[flang][driver] Disallow non-existent input files in the frontend driver

[awarzynski]

Summary

This patch adds a check that verifies that the input file used when
calling the frontend driver (i.e. flang-new -fc1) actually exists.
This was not required for the compiler driver, flang-new, as that's
already handled in libclangDriver.

Once all input/output file management is moved to the driver, we should
also check that for input from stdin the corresponding file descriptor
was successfully acquired.

This patch also makes sure that the default action in the frontend is
ParseSyntaxOnly. This is consistent with Clang. Before this change
flang-new -fc1 would do nothing, which makes testing changes like the
one introduced here a bit tricky.

[tskeith]

flang/lib/Frontend/FrontendAction.cpp

40

What happens if the argument exists but is not a file?

42

It looks like this only says "error reading <file>". It would be nice to say what the error is.

flang/test/Flang-Driver/missing-input.f90

13

NOEXISITANT -> NONEXISTENT ?

[awarzynski]

Update diagnostic message and add a check for directories

[awarzynski]

@tskeith Thank for you reviewing! I think that this covers all of your suggestions.

flang/lib/Frontend/FrontendAction.cpp

40

Updated - this will now make sure that the input:

• exists
• is not a directory

If any of these ^^^ is not true, a diagnostic is generated (different for each condition).

[tskeith]

flang/lib/Frontend/FrontendAction.cpp

37

The input may be a regular file but still not readable, e.g. because of permissions. Should that be caught here too for consistency?

Why is this checking needed at all? The front end will report an error if it can't read the file.

flang/test/Flang-Driver/missing-input.f90

14

NONEXISITENT -> NONEXISTENT ?

[awarzynski]

flang/lib/Frontend/FrontendAction.cpp

37

The input may be a regular file but still not readable, e.g. because of permissions. Should that be caught here too for consistency?

Initially I wanted to keep this simple and catch the most obvious things.

Why is this checking needed at all? The front end will report an error if it can't read the file.

The long term goal is for the driver makes sure that the frontend is not entered before all input is validated. This includes managing input files. This is a small step in that direction.

[awarzynski]

Fix typo in test

[SouraVX]

LGTM! Please wait for @sameeranjoshi to have a look.

[awarzynski]

@sameeranjoshi @SouraVX This is now merged so that I can focus on other patches. But if you have further comments, I'll happily address them!

Thank you for reviewing!

flang/lib/Frontend/CompilerInvocation.cpp

 //===- CompilerInvocation.cpp ---------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 #include "flang/Frontend/CompilerInvocation.h"
 #include "flang/Frontend/PreprocessorOptions.h"
 #include "flang/Version.inc"
 #include "clang/Basic/AllDiagnostics.h"
 #include "clang/Basic/DiagnosticDriver.h"
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Driver/DriverDiagnostic.h"
 #include "clang/Driver/Options.h"
 #include "llvm/ADT/StringRef.h"
bool Fortran::frontend::ParseDiagnosticArgs(clang::DiagnosticOptions &opts,
     llvm::opt::ArgList &args, bool defaultDiagColor) {
   opts.ShowColors = parseShowColorsArgs(args, defaultDiagColor);
 
   return true;
 }
 
 static InputKind ParseFrontendArgs(FrontendOptions &opts,
     llvm::opt::ArgList &args, clang::DiagnosticsEngine &diags) {
+
+  // By default the frontend driver creates a ParseSyntaxOnly action.
+  opts.programAction_ = ParseSyntaxOnly;
+
   // Identify the action (i.e. opts.ProgramAction)
   if (const llvm::opt::Arg *a =
           args.getLastArg(clang::driver::options::OPT_Action_Group)) {
     switch (a->getOption().getID()) {
     default: {
       llvm_unreachable("Invalid option in group!");
     }
     case clang::driver::options::OPT_test_io:

flang/lib/Frontend/FrontendAction.cpp

 //===--- FrontendAction.cpp -----------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
 #include "flang/Frontend/FrontendAction.h"
 #include "flang/Frontend/CompilerInstance.h"
 #include "flang/Frontend/FrontendActions.h"
 #include "flang/Frontend/FrontendOptions.h"
 #include "flang/FrontendTool/Utils.h"
+#include "clang/Basic/DiagnosticFrontend.h"
 #include "llvm/Support/Errc.h"
+#include "llvm/Support/VirtualFileSystem.h"
 
 using namespace Fortran::frontend;
 
 void FrontendAction::set_currentInput(const FrontendInputFile &currentInput) {
   this->currentInput_ = currentInput;
 }
 
 // Call this method if BeginSourceFile fails.
 // Deallocate compiler instance, input and output descriptors
 static void BeginSourceFileCleanUp(FrontendAction &fa, CompilerInstance &ci) {
   ci.ClearOutputFiles(/*EraseFiles=*/true);
   fa.set_currentInput(FrontendInputFile());
   fa.set_instance(nullptr);
 }
 
 bool FrontendAction::BeginSourceFile(
     CompilerInstance &ci, const FrontendInputFile &realInput) {
 
   FrontendInputFile input(realInput);
+
+  // Return immediately if the input file does not exist. Note that we cannot
+  // check this for input from stdin.
+  if (input.file() != "-") {
+    if (!llvm::vfs::getRealFileSystem()->exists(input.file())) {
+      ci.diagnostics().Report(clang::diag::err_fe_error_reading)
+          << input.file();
+      BeginSourceFileCleanUp(*this, ci);
+      return false;
+    }
+  }
+
   assert(!instance_ && "Already processing a source file!");
   assert(!realInput.IsEmpty() && "Unexpected empty filename!");
   set_currentInput(realInput);
   set_instance(&ci);
   if (!ci.HasAllSources()) {
     BeginSourceFileCleanUp(*this, ci);
     return false;
   }

flang/test/Flang-Driver/missing-input.f90

-! RUN: not %flang-new  2>&1 | FileCheck %s
-
 ! REQUIRES: new-flang-driver
 
-! CHECK: flang-new: error: no input files
+! Test the behaviour when input is missing. Note that with the compiler driver,
+! the input _has_ to be specified. Indeed, the driver decides what to do based
+! on the file extension. No input file means that it doesn't know what to do
+! (compile? preprocess? link?). Whereas the frontend driver simply assumes
+! that "no explicit input == read from stdin"
+
+!--------------------------
+! FLANG DRIVER (flang-new)
+!--------------------------
+! RUN: not %flang-new  2>&1 | FileCheck %s --check-prefix=FLANG-NO-FILE
+! RUN: not %flang-new %t 2>&1 | FileCheck %s --check-prefix=FLANG-NOEXISITANT-FILE
+
+!-----------------------------------------
+! FLANG FRONTEND DRIVER (flang-new -fc1)
+!-----------------------------------------
+! RUN: not %flang-new -fc1 %t 2>&1  | FileCheck %s --check-prefix=FLANG-FC1-NOEXISITANT-FILE
+
+!-----------------------
+! EXPECTED OUTPUT
+!-----------------------
+! FLANG-NO-FILE: flang-new: error: no input files
+
+! FLANG-NOEXISITANT-FILE: flang-new: error: no such file or directory: {{.*}}
+! FLANG-NOEXISITANT-FILE: flang-new: error: no input files
+
+! FLANG-FC1-NOEXISITANT-FILE: error: error reading {{.*}}