Improve parser recovery when we encounter a dependent template name
that is missing the 'template' keyword, e.g.,
t->getAs<T>()
where getAs is a member of an unknown specialization. C++ requires
that we treat "getAs" as a value, but that would fail to parse since T
is the name of a type. We would then fail at the '>', since a type
cannot be followed by a '>'.
This is a very common error for C++ programmers to make, especially
since GCC occasionally allows it when it shouldn't (as does Visual
C++). So, when we are in this case, we use tentative parsing to see if
the tokens starting at "<" can only be parsed as a template argument
list. If so, we produce a diagnostic with a fix-it that states that
the 'template' keyword is needed:
test/SemaTemplate/dependent-template-recover.cpp:5:8: error: 'template' keyword
is required to treat 'getAs' as a dependent template name
t->getAs<T>();
^
template
This is just a start of this patch; I'd like to apply the same
approach to everywhere that a template-id with dependent template name
can be parsed.
llvm-svn: 104406
diff --git a/clang/lib/Parse/ParseTemplate.cpp b/clang/lib/Parse/ParseTemplate.cpp
index 9319781..8b9142c 100644
--- a/clang/lib/Parse/ParseTemplate.cpp
+++ b/clang/lib/Parse/ParseTemplate.cpp
@@ -902,10 +902,12 @@
ConsumeToken(); // the identifier
if (isEndOfTemplateArgument(Tok)) {
+ bool MemberOfUnknownSpecialization;
TemplateNameKind TNK = Actions.isTemplateName(CurScope, SS, Name,
/*ObjectType=*/0,
/*EnteringContext=*/false,
- Template);
+ Template,
+ MemberOfUnknownSpecialization);
if (TNK == TNK_Dependent_template_name || TNK == TNK_Type_template) {
// We have an id-expression that refers to a class template or
// (C++0x) template alias.
@@ -966,6 +968,32 @@
ExprArg.release(), Loc);
}
+/// \brief Determine whether the current tokens can only be parsed as a
+/// template argument list (starting with the '<') and never as a '<'
+/// expression.
+bool Parser::IsTemplateArgumentList() {
+ struct AlwaysRevertAction : TentativeParsingAction {
+ AlwaysRevertAction(Parser &P) : TentativeParsingAction(P) { }
+ ~AlwaysRevertAction() { Revert(); }
+ } Tentative(*this);
+
+ // '<'
+ if (!Tok.is(tok::less))
+ return false;
+ ConsumeToken();
+
+ // An empty template argument list.
+ if (Tok.is(tok::greater))
+ return true;
+
+ // See whether we have declaration specifiers, which indicate a type.
+ while (isCXXDeclarationSpecifier() == TPResult::True())
+ ConsumeToken();
+
+ // If we have a '>' or a ',' then this is a template argument list.
+ return Tok.is(tok::greater) || Tok.is(tok::comma);
+}
+
/// ParseTemplateArgumentList - Parse a C++ template-argument-list
/// (C++ [temp.names]). Returns true if there was an error.
///