[clang] Introduce diagnostics suppression mappings (#112517)

This implements

https://discourse.llvm.org/t/rfc-add-support-for-controlling-diagnostics-severities-at-file-level-granularity-through-command-line/81292.

Users now can suppress warnings for certain headers by providing a
mapping with globs, a sample file looks like:
```
[unused]
src:*
src:*clang/*=emit
```

This will suppress warnings from `-Wunused` group in all files that
aren't under `clang/` directory. This mapping file can be passed to
clang via `--warning-suppression-mappings=foo.txt`.

At a high level, mapping file is stored in DiagnosticOptions and then
processed with rest of the warning flags when creating a
DiagnosticsEngine. This is a functor that uses SpecialCaseLists
underneath to match against globs coming from the mappings file.

This implies processing warning options now performs IO, relevant
interfaces are updated to take in a VFS, falling back to RealFileSystem
when one is not available.

1 files changed, 8 insertions, 0 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index b5fd35a..e3145dc 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2521,6 +2521,11 @@ void CompilerInvocationBase::GenerateDiagnosticArgs(
 
     Consumer(StringRef("-R") + Remark);
   }
+
+  if (!Opts.DiagnosticSuppressionMappingsFile.empty()) {
+    GenerateArg(Consumer, OPT_warning_suppression_mappings_EQ,
+                Opts.DiagnosticSuppressionMappingsFile);
+  }
 }
 
 std::unique_ptr<DiagnosticOptions>
@@ -2597,6 +2602,9 @@ bool clang::ParseDiagnosticArgs(DiagnosticOptions &Opts, ArgList &Args,
     Opts.TabStop = DiagnosticOptions::DefaultTabStop;
   }
 
+  if (const Arg *A = Args.getLastArg(OPT_warning_suppression_mappings_EQ))
+    Opts.DiagnosticSuppressionMappingsFile = A->getValue();
+
   addDiagnosticArgs(Args, OPT_W_Group, OPT_W_value_Group, Opts.Warnings);
   addDiagnosticArgs(Args, OPT_R_Group, OPT_R_value_Group, Opts.Remarks);