From 2a1f7998a10fbe08f60877440bb3165fd5c0c7f4 Mon Sep 17 00:00:00 2001
From: metagn <metagngn@gmail.com>
Date: Thu, 21 Nov 2024 15:07:44 +0300
Subject: [PATCH] fix crash with tyBuiltInTypeClass matching itself

fixes #24449
---
 compiler/sigmatch.nim            |  5 ++++-
 tests/overload/tvartypeclass.nim | 25 +++++++++++++++----------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/compiler/sigmatch.nim b/compiler/sigmatch.nim
index 848cc684d602..14661ffcf873 100644
--- a/compiler/sigmatch.nim
+++ b/compiler/sigmatch.nim
@@ -1878,9 +1878,12 @@ proc typeRel(c: var TCandidate, f, aOrig: PType,
       let target = f.genericHead
       let targetKind = target.kind
       var effectiveArgType = reduceToBase(a)
+      # the skipped child of tyBuiltInTypeClass can be structured differently,
+      # newConstraint constructs them with no children
+      let typeClassArg = effectiveArgType.kind == tyBuiltInTypeClass
       effectiveArgType = effectiveArgType.skipTypes({tyBuiltInTypeClass})
       if targetKind == effectiveArgType.kind:
-        if effectiveArgType.isEmptyContainer:
+        if not typeClassArg and effectiveArgType.isEmptyContainer:
           return isNone
         if targetKind == tyProc:
           if target.flags * {tfIterator} != effectiveArgType.flags * {tfIterator}:
diff --git a/tests/overload/tvartypeclass.nim b/tests/overload/tvartypeclass.nim
index 04f3f5a910c7..c47e2102cf17 100644
--- a/tests/overload/tvartypeclass.nim
+++ b/tests/overload/tvartypeclass.nim
@@ -1,11 +1,16 @@
-# issue #13302
+block: # issue #13302
+  proc foo(x: object): int = x.i*2
+  proc foo(x: var object) = x.i*=2
+  type Foo = object
+    i: int
+  let x = Foo(i: 3)
+  var y = Foo(i: 4)
+  doAssert foo(x) == 6
+  foo(y)
+  doAssert y.i == 8
 
-proc foo(x: object): int = x.i*2
-proc foo(x: var object) = x.i*=2
-type Foo = object
-  i: int
-let x = Foo(i: 3)
-var y = Foo(i: 4)
-doAssert foo(x) == 6
-foo(y)
-doAssert y.i == 8
+block: # issue #24449
+  proc p(x: var seq)= discard
+  proc p(x: seq)= discard
+  var s : seq[int]
+  p(s)