[PATCH] D45680: [C++2a] Add operator<=> Rewriting - Early Attempt

[Eric Fiselier via Phabricator via cfe-commits]

EricWF added inline comments.


================
Comment at: lib/Sema/SemaOverload.cpp:9218-9219
+    // --- F2 is a rewritten candidate ([over.match.oper]) and F1 is not.
+    if (Cand2.getRewrittenKind() && !Cand1.getRewrittenKind())
+      return true;
+    if (Cand1.getRewrittenKind() && Cand2.getRewrittenKind() &&
----------------
EricWF wrote:
> rsmith wrote:
> > You also need to check the reverse condition and return false (the "or if not that" is ... somehow ... supposed to imply that).
> Hmm. So I'm wondering what is intended by the language `F1 and F2 are rewritten candidates, and F2 is a synthesized candidate with reversed order of parameters and F1 is not`. For example, what happens when comparing two distinct member functions with only one explicit parameter?
> 
> ```
> struct T;
> struct U { auto operator<=>(T); };
> struct T { auto operator<=>(U); };
> auto r = T{} < U{}; // Are the synthesized and rewritten overloads ambiguous? 
> ```
And what about 

```
struct U {};
struct T { auto operator<=>(U); };
auto operator<=>(U, T);
auto r = T{} < U{};
```


Repository:
  rC Clang

https://reviews.llvm.org/D45680