Fix valid-for-expr ellipses eaten as invalid decl

Summary:
The trial parse for declarative syntax accepts an invalid pack
declaration syntax, which is ambiguous with valid pack expansions of
expressions. This commit removes the invalid pack declaration syntax to
avoid mistaking valid pack expansions as invalid declarator components.

Additionally, the trial parse of a //template-argument-list// then needs
to handle the optional ellipsis that is part of that grammar, as opposed
to relying on the trial parse for declarators accepting stray ellipses.

Reviewers: rsmith, rcraik, aaron.ballman

Reviewed By: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D33339


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@303472 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Parse/ParseTentative.cpp

@@ -481,10 +481,10 @@ Parser::isCXXConditionDeclarationOrInitStatement(bool CanBeInitStatement) {
   /// the corresponding ')'. If the context is
   /// TypeIdAsTemplateArgument, we've already parsed the '<' or ','
   /// before this template argument, and will cease lookahead when we
-  /// hit a '>', '>>' (in C++0x), or ','. Returns true for a type-id
-  /// and false for an expression.  If during the disambiguation
-  /// process a parsing error is encountered, the function returns
-  /// true to let the declaration parsing code handle it.
+  /// hit a '>', '>>' (in C++0x), or ','; or, in C++0x, an ellipsis immediately
+  /// preceding such. Returns true for a type-id and false for an expression.
+  /// If during the disambiguation process a parsing error is encountered,
+  /// the function returns true to let the declaration parsing code handle it.
   ///
   /// type-id:
   ///   type-specifier-seq abstract-declarator[opt]
@@ -533,10 +533,15 @@ bool Parser::isCXXTypeId(TentativeCXXTypeIdContext Context, bool &isAmbiguous) {
 
     // We are supposed to be inside a template argument, so if after
     // the abstract declarator we encounter a '>', '>>' (in C++0x), or
-    // ',', this is a type-id. Otherwise, it's an expression.
+    // ','; or, in C++0x, an ellipsis immediately preceding such, this
+    // is a type-id. Otherwise, it's an expression.
     } else if (Context == TypeIdAsTemplateArgument &&
                (Tok.isOneOf(tok::greater, tok::comma) ||
-                (getLangOpts().CPlusPlus11 && Tok.is(tok::greatergreater)))) {
+                (getLangOpts().CPlusPlus11 &&
+                 (Tok.is(tok::greatergreater) ||
+                  (Tok.is(tok::ellipsis) &&
+                   NextToken().isOneOf(tok::greater, tok::greatergreater,
+                                       tok::comma)))))) {
       TPR = TPResult::True;
       isAmbiguous = true;
 
@@ -829,14 +834,14 @@ Parser::TPResult Parser::TryParseOperatorId() {
 ///         abstract-declarator:
 ///           ptr-operator abstract-declarator[opt]
 ///           direct-abstract-declarator
-///           ...
 ///
 ///         direct-abstract-declarator:
 ///           direct-abstract-declarator[opt]
-///           '(' parameter-declaration-clause ')' cv-qualifier-seq[opt]
+///                 '(' parameter-declaration-clause ')' cv-qualifier-seq[opt]
 ///                 exception-specification[opt]
 ///           direct-abstract-declarator[opt] '[' constant-expression[opt] ']'
 ///           '(' abstract-declarator ')'
+/// [C++0x]   ...
 ///
 ///         ptr-operator:
 ///           '*' cv-qualifier-seq[opt]
@@ -928,10 +933,6 @@ Parser::TPResult Parser::TryParseDeclarator(bool mayBeAbstract,
   while (1) {
     TPResult TPR(TPResult::Ambiguous);
 
-    // abstract-declarator: ...
-    if (Tok.is(tok::ellipsis))
-      ConsumeToken();
-
     if (Tok.is(tok::l_paren)) {
       // Check whether we have a function declarator or a possible ctor-style
       // initializer that follows the declarator. Note that ctor-style

test/Parser/cxx0x-ambig.cpp

@@ -132,6 +132,32 @@ namespace ellipsis {
     void l(int(*...)(T)); // expected-warning {{ISO C++11 requires a parenthesized pack declaration to have a name}}
     void l(int(S<int>::*...)(T)); // expected-warning {{ISO C++11 requires a parenthesized pack declaration to have a name}}
   };
+
+  struct CtorSink {
+    template <typename ...T> constexpr CtorSink(T &&...t) { }
+    constexpr operator int() const { return 42; }
+  };
+
+  template <unsigned ...N> struct UnsignedTmplArgSink;
+
+  template <typename ...T>
+  void foo(int x, T ...t) {
+    // Have a variety of cases where the syntax is technically unambiguous, but hinges on careful treatment of ellipses.
+    CtorSink(t ...), x; // ok, expression; expected-warning 2{{expression result unused}}
+
+    int x0(CtorSink(t ...)); // ok, declares object x0
+    int *p0 = &x0;
+    (void)p0;
+
+    CtorSink x1(int(t) ..., int(x)); // ok, declares object x1
+    CtorSink *p1 = &x1;
+    (void)p1;
+
+    UnsignedTmplArgSink<T(CtorSink(t ...)) ...> *t0; // ok
+    UnsignedTmplArgSink<((T *)0, 42u) ...> **t0p = &t0;
+  }
+
+  template void foo(int, int, int); // expected-note {{in instantiation of function template specialization 'ellipsis::foo<int, int>' requested here}}
 }
 
 namespace braced_init_list {