[c++1z] Implement N3994: a range-based for loop can declare a variable with super-terse notation

  for (x : range) { ... }

which is equivalent to

  for (auto &&x : range) { ... }

llvm-svn: 211267

3 files changed, 87 insertions, 8 deletions

diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 5ec899f5898..33e3cab8671 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -3390,13 +3390,23 @@ void Parser::ParseCXX11Attributes(ParsedAttributesWithRange &attrs,
 }
 
 void Parser::DiagnoseAndSkipCXX11Attributes() {
-  if (!isCXX11AttributeSpecifier())
-    return;
-
   // Start and end location of an attribute or an attribute list.
   SourceLocation StartLoc = Tok.getLocation();
+  SourceLocation EndLoc = SkipCXX11Attributes();
+
+  if (EndLoc.isValid()) {
+    SourceRange Range(StartLoc, EndLoc);
+    Diag(StartLoc, diag::err_attributes_not_allowed)
+      << Range;
+  }
+}
+
+SourceLocation Parser::SkipCXX11Attributes() {
   SourceLocation EndLoc;
 
+  if (!isCXX11AttributeSpecifier())
+    return EndLoc;
+
   do {
     if (Tok.is(tok::l_square)) {
       BalancedDelimiterTracker T(*this, tok::l_square);
@@ -3413,11 +3423,7 @@ void Parser::DiagnoseAndSkipCXX11Attributes() {
     }
   } while (isCXX11AttributeSpecifier());
 
-  if (EndLoc.isValid()) {
-    SourceRange Range(StartLoc, EndLoc);
-    Diag(StartLoc, diag::err_attributes_not_allowed)
-      << Range;
-  }
+  return EndLoc;
 }
 
 /// ParseMicrosoftAttributes - Parse a Microsoft attribute [Attr]
diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
index 059c2b6a3f8..536e92c0cc6 100644
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -1388,6 +1388,25 @@ StmtResult Parser::ParseDoStatement() {
                              Cond.get(), T.getCloseLocation());
 }
 
+bool Parser::isForRangeIdentifier() {
+  assert(Tok.is(tok::identifier));
+
+  const Token &Next = NextToken();
+  if (Next.is(tok::colon))
+    return true;
+
+  if (Next.is(tok::l_square) || Next.is(tok::kw_alignas)) {
+    TentativeParsingAction PA(*this);
+    ConsumeToken();
+    SkipCXX11Attributes();
+    bool Result = Tok.is(tok::colon);
+    PA.Revert();
+    return Result;
+  }
+
+  return false;
+}
+
 /// ParseForStatement
 ///       for-statement: [C99 6.8.5.3]
 ///         'for' '(' expr[opt] ';' expr[opt] ';' expr[opt] ')' statement
@@ -1471,6 +1490,29 @@ StmtResult Parser::ParseForStatement(SourceLocation *TrailingElseLoc) {
     ProhibitAttributes(attrs);
     // no first part, eat the ';'.
     ConsumeToken();
+  } else if (getLangOpts().CPlusPlus && Tok.is(tok::identifier) &&
+             isForRangeIdentifier()) {
+    ProhibitAttributes(attrs);
+    IdentifierInfo *Name = Tok.getIdentifierInfo();
+    SourceLocation Loc = ConsumeToken();
+    MaybeParseCXX11Attributes(attrs);
+
+    ForRangeInit.ColonLoc = ConsumeToken();
+    if (Tok.is(tok::l_brace))
+      ForRangeInit.RangeExpr = ParseBraceInitializer();
+    else
+      ForRangeInit.RangeExpr = ParseExpression();
+
+    Diag(Loc, getLangOpts().CPlusPlus1z
+                  ? diag::warn_cxx1y_compat_for_range_identifier
+                  : diag::ext_for_range_identifier)
+      << ((getLangOpts().CPlusPlus11 && !getLangOpts().CPlusPlus1z)
+              ? FixItHint::CreateInsertion(Loc, "auto &&")
+              : FixItHint());
+
+    FirstPart = Actions.ActOnCXXForRangeIdentifier(getCurScope(), Loc, Name,
+                                                   attrs, attrs.Range.getEnd());
+    ForRange = true;
   } else if (isForInitDeclaration()) {  // for (int X = 4;
     // Parse declaration, which eats the ';'.
     if (!C99orCXXorObjC)   // Use of C99-style for loops in C90 mode?
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index e4b2096bec7..bdc8609116f 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -8941,6 +8941,37 @@ void Sema::ActOnCXXForRangeDecl(Decl *D) {
   }
 }
 
+StmtResult
+Sema::ActOnCXXForRangeIdentifier(Scope *S, SourceLocation IdentLoc,
+                                 IdentifierInfo *Ident,
+                                 ParsedAttributes &Attrs,
+                                 SourceLocation AttrEnd) {
+  // C++1y [stmt.iter]p1:
+  //   A range-based for statement of the form
+  //      for ( for-range-identifier : for-range-initializer ) statement
+  //   is equivalent to
+  //      for ( auto&& for-range-identifier : for-range-initializer ) statement
+  DeclSpec DS(Attrs.getPool().getFactory());
+
+  const char *PrevSpec;
+  unsigned DiagID;
+  DS.SetTypeSpecType(DeclSpec::TST_auto, IdentLoc, PrevSpec, DiagID,
+                     getPrintingPolicy());
+
+  Declarator D(DS, Declarator::ForContext);
+  D.SetIdentifier(Ident, IdentLoc);
+  D.takeAttributes(Attrs, AttrEnd);
+
+  ParsedAttributes EmptyAttrs(Attrs.getPool().getFactory());
+  D.AddTypeInfo(DeclaratorChunk::getReference(0, IdentLoc, /*lvalue*/false),
+                EmptyAttrs, IdentLoc);
+  Decl *Var = ActOnDeclarator(S, D);
+  cast<VarDecl>(Var)->setCXXForRangeDecl(true);
+  FinalizeDeclaration(Var);
+  return ActOnDeclStmt(FinalizeDeclaratorGroup(S, DS, Var), IdentLoc,
+                       AttrEnd.isValid() ? AttrEnd : IdentLoc);
+}
+
 void Sema::CheckCompleteVariableDeclaration(VarDecl *var) {
   if (var->isInvalidDecl()) return;