From 58813a3b2e375d91a307645168765372fb4584c8 Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Tue, 20 Aug 2024 12:41:50 +0300
Subject: [PATCH] make all generic aliases tyAlias (#23978)

fixes #23977

The problem is that for *any* body of a generic declaration,
[semstmts](https://github.com/nim-lang/Nim/blob/2e4d344b43b040a4dce2c478ca13e49979e491fc/compiler/semstmts.nim#L1610-L1611)
sets the sym of its value to the generic type name, and
[semtypes](https://github.com/nim-lang/Nim/blob/2e4d344b43b040a4dce2c478ca13e49979e491fc/compiler/semtypes.nim#L2143)
just directly gives the referenced type *specifically* when the
expression is a generic body. I'm blaming `semtypes` here because it's
responsible for the type given but the exact opposite behavior
specifically written in makes me think generating an alias type here
maybe breaks something.
---
 compiler/semtypes.nim           | 3 ++-
 tests/generics/taliashijack.nim | 8 ++++++++
 tests/vm/tvmmisc.nim            | 2 +-
 3 files changed, 11 insertions(+), 2 deletions(-)
 create mode 100644 tests/generics/taliashijack.nim

diff --git a/compiler/semtypes.nim b/compiler/semtypes.nim
index 1219d6ed83..a5cd5b5b02 100644
--- a/compiler/semtypes.nim
+++ b/compiler/semtypes.nim
@@ -1646,7 +1646,8 @@ proc semGeneric(c: PContext, n: PNode, s: PSym, prev: PType): PType =
     recomputeFieldPositions(tx, tx.n, position)
 
 proc maybeAliasType(c: PContext; typeExpr, prev: PType): PType =
-  if typeExpr.kind in {tyObject, tyEnum, tyDistinct, tyForward, tyGenericBody} and prev != nil:
+  if prev != nil and (prev.kind == tyGenericBody or
+      typeExpr.kind in {tyObject, tyEnum, tyDistinct, tyForward, tyGenericBody}):
     result = newTypeS(tyAlias, c)
     result.rawAddSon typeExpr
     result.sym = prev.sym
diff --git a/tests/generics/taliashijack.nim b/tests/generics/taliashijack.nim
new file mode 100644
index 0000000000..fdebadded2
--- /dev/null
+++ b/tests/generics/taliashijack.nim
@@ -0,0 +1,8 @@
+# issue #23977
+
+type Foo[T] = int
+
+proc foo(T: typedesc) =
+  var a: T
+
+foo(int)
diff --git a/tests/vm/tvmmisc.nim b/tests/vm/tvmmisc.nim
index d28f765740..3c4b47c48d 100644
--- a/tests/vm/tvmmisc.nim
+++ b/tests/vm/tvmmisc.nim
@@ -566,7 +566,7 @@ block:
 block:
   static:
     let x = int 1
-    doAssert $(x.type) == "Foo"  # Foo
+    doAssert $(x.type) == "int"  # Foo
 
 block:
   static: