[clang] Enable unguarded availability diagnostic on instantiated template functions (PR #91699)

[Cooper Partin via cfe-commits]

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@@ -177,16 +177,19 @@ void justAtAvailable(void) {
 
 #ifdef OBJCPP
 
-int f(char) AVAILABLE_10_12;
+int f(char) AVAILABLE_10_12; // #f_char_def
 int f(int);
 
 template <class T> int use_f() {
-  // FIXME: We should warn here!
-  return f(T());
+  // expected-warning@#f_call {{'f' is only available on macOS 10.12 or newer}}
+  // expected-note@#f_char_inst {{in instantiation of function template specialization 'use_f<char>' requested here}}
+  // expected-note@#f_char_def {{'f' has been marked as being introduced in macOS 10.12 here, but the deployment target is macOS 10.9}}
+  // expected-note@#f_call {{enclose 'f' in an @available check to silence this warning}}
+  return f(T()); // #f_call
 }
 
 int a = use_f<int>();
-int b = use_f<char>();
+int b = use_f<char>(); // #f_char_inst
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coopp wrote:

I don't see other "// $f_foo_inst" comments in other parts of the code.  Why was this one special to get one?  Was it just for tracking the change?

https://github.com/llvm/llvm-project/pull/91699