[PATCH] D118471: [clang][Lexer] Make raw and normal lexer behave the same for line comments

[Kadir Cetinkaya via Phabricator via cfe-commits]

kadircet created this revision.
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Normally there are heruistics in lexer to treat `//*` specially in
language modes that don't have line comments (to emit `/`). Unfortunately this
only applied to the first occurence of a line comment inside the file, as the
subsequent line comments were treated as if language had support for them.

This unfortunately only holds in normal lexing mode, as in raw mode all
occurences of line comments received this treatment, which created discrepancies
when comparing expanded and spelled tokens.

The proper fix would be to just make sure we treat all the line comments with a
subsequent `*` the same way, but it would imply breaking some code that's
accepted by clang today. So instead we introduce the same bug into raw lexing
mode.

Fixes https://github.com/clangd/clangd/issues/1003.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D118471

Files:
  clang/lib/Lex/Lexer.cpp
  clang/unittests/Lex/LexerTest.cpp


Index: clang/unittests/Lex/LexerTest.cpp
===================================================================
--- clang/unittests/Lex/LexerTest.cpp
+++ clang/unittests/Lex/LexerTest.cpp
@@ -23,6 +23,8 @@
 #include "clang/Lex/ModuleLoader.h"
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Lex/PreprocessorOptions.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <memory>
@@ -632,4 +634,27 @@
   EXPECT_EQ(SourceMgr.getNumCreatedFIDsForFileID(PP->getPredefinesFileID()),
             1U);
 }
+
+TEST_F(LexerTest, RawAndNormalLexSameForLineComments) {
+  const llvm::StringLiteral Source = R"cpp(
+  // First line comment.
+  //* Second line comment which is ambigious.
+  )cpp";
+  LangOpts.LineComment = false;
+  auto Toks = Lex(Source);
+  auto &SM = PP->getSourceManager();
+  auto SrcBuffer = SM.getBufferData(SM.getMainFileID());
+  Lexer L(SM.getLocForStartOfFile(SM.getMainFileID()), PP->getLangOpts(),
+          SrcBuffer.data(), SrcBuffer.data(),
+          SrcBuffer.data() + SrcBuffer.size());
+
+  auto ToksView = llvm::makeArrayRef(Toks);
+  clang::Token T;
+  while (!L.LexFromRawLexer(T)) {
+    ASSERT_TRUE(!ToksView.empty());
+    EXPECT_EQ(T.getKind(), ToksView.front().getKind());
+    ToksView = ToksView.drop_front();
+  }
+  EXPECT_TRUE(ToksView.empty());
+}
 } // anonymous namespace
Index: clang/lib/Lex/Lexer.cpp
===================================================================
--- clang/lib/Lex/Lexer.cpp
+++ clang/lib/Lex/Lexer.cpp
@@ -2378,8 +2378,9 @@
                             bool &TokAtPhysicalStartOfLine) {
   // If Line comments aren't explicitly enabled for this language, emit an
   // extension warning.
-  if (!LangOpts.LineComment && !isLexingRawMode()) {
-    Diag(BufferPtr, diag::ext_line_comment);
+  if (!LangOpts.LineComment) {
+    if (!isLexingRawMode()) // There's no PP in raw mode, so can't emit diags.
+      Diag(BufferPtr, diag::ext_line_comment);
 
     // Mark them enabled so we only emit one warning for this translation
     // unit.


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