[clang] [clang-tools-extra] [clang] Extend diagnose_if to accept more detailed warning information (PR #70976)

[Aaron Ballman via cfe-commits]

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@@ -286,6 +334,18 @@ DiagnosticMapping DiagnosticIDs::getDefaultMapping(unsigned DiagID) {
   return Info;
 }
 
+void DiagnosticIDs::initCustomDiagMapping(DiagnosticMapping &Mapping,
+                                          unsigned DiagID) {
+  assert(IsCustomDiag(DiagID));
+  const auto &Diag = CustomDiagInfo->getDescription(DiagID);
+  if (auto Group = Diag.GetGroup()) {
+    auto GroupInfo = GroupInfos[static_cast<size_t>(*Group)];
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AaronBallman wrote:

Not a good use of `auto` because the type is not particularly obvious from the initialization.

https://github.com/llvm/llvm-project/pull/70976