From bd709f9b4c4911755c7cfb7567ddae71b2f9ac46 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Sun, 1 Mar 2026 06:01:09 +0800
Subject: [PATCH] fixes #25262; proc v[T: typedesc]() = discard / v[0]()
 compiles even though 0 isn't a typedesc (#25558)

fixes #25262

```nim
if constraint != nil and constraint.kind == tyTypeDesc:
  n[i].typ = e.typ
else:
  n[i].typ = e.typ.skipTypes({tyTypeDesc})
```
at least when `constraint` is a typedesc, it should not skip
`tyTypeDesc`


```nim
if arg.kind != tyTypeDesc:
  arg = makeTypeDesc(m.c, arg)
```
Wrappers literals into typedesc, which can cause problems. Though, it
doesn't seem to be necessary
---
 compiler/semcall.nim             |  2 +-
 compiler/sigmatch.nim            |  3 +--
 tests/generics/tpointerprocs.nim |  2 +-
 tests/typerel/t25262.nim         | 13 +++++++++++++
 4 files changed, 16 insertions(+), 4 deletions(-)
 create mode 100644 tests/typerel/t25262.nim

diff --git a/compiler/semcall.nim b/compiler/semcall.nim
index 4557ab4c69..29d19875d4 100644
--- a/compiler/semcall.nim
+++ b/compiler/semcall.nim
@@ -981,7 +981,7 @@ proc setGenericParams(c: PContext, n, expectedParams: PNode) =
     if e.typ == nil:
       n[i].typ = errorType(c)
     else:
-      n[i].typ = e.typ.skipTypes({tyTypeDesc})
+      n[i].typ = e.typ
 
 proc explicitGenericInstantiation(c: PContext, n: PNode, s: PSym, doError: bool): PNode =
   assert n.kind == nkBracketExpr
diff --git a/compiler/sigmatch.nim b/compiler/sigmatch.nim
index 7839a1a5cb..2e46d508ae 100644
--- a/compiler/sigmatch.nim
+++ b/compiler/sigmatch.nim
@@ -160,8 +160,7 @@ proc matchGenericParam(m: var TCandidate, formal: PType, n: PNode) =
       arg = newTypeS(tyStatic, m.c, son = evaluated.typ)
       arg.n = evaluated
   elif formalBase.kind == tyTypeDesc:
-    if arg.kind != tyTypeDesc:
-      arg = makeTypeDesc(m.c, arg)
+    discard # if arg is not tyTypeDesc, typeRel will report the mismatch
   else:
     arg = arg.skipTypes({tyTypeDesc})
   let tm = typeRel(m, formal, arg)
diff --git a/tests/generics/tpointerprocs.nim b/tests/generics/tpointerprocs.nim
index 29c4f2954f..ba99044645 100644
--- a/tests/generics/tpointerprocs.nim
+++ b/tests/generics/tpointerprocs.nim
@@ -3,7 +3,7 @@ cmd: "nim check $options --hints:off $file"
 action: "reject"
 nimout:'''
 tpointerprocs.nim(22, 11) Error: 'foo' doesn't have a concrete type, due to unspecified generic parameters.
-tpointerprocs.nim(34, 14) Error: type mismatch: got <int>
+tpointerprocs.nim(34, 14) Error: type mismatch: got <typedesc[int]>
 but expected one of:
 proc foo(x: int | float; y: int or string): float
   first type mismatch at position: 2 in generic parameters
diff --git a/tests/typerel/t25262.nim b/tests/typerel/t25262.nim
new file mode 100644
index 0000000000..182561dde3
--- /dev/null
+++ b/tests/typerel/t25262.nim
@@ -0,0 +1,13 @@
+discard """
+   errormsg: "type mismatch"
+   output: '''
+t25262.nim(13, 5) Error: type mismatch: got <>
+but expected one of:
+proc v[T: typedesc]()
+
+expression: v[0]()
+'''
+"""
+
+proc v[T: typedesc]() = discard
+v[0]()
\ No newline at end of file