Expand hoisted default params in sem (#15270)

* Expand hoisted default params in sem
Introduce ast.newTree{I,IT}
Add test for default params in procs

* Cleanup

* Simplify hoist transformation and expand test

compiler/semexprs.nim

@@ -1556,10 +1556,9 @@ proc propertyWriteAccess(c: PContext, n, nOrig, a: PNode): PNode =
   # this is ugly. XXX Semantic checking should use the ``nfSem`` flag for
   # nodes?
   let aOrig = nOrig[0]
-  result = newNode(nkCall, n.info, sons = @[setterId, a[0],
-                                            semExprWithType(c, n[1])])
+  result = newTreeI(nkCall, n.info, setterId, a[0], semExprWithType(c, n[1]))
   result.flags.incl nfDotSetter
-  let orig = newNode(nkCall, n.info, sons = @[setterId, aOrig[0], nOrig[1]])
+  let orig = newTreeI(nkCall, n.info, setterId, aOrig[0], nOrig[1])
   result = semOverloadedCallAnalyseEffects(c, result, orig, {})
 
   if result != nil:
@@ -2041,7 +2040,7 @@ proc semQuoteAst(c: PContext, n: PNode): PNode =
     dummyTemplate[paramsPos].add getSysSym(c.graph, n.info, "untyped").newSymNode # return type
     ids.add getSysSym(c.graph, n.info, "untyped").newSymNode # params type
     ids.add c.graph.emptyNode # no default value
-    dummyTemplate[paramsPos].add newNode(nkIdentDefs, n.info, ids)
+    dummyTemplate[paramsPos].add newTreeI(nkIdentDefs, n.info, ids)
 
   var tmpl = semTemplateDef(c, dummyTemplate)
   quotes[0] = tmpl[namePos]
@@ -2053,10 +2052,10 @@ proc semQuoteAst(c: PContext, n: PNode): PNode =
                     newIdentNode(getIdent(c.cache, "newIdentNode"), n.info)
                   else:
                     identNodeSym.newSymNode
-  quotes[1] = newNode(nkCall, n.info, @[identNode, newStrNode(nkStrLit, "result")])
-  result = newNode(nkCall, n.info, @[
+  quotes[1] = newTreeI(nkCall, n.info, identNode, newStrNode(nkStrLit, "result"))
+  result = newTreeI(nkCall, n.info, 
      createMagic(c.graph, "getAst", mExpandToAst).newSymNode,
-    newNode(nkCall, n.info, quotes)])
+     newTreeI(nkCall, n.info, quotes))
   result = semExpandToAst(c, result)
 
 proc tryExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
@@ -2579,6 +2578,43 @@ proc shouldBeBracketExpr(n: PNode): bool =
           n[0] = be
           return true
 
+proc hoistParamsUsedInDefault(c: PContext, call, letSection, defExpr: var PNode) =
+  # This takes care of complicated signatures such as:
+  # proc foo(a: int, b = a)
+  # proc bar(a: int, b: int, c = a + b)
+  #
+  # The recursion may confuse you. It performs two duties:
+  #
+  # 1) extracting all referenced params from default expressions
+  #    into a let section preceding the call
+  #
+  # 2) replacing the "references" within the default expression
+  #    with these extracted skLet symbols.
+  #
+  # The first duty is carried out directly in the code here, while the second
+  # duty is activated by returning a non-nil value. The caller is responsible
+  # for replacing the input to the function with the returned non-nil value.
+  # (which is the hoisted symbol)
+  if defExpr.kind == nkSym and defExpr.sym.kind == skParam and defExpr.sym.owner == call[0].sym:
+    let paramPos = defExpr.sym.position + 1
+
+    if call[paramPos].kind != nkSym:
+      let hoistedVarSym = newSym(skLet, getIdent(c.graph.cache, genPrefix), c.p.owner, letSection.info, c.p.owner.options)
+      hoistedVarSym.typ = call[paramPos].typ
+
+      letSection.add newTreeI(nkIdentDefs, letSection.info,
+        newSymNode(hoistedVarSym),
+        newNodeI(nkEmpty, letSection.info),
+        call[paramPos])
+
+      call[paramPos] = newSymNode(hoistedVarSym) # Refer the original arg to its hoisted sym
+
+    # arg we refer to is a sym, wether introduced by hoisting or not doesn't matter, we simply reuse it
+    defExpr = call[paramPos]
+  else:
+    for i in 0..<defExpr.safeLen:
+      hoistParamsUsedInDefault(c, call, letSection, defExpr[i])
+
 proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
   when defined(nimCompilerStackraceHints):
     setFrameMsg c.config$n.info & " " & $n.kind
@@ -2707,6 +2743,15 @@ proc semExpr(c: PContext, n: PNode, flags: TExprFlags = {}): PNode =
       result = semDirectOp(c, n, flags)
     else:
       result = semIndirectOp(c, n, flags)
+
+    if nfDefaultRefsParam in result.flags:
+      result = result.copyTree #XXX: Figure out what causes default param nodes to be shared.. (sigmatch bug?)
+      # We've found a default value that references another param.
+      # See the notes in `hoistParamsUsedInDefault` for more details.
+      var hoistedParams = newNodeI(nkLetSection, result.info)
+      for i in 1..<result.len:
+        hoistParamsUsedInDefault(c, result, hoistedParams, result[i])
+      result = newTreeIT(nkStmtListExpr, result.info, result.typ, hoistedParams, result)
   of nkWhen:
     if efWantStmt in flags:
       result = semWhen(c, n, true)