[llvm-dev] warnings and error messages always go to standard error

[Geoff Levner via llvm-dev]

Well, if anybody on this list is interested, the solution was pointed out
to me by Eli Friedman on the cfe-dev list (it is in fact a Clang problem).

The DiagnosticsEngine passed to the Driver is used only by the Driver
itself, not by the resulting compilation. To retrieve the diagnostics from
the compilation, I have to pass my TextDiagnosticPrinter to
CompilerInstance::createDiagnostics().

Thanks to Eli.

On Sun, 26 Aug 2018 at 13:22, Geoff Levner <glevner at gmail.com> wrote:

> Greeting, LLVM wizards,
>
> We are using Clang and LLVM in an application to compile and execute C++
> code on the fly. If the code fails to compile, I would like to be able to
> pop up a dialog box telling the user why. But warnings and error messages
> go straight to standard error.
>
> I have tried passing a raw_string_stream to TextDiagnosticPrinter instead
> of errs(), but that seems to have no effect. What is that stream actually
> used for? Am I doing something wrong? I have attached the code we use to
> compile (simplified a bit).
>
> Thanks,
> Geoff
>
>
>     IntrusiveRefCntPtr<DiagnosticOptions> diag_opts(new DiagnosticOptions);
>     std::string diagnostics;
>     raw_string_ostream diag_stream(diagnostics);
>     TextDiagnosticPrinter *diag_client =
>         new TextDiagnosticPrinter(diag_stream, diag_opts.get());
>     IntrusiveRefCntPtr<DiagnosticIDs> diag_ids(new DiagnosticIDs);
>     DiagnosticsEngine diags(diag_ids, diag_opts.get(), diag_client);
>     Driver driver(executable, llvm::sys::getDefaultTargetTriple(), diags);
>
>     SmallVector<const char*, 16> args;
>     // various arguments...
>
>     std::unique_ptr<Compilation>
> compilation(driver.BuildCompilation(args));
>     const JobList& jobs = compilation->getJobs();
>     const Command& cmd = llvm::cast<Command>(*jobs.begin());
>     const ArgStringList& ccargs = cmd.getArguments();
>     std::unique_ptr<CompilerInvocation> invocation(new CompilerInvocation);
>     CompilerInvocation::CreateFromArgs(
>         *invocation,
>         const_cast<const char**>(ccargs.data()),
>         const_cast<const char**>(ccargs.data()) + ccargs.size(),
>         diags);
>
>     CompilerInstance clang;
>     clang.setInvocation(std::move(invocation));
>     clang.createDiagnostics();
>
>     std::unique_ptr<CodeGenAction> action(
>         new EmitLLVMOnlyAction(&my_llvm_context));
>     if (!clang.ExecuteAction(*action)) {
>         if (diag_stream.str().empty()) {
>             setError("Compilation failed: see standard error for
> details.");
>         } else {
>             setError("Compilation failed:\n" + diag_stream.str());
>         }
>     }
>
>
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