[clang] [APINotes] Diagnose invalid Where.Parameters selectors (PR #209408)

[John Hui via cfe-commits]

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@@ -0,0 +1,41 @@
+// RUN: not %clang_cc1 -fsyntax-only -fapinotes %s -I %S/Inputs/WhereParametersDuplicateSelectorDiag 2>&1 | FileCheck %s --check-prefix=DUPLICATE
+// RUN: rm -rf %t && mkdir -p %t
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j-hui wrote:

I'm wondering whether this should be written as a single-file `split-file` test, and whether the `CHECK` lines should be written into the API notes YAML file.

As written, it's not immediately clear _why_ something is an error, or why something isn't.

https://github.com/llvm/llvm-project/pull/209408