[clang] NFC: Extract DiagnosticOptions parsing

The way we parse `DiagnosticOptions` is a bit involved.

`DiagnosticOptions` are parsed as part of the cc1-parsing function `CompilerInvocation::CreateFromArgs` which takes `DiagnosticsEngine` as an argument to be able to report errors in command-line arguments. But to create `DiagnosticsEngine`, `DiagnosticOptions` are needed. This is solved by exposing the `ParseDiagnosticArgs` to clients and making its `DiagnosticsEngine` argument optional, essentially breaking the dependency cycle.

The `ParseDiagnosticArgs` function takes `llvm::opt::ArgList &`, which each client needs to create from the command-line (typically represented as `std::vector<const char *>`). Creating this data structure in this context is somewhat particular. This code pattern is copy-pasted in some places across the upstream code base and also in downstream repos. To make things a bit more uniform, this patch extracts the code into a new reusable function: `CreateAndPopulateDiagOpts`.

Reviewed By: dexonsmith

Differential Revision: https://reviews.llvm.org/D108918

1 files changed, 13 insertions, 0 deletions

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 64800b1..0da2cb3e 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2256,6 +2256,19 @@ void CompilerInvocation::GenerateDiagnosticArgs(
   }
 }
 
+std::unique_ptr<DiagnosticOptions>
+clang::CreateAndPopulateDiagOpts(ArrayRef<const char *> Argv) {
+  auto DiagOpts = std::make_unique<DiagnosticOptions>();
+  unsigned MissingArgIndex, MissingArgCount;
+  InputArgList Args = getDriverOptTable().ParseArgs(
+      Argv.slice(1), MissingArgIndex, MissingArgCount);
+  // We ignore MissingArgCount and the return value of ParseDiagnosticArgs.
+  // Any errors that would be diagnosed here will also be diagnosed later,
+  // when the DiagnosticsEngine actually exists.
+  (void)ParseDiagnosticArgs(*DiagOpts, Args);
+  return DiagOpts;
+}
+
 bool clang::ParseDiagnosticArgs(DiagnosticOptions &Opts, ArgList &Args,
                                 DiagnosticsEngine *Diags,
                                 bool DefaultDiagColor) {