[clang] [clang][Sema] Bugfix for choosing the more specialized overload (PR #83279)

[via cfe-commits]

================
@@ -5548,13 +5493,76 @@ static bool isAtLeastAsSpecializedAs(Sema &S,
 FunctionTemplateDecl *Sema::getMoreSpecializedTemplate(
     FunctionTemplateDecl *FT1, FunctionTemplateDecl *FT2, SourceLocation Loc,
     TemplatePartialOrderingContext TPOC, unsigned NumCallArguments1,
-    unsigned NumCallArguments2, bool Reversed) {
+    QualType RawObj1Ty, QualType RawObj2Ty, bool Reversed) {
+  SmallVector<QualType> Args1;
+  SmallVector<QualType> Args2;
+  const FunctionDecl *FD1 = FT1->getTemplatedDecl();
+  const FunctionDecl *FD2 = FT2->getTemplatedDecl();
+  bool shouldConvert1 = false;
+  bool shouldConvert2 = false;
+  QualType Obj1Ty;
+  QualType Obj2Ty;
+  if (TPOC == TPOC_Call) {
+    const FunctionProtoType *Proto1 =
+        FD1->getType()->getAs<FunctionProtoType>();
+    const FunctionProtoType *Proto2 =
+        FD2->getType()->getAs<FunctionProtoType>();
 
-  bool Better1 = isAtLeastAsSpecializedAs(*this, Loc, FT1, FT2, TPOC,
-                                          NumCallArguments1, Reversed);
-  bool Better2 = isAtLeastAsSpecializedAs(*this, Loc, FT2, FT1, TPOC,
-                                          NumCallArguments2, Reversed);
+    //   - In the context of a function call, the function parameter types are
+    //     used.
+    const CXXMethodDecl *Method1 = dyn_cast<CXXMethodDecl>(FD1);
+    const CXXMethodDecl *Method2 = dyn_cast<CXXMethodDecl>(FD2);
+    // C++20 [temp.func.order]p3
+    //   [...] Each function template M that is a member function is
+    //   considered to have a new first parameter of type
+    //   X(M), described below, inserted in its function parameter list.
+    //
+    // Note that we interpret "that is a member function" as
+    // "that is a member function with no expicit object argument".
+    // Otherwise the ordering rules for methods with expicit objet arguments
+    // against anything else make no sense.
+    shouldConvert1 = Method1 && !Method1->isExplicitObjectMemberFunction();
+    shouldConvert2 = Method2 && !Method2->isExplicitObjectMemberFunction();
----------------
whisperity wrote:

```suggestion
    ShouldConvert1 = Method1 && !Method1->isExplicitObjectMemberFunction();
    ShouldConvert2 = Method2 && !Method2->isExplicitObjectMemberFunction();
```

Style nit formatting, if we're changing the code even though it might largely be a move/refactor, you can fix the formatting now!

https://github.com/llvm/llvm-project/pull/83279