fixes #23902; Compiler infers sink in return type from auto (#23904)

fixes #23902

compiler/semexprs.nim

@@ -2003,7 +2003,7 @@ proc semAsgn(c: PContext, n: PNode; mode=asgnNormal): PNode =
         if rhsTyp.kind in tyUserTypeClasses and rhsTyp.isResolvedUserTypeClass:
           rhsTyp = rhsTyp.last
         if lhs.sym.typ.kind == tyAnything:
-          rhsTyp = rhsTyp.skipIntLit(c.idgen)
+          rhsTyp = rhsTyp.skipTypes({tySink}).skipIntLit(c.idgen)
         if cmpTypes(c, lhs.typ, rhsTyp) in {isGeneric, isEqual}:
           internalAssert c.config, c.p.resultSym != nil
           # Make sure the type is valid for the result variable
@@ -2825,7 +2825,7 @@ proc semTupleFieldsConstr(c: PContext, n: PNode, flags: TExprFlags; expectedType
       n[i][1].typ = errorType(c)
 
     var f = newSymS(skField, n[i][0], c)
-    f.typ = skipIntLit(n[i][1].typ, c.idgen)
+    f.typ = skipIntLit(n[i][1].typ.skipTypes({tySink}), c.idgen)
     f.position = i
     rawAddSon(typ, f.typ)
     typ.n.add newSymNode(f)
@@ -2851,7 +2851,7 @@ proc semTuplePositionsConstr(c: PContext, n: PNode, flags: TExprFlags; expectedT
       # `const foo = [(1, {}), (2, {false})]`,
       # `const foo = if true: (0, nil) else: (1, new(int))`
       n[i] = fitNode(c, expectedElemType, n[i], n[i].info)
-    addSonSkipIntLit(typ, n[i].typ, c.idgen)
+    addSonSkipIntLit(typ, n[i].typ.skipTypes({tySink}), c.idgen)
   result.typ = typ
 
 include semobjconstr

tests/destructor/tsink.nim

@@ -14,3 +14,11 @@ proc foo = # bug #23359
   doAssert bar.value == 42
 
 foo()
+
+block: # bug #23902
+  proc foo(a: sink string): auto = (a, a)
+
+  proc bar(a: sink int): auto = return a
+
+  proc foo(a: sink string) =
+    var x = (a, a)