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

7 files changed, 56 insertions, 0 deletions

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index b6887b87584..49708e7d724 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2306,6 +2306,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (!Args.hasFlag(options::OPT_fstrict_return, options::OPT_fno_strict_return,
                     true))
     CmdArgs.push_back("-fno-strict-return");
+  if (Args.hasFlag(options::OPT_fallow_editor_placeholders,
+                   options::OPT_fno_allow_editor_placeholders, false))
+    CmdArgs.push_back("-fallow-editor-placeholders");
   if (Args.hasFlag(options::OPT_fstrict_vtable_pointers,
                    options::OPT_fno_strict_vtable_pointers,
                    false))
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 05db4577ab9..0e0eb40eb33 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2322,6 +2322,9 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
       Args.getAllArgValues(OPT_fxray_always_instrument);
   Opts.XRayNeverInstrumentFiles =
       Args.getAllArgValues(OPT_fxray_never_instrument);
+
+  // -fallow-editor-placeholders
+  Opts.AllowEditorPlaceholders = Args.hasArg(OPT_fallow_editor_placeholders);
 }
 
 static void ParsePreprocessorArgs(PreprocessorOptions &Opts, ArgList &Args,
diff --git a/clang/lib/Lex/Lexer.cpp b/clang/lib/Lex/Lexer.cpp
index dc911ef91b6..003c9b5eed1 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;
     }
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index 265c12d7d5e..edbfc636bc4 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -851,6 +851,10 @@ Parser::ParseExternalDeclaration(ParsedAttributesWithRange &attrs,
 
   default:
   dont_know:
+    if (Tok.isEditorPlaceholder()) {
+      ConsumeToken();
+      return nullptr;
+    }
     // We can't tell whether this is a function-definition or declaration yet.
     return ParseDeclarationOrFunctionDefinition(attrs, DS);
   }
@@ -1679,6 +1683,8 @@ bool Parser::TryAnnotateTypeOrScopeToken() {
           return false;
         }
       }
+      if (Tok.isEditorPlaceholder())
+        return true;
 
       Diag(Tok.getLocation(), diag::err_expected_qualified_after_typename);
       return true;
diff --git a/clang/lib/Sema/SemaCXXScopeSpec.cpp b/clang/lib/Sema/SemaCXXScopeSpec.cpp
index 57471de78d3..6da4d2a2619 100644
--- a/clang/lib/Sema/SemaCXXScopeSpec.cpp
+++ b/clang/lib/Sema/SemaCXXScopeSpec.cpp
@@ -480,6 +480,8 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
                                        bool ErrorRecoveryLookup,
                                        bool *IsCorrectedToColon,
                                        bool OnlyNamespace) {
+  if (IdInfo.Identifier->isEditorPlaceholder())
+    return true;
   LookupResult Found(*this, IdInfo.Identifier, IdInfo.IdentifierLoc,
                      OnlyNamespace ? LookupNamespaceName
                                    : LookupNestedNameSpecifierName);
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 075e87b75cd..f3ffcf5d696 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -628,6 +628,9 @@ void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
                                    CXXScopeSpec *SS,
                                    ParsedType &SuggestedType,
                                    bool AllowClassTemplates) {
+  // Don't report typename errors for editor placeholders.
+  if (II->isEditorPlaceholder())
+    return;
   // We don't have anything to suggest (yet).
   SuggestedType = nullptr;
 
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index bb174521c72..5a56f709377 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -2129,6 +2129,12 @@ Sema::ActOnIdExpression(Scope *S, CXXScopeSpec &SS,
   IdentifierInfo *II = Name.getAsIdentifierInfo();
   SourceLocation NameLoc = NameInfo.getLoc();
 
+  if (II && II->isEditorPlaceholder()) {
+    // FIXME: When typed placeholders are supported we can create a typed
+    // placeholder expression node.
+    return ExprError();
+  }
+
   // C++ [temp.dep.expr]p3:
   //   An id-expression is type-dependent if it contains:
   //     -- an identifier that was declared with a dependent type,