Add support for editor placeholders to Clang

This commit teaches Clang to recognize editor placeholders that are produced
when an IDE like Xcode inserts a code-completion result that includes a
placeholder. Now when the lexer sees a placeholder token, it emits an
'editor placeholder in source file' error and creates an identifier token
that represents the placeholder. The parser/sema can now recognize the
placeholders and can suppress the diagnostics related to the placeholders. This
ensures that live issues in an IDE like Xcode won't get spurious diagnostics
related to placeholders.

This commit also adds a new compiler option named '-fallow-editor-placeholders'
that silences the 'editor placeholder in source file' error. This is useful
for an IDE like Xcode as we don't want to display those errors in live issues.

rdar://31581400

Differential Revision: https://reviews.llvm.org/D32081

llvm-svn: 300667

1 files changed, 33 insertions, 0 deletions

diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index dc911ef..003c9b5 100644
--- a/clang/lib/Lex/Lexer.cpp
+++ b/clang/lib/Lex/Lexer.cpp
@@ -2716,6 +2716,37 @@ bool Lexer::HandleEndOfConflictMarker(const char *CurPtr) {
   return false;
 }
 
+static const char *findPlaceholderEnd(const char *CurPtr,
+                                      const char *BufferEnd) {
+  if (CurPtr == BufferEnd)
+    return nullptr;
+  BufferEnd -= 1; // Scan until the second last character.
+  for (; CurPtr != BufferEnd; ++CurPtr) {
+    if (CurPtr[0] == '#' && CurPtr[1] == '>')
+      return CurPtr + 2;
+  }
+  return nullptr;
+}
+
+bool Lexer::lexEditorPlaceholder(Token &Result, const char *CurPtr) {
+  assert(CurPtr[-1] == '<' && CurPtr[0] == '#' && "Not a placeholder!");
+  if (!PP || LexingRawMode)
+    return false;
+  const char *End = findPlaceholderEnd(CurPtr + 1, BufferEnd);
+  if (!End)
+    return false;
+  const char *Start = CurPtr - 1;
+  if (!LangOpts.AllowEditorPlaceholders)
+    Diag(Start, diag::err_placeholder_in_source);
+  Result.startToken();
+  FormTokenWithChars(Result, End, tok::raw_identifier);
+  Result.setRawIdentifierData(Start);
+  PP->LookUpIdentifierInfo(Result);
+  Result.setFlag(Token::IsEditorPlaceholder);
+  BufferPtr = End;
+  return true;
+}
+
 bool Lexer::isCodeCompletionPoint(const char *CurPtr) const {
   if (PP && PP->isCodeCompletionEnabled()) {
     SourceLocation Loc = FileLoc.getLocWithOffset(CurPtr-BufferStart);
@@ -3473,6 +3504,8 @@ LexNextToken:
     } else if (LangOpts.Digraphs && Char == '%') {     // '<%' -> '{'
       CurPtr = ConsumeChar(CurPtr, SizeTmp, Result);
       Kind = tok::l_brace;
+    } else if (Char == '#' && lexEditorPlaceholder(Result, CurPtr)) {
+      return true;
     } else {
       Kind = tok::less;
     }