[clang-repl] Handle frontend options for clang-repl before calling executeAction

[anutosh491]

1. How usual clang works

It goes from Creating the Compiler Instance -> Addressing these llvmargs -> calling executeAction

2. what clang-repl does is create the Compiler Instance -> calls executeAction (and doesn't handle some options in between)

So ExecuteAction is framed like this

bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
  assert(hasDiagnostics() && "Diagnostics engine is not initialized!");
  assert(!getFrontendOpts().ShowHelp && "Client must handle '-help'!");
  assert(!getFrontendOpts().ShowVersion && "Client must handle '-version'!");
....

And clang-repl would need to handle these before getting to executeAction.

Otherwise

1. processing the -Xclang -version flag would give us the following (as shown while running clang-repl in the browser)

2. This would also help us process a try-catch block while running clang-repl in the browser which can't be done currently

[llvmbot]

@llvm/pr-subscribers-clang

Author: Anutosh Bhat (anutosh491)

Changes

1. How usual clang works

It goes from Creating the Compiler Instance -> Addressing these llvmargs -> calling executeAction

2. what clang-repl does is create the Compiler Instance -> calls executeAction (and doesn't handle some options in between)

So ExecuteAction is framed like this

bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
  assert(hasDiagnostics() && "Diagnostics engine is not initialized!");
  assert(!getFrontendOpts().ShowHelp && "Client must handle '-help'!");
  assert(!getFrontendOpts().ShowVersion && "Client must handle '-version'!");
....

And clang-repl would need to handle these before getting to executeAction.

Otherwise

1. processing the -Xclang -version flag would give us the following (as shown while running clang-repl in the browser)

2. This would also help us process a try-catch block while running clang-repl in the browser which can't be done currently

---

Full diff: https://github.com/llvm/llvm-project/pull/132670.diff

1 Files Affected:

• (modified) clang/lib/Interpreter/Interpreter.cpp (+37-1)

diff --git a/clang/lib/Interpreter/Interpreter.cpp b/clang/lib/Interpreter/Interpreter.cpp
index fa4c1439c9261..5f48117dbf3b8 100644
--- a/clang/lib/Interpreter/Interpreter.cpp
+++ b/clang/lib/Interpreter/Interpreter.cpp
@@ -141,6 +141,37 @@ CreateCI(const llvm::opt::ArgStringList &Argv) {
   return std::move(Clang);
 }
 
+static llvm::Error HandleFrontendOptions(const CompilerInstance &CI) {
+  const auto &FrontendOpts = CI.getFrontendOpts();
+
+  if (FrontendOpts.ShowHelp) {
+    driver::getDriverOptTable().printHelp(
+        llvm::outs(), "clang -cc1 [options] file...",
+        "LLVM 'Clang' Compiler: http://clang.llvm.org",
+        /*ShowHidden=*/false, /*ShowAllAliases=*/false,
+        llvm::opt::Visibility(driver::options::CC1Option));
+    return llvm::createStringError(llvm::errc::not_supported, "Help displayed");
+  }
+
+  if (FrontendOpts.ShowVersion) {
+    llvm::cl::PrintVersionMessage();
+    return llvm::createStringError(llvm::errc::not_supported, "Version displayed");
+  }
+
+  if (!FrontendOpts.LLVMArgs.empty()) {
+    unsigned NumArgs = FrontendOpts.LLVMArgs.size();
+    auto Args = std::make_unique<const char*[]>(NumArgs + 2);
+    Args[0] = "clang-repl (LLVM option parsing)";
+    for (unsigned i = 0; i != NumArgs; ++i)
+      Args[i + 1] = FrontendOpts.LLVMArgs[i].c_str();
+    Args[NumArgs + 1] = nullptr;
+    llvm::errs() << "Parsing LLVM backend options via cl::ParseCommandLineOptions...\n";
+    llvm::cl::ParseCommandLineOptions(NumArgs + 1, Args.get());
+  }
+
+  return llvm::Error::success();
+}
+
 } // anonymous namespace
 
 namespace clang {
@@ -451,7 +482,12 @@ const char *const Runtimes = R"(
 
 llvm::Expected<std::unique_ptr<Interpreter>>
 Interpreter::create(std::unique_ptr<CompilerInstance> CI) {
-  llvm::Error Err = llvm::Error::success();
+
+  llvm::Error Err = HandleFrontendOptions(*CI);
+  if (Err) {
+    return std::move(Err);
+  }
+
   auto Interp =
       std::unique_ptr<Interpreter>(new Interpreter(std::move(CI), Err));
   if (Err)

[anutosh491]

After handling these args we should see

(base) anutosh491@Anutoshs-MacBook-Air bin % ./clang-repl --Xcc -Xclang --Xcc -version                                      
LLVM (http://llvm.org/):
  LLVM version 21.0.0git
  Optimized build.
clang-repl: Version displayed

rather than the abort.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[anutosh491]

I see clang handle 4 types of FrontendOpts before calling ExecuteAction

1. help
2. version
3. Plugins through LoadRequestedPlugins
4. llvmargs

We might be interesting in 1, 2 and 4 for clang-repl
Also clang-repl uses IncrementalAction unlike FrontendAction so simply calling ExecuteCompilerInvocation won't do the job. So not sure if we can maybe refactor out 1/2/4 and use it from clang itself.

[serge-sans-paille]

Hey @anutosh491 can you add some testing?