[llvm-tapi-diff] Replicate diff utility error handling

[cishida]

Summary

For scripting purposes, use different error code for cases that aren't a
result of different tbd files, e.g. bad input like a path to a broken
symlink. This behaves more similiarly to how the unix diff command behaves.
This also includes minor tweaks on error messages.

[JDevlieghere]

LGTM

llvm/test/tools/llvm-tapi-diff/tapi-diff-incorrect-format.test

 ; RUN: mkdir -p %t
 ; RUN: yaml2obj %S/Inputs/macho.yaml -o %t/macho.dylib
 ; RUN: not llvm-tapi-diff %S/Inputs/v4A.tbd %t/macho.dylib 2>&1 | FileCheck %s
 
-; CHECK: {{.*}}: error: {{.*}}macho.dylib: Error when parsing file, unsupported file format
+; CHECK: error: {{.*}}macho.dylib' unsupported file format
 ; CHECK-NOT: error:
 ; CHECK-NOT: warning:

llvm/test/tools/llvm-tapi-diff/tapi-diff-misspelled-tbd.test

-; RUN: not llvm-tapi-diff %S/Inputs/v4A.tbd %S/Inputs/v4.tbd 2>&1 | FileCheck %s -DMSG=%errc_ENOENT
+; RUN: not llvm-tapi-diff %S/Inputs/v4A.tbd %S/Inputs/v4.tbd 2>&1 | FileCheck %s
 
-; CHECK: {{.*}}: error: {{.*}}v4.tbd: [[MSG]]
-; CHECK-NOT: error:
-; CHECK-NOT: warning:
+; CHECK: error: {{.*}}v4.tbd' {{[Nn]}}o such file or directory

llvm/tools/llvm-tapi-diff/llvm-tapi-diff.cpp

-//===-- llvm-tapi-diff.cpp - tbd comparator command-line driver ---*-
-// C++
-//-*-===//
+//===-- llvm-tapi-diff.cpp - tbd comparator command-line driver --*- C++-*-===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the command-line driver for the llvm-tapi difference

 using namespace object;
 
 namespace {
 cl::OptionCategory NMCat("llvm-tapi-diff Options");
 cl::opt<std::string> InputFileNameLHS(cl::Positional, cl::desc("<first file>"),
                                       cl::cat(NMCat));
 cl::opt<std::string> InputFileNameRHS(cl::Positional, cl::desc("<second file>"),
                                       cl::cat(NMCat));
-
-std::string ToolName;
 } // anonymous namespace
 
-ExitOnError ExitOnErr;
-
-void setErrorBanner(ExitOnError &ExitOnErr, std::string InputFile) {
-  ExitOnErr.setBanner(ToolName + ": error: " + InputFile + ": ");
-}
-
 Expected<std::unique_ptr<Binary>> convertFileToBinary(std::string &Filename) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
       MemoryBuffer::getFileOrSTDIN(Filename);
   if (BufferOrErr.getError())
     return errorCodeToError(BufferOrErr.getError());
   return createBinary(BufferOrErr.get()->getMemBufferRef());
 }
 
 int main(int Argc, char **Argv) {
   InitLLVM X(Argc, Argv);
   cl::HideUnrelatedOptions(NMCat);
-  cl::ParseCommandLineOptions(
-      Argc, Argv,
-      "This tool will compare two tbd files and return the "
-      "differences in those files.");
+  cl::ParseCommandLineOptions(Argc, Argv, "Text-based Stubs Comparison Tool");
   if (InputFileNameLHS.empty() || InputFileNameRHS.empty()) {
     cl::PrintHelpMessage();
     return EXIT_FAILURE;
   }
 
-  ToolName = Argv[0];
-
-  setErrorBanner(ExitOnErr, InputFileNameLHS);
+  ExitOnError ExitOnErr("error: '" + InputFileNameLHS + "' ",
+                        /*DefaultErrorExitCode=*/2);
   auto BinLHS = ExitOnErr(convertFileToBinary(InputFileNameLHS));
 
   TapiUniversal *FileLHS = dyn_cast<TapiUniversal>(BinLHS.get());
   if (!FileLHS) {
-    ExitOnErr(
-        createStringError(std::errc::executable_format_error,
-                          "Error when parsing file, unsupported file format"));
+    ExitOnErr(createStringError(std::errc::executable_format_error,
+                                "unsupported file format"));
   }
 
-  setErrorBanner(ExitOnErr, InputFileNameRHS);
+  ExitOnErr.setBanner("error: '" + InputFileNameRHS + "' ");
   auto BinRHS = ExitOnErr(convertFileToBinary(InputFileNameRHS));
 
   TapiUniversal *FileRHS = dyn_cast<TapiUniversal>(BinRHS.get());
   if (!FileRHS) {
-    ExitOnErr(
-        createStringError(std::errc::executable_format_error,
-                          "Error when parsing file, unsupported file format"));
+    ExitOnErr(createStringError(std::errc::executable_format_error,
+                                "unsupported file format"));
   }
 
   raw_ostream &OS = outs();
 
   return DiffEngine(FileLHS, FileRHS).compareFiles(OS);
 }