[clang] Include the error message in file reading error diagnostic

[hans]

Summary

in order to provide as much information as possible to the user. The diagnostic will now look like for example:

error: error reading '/tmp/foo.c': Permission denied

(This addresses a FIXME from 2019, 9ef6c49baf45)

[thakis]

Lg

[thakis]

(if the presubmit is related, maybe some flang test needs updating? Weird that flang uses clang's diags.)

[hans]

In D146280#4201769, @thakis wrote:

(if the presubmit is related, maybe some flang test needs updating? Weird that flang uses clang's diags.)

The presubmit errors look unrelated and the flang tests seem fine locally.

clang/include/clang/Basic/DiagnosticFrontendKinds.td

 //==--- DiagnosticFrontendKinds.td - frontend diagnostics -----------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 class BackendInfo : CatBackend, ShowInSystemHeader;
 
 let Component = "Frontend" in {
 
 def err_fe_error_opening : Error<"error opening '%0': %1">;
-def err_fe_error_reading : Error<"error reading '%0'">;
+def err_fe_error_reading : Error<"error reading '%0': %1">;
 def err_fe_error_reading_stdin : Error<"error reading stdin: %0">;
 def err_fe_error_backend : Error<"error in backend: %0">, DefaultFatal;
 
 def err_fe_inline_asm : Error<"%0">, CatInlineAsm;
 def warn_fe_inline_asm : Warning<"%0">, CatInlineAsm, InGroup<BackendInlineAsm>;
 def note_fe_inline_asm : Note<"%0">, CatInlineAsm;
 def note_fe_inline_asm_here : Note<"instantiated into assembly here">;
 def err_fe_source_mgr : Error<"%0">, CatSourceMgr;

clang/lib/Frontend/CompilerInstance.cpp

bool CompilerInstance::InitializeSourceManager(const FrontendInputFile &Input,
 
   StringRef InputFile = Input.getFile();
 
   // Figure out where to get and map in the main file.
   auto FileOrErr = InputFile == "-"
                        ? FileMgr.getSTDIN()
                        : FileMgr.getFileRef(InputFile, /*OpenFile=*/true);
   if (!FileOrErr) {
-    // FIXME: include the error in the diagnostic even when it's not stdin.
     auto EC = llvm::errorToErrorCode(FileOrErr.takeError());
     if (InputFile != "-")
-      Diags.Report(diag::err_fe_error_reading) << InputFile;
+      Diags.Report(diag::err_fe_error_reading) << InputFile << EC.message();
     else
       Diags.Report(diag::err_fe_error_reading_stdin) << EC.message();
     return false;
   }
 
   SourceMgr.setMainFileID(
       SourceMgr.createFileID(*FileOrErr, SourceLocation(), Kind));
 

clang/tools/driver/cc1as_main.cpp

static bool ExecuteAssemblerImpl(AssemblerInvocation &Opts,
   const Target *TheTarget = TargetRegistry::lookupTarget(Opts.Triple, Error);
   if (!TheTarget)
     return Diags.Report(diag::err_target_unknown_triple) << Opts.Triple;
 
   ErrorOr<std::unique_ptr<MemoryBuffer>> Buffer =
       MemoryBuffer::getFileOrSTDIN(Opts.InputFile, /*IsText=*/true);
 
   if (std::error_code EC = Buffer.getError()) {
-    Error = EC.message();
-    return Diags.Report(diag::err_fe_error_reading) << Opts.InputFile;
+    return Diags.Report(diag::err_fe_error_reading)
+           << Opts.InputFile << EC.message();
   }
 
   SourceMgr SrcMgr;
 
   // Tell SrcMgr about this buffer, which is what the parser will pick up.
   unsigned BufferIndex = SrcMgr.AddNewSourceBuffer(std::move(*Buffer), SMLoc());
 
   // Record the location of the include directories so that the lexer can find

flang/lib/Frontend/FrontendAction.cpp

bool FrontendAction::beginSourceFile(CompilerInstance &ci,
   // Return immediately if the input file does not exist or is not a file. Note
   // that we cannot check this for input from stdin.
   if (input.getFile() != "-") {
     if (!llvm::sys::fs::is_regular_file(input.getFile())) {
       // Create an diagnostic ID to report
       unsigned diagID;
       if (llvm::vfs::getRealFileSystem()->exists(input.getFile())) {
         ci.getDiagnostics().Report(clang::diag::err_fe_error_reading)
-            << input.getFile();
+            << input.getFile() << "not a regular file";
         diagID = ci.getDiagnostics().getCustomDiagID(
             clang::DiagnosticsEngine::Error, "%0 is not a regular file");
       } else {
         diagID = ci.getDiagnostics().getCustomDiagID(
             clang::DiagnosticsEngine::Error, "%0 does not exist");
       }
 
       // Report the diagnostic and return