[clang] Add an option for hiding line numbers in diagnostics

Clang offers a `-f[no]-show-column` flag for hiding the column numbers when
printing diagnostics but there is no option for doing the same with line
numbers.

In LLDB having this option would be useful, as LLDB sometimes only knows the
file name for a SourceLocation and just assigns it the dummy line/column `1:1`.
These fake line/column numbers are confusing to the user and LLDB should be able
to tell clang to hide *both* the column and the line number when rendering text
diagnostics.

This patch adds a flag for also hiding the line numbers. It's not exposed via
the command line flags as it's most likely not very useful for any user and can
lead to ambiguous output when the user decides to only hide either the line or
the column number (where `file:1: ...` could now refer to both line 1 or column
1 depending on the compiler flags). LLDB can just access the DiagnosticOptions
directly when constructing its internal Clang instance.

The effect doesn't apply to Vi/MSVC style diagnostics because it's not defined
how these diagnostic styles would show an omitted line number (MSVC doesn't have
such an option and Vi's line mode is theory only supporting line numbers if I
understand it correctly).

Reviewed By: thakis, MaskRay

Differential Revision: https://reviews.llvm.org/D83038

clang/include/clang/Basic/DiagnosticOptions.def

@@ -47,6 +47,7 @@ SEMANTIC_DIAGOPT(IgnoreWarnings, 1, 0)   /// -w
 DIAGOPT(NoRewriteMacros, 1, 0)  /// -Wno-rewrite-macros
 DIAGOPT(Pedantic, 1, 0)         /// -pedantic
 DIAGOPT(PedanticErrors, 1, 0)   /// -pedantic-errors
+DIAGOPT(ShowLine, 1, 1)         /// Show line number on diagnostics.
 DIAGOPT(ShowColumn, 1, 1)       /// Show column number on diagnostics.
 DIAGOPT(ShowLocation, 1, 1)     /// Show source location information.
 DIAGOPT(ShowLevel, 1, 1)        /// Show diagnostic level.

clang/lib/Frontend/TextDiagnostic.cpp

@@ -827,7 +827,10 @@ void TextDiagnostic::emitDiagnosticLoc(FullSourceLoc Loc, PresumedLoc PLoc,
 
   emitFilename(PLoc.getFilename(), Loc.getManager());
   switch (DiagOpts->getFormat()) {
-  case DiagnosticOptions::Clang: OS << ':'  << LineNo; break;
+  case DiagnosticOptions::Clang:
+    if (DiagOpts->ShowLine)
+      OS << ':' << LineNo;
+    break;
   case DiagnosticOptions::MSVC:  OS << '('  << LineNo; break;
   case DiagnosticOptions::Vi:    OS << " +" << LineNo; break;
   }

clang/unittests/Frontend/CMakeLists.txt

@@ -12,6 +12,7 @@ add_clang_unittest(FrontendTests
   ParsedSourceLocationTest.cpp
   PCHPreambleTest.cpp
   OutputStreamTest.cpp
+  TextDiagnosticTest.cpp
   )
 clang_target_link_libraries(FrontendTests
   PRIVATE

clang/unittests/Frontend/TextDiagnosticTest.cpp

@@ -0,0 +1,100 @@
+//===- unittests/Frontend/TextDiagnosticTest.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 "clang/Frontend/TextDiagnostic.h"
+#include "clang/Basic/FileManager.h"
+#include "clang/Basic/LangOptions.h"
+#include "clang/Basic/SourceManager.h"
+#include "llvm/Support/SmallVectorMemoryBuffer.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace clang;
+
+namespace {
+
+/// Prints a diagnostic with the given DiagnosticOptions and the given
+/// SourceLocation and returns the printed diagnostic text.
+static std::string PrintDiag(const DiagnosticOptions &Opts, FullSourceLoc Loc) {
+  std::string Out;
+  llvm::raw_string_ostream OS(Out);
+  clang::LangOptions LangOpts;
+  // Owned by TextDiagnostic.
+  DiagnosticOptions *DiagOpts = new DiagnosticOptions(Opts);
+  TextDiagnostic Diag(OS, LangOpts, DiagOpts);
+  // Emit a dummy diagnostic that is just 'message'.
+  Diag.emitDiagnostic(Loc, DiagnosticsEngine::Level::Warning, "message",
+                      /*Ranges=*/{}, /*FixItHints=*/{});
+  OS.flush();
+  return Out;
+}
+
+TEST(TextDiagnostic, ShowLine) {
+  // Create dummy FileManager and SourceManager.
+  FileSystemOptions FSOpts;
+  FileManager FileMgr(FSOpts);
+  IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs);
+  DiagnosticsEngine DiagEngine(DiagID, new DiagnosticOptions,
+                               new IgnoringDiagConsumer());
+  SourceManager SrcMgr(DiagEngine, FileMgr);
+
+  // Create a dummy file with some contents to produce a test SourceLocation.
+  const llvm::StringRef file_path = "main.cpp";
+  const llvm::StringRef main_file_contents = "some\nsource\ncode\n";
+  const clang::FileEntry &fe = *FileMgr.getVirtualFile(
+      file_path,
+      /*Size=*/static_cast<off_t>(main_file_contents.size()),
+      /*ModificationTime=*/0);
+
+  llvm::SmallVector<char, 64> buffer;
+  buffer.append(main_file_contents.begin(), main_file_contents.end());
+  auto file_contents = std::make_unique<llvm::SmallVectorMemoryBuffer>(
+      std::move(buffer), file_path);
+  SrcMgr.overrideFileContents(&fe, std::move(file_contents));
+
+  // Create the actual file id and use it as the main file.
+  clang::FileID fid =
+      SrcMgr.createFileID(&fe, SourceLocation(), clang::SrcMgr::C_User);
+  SrcMgr.setMainFileID(fid);
+
+  // Create the source location for the test diagnostic.
+  FullSourceLoc Loc(SrcMgr.translateLineCol(fid, /*Line=*/1, /*Col=*/2),
+                    SrcMgr);
+
+  DiagnosticOptions DiagOpts;
+  DiagOpts.ShowLine = true;
+  DiagOpts.ShowColumn = true;
+  // Hide printing the source line/caret to make the diagnostic shorter and it's
+  // not relevant for this test.
+  DiagOpts.ShowCarets = false;
+  EXPECT_EQ("main.cpp:1:2: warning: message\n", PrintDiag(DiagOpts, Loc));
+
+  // Check that ShowLine doesn't influence the Vi/MSVC diagnostic formats as its
+  // a Clang-specific diagnostic option.
+  DiagOpts.setFormat(TextDiagnosticFormat::Vi);
+  DiagOpts.ShowLine = false;
+  EXPECT_EQ("main.cpp +1:2: warning: message\n", PrintDiag(DiagOpts, Loc));
+
+  DiagOpts.setFormat(TextDiagnosticFormat::MSVC);
+  DiagOpts.ShowLine = false;
+  EXPECT_EQ("main.cpp(1,2): warning: message\n", PrintDiag(DiagOpts, Loc));
+
+  // Reset back to the Clang format.
+  DiagOpts.setFormat(TextDiagnosticFormat::Clang);
+
+  // Hide line number but show column.
+  DiagOpts.ShowLine = false;
+  EXPECT_EQ("main.cpp:2: warning: message\n", PrintDiag(DiagOpts, Loc));
+
+  // Show line number but hide column.
+  DiagOpts.ShowLine = true;
+  DiagOpts.ShowColumn = false;
+  EXPECT_EQ("main.cpp:1: warning: message\n", PrintDiag(DiagOpts, Loc));
+}
+
+} // anonymous namespace