From 5cecd81a05de0f3db3d77407e70a33d65bd9df2c Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Wed, 8 May 2024 18:35:26 +0300
Subject: [PATCH] fix semFinishOperands for bracket expressions [backport:2.0]
 (#23571)

fixes #23568, fixes #23310

In #23091 `semFinishOperands` was changed to not be called for `mArrGet`
and `mArrPut`, presumably in preparation for #23188 (not sure why it was
needed in #23091, maybe they got mixed together), since the compiler
handles these later and needs the first argument to not be completely
"typed" since brackets can serve as explicit generic instantiations in
which case the first argument would have to be an unresolved generic
proc (not accepted by `finishOperand`).

In this PR we just make it so `mArrGet` and `mArrPut` specifically skip
calling `finishOperand` on the first argument. This way the generic
arguments in the explicit instantiation get typed, but not the
unresolved generic proc.

(cherry picked from commit 09bd9d0b19a69a56b875eff6e6d119aaf67664fd)
---
 compiler/semexprs.nim            | 15 ++++++++-------
 tests/generics/tnestedissues.nim | 24 ++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 7 deletions(-)
 create mode 100644 tests/generics/tnestedissues.nim

diff --git a/compiler/semexprs.nim b/compiler/semexprs.nim
index 8b22555ae2..a179c68d7b 100644
--- a/compiler/semexprs.nim
+++ b/compiler/semexprs.nim
@@ -1012,10 +1012,14 @@ proc finishOperand(c: PContext, a: PNode): PNode =
     localError(c.config, a.info, err)
   considerGenSyms(c, result)
 
-proc semFinishOperands(c: PContext; n: PNode) =
+proc semFinishOperands(c: PContext; n: PNode; isBracketExpr = false) =
   # this needs to be called to ensure that after overloading resolution every
-  # argument has been sem'checked:
-  for i in 1..<n.len:
+  # argument has been sem'checked
+
+  # skip the first argument for operands of `[]` since it may be an unresolved
+  # generic proc, which is handled in semMagic
+  let start = 1 + ord(isBracketExpr)
+  for i in start..<n.len:
     n[i] = finishOperand(c, n[i])
 
 proc afterCallActions(c: PContext; n, orig: PNode, flags: TExprFlags; expectedType: PType = nil): PNode =
@@ -1038,10 +1042,7 @@ proc afterCallActions(c: PContext; n, orig: PNode, flags: TExprFlags; expectedTy
   of skMacro: result = semMacroExpr(c, result, orig, callee, flags, expectedType)
   of skTemplate: result = semTemplateExpr(c, result, callee, flags, expectedType)
   else:
-    if callee.magic notin {mArrGet, mArrPut, mNBindSym}:
-      # calls to `[]` can be explicit generic instantiations,
-      # don't sem every operand now, leave it to semmagic
-      semFinishOperands(c, result)
+    semFinishOperands(c, result, isBracketExpr = callee.magic in {mArrGet, mArrPut})
     activate(c, result)
     fixAbstractType(c, result)
     analyseIfAddressTakenInCall(c, result)
diff --git a/tests/generics/tnestedissues.nim b/tests/generics/tnestedissues.nim
new file mode 100644
index 0000000000..e96a1927e6
--- /dev/null
+++ b/tests/generics/tnestedissues.nim
@@ -0,0 +1,24 @@
+block: # issue #23568
+  type G[T] = object
+    j: T
+  proc s[T](u: int) = discard
+  proc s[T]() = discard
+  proc c(e: int | int): G[G[G[int]]] = s[G[G[int]]]()
+  discard c(0)
+
+import std/options
+
+block: # issue #23310
+  type
+    BID = string or uint64
+    Future[T] = ref object of RootObj
+      internalValue: T
+    InternalRaisesFuture[T] = ref object of Future[T]
+  proc newInternalRaisesFutureImpl[T](): InternalRaisesFuture[T] =
+    let fut = InternalRaisesFuture[T]()
+  template newFuture[T](): auto =
+    newInternalRaisesFutureImpl[T]()
+  proc problematic(blockId: BID): Future[Option[seq[int]]] =
+    let resultFuture = newFuture[Option[seq[int]]]()
+    return resultFuture
+  let x = problematic("latest")