From e449813c61fbdbb150b197fca98610424e1107ad Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Wed, 26 Feb 2025 00:08:22 +0800
Subject: [PATCH] fixes #24725; Invalid =sink generated for pure inheritable
 object (#24726)

fixes #24725

`lacksMTypeField` doesn't take the base types into consideration. And
for ` {.inheritable, pure.}`, it shouldn't generate a `m_type` field.
---
 compiler/ccgtypes.nim        |  4 ----
 compiler/liftdestructors.nim |  2 +-
 compiler/types.nim           |  9 +++++++++
 tests/ccgbugs/tcgbug.nim     | 18 ++++++++++++++++++
 4 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/compiler/ccgtypes.nim b/compiler/ccgtypes.nim
index 92b439891d..ef7550d2c0 100644
--- a/compiler/ccgtypes.nim
+++ b/compiler/ccgtypes.nim
@@ -247,10 +247,6 @@ proc hasNoInit(t: PType): bool =
 
 proc getTypeDescAux(m: BModule; origTyp: PType, check: var IntSet; kind: TypeDescKind): Rope
 
-proc isObjLackingTypeField(typ: PType): bool {.inline.} =
-  result = (typ.kind == tyObject) and ((tfFinal in typ.flags) and
-      (typ.baseClass == nil) or isPureObject(typ))
-
 proc isInvalidReturnType(conf: ConfigRef; typ: PType, isProc = true): bool =
   # Arrays and sets cannot be returned by a C procedure, because C is
   # such a poor programming language.
diff --git a/compiler/liftdestructors.nim b/compiler/liftdestructors.nim
index 9020a6f7ff..c948916132 100644
--- a/compiler/liftdestructors.nim
+++ b/compiler/liftdestructors.nim
@@ -1197,7 +1197,7 @@ proc produceSym(g: ModuleGraph; c: PContext; typ: PType; kind: TTypeAttachedOp;
       fillStrOp(a, typ, result.ast[bodyPos], d, src)
     else:
       fillBody(a, typ, result.ast[bodyPos], d, src)
-      if tk == tyObject and a.kind in {attachedAsgn, attachedSink, attachedDeepCopy, attachedDup} and not lacksMTypeField(typ):
+      if tk == tyObject and a.kind in {attachedAsgn, attachedSink, attachedDeepCopy, attachedDup} and not isObjLackingTypeField(typ):
         # bug #19205: Do not forget to also copy the hidden type field:
         genTypeFieldCopy(a, typ, result.ast[bodyPos], d, src)
 
diff --git a/compiler/types.nim b/compiler/types.nim
index 1834acdffa..16853e5ffa 100644
--- a/compiler/types.nim
+++ b/compiler/types.nim
@@ -1485,8 +1485,17 @@ proc commonSuperclass*(a, b: PType): PType =
     y = y.baseClass
 
 proc lacksMTypeField*(typ: PType): bool {.inline.} =
+  ## Returns true if the type is an object that lacks a m_type field.
+  ## It doesn't check base classes.
   (typ.sym != nil and sfPure in typ.sym.flags) or tfFinal in typ.flags
 
+proc isObjLackingTypeField*(typ: PType): bool {.inline.} =
+  ## Returns true if the type is an object that lacks a type field.
+  ## Object types that store type headers are not final or pure and
+  ## have inheritable root types, which are not pure, neither.
+  result = (typ.kind == tyObject) and ((tfFinal in typ.flags) and
+      (typ.baseClass == nil) or isPureObject(typ))
+
 include sizealignoffsetimpl
 
 proc computeSize*(conf: ConfigRef; typ: PType): BiggestInt =
diff --git a/tests/ccgbugs/tcgbug.nim b/tests/ccgbugs/tcgbug.nim
index 2eddc6fddc..0db2b12ea4 100644
--- a/tests/ccgbugs/tcgbug.nim
+++ b/tests/ccgbugs/tcgbug.nim
@@ -161,3 +161,21 @@ typedef struct { int base; } S;
 
   var t = newT()
   doAssert t.s.base == 1
+
+type QObject* {.inheritable, pure.} = object
+  h*: pointer
+
+proc `=destroy`(self: var QObject) =discard
+
+proc `=copy`(dest: var QObject, source: QObject) {.error.}
+
+type QAbstractItemModel* = object of QObject
+
+type VTable = ref object
+  inst:  QAbstractItemModel
+
+proc g() =
+  var x: VTable = VTable()
+  x.inst = QAbstractItemModel()
+
+g()