Reject varargs '...' in function prototype if there are more parameters after

it. Diagnose with recovery if it appears after a function parameter that was
obviously supposed to be a parameter pack. Otherwise, warn if it immediately
follows a function parameter pack, because the user most likely didn't intend
to write a parameter pack followed by a C-style varargs ellipsis.

This warning can be syntactically disabled by using ", ..." instead of "...".

llvm-svn: 215408

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -503,6 +503,17 @@ def note_bracket_depth : Note<
 def err_misplaced_ellipsis_in_declaration : Error<
   "'...' must %select{immediately precede declared identifier|"
   "be innermost component of anonymous pack declaration}0">;
+def warn_misplaced_ellipsis_vararg : Warning<
+  "'...' in this location creates a C-style varargs function"
+  "%select{, not a function parameter pack|}0">,
+  InGroup<DiagGroup<"ambiguous-ellipsis">>;
+def note_misplaced_ellipsis_vararg_existing_ellipsis : Note<
+  "preceding '...' declares a function parameter pack">;
+def note_misplaced_ellipsis_vararg_add_ellipsis : Note<
+  "place '...' %select{immediately before declared identifier|here}0 "
+  "to declare a function parameter pack">;
+def note_misplaced_ellipsis_vararg_add_comma : Note<
+  "insert ',' before '...' to silence this warning">;
 def ext_abstract_pack_declarator_parens : ExtWarn<
   "ISO C++11 requires a parenthesized pack declaration to have a name">,
   InGroup<DiagGroup<"anonymous-pack-parens">>;

clang/include/clang/Sema/Sema.h

@@ -5585,6 +5585,10 @@ public:
   // C++ Variadic Templates (C++0x [temp.variadic])
   //===--------------------------------------------------------------------===//
 
+  /// Determine whether an unexpanded parameter pack might be permitted in this
+  /// location. Useful for error recovery.
+  bool isUnexpandedParameterPackPermitted();
+
   /// \brief The context in which an unexpanded parameter pack is
   /// being diagnosed.
   ///

clang/lib/Parse/ParseDecl.cpp

@@ -5426,6 +5426,15 @@ void Parser::ParseParameterDeclarationClause(
       // Otherwise, we have something.  Add it and let semantic analysis try
       // to grok it and add the result to the ParamInfo we are building.
 
+      // Last chance to recover from a misplaced ellipsis in an attempted
+      // parameter pack declaration.
+      if (Tok.is(tok::ellipsis) &&
+          (NextToken().isNot(tok::r_paren) ||
+           (!ParmDeclarator.getEllipsisLoc().isValid() &&
+            !Actions.isUnexpandedParameterPackPermitted())) &&
+          Actions.containsUnexpandedParameterPacks(ParmDeclarator))
+        DiagnoseMisplacedEllipsisInDeclarator(ConsumeToken(), ParmDeclarator);
+
       // Inform the actions module about the parameter declarator, so it gets
       // added to the current scope.
       Decl *Param = Actions.ActOnParamDeclarator(getCurScope(), 
@@ -5492,12 +5501,34 @@ void Parser::ParseParameterDeclarationClause(
                                           Param, DefArgToks));
     }
 
-    if (TryConsumeToken(tok::ellipsis, EllipsisLoc) &&
-        !getLangOpts().CPlusPlus) {
-      // We have ellipsis without a preceding ',', which is ill-formed
-      // in C. Complain and provide the fix.
-      Diag(EllipsisLoc, diag::err_missing_comma_before_ellipsis)
+    if (TryConsumeToken(tok::ellipsis, EllipsisLoc)) {
+      if (!getLangOpts().CPlusPlus) {
+        // We have ellipsis without a preceding ',', which is ill-formed
+        // in C. Complain and provide the fix.
+        Diag(EllipsisLoc, diag::err_missing_comma_before_ellipsis)
+            << FixItHint::CreateInsertion(EllipsisLoc, ", ");
+      } else if (ParmDeclarator.getEllipsisLoc().isValid() ||
+                 Actions.containsUnexpandedParameterPacks(ParmDeclarator)) {
+        // It looks like this was supposed to be a parameter pack. Warn and
+        // point out where the ellipsis should have gone.
+        SourceLocation ParmEllipsis = ParmDeclarator.getEllipsisLoc();
+        Diag(EllipsisLoc, diag::warn_misplaced_ellipsis_vararg)
+          << ParmEllipsis.isValid() << ParmEllipsis;
+        if (ParmEllipsis.isValid()) {
+          Diag(ParmEllipsis,
+               diag::note_misplaced_ellipsis_vararg_existing_ellipsis);
+        } else {
+          Diag(ParmDeclarator.getIdentifierLoc(),
+               diag::note_misplaced_ellipsis_vararg_add_ellipsis)
+            << FixItHint::CreateInsertion(ParmDeclarator.getIdentifierLoc(),
+                                          "...")
+            << !ParmDeclarator.hasName();
+        }
+        Diag(EllipsisLoc, diag::note_misplaced_ellipsis_vararg_add_comma)
           << FixItHint::CreateInsertion(EllipsisLoc, ", ");
+      }
+
+      // We can't have any more parameters after an ellipsis.
       break;
     }
 

clang/lib/Sema/SemaTemplateVariadic.cpp

@@ -197,6 +197,20 @@ namespace {
   };
 }
 
+/// \brief Determine whether it's possible for an unexpanded parameter pack to
+/// be valid in this location. This only happens when we're in a declaration
+/// that is nested within an expression that could be expanded, such as a
+/// lambda-expression within a function call.
+///
+/// This is conservatively correct, but may claim that some unexpanded packs are
+/// permitted when they are not.
+bool Sema::isUnexpandedParameterPackPermitted() {
+  for (auto *SI : FunctionScopes)
+    if (isa<sema::LambdaScopeInfo>(SI))
+      return true;
+  return false;
+}
+
 /// \brief Diagnose all of the unexpanded parameter packs in the given
 /// vector.
 bool

clang/test/CXX/dcl.decl/dcl.meaning/dcl.fct/p14.cpp

@@ -1,5 +1,4 @@
 // RUN: %clang_cc1 -std=c++11 -fsyntax-only -verify %s
-// expected-no-diagnostics
 
 template<typename T> struct identity;
 template<typename ...Types> struct tuple;
@@ -22,7 +21,7 @@ template<typename T> struct is_same<T, T> {
 template<typename T, typename ...Types>
 struct X0 {
   typedef identity<T(Types...)> function_pack_1;
-  typedef identity<T(Types......)> variadic_function_pack_1;
+  typedef identity<T(Types......)> variadic_function_pack_1; // expected-warning {{varargs}} expected-note {{pack}} expected-note {{insert ','}}
   typedef identity<T(T...)> variadic_1;
   typedef tuple<T(Types, ...)...> template_arg_expansion_1;
 };

clang/test/CXX/temp/temp.decls/temp.variadic/metafunctions.cpp

@@ -243,7 +243,7 @@ namespace FunctionTypes {
   };
 
   template<typename R, typename ...Types>
-  struct Arity<R(Types......)> {
+  struct Arity<R(Types......)> { // expected-warning {{varargs}} expected-note {{pack}} expected-note {{insert ','}}
     static const unsigned value = sizeof...(Types);
   };
 

clang/test/Parser/cxx-variadic-func.cpp

@@ -1,5 +1,8 @@
-// RUN: %clang_cc1 -fsyntax-only  %s
+// RUN: %clang_cc1 -fsyntax-only -verify %s
 
 void f(...) {
-  int g(int(...));
+  // FIXME: There's no disambiguation here; this is unambiguous.
+  int g(int(...)); // expected-warning {{disambiguated}} expected-note {{paren}}
 }
+
+void h(int n..., int m); // expected-error {{expected ')'}} expected-note {{to match}}

clang/test/Parser/cxx11-templates.cpp

@@ -7,3 +7,40 @@ struct S {
 
 template <typename Ty = char>
 static_assert(sizeof(Ty) != 1, "Not a char"); // expected-error {{a static_assert declaration cannot be a template}}
+
+namespace Ellipsis {
+  template<typename ...T> void f(T t..., int n); // expected-error {{must immediately precede declared identifier}}
+  template<typename ...T> void f(int n, T t...); // expected-error {{must immediately precede declared identifier}}
+  template<typename ...T> void f(int n, T t, ...); // expected-error {{unexpanded parameter pack}}
+  template<typename ...T> void f() {
+    f([]{
+      void g(T
+             t // expected-note {{place '...' immediately before declared identifier to declare a function parameter pack}}
+             ... // expected-warning {{'...' in this location creates a C-style varargs function, not a function parameter pack}}
+             // expected-note@-1 {{insert ',' before '...' to silence this warning}}
+             );
+      void h(T (&
+              ) // expected-note {{place '...' here to declare a function parameter pack}}
+             ... // expected-warning {{'...' in this location creates a C-style varargs function, not a function parameter pack}}
+             // expected-note@-1 {{insert ',' before '...' to silence this warning}}
+             );
+      void i(T (&), ...);
+    }...);
+  }
+  template<typename ...T> struct S {
+    void f(T t...); // expected-error {{must immediately precede declared identifier}}
+    void f(T ... // expected-note {{preceding '...' declares a function parameter pack}}
+           t...); // expected-warning-re {{'...' in this location creates a C-style varargs function{{$}}}}
+           // expected-note@-1 {{insert ',' before '...' to silence this warning}}
+  };
+
+  // FIXME: We should just issue a single error in this case pointing out where
+  // the '...' goes. It's tricky to recover correctly in this case, though,
+  // because the parameter is in scope in the default argument, so must be
+  // passed to Sema before we reach the ellipsis.
+  template<typename...T> void f(T n = 1 ...);
+  // expected-warning@-1 {{creates a C-style varargs}}
+  // expected-note@-2 {{place '...' immediately before declared identifier}}
+  // expected-note@-3 {{insert ','}}
+  // expected-error@-4 {{unexpanded parameter pack}}
+}

clang/test/SemaCXX/issue547.cpp

@@ -27,32 +27,32 @@ struct classify_function<R(Args...) const volatile> {
 };
 
 template<typename R, typename ...Args>
-struct classify_function<R(Args......)> {
+struct classify_function<R(Args..., ...)> {
   static const unsigned value = 5;
 };
 
 template<typename R, typename ...Args>
-struct classify_function<R(Args......) const> {
+struct classify_function<R(Args..., ...) const> {
   static const unsigned value = 6;
 };
 
 template<typename R, typename ...Args>
-struct classify_function<R(Args......) volatile> {
+struct classify_function<R(Args..., ...) volatile> {
   static const unsigned value = 7;
 };
 
 template<typename R, typename ...Args>
-struct classify_function<R(Args......) const volatile> {
+struct classify_function<R(Args..., ...) const volatile> {
   static const unsigned value = 8;
 };
 
 template<typename R, typename ...Args>
-struct classify_function<R(Args......) &&> {
+struct classify_function<R(Args..., ...) &&> {
   static const unsigned value = 9;
 };
 
 template<typename R, typename ...Args>
-struct classify_function<R(Args......) const &> {
+struct classify_function<R(Args..., ...) const &> {
   static const unsigned value = 10;
 };