[clang] [Clang] Silently ignore unknown warnings in `--warning-suppression-mappings` (PR #124141)

[kadir çetinkaya via cfe-commits]

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@@ -547,11 +547,9 @@ void WarningsSpecialCaseList::processSections(DiagnosticsEngine &Diags) {
     StringRef DiagGroup = SectionEntry->getKey();
     if (Diags.getDiagnosticIDs()->getDiagnosticsInGroup(
             WarningFlavor, DiagGroup, GroupDiags)) {
-      StringRef Suggestion =
-          DiagnosticIDs::getNearestOption(WarningFlavor, DiagGroup);
-      Diags.Report(diag::warn_unknown_diag_option)
-          << static_cast<unsigned>(WarningFlavor) << DiagGroup
-          << !Suggestion.empty() << Suggestion;
+      // If a diagnostic group name is unknown, simply ignore the
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kadircet wrote:

> I realize it was intentional to emit unknown-warning diagnostics, but I really think we should not.

i still feel a little bit uneasy about leaving the user in the dark, when they're trying to use the suppression mapping and it silently doesn't work (even if it's due to a configuration error). so i'd rather punt on silently ignoring, until concerns like version skew is really biting us in practice. 

Most of the projects that maintain their own toolchain already needs to put effort into fiddling with warning flags as they update their toolchain hence I don't think we're creating any new maintenance surface here.

> Why parse the suppression file in the driver? Even if we do check ReportDiags, isn't it just wasted work to read it at all?

sorry my comment was a little misleading. i agree that we shouldn't try parsing this in driver, there's simply no need. but we should still respect `ReportDiags` in the implementation.

> I'd be happy to have you do so! (Even if a bit less happy than going with the simpler proposal, here).

thanks! i'll put together a patch soon

https://github.com/llvm/llvm-project/pull/124141