[Concepts] Fix an assertion failure while diagnosing constrained function candidates

[royjacobson]

Summary

See: https://github.com/llvm/llvm-project/issues/54379

I tried to see if I can reuse ResolveAddressOfOverloadedFunction for explicit function instantiation and so I managed to hit this ICE.

Bug was the diagnostic required an argument (%0) and specific code path didn't pass an argument.

[erichkeane]

This seems acceptable to me. Though, I wonder if getTemplateArgumentBindingsText should produce the leading space, that way we could just pass the result of it directly, rather than have to create a SmallString everywhere. WDYT?

clang/lib/Sema/SemaOverload.cpp

10261

.clear shouldn't be required as you just constructed it.

[royjacobson]

In D121646#3380893, @erichkeane wrote:

This seems acceptable to me. Though, I wonder if getTemplateArgumentBindingsText should produce the leading space, that way we could just pass the result of it directly, rather than have to create a SmallString everywhere. WDYT?

There are other places (outside SemaOverload) that use this function and don't need a space, though.
I thought about just putting the space in the diagnostic itself, but then sometimes you don't get template arguments and it fails.

[erichkeane]

In D121646#3380902, @royjacobson wrote:

In D121646#3380893, @erichkeane wrote:

This seems acceptable to me. Though, I wonder if getTemplateArgumentBindingsText should produce the leading space, that way we could just pass the result of it directly, rather than have to create a SmallString everywhere. WDYT?

There are other places (outside SemaOverload) that use this function and don't need a space, though.
I thought about just putting the space in the diagnostic itself, but then sometimes you don't get template arguments and it fails.

I see. I was hoping that wasn't the case! OK, LGTM. Let me know if you need me to commit this for you.

[royjacobson]

In D121646#3382243, @erichkeane wrote:

In D121646#3380902, @royjacobson wrote:

In D121646#3380893, @erichkeane wrote:

This seems acceptable to me. Though, I wonder if getTemplateArgumentBindingsText should produce the leading space, that way we could just pass the result of it directly, rather than have to create a SmallString everywhere. WDYT?

There are other places (outside SemaOverload) that use this function and don't need a space, though.
I thought about just putting the space in the diagnostic itself, but then sometimes you don't get template arguments and it fails.

I see. I was hoping that wasn't the case! OK, LGTM. Let me know if you need me to commit this for you.

Yes, thank you :)
(with author as "Roy Jacobson <[e-mail]>")

clang/lib/Sema/SemaOverload.cpp

static bool checkAddressOfFunctionIsAvailable(Sema &S, const FunctionDecl *FD,
   }
 
   if (FD->getTrailingRequiresClause()) {
     ConstraintSatisfaction Satisfaction;
     if (S.CheckFunctionConstraints(FD, Satisfaction, Loc))
       return false;
     if (!Satisfaction.IsSatisfied) {
       if (Complain) {
-        if (InOverloadResolution)
+        if (InOverloadResolution) {
+          SmallString<128> TemplateArgString;
+          if (FunctionTemplateDecl *FunTmpl = FD->getPrimaryTemplate()) {
+            TemplateArgString += " ";
+            TemplateArgString += S.getTemplateArgumentBindingsText(
+                FunTmpl->getTemplateParameters(),
+                *FD->getTemplateSpecializationArgs());
+          }
+
           S.Diag(FD->getBeginLoc(),
-                 diag::note_ovl_candidate_unsatisfied_constraints);
-        else
+                 diag::note_ovl_candidate_unsatisfied_constraints)
+              << TemplateArgString;
+        } else
           S.Diag(Loc, diag::err_addrof_function_constraints_not_satisfied)
               << FD;
         S.DiagnoseUnsatisfiedConstraint(Satisfaction);
       }
       return false;
     }
   }
 

clang/test/SemaTemplate/concepts.cpp

namespace PR53911 {
 
   C auto *f1() {
     return (void*)nullptr; // FIXME: should error
   }
   C auto *f2() {
     return (int*)nullptr; // FIXME: should error
   }
 }
+
+namespace PR54379 {
+template <int N>
+struct A {
+  static void f() requires (N == 0) { return; } // expected-note {{candidate template ignored: constraints not satisfied}} expected-note {{evaluated to false}}
+  static void f() requires (N == 1) { return; } // expected-note {{candidate template ignored: constraints not satisfied}} expected-note {{evaluated to false}}
+};
+void (*f1)() = A<2>::f; // expected-error {{address of overloaded function 'f' does not match required type}}
+
+struct B {
+  template <int N2 = 1> static void f() requires (N2 == 0) { return; }  // expected-note {{candidate template ignored: constraints not satisfied [with N2 = 1]}} expected-note {{evaluated to false}}
+};
+void (*f2)() = B::f; // expected-error {{address of overloaded function 'f' does not match required type}}
+}