.mode == Addressing_Variable || is_ptr;
				array_add(&vals, t->Array.elem);
				array_add(&vals, t_int);
				break;

			case Type_DynamicArray:
				is_possibly_addressable = true;
				array_add(&vals, t->DynamicArray.elem);
				array_add(&vals, t_int);
				break;

			case Type_Slice:
				is_possibly_addressable = true;
				array_add(&vals, t->Slice.elem);
				array_add(&vals, t_int);
				break;

			case Type_Map:
				is_possibly_addressable = true;
				is_map = true;
				array_add(&vals, t->Map.key);
				array_add(&vals, t->Map.value);
				if (is_reverse) {
					error(node, "#reverse for is not supported for map types, as maps are unordered");
				}
				if (rs->vals.count == 1 && rs->vals[0] && rs->vals[0]->kind == Ast_Ident) {
					String name = rs->vals[0]->Ident.token.string;
					Entity *found = scope_lookup(ctx->scope, name);
					if (found && are_types_identical(found->type, t->Map.key)) {
						ERROR_BLOCK();
						gbString s = expr_to_string(expr);
						error(rs->vals[0], "'%.*s' shadows a previous declaration which might be ambiguous with 'for (%.*s in %s)'", LIT(name), LIT(name), s);
						error_line("\tSuggestion: Use a different identifier if iteration is wanted, or surround in parentheses if a normal for loop is wanted\n");
						gb_string_free(s);
					}
				}
				break;

			case Type_Tuple:
				{
					is_possibly_addressable = false;

					isize count = t->Tuple.variables.count;
					if (count < 1) {
						ERROR_BLOCK();
						check_not_tuple(ctx, &operand);
						error_line("\tMultiple return valued parameters in a range statement are limited to a minimum of 1 usable values with a trailing boolean for the conditional, got %td\n", count);
						break;
					}
					enum : isize {MAXIMUM_COUNT = 100};
					if (count > MAXIMUM_COUNT) {
						ERROR_BLOCK();
						check_not_tuple(ctx, &operand);
						error_line("\tMultiple return valued parameters in a range statement are limited to a maximum of %td usable values with a trailing boolean for the conditional, got %td\n", MAXIMUM_COUNT, count);
						break;
					}

					Type *cond_type = t->Tuple.variables[count-1]->type;
					if (!is_type_boolean(cond_type)) {
						gbString s = type_to_string(cond_type);
						error(operand.expr, "The final type of %td-valued expression must be a boolean, got %s", count, s);
						gb_string_free(s);
						break;
					}

					max_val_count = count;

					for (Entity *e : t->Tuple.variables) {
						array_add(&vals, e->type);
					}

					bool do_break = false;
					for (isize i = rs->vals.count-1; i >= 0; i--) {
						if (rs->vals[i] != nullptr && count < i+2) {
							gbString s = type_to_string(t);
							error(operand.expr, "Expected a %td-valued expression on the rhs, got (%s)", i+2, s);
							gb_string_free(s);
							do_break = true;
							break;
						}
					}

					if (is_reverse) {
						error(node, "#reverse for is not supported for multiple return valued parameters");
					}
				}
				break;

			case Type_Struct:
				if (t->Struct.soa_kind != StructSoa_None) {
					if (t->Struct.soa_kind == StructSoa_Fixed) {
						is_possibly_addressable = operand.mode == Addressing_Variable || is_ptr;
					} else {
						is_possibly_addressable = true;
					}
					is_soa = true;
					array_add(&vals, t->Struct.soa_elem);
					array_add(&vals, t_int);
				}
				break;
			}
		}

		if (vals.count == 0 || vals[0] == nullptr) {
			gbString s = expr_to_string(operand.expr);
			gbString t = type_to_string(operand.type);
			defer (gb_string_free(s));
			defer (gb_string_free(t));

			ERROR_BLOCK();

			error(operand.expr, "Cannot iterate over '%s' of type '%s'", s, t);

			if (rs->vals.count == 1) {
				Type *t = type_deref(operand.type);
				if (t != NULL && (is_type_map(t) || is_type_bit_set(t))) {
					gbString v = expr_to_string(rs->vals[0]);
					defer (gb_string_free(v));
					error_line("\tSuggestion: place parentheses around the expression\n");
					error_line("\t            for (%s in %s) {\n", v, s);
				}
			}
		}
	}

	skip_expr_range_stmt:; // NOTE(zhiayang): again, declaring a variable immediately after a label... weird.

	if (rs->vals.count > max_val_count) {
		error(rs->vals[max_val_count], "Expected a maximum of %td identifier%s, got %td", max_val_count, max_val_count == 1 ? "" : "s", rs->vals.count);
	}

	auto rhs = slice_from_array(vals);
	auto lhs = slice_make<Ast *>(temporary_allocator(), rhs.count);
	slice_copy(&lhs, rs->vals);

	isize addressable_index = cast(isize)is_map;

	for_array(i, rhs) {
		if (lhs[i] == nullptr) {
			continue;
		}
		Ast * name = lhs[i];
		Type *type = rhs[i];
		Entity *entity = nullptr;

		bool is_addressed = false;
		if (name->kind == Ast_UnaryExpr && name->UnaryExpr.op.kind == Token_And) {
			is_addressed = true;
			name = name->UnaryExpr.expr;
		}
		if (name->kind == Ast_Ident) {
			Token token = name->Ident.token;
			String str = token.string;
			Entity *found = nullptr;

			if (!is_blank_ident(str)) {
				found = scope_lookup_current(ctx->scope, str);
			}
			if (found == nullptr) {
				entity = alloc_entity_variable(ctx->scope, token, type, EntityState_Resolved);
				if (!is_range) {
					entity->flags |= EntityFlag_ForValue;
				}
				entity->flags |= EntityFlag_Value;
				entity->identifier = name;
				entity->Variable.for_loop_parent_type = type_of_expr(expr);

				if (is_addressed) {
					if (is_possibly_addressable && i == addressable_index) {
						entity->flags &= ~EntityFlag_Value;
					} else {
						char const *idx_name = is_map ? "key" : (is_bit_set || i == 0) ? "element" : "index";
						error(token, "The %s variable '%.*s' cannot be made addressable", idx_name, LIT(str));
					}
				}
				if (is_soa) {
					if (i == 0) {
						entity->flags |= EntityFlag_SoaPtrField;
					}
				}

				add_entity_definition(&ctx->checker->info, name, entity);
			} else {
				TokenPos pos = found->token.pos;
				error(token,
				      "Redeclaration of '%.*s' in this scope\n"
				      "\tat %s",
				      LIT(str), token_pos_to_string(pos));
				entity = found;
			}
		} else {
			error_var_decl_identifier(name);
		}

		if (entity == nullptr) {
			entity = alloc_entity_dummy_variable(builtin_pkg->scope, ast_token(name));
			entity->identifier = name; // might not be an identifier
		}

		array_add(&entities, entity);

		if (type == nullptr) {
			entity->type = t_invalid;
			entity->flags |= EntityFlag_Used;
		}
	}

	for (Entity *e : entities) {
		DeclInfo *d = decl_info_of_entity(e);
		GB_ASSERT(d == nullptr);
		add_entity(ctx, ctx->scope, e->identifier, e);
		d = make_decl_info(ctx->scope, ctx->decl);
		add_entity_and_decl_info(ctx, e->identifier, e, d);
	}

	check_stmt(ctx, rs->body, new_flags);

	check_close_scope(ctx);
}

gb_internal void check_value_decl_stmt(CheckerContext *ctx, Ast *node, u32 mod_flags) {
	ast_node(vd, ValueDecl, node);
	if (!vd->is_mutable) {
		// constant value declaration
		// NOTE(bill): Check `_` declarations
		for (Ast *name : vd->names) {
			if (is_blank_ident(name)) {
				Entity *e = name->Ident.entity;
				DeclInfo *d = decl_info_of_entity(e);
				if (d != nullptr) {
					check_entity_decl(ctx, e, d, nullptr);
				}
			}
		}
		return;
	}
	Entity **entities = gb_alloc_array(permanent_allocator(), Entity *, vd->names.count);
	isize entity_count = 0;

	isize new_name_count = 0;
	for (Ast *name : vd->names) {
		Entity *entity = nullptr;
		if (name->kind != Ast_Ident) {
			error_var_decl_identifier(name);
		} else {
			Token token = name->Ident.token;
			String str = token.string;
			Entity *found = nullptr;
			// NOTE(bill): Ignore assignments to '_'
			if (!is_blank_ident(str)) {
				found = scope_lookup_current(ctx->scope, str);
				new_name_count += 1;
			}
			if (found == nullptr) {
				entity = alloc_entity_variable(ctx->scope, token, nullptr);
				entity->identifier = name;

				Ast *fl = ctx->foreign_context.curr_library;
				if (fl != nullptr) {
					GB_ASSERT(fl->kind == Ast_Ident);
					entity->Variable.is_foreign = true;
					entity->Variable.foreign_library_ident = fl;
				}
			} else {
				TokenPos pos = found->token.pos;
				error(token,
				      "Redeclaration of '%.*s' in this scope\n"
				      "\tat %s",
				      LIT(str), token_pos_to_string(pos));
				entity = found;
			}
		}
		if (entity == nullptr) {
			entity = alloc_entity_dummy_variable(builtin_pkg->scope, ast_token(name));
		}
		entity->parent_proc_decl = ctx->curr_proc_decl;
		entities[entity_count++] = entity;
		if (name->kind == Ast_Ident) {
			name->Ident.entity = entity;
		}
	}

	if (new_name_count == 0) {
		ERROR_BLOCK();
		error(node, "No new declarations on the left hand side");
		bool all_underscore = true;
		for (Ast *name : vd->names) {
			if (name->kind == Ast_Ident) {
				if (!is_blank_ident(name)) {
					all_underscore = false;
					break;
				}
			} else {
				all_underscore = false;
				break;
			}
		}
		if (all_underscore) {
			error_line("\tSuggestion: Try changing the declaration (:=) to an assignment (=)\n");
		}

	}

	Type *init_type = nullptr;
	if (vd->type != nullptr) {
		init_type = check_type(ctx, vd->type);
		if (init_type == nullptr) {
			init_type = t_invalid;
		} else if (is_type_polymorphic(base_type(init_type))) {
			/* DISABLED: This error seems too aggressive for instantiated generic types.
			gbString str = type_to_string(init_type);
			error(vd->type, "Invalid use of a polymorphic type '%s' in variable declaration", str);
			gb_string_free(str);
			init_type = t_invalid;
			*/
		}
		if (init_type == t_invalid && entity_count == 1 && (mod_flags & (Stmt_BreakAllowed|Stmt_FallthroughAllowed))) {
			Entity *e = entities[0];
			if (e != nullptr && e->token.string == "default") {
				warning(e->token, "Did you mean 'case:'?");
			}
		}
	}


	// TODO NOTE(bill): This technically checks things multple times
	AttributeContext ac = make_attribute_context(ctx->foreign_context.link_prefix, ctx->foreign_context.link_suffix);
	check_decl_attributes(ctx, vd->attributes, var_decl_attribute, &ac);

	for (isize i = 0; i < entity_count; i++) {
		Entity *e = entities[i];
		GB_ASSERT(e != nullptr);
		if (e->flags & EntityFlag_Visited) {
			e->type = t_invalid;
			continue;
		}
		e->flags |= EntityFlag_Visited;

		e->state = EntityState_InProgress;
		if (e->type == nullptr) {
			e->type = init_type;
			e->state = EntityState_Resolved;
		}
		ac.link_name = handle_link_name(ctx, e->token, ac.link_name, ac.link_prefix, ac.link_suffix);

		if (ac.link_name.len > 0) {
			e->Variable.link_name = ac.link_name;
		}

		e->flags &= ~EntityFlag_Static;
		if (ac.is_static) {
			String name = e->token.string;
			if (name == "_") {
				error(e->token, "The 'static' attribute is not allowed to be applied to '_'");
			} else {
				e->flags |= EntityFlag_Static;
				if (ctx->in_defer) {
					error(e->token, "'static' variables cannot be declared within a defer statement");
				}
			}
		}
		if (ac.rodata) {
			if (ac.is_static) {
				e->Variable.is_rodata = true;
			} else {
				error(e->token, "Only global or @(static) variables can have @(rodata) applied");
			}
		}
		if (ac.thread_local_model != "") {
			String name = e->token.string;
			if (name == "_") {
				error(e->token, "The 'thread_local' attribute is not allowed to be applied to '_'");
			} else {
				e->flags |= EntityFlag_Static;
				if (ctx->in_defer) {
					error(e->token, "'thread_local' variables cannot be declared within a defer statement");
				}
			}
			e->Variable.thread_local_model = ac.thread_local_model;
		}

		if (ac.is_static && ac.thread_local_model != "") {
			error(e->token, "The 'static' attribute is not needed if 'thread_local' is applied");
		}
	}

	// NOTE(bill): This is to improve error handling for things like `x: [?]T = {...}`
	Ast *prev_type_hint_expr = ctx->type_hint_expr;
	ctx->type_hint_expr = vd->type;

	check_init_variables(ctx, entities, entity_count, vd->values, str_lit("variable declaration"));

	ctx->type_hint_expr = prev_type_hint_expr;

	check_arity_match(ctx, vd, false);

	for (isize i = 0; i < entity_count; i++) {
		Entity *e = entities[i];

		if (e->Variable.is_foreign) {
			if (vd->values.count > 0) {
				error(e->token, "A foreign variable declaration cannot have a default value");
			}

			String name = e->token.string;
			if (e->Variable.link_name.len > 0) {
				name = e->Variable.link_name;
			}

			if (vd->values.count > 0) {
				error(e->token, "A foreign variable declaration cannot have a default value");
			}
			init_entity_foreign_library(ctx, e);

			auto *fp = &ctx->checker->info.foreigns;
			StringHashKey key = string_hash_string(name);
			Entity **found = string_map_get(fp, key);
			if (found) {
				Entity *f = *found;
				TokenPos pos = f->token.pos;
				Type *this_type = base_type(e->type);
				Type *other_type = base_type(f->type);
				if (!signature_parameter_similar_enough(this_type, other_type)) {
					error(e->token,
					      "Foreign entity '%.*s' previously declared elsewhere with a different type\n"
					      "\tat %s",
					      LIT(name), token_pos_to_string(pos));
				}
			} else {
				string_map_set(fp, key, e);
			}
		} else if (e->flags & EntityFlag_Static) {
			if (vd->values.count > 0) {
				if (entity_count != vd->values.count) {
					error(e->token, "A static variable declaration with a default value must be constant");
				} else {
					Ast *value = vd->values[i];
					if (value->tav.mode != Addressing_Constant) {
						error(e->token, "A static variable declaration with a default value must be constant");
					}
				}
			}
		}
		add_entity(ctx, ctx->scope, e->identifier, e);
	}

	if (vd->is_using != 0) {
		Token token = ast_token(node);
		if (vd->type != nullptr && entity_count > 1) {
			error(token, "'using' can only be applied to one variable of the same type");
			// NOTE(bill): `using` will only be applied to a single declaration
		}

		for (isize entity_index = 0; entity_index < 1; entity_index++) {
			Entity *e = entities[entity_index];
			if (e == nullptr) {
				continue;
			}
			if (e->kind != Entity_Variable) {
				continue;
			}
			String name = e->token.string;
			Type *t = base_type(type_deref(e->type));

			if (is_blank_ident(name)) {
				error(token, "'using' cannot be applied variable declared as '_'");
			} else if (is_type_struct(t) || is_type_raw_union(t)) {
				ERROR_BLOCK();

				Scope *scope = t->Struct.scope;
				GB_ASSERT(scope != nullptr);
				for (auto const &entry : scope->elements) {
					Entity *f = entry.value;
					if (f->kind == Entity_Variable) {
						Entity *uvar = alloc_entity_using_variable(e, f->token, f->type, e->identifier);
						uvar->flags |= (e->flags & EntityFlag_Value);
						Entity *prev = scope_insert(ctx->scope, uvar);
						if (prev != nullptr) {
							error(token, "Namespace collision while 'using' '%.*s' of: %.*s", LIT(name), LIT(prev->token.string));
							return;
						}
					}
				}

				add_entity_use(ctx, nullptr, e);
			} else {
				// NOTE(bill): skip the rest to remove extra errors
				error(token, "'using' can only be applied to variables of type struct or raw_union");
				return;
			}
		}
	}
}

gb_internal void check_expr_stmt(CheckerContext *ctx, Ast *node) {
	ast_node(es, ExprStmt, node);

	Operand operand = {Addressing_Invalid};
	ExprKind kind = check_expr_base(ctx, &operand, es->expr, nullptr);
	switch (operand.mode) {
	case Addressing_Type:
		{
			gbString str = type_to_string(operand.type);
			error(node, "'%s' is not an expression but a type and cannot be used as a statement", str);
			gb_string_free(str);
			break;
		}
	case Addressing_NoValue:
		return;
	}
	if (kind == Expr_Stmt) {
		return;
	}

	Ast *expr = strip_or_return_expr(operand.expr);
	if (expr && expr->kind == Ast_CallExpr) {
		BuiltinProcId builtin_id = BuiltinProc_Invalid;
		bool do_require = false;

		AstCallExpr *ce = &expr->CallExpr;
		Type *t = base_type(type_of_expr(ce->proc));
		if (t && t->kind == Type_Proc) {
			do_require = t->Proc.require_results;
		} else if (check_stmt_internal_builtin_proc_id(ce->proc, &builtin_id)) {
			auto const &bp = builtin_procs[builtin_id];
			do_require = bp.kind == Expr_Expr && !bp.ignore_results;
		}
		if (do_require) {
			gbString expr_str = expr_to_string(ce->proc);
			defer (gb_string_free(expr_str));
			if (builtin_id) {
				String real_name = builtin_procs[builtin_id].name;
				if (real_name != make_string(cast(u8 const *)expr_str, gb_string_length(expr_str))) {
					error(node, "'%s' ('%.*s.%.*s') requires that its results must be handled", expr_str,
					      LIT(builtin_proc_pkg_name[builtin_procs[builtin_id].pkg]), LIT(real_name));
					return;
				}
			}
			error(node, "'%s' requires that its results must be handled", expr_str);
		}
		return;
	} else if (expr && expr->kind == Ast_SelectorCallExpr) {
		BuiltinProcId builtin_id = BuiltinProc_Invalid;
		bool do_require = false;

		AstSelectorCallExpr *se = &expr->SelectorCallExpr;
		ast_node(ce, CallExpr, se->call);
		Type *t = base_type(type_of_expr(ce->proc));
		if (t == nullptr) {
			gbString expr_str = expr_to_string(ce->proc);
			error(node, "'%s' is not a value field nor procedure", expr_str);
			gb_string_free(expr_str);
			return;
		}
		if (t->kind == Type_Proc) {
			do_require = t->Proc.require_results;
		} else if (check_stmt_internal_builtin_proc_id(ce->proc, &builtin_id)) {
			auto const &bp = builtin_procs[builtin_id];
			do_require = bp.kind == Expr_Expr && !bp.ignore_results;
		}
		if (do_require) {
			gbString expr_str = expr_to_string(ce->proc);
			error(node, "'%s' requires that its results must be handled", expr_str);
			gb_string_free(expr_str);
		}
		return;
	}

	ERROR_BLOCK();

	gbString expr_str = expr_to_string(operand.expr);
	error(node, "Expression is not used: '%s'", expr_str);
	gb_string_free(expr_str);
	if (operand.expr->kind == Ast_BinaryExpr) {
		ast_node(be, BinaryExpr, operand.expr);
		if (be->op.kind != Token_CmpEq) {
			return;
		}

		switch (be->left->tav.mode) {
		case Addressing_Context:
		case Addressing_Variable:
		case Addressing_MapIndex:
		case Addressing_SoaVariable:
			{
				gbString lhs = expr_to_string(be->left);
				gbString rhs = expr_to_string(be->right);
				error_line("\tSuggestion: Did you mean to do an assignment?\n", lhs, rhs);
				error_line("\t            '%s = %s;'\n", lhs, rhs);
				gb_string_free(rhs);
				gb_string_free(lhs);
			}
			break;
		}
	}
}

gb_internal void check_assign_stmt(CheckerContext *ctx, Ast *node) {
	ast_node(as, AssignStmt, node);

	if (as->op.kind == Token_Eq) {
		// a, b, c = 1, 2, 3;  // Multisided

		isize lhs_count = as->lhs.count;
		if (lhs_count == 0) {
			error(as->op, "Missing lhs in assignment statement");
			return;
		}

		TEMPORARY_ALLOCATOR_GUARD();

		// NOTE(bill): If there is a bad syntax error, rhs > lhs which would mean there would need to be
		// an extra allocation
		auto lhs_operands = array_make<Operand>(temporary_allocator(), lhs_count);
		auto rhs_operands = array_make<Operand>(temporary_allocator(), 0, 2*lhs_count);

		for_array(i, as->lhs) {
			if (is_blank_ident(as->lhs[i])) {
				Operand *o = &lhs_operands[i];
				o->expr = as->lhs[i];
				o->mode = Addressing_Value;
			} else {
				ctx->assignment_lhs_hint = unparen_expr(as->lhs[i]);
				check_expr(ctx, &lhs_operands[i], as->lhs[i]);
			}
		}
		ctx->assignment_lhs_hint = nullptr; // Reset the assignment_lhs_hint

		check_assignment_arguments(ctx, lhs_operands, &rhs_operands, as->rhs);

		auto lhs_to_ignore = array_make<bool>(temporary_allocator(), lhs_count);

		isize rhs_count = rhs_operands.count;
		isize max = gb_min(lhs_count, rhs_count);
		for (isize i = 0; i < max; i++) {
			if (lhs_to_ignore[i]) {
				continue;
			}
			check_assignment_variable(ctx, &lhs_operands[i], &rhs_operands[i]);
		}
		if (lhs_count != rhs_count) {
			error(as->lhs[0], "Assignment count mismatch '%td' = '%td'", lhs_count, rhs_count);
		}

	} else {
		// a += 1; // Single-sided
		Token op = as->op;
		if (as->lhs.count != 1 || as->rhs.count != 1) {
			error(op, "Assignment operation '%.*s' requires single-valued expressions", LIT(op.string));
			return;
		}
		if (!gb_is_between(op.kind, Token__AssignOpBegin+1, Token__AssignOpEnd-1)) {
			error(op, "Unknown Assignment operation '%.*s'", LIT(op.string));
			return;
		}
		Operand lhs = {Addressing_Invalid};
		Operand rhs = {Addressing_Invalid};
		Ast *binary_expr = alloc_ast_node(node->file(), Ast_BinaryExpr);
		ast_node(be, BinaryExpr, binary_expr);
		be->op = op;
		be->op.kind = cast(TokenKind)(cast(i32)be->op.kind - (Token_AddEq - Token_Add));
		 // NOTE(bill): Only use the first one will be used
		be->left  = as->lhs[0];
		be->right = as->rhs[0];

		check_expr(ctx, &lhs, as->lhs[0]);
		check_binary_expr(ctx, &rhs, binary_expr, nullptr, true);
		if (rhs.mode != Addressing_Invalid) {
			// NOTE(bill): Only use the first one will be used
			check_assignment_variable(ctx, &lhs, &rhs);
		}
	}
}

gb_internal void check_if_stmt(CheckerContext *ctx, Ast *node, u32 mod_flags) {
	ast_node(is, IfStmt, node);
	check_open_scope(ctx, node);

	check_label(ctx, is->label, node);

	if (is->init != nullptr) {
		check_stmt(ctx, is->init, 0);
	}

	Operand operand = {Addressing_Invalid};
	check_expr(ctx, &operand, is->cond);
	if (operand.mode != Addressing_Invalid && !is_type_boolean(operand.type)) {
		error(is->cond, "Non-boolean condition in 'if' statement");
	}

	check_stmt(ctx, is->body, mod_flags);

	if (is->else_stmt != nullptr) {
		switch (is->else_stmt->kind) {
		case Ast_IfStmt:
		case Ast_BlockStmt:
			check_stmt(ctx, is->else_stmt, mod_flags);
			break;
		default:
			error(is->else_stmt, "Invalid 'else' statement in 'if' statement");
			break;
		}
	}

	check_close_scope(ctx);
}

gb_internal void check_return_stmt(CheckerContext *ctx, Ast *node) {
	ast_node(rs, ReturnStmt, node);

	GB_ASSERT(ctx->curr_proc_sig != nullptr);

	if (ctx->in_defer) {
		error(rs->token, "'return' cannot be used within a defer statement");
		return;
	}

	Type *proc_type = ctx->curr_proc_sig;
	GB_ASSERT(proc_type != nullptr);
	GB_ASSERT(proc_type->kind == Type_Proc);

	TypeProc *pt = &proc_type->Proc;
	if (pt->diverging) {
		error(rs->token, "Diverging procedures may not return");
		return;
	}

	Entity **result_entities = nullptr;
	isize result_count = 0;
	bool has_named_results = pt->has_named_results;
	if (pt->results) {
		result_entities = proc_type->Proc.results->Tuple.variables.data;
		result_count = proc_type->Proc.results->Tuple.variables.count;
	}

	auto operands = array_make<Operand>(heap_allocator(), 0, 2*rs->results.count);
	defer (array_free(&operands));

	check_unpack_arguments(ctx, result_entities, result_count, &operands, rs->results, UnpackFlag_AllowOk);

	if (result_count == 0 && rs->results.count > 0) {
		error(rs->results[0], "No return values expected");
	} else if (has_named_results && operands.count == 0) {
		// Okay
	} else if (operands.count != result_count) {
		// Ignore error message as it has most likely already been reported
		if (all_operands_valid(operands)) {
			if (operands.count == 1) {
				gbString t = type_to_string(operands[0].type);
				error(node, "Expected %td return values, got %td (%s)", result_count, operands.count, t);
				gb_string_free(t);
			} else {
				error(node, "Expected %td return values, got %td", result_count, operands.count);
			}
		}
	} else {
		for (isize i = 0; i < result_count; i++) {
			Entity *e = pt->results->Tuple.variables[i];
			Operand *o = &operands[i];
			check_assignment(ctx, o, e->type, str_lit("return statement"));
			if (is_type_untyped(o->type)) {
				update_untyped_expr_type(ctx, o->expr, e->type, true);
			}
		}
	}

	for (Operand &o : operands) {
		if (o.expr == nullptr) {
			continue;
		}
		Ast *expr = unparen_expr(o.expr);
		while (expr->kind == Ast_CallExpr && expr->CallExpr.proc->tav.mode == Addressing_Type) {
			if (expr->CallExpr.args.count != 1) {
				break;
			}
			Ast *arg = expr->CallExpr.args[0];
			if (arg->kind == Ast_FieldValue || !are_types_identical(arg->tav.type, expr->tav.type)) {
				break;
			}
			expr = unparen_expr(arg);
		}

		auto unsafe_return_error = [](Operand const &o, char const *msg, Type *extra_type=nullptr) {
			gbString s = expr_to_string(o.expr);
			if (extra_type) {
				gbString t = type_to_string(extra_type);
				error(o.expr, "It is unsafe to return %s ('%s') of type ('%s') from a procedure, as it uses the current stack frame's memory", msg, s, t);
				gb_string_free(t);
			} else {
				error(o.expr, "It is unsafe to return %s ('%s') from a procedure, as it uses the current stack frame's memory", msg, s);
			}
			gb_string_free(s);
		};


		// NOTE(bill): This is very basic escape analysis
		// This needs to be improved tremendously, and a lot of it done during the
		// middle-end (or LLVM side) to improve checks and error messages
		if (expr->kind == Ast_CompoundLit && is_type_slice(o.type)) {
			ast_node(cl, CompoundLit, expr);
			if (cl->elems.count == 0) {
				continue;
			}
			unsafe_return_error(o, "a compound literal of a slice");
		} else if (expr->kind == Ast_UnaryExpr && expr->UnaryExpr.op.kind == Token_And) {
			Ast *x = unparen_expr(expr->UnaryExpr.expr);
			Entity *e = entity_of_node(x);
			if (is_entity_local_variable(e)) {
				unsafe_return_error(o, "the address of a local variable");
			} else if (x->kind == Ast_CompoundLit) {
				unsafe_return_error(o, "the address of a compound literal");
			} else if (x->kind == Ast_IndexExpr) {
				Entity *f = entity_of_node(x->IndexExpr.expr);
				if (f && (is_type_array_like(f->type) || is_type_matrix(f->type))) {
					if (is_entity_local_variable(f)) {
						unsafe_return_error(o, "the address of an indexed variable", f->type);
					}
				}
			} else if (x->kind == Ast_MatrixIndexExpr) {
				Entity *f = entity_of_node(x->MatrixIndexExpr.expr);
				if (f && (is_type_matrix(f->type) && is_entity_local_variable(f))) {
					unsafe_return_error(o, "the address of an indexed variable", f->type);
				}
			}
		} else if (expr->kind == Ast_SliceExpr) {
			Ast *x = unparen_expr(expr->SliceExpr.expr);
			Entity *e = entity_of_node(x);
			if (is_entity_local_variable(e) && is_type_array(e->type)) {
				unsafe_return_error(o, "a slice of a local variable");
			} else if (x->kind == Ast_CompoundLit) {
				unsafe_return_error(o, "a slice of a compound literal");
			}
		} else if (o.mode == Addressing_Constant && is_type_slice(o.type)) {
			ERROR_BLOCK();
			unsafe_return_error(o, "a compound literal of a slice");
			error_line("\tNote: A constant slice value will use the memory of the current stack frame\n");
		}
	}

}

gb_internal void check_for_stmt(CheckerContext *ctx, Ast *node, u32 mod_flags) {
	ast_node(fs, ForStmt, node);
	mod_flags |= Stmt_BreakAllowed | Stmt_ContinueAllowed;

	check_open_scope(ctx, node);
	check_label(ctx, fs->label, node);

	if (fs->init != nullptr) {
		check_stmt(ctx, fs->init, 0);
	}
	if (fs->cond != nullptr) {
		Operand o = {Addressing_Invalid};
		check_expr(ctx, &o, fs->cond);
		if (o.mode != Addressing_Invalid && !is_type_boolean(o.type)) {
			error(fs->cond, "Non-boolean condition in 'for' statement");
		} else {
			Ast *cond = unparen_expr(o.expr);
			if (cond && cond->kind == Ast_BinaryExpr &&
			    cond->BinaryExpr.left && cond->BinaryExpr.right &&
			    cond->BinaryExpr.op.kind == Token_GtEq &&
			    type_of_expr(cond->BinaryExpr.left) != nullptr &&
			    is_type_unsigned(type_of_expr(cond->BinaryExpr.left)) &&
			    cond->BinaryExpr.right->tav.value.kind == ExactValue_Integer &&
			    is_exact_value_zero(cond->BinaryExpr.right->tav.value)) {
				warning(cond, "Expression is always true since unsigned numbers are always >= 0");
			} else if (cond && cond->kind == Ast_BinaryExpr &&
			    cond->BinaryExpr.left && cond->BinaryExpr.right &&
			    cond->BinaryExpr.op.kind == Token_LtEq &&
			    type_of_expr(cond->BinaryExpr.right) != nullptr &&
			    is_type_unsigned(type_of_expr(cond->BinaryExpr.right)) &&
			    cond->BinaryExpr.left->tav.value.kind == ExactValue_Integer &&
			    is_exact_value_zero(cond->BinaryExpr.left->tav.value)) {
				warning(cond, "Expression is always true since unsigned numbers are always >= 0");
			}
		}
	}
	if (fs->post != nullptr) {
		check_stmt(ctx, fs->post, 0);

		if (fs->post->kind != Ast_AssignStmt) {
			error(fs->post, "'for' statement post statement must be a simple statement");
		}
	}
	check_stmt(ctx, fs->body, mod_flags);

	check_close_scope(ctx);
}


gb_internal void check_stmt_internal(CheckerContext *ctx, Ast *node, u32 flags) {
	u32 mod_flags = flags & (~Stmt_FallthroughAllowed);
	switch (node->kind) {
	case_ast_node(_, EmptyStmt, node); case_end;
	case_ast_node(_, BadStmt,   node); case_end;
	case_ast_node(_, BadDecl,   node); case_end;

	case_ast_node(es, ExprStmt, node)
		check_expr_stmt(ctx, node);
	case_end;

	case_ast_node(as, AssignStmt, node);
		check_assign_stmt(ctx, node);
	case_end;

	case_ast_node(bs, BlockStmt, node);
		check_open_scope(ctx, node);
		check_label(ctx, bs->label, node);

		check_stmt_list(ctx, bs->stmts, flags);
		check_block_stmt_for_errors(ctx, node);
		check_close_scope(ctx);
	case_end;

	case_ast_node(is, IfStmt, node);
		check_if_stmt(ctx, node, mod_flags);
	case_end;

	case_ast_node(ws, WhenStmt, node);
		check_when_stmt(ctx, ws, flags);
	case_end;

	case_ast_node(rs, ReturnStmt, node);
		check_return_stmt(ctx, node);
	case_end;

	case_ast_node(fs, ForStmt, node);
		check_for_stmt(ctx, node, mod_flags);
	case_end;

	case_ast_node(rs, RangeStmt, node);
		check_range_stmt(ctx, node, mod_flags);
	case_end;

	case_ast_node(irs, UnrollRangeStmt, node);
		check_unroll_range_stmt(ctx, node, mod_flags);
	case_end;

	case_ast_node(ss, SwitchStmt, node);
		check_switch_stmt(ctx, node, mod_flags);
	case_end;

	case_ast_node(ss, TypeSwitchStmt, node);
		check_type_switch_stmt(ctx, node, mod_flags);
	case_end;


	case_ast_node(ds, DeferStmt, node);
		if (is_ast_decl(ds->stmt)) {
			error(ds->token, "You cannot defer a declaration");
		} else {
			bool out_in_defer = ctx->in_defer;
			ctx->in_defer = true;
			check_stmt(ctx, ds->stmt, 0);
			ctx->in_defer = out_in_defer;
			if (ctx->decl) {
				ctx->decl->defer_used += 1;
			}

			// NOTE(bill): Handling errors/warnings

			Ast *stmt = ds->stmt;
			Ast *original_stmt = stmt;

			bool is_singular = true;
			while (is_singular && stmt->kind == Ast_BlockStmt) {
				Ast *inner_stmt = nullptr;
				for (Ast *s : stmt->BlockStmt.stmts) {
					if (s->kind == Ast_EmptyStmt) {
						continue;
					}
					if (inner_stmt != nullptr) {
						is_singular = false;
						break;
					}
					inner_stmt = s;
				}

				if (inner_stmt != nullptr) {
					stmt = inner_stmt;
				}
			}
			if (!is_singular) {
				stmt = original_stmt;
			}

			switch (stmt->kind) {
			case_ast_node(as, AssignStmt, stmt);
				if (as->op.kind != Token_Eq) {
					break;
				}
				for (Ast *lhs : as->lhs) {
					Entity *e = entity_of_node(lhs);
					if (e && e->flags & EntityFlag_Result) {
						error(lhs, "Assignments to named return values within 'defer' will not affect the value that is returned");
					}
				}
			case_end;
			}
		}
	case_end;

	case_ast_node(bs, BranchStmt, node);
		Token token = bs->token;
		switch (token.kind) {
		case Token_break:
			if ((flags & Stmt_BreakAllowed) == 0 && bs->label == nullptr) {
				error(token, "'break' only allowed in non-inline loops or 'switch' statements");
			}
			break;
		case Token_continue:
			if ((flags & Stmt_ContinueAllowed) == 0 && bs->label == nullptr) {
				error(token, "'continue' only allowed in non-inline loops");
			}
			break;
		case Token_fallthrough:
			if ((flags & Stmt_FallthroughAllowed) == 0) {
				if ((flags & Stmt_TypeSwitch) != 0) {
					error(token, "'fallthrough' statement not allowed within a type switch statement");
				} else {
					error(token, "'fallthrough' statement in illegal position, expected at the end of a 'case' block");
				}
			} else if (bs->label != nullptr) {
				error(token, "'fallthrough' cannot have a label");
			}
			break;
		default:
			error(token, "Invalid AST: Branch Statement '%.*s'", LIT(token.string));
			break;
		}

		if (bs->label != nullptr) {
			if (bs->label->kind != Ast_Ident) {
				error(bs->label, "A branch statement's label name must be an identifier");
				return;
			}

			Ast *ident = bs->label;
			String name = ident->Ident.token.string;
			Operand o = {};
			Entity *e = check_ident(ctx, &o, ident, nullptr, nullptr, false);
			if (e == nullptr) {
				error(ident, "Undeclared label name: %.*s", LIT(name));
				return;
			}
			add_entity_use(ctx, ident, e);
			if (e->kind != Entity_Label) {
				error(ident, "'%.*s' is not a label", LIT(name));
				return;
			}
			Ast *parent = e->Label.parent;
			GB_ASSERT(parent != nullptr);
			switch (parent->kind) {
			case Ast_BlockStmt:
			case Ast_IfStmt:
			case Ast_SwitchStmt:
			case Ast_TypeSwitchStmt:
				if (token.kind != Token_break) {
					error(bs->label, "Label '%.*s' can only be used with 'break'", LIT(e->token.string));
				}
				break;
			case Ast_RangeStmt:
			case Ast_ForStmt:
				if ((token.kind != Token_break) && (token.kind != Token_continue)) {
					error(bs->label, "Label '%.*s' can only be used with 'break' and 'continue'", LIT(e->token.string));
				}
				break;

			}

			if (ctx->in_defer) {
				error(bs->label, "A labelled '%.*s' cannot be used within a 'defer'", LIT(token.string));
			}
		}

	case_end;

	case_ast_node(us, UsingStmt, node);
		if (us->list.count == 0) {
			error(us->token, "Empty 'using' list");
			return;
		}
		if (check_vet_flags(node) & VetFlag_UsingStmt) {
			ERROR_BLOCK();
			error(node, "'using' as a statement is not allowed when '-vet' or '-vet-using' is applied");
			error_line("\t'using' is considered bad practice to use as a statement outside of immediate refactoring\n");
		}

		for (Ast *expr : us->list) {
			expr = unparen_expr(expr);
			Entity *e = nullptr;

			bool is_selector = false;
			Operand o = {};
			switch (expr->kind) {
			case Ast_Ident:
				e = check_ident(ctx, &o, expr, nullptr, nullptr, true);
				break;
			case Ast_SelectorExpr:
				e = check_selector(ctx, &o, expr, nullptr);
				is_selector = true;
				break;
			case Ast_Implicit:
				error(us->token, "'using' applied to an implicit value");
				continue;
			default:
				error(us->token, "'using' can only be applied to an entity, got %.*s", LIT(ast_strings[expr->kind]));
				continue;
			}

			if (!check_using_stmt_entity(ctx, us, expr, is_selector, e)) {
				return;
			}
		}
	case_end;

	case_ast_node(fb, ForeignBlockDecl, node);
		Ast *foreign_library = fb->foreign_library;
		CheckerContext c = *ctx;
		if (foreign_library->kind != Ast_Ident) {
			error(foreign_library, "foreign library name must be an identifier");
		} else {
			c.foreign_context.curr_library = foreign_library;
			c.foreign_context.default_cc = ProcCC_CDecl;
		}

		check_decl_attributes(&c, fb->attributes, foreign_block_decl_attribute, nullptr);

		ast_node(block, BlockStmt, fb->body);
		for (Ast *decl : block->stmts) {
			if (decl->kind == Ast_ValueDecl && decl->ValueDecl.is_mutable) {
				check_stmt(&c, decl, flags);
			}
		}
	case_end;

	case_ast_node(vd, ValueDecl, node);
		check_value_decl_stmt(ctx, node, mod_flags);
	case_end;
	}
}