[clang] [Clang] Fix warning for non std functions with name `infinity` (PR #123417)

[Erich Keane via cfe-commits]

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@@ -216,11 +244,18 @@ int compareit(float a, float b) {
 
 // no-inf-no-nan-warning at +2 {{use of infinity is undefined behavior due to the currently enabled floating-point options}}
 // no-inf-warning at +1 {{use of infinity is undefined behavior due to the currently enabled floating-point options}}
-  double y = i * numeric_limits<double>::infinity();
+  double y = i * std::numeric_limits<double>::infinity();
+
+  y = i * numeric_limits<double>::infinity(); // expected-no-diagnostics
 
 // no-inf-no-nan-warning at +2 {{use of infinity is undefined behavior due to the currently enabled floating-point options}}
 // no-inf-warning at +1 {{use of infinity is undefined behavior due to the currently enabled floating-point options}}
-  j = numeric_limits<float>::infinity();
+  j = std::numeric_limits<float>::infinity();
+
+  j = numeric_limits<float>::infinity(); // expected-no-diagnostics
+
+  y = infinity(); // expected-no-diagnostics
+
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erichkeane wrote:

We cannot really, since there is no such thing as 'phase 2' for most of the program (non templates).  Typically if you want something ONLY during phase 2, you do it during tree-transform or during the calls to the 'Rebuild' functions.

So you ALSO have to do it during phase-1, but the phase-2 work can suppress its diagnostic if it has already been done (assuming you are close enough to rebuild to do that).

The fix is likely that you'll have to mvoe where this is diagnosed to somewhere that isn't currently being called by the template instantiation, and re-add it then.

https://github.com/llvm/llvm-project/pull/123417