[cfe-dev] Tooling vs -fdelayed-template-parsing WAS: Clang-cl.exe and the VC++ preprocessor

[Kim Gräsman]

On Mon, Aug 4, 2014 at 7:14 PM, Manuel Klimek <klimek at google.com> wrote:

>
> why are those not instantiated when a FrontendAction is run?
>

My choice of words was bad -- the template is not instantiated here, merely
parsed. We don't have any template arguments to give it.

We just (a few minutes ago, while experimenting with this) found a case
where late-parsing a template whose body contains undefined symbols would
generate an incomplete AST, e.g.

template<class T>
void foo(const T& t) {
  UndefinedSymbol::bar(t);  // colon-colon
}

$ clang-check.exe -ast-dump incomplete.cpp -- -fno-delayed-template-parsing
TranslationUnitDecl 0xebe7e0 <<invalid sloc>> <invalid sloc>
|-CXXRecordDecl 0xebeaa0 <<invalid sloc>> <invalid sloc> implicit class
type_info
|-TypedefDecl 0xebeb20 <<invalid sloc>> <invalid sloc> implicit size_t
'unsigned int'
|-TypedefDecl 0xebeb80 <<invalid sloc>> <invalid sloc> implicit
__builtin_va_list 'char *'
`-FunctionTemplateDecl 0xebed80 <incomplete.cpp:2:1, line:5:1> line:3:6 foo
  |-TemplateTypeParmDecl 0xebebb0 <line:2:10, col:16> col:16 class T
  `-FunctionDecl 0xebed10 <line:3:1, line:5:1> line:3:6 foo 'void (const T
&)'
    |-ParmVarDecl 0xebec80 <col:10, col:19> col:19 referenced t 'const T &'
    `-CompoundStmt 0xebee40 <col:22, line:5:1>
      `-CallExpr 0xebee20 <line:4:3, col:25> '<dependent type>'
        |-DependentScopeDeclRefExpr 0xebede0 <col:3, col:20> '<dependent
type>' lvalue
        `-DeclRefExpr 0xebee04 <col:24> 'const T' lvalue ParmVar 0xebec80
't' 'const T &'

This runs without error, while this:

template<class T>
void foo(const T& t) {
  UndefinedSymbol.bar(t);  // dot
}

throws an error, as expected:

  incomplete.cpp:4:4: error: use of undeclared identifier 'UndefinedSymbol'
     UndefinedSymbol.bar(t);
     ^

I don't know if this is a general bug in the parser, but it'd be nice to
always get a diagnostic here.

- Kim
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