Show better errors for LLVM IR output

I was trying to output LLVM IR directly to the console:

    $ rustc hello.rs --emit=llvm-ir -o /dev/stdout
    LLVM ERROR: IO failure on output stream: Bad file descriptor

Now `LLVMRustPrintModule` returns an error, and we print:

    error: failed to write LLVM IR to /dev/stdout.hello.7rcbfp3g-cgu.0.rcgu.ll: Permission denied

... which is more informative.

1 files changed, 9 insertions, 2 deletions

diff --git a/src/rustllvm/PassWrapper.cpp b/src/rustllvm/PassWrapper.cpp
index 25595e14982..319c66a21f1 100644
--- a/src/rustllvm/PassWrapper.cpp
+++ b/src/rustllvm/PassWrapper.cpp
@@ -646,8 +646,9 @@ char RustPrintModulePass::ID = 0;
 INITIALIZE_PASS(RustPrintModulePass, "print-rust-module",
                 "Print rust module to stderr", false, false)
 
-extern "C" void LLVMRustPrintModule(LLVMPassManagerRef PMR, LLVMModuleRef M,
-                                    const char *Path, DemangleFn Demangle) {
+extern "C" LLVMRustResult
+LLVMRustPrintModule(LLVMPassManagerRef PMR, LLVMModuleRef M,
+                    const char *Path, DemangleFn Demangle) {
   llvm::legacy::PassManager *PM = unwrap<llvm::legacy::PassManager>(PMR);
   std::string ErrorInfo;
 
@@ -655,12 +656,18 @@ extern "C" void LLVMRustPrintModule(LLVMPassManagerRef PMR, LLVMModuleRef M,
   raw_fd_ostream OS(Path, EC, sys::fs::F_None);
   if (EC)
     ErrorInfo = EC.message();
+  if (ErrorInfo != "") {
+    LLVMRustSetLastError(ErrorInfo.c_str());
+    return LLVMRustResult::Failure;
+  }
 
   formatted_raw_ostream FOS(OS);
 
   PM->add(new RustPrintModulePass(FOS, Demangle));
 
   PM->run(*unwrap(M));
+
+  return LLVMRustResult::Success;
 }
 
 extern "C" void LLVMRustPrintPasses() {