From 2d1533f34f74d69978f20d09be28740be2ec721c Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Thu, 6 Jun 2024 02:54:00 +0800
Subject: [PATCH] fixes #5901 #21211; don't fold cast function types because of
 gcc 14 (#23683)

follow up https://github.com/nim-lang/Nim/pull/6265

fixes #5901
fixes #21211

It causes many problems with gcc14 if we fold the cast function types.
Let's check what it will break
---
 compiler/semfold.nim | 3 ++-
 tests/misc/tcast.nim | 7 ++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/compiler/semfold.nim b/compiler/semfold.nim
index f7da4ea752..466df2e4eb 100644
--- a/compiler/semfold.nim
+++ b/compiler/semfold.nim
@@ -771,7 +771,8 @@ proc getConstExpr(m: PSym, n: PNode; idgen: IdGenerator; g: ModuleGraph): PNode
   of nkCast:
     var a = getConstExpr(m, n[1], idgen, g)
     if a == nil: return
-    if n.typ != nil and n.typ.kind in NilableTypes:
+    if n.typ != nil and n.typ.kind in NilableTypes and
+        not (n.typ.kind == tyProc and a.typ.kind == tyProc):
       # we allow compile-time 'cast' for pointer types:
       result = a
       result.typ = n.typ
diff --git a/tests/misc/tcast.nim b/tests/misc/tcast.nim
index 6d67b1c528..73196e76cb 100644
--- a/tests/misc/tcast.nim
+++ b/tests/misc/tcast.nim
@@ -1,6 +1,7 @@
 discard """
   output: '''
 Hello World
+Hello World
 Hello World'''
   joinable: false
 """
@@ -8,7 +9,7 @@ type MyProc = proc() {.cdecl.}
 type MyProc2 = proc() {.nimcall.}
 type MyProc3 = proc() #{.closure.} is implicit
 
-proc testProc()  = echo "Hello World"
+proc testProc() {.exportc:"foo".} = echo "Hello World"
 
 template reject(x) = doAssert(not compiles(x))
 
@@ -23,6 +24,10 @@ proc callPointer(p: pointer) =
   ffunc0()
   ffunc1()
 
+    # bug #5901
+  proc foo() {.importc.}
+  (cast[proc(a: int) {.cdecl.}](foo))(5)
+
 callPointer(cast[pointer](testProc))
 
 reject: discard cast[enum](0)