[cfe-commits] patch: detect missing typename in dependent context.

[Richard Smith]

Can you use isCXXDeclarationSpecifier() instead of manually checking for
kw_const, kw_volatile and kw_restrict? That should disambiguate a bunch more
cases. Also, a test covering the 'Dependent::identifier decl-specifier' case
would be great.

Subject to that, LGTM.

On Tue, January 24, 2012 20:14, Nick Lewycky wrote:
> Ping! Sorry for the <1 week ping, but I just got another bug report about
> this issue. Testcase:
>
> #include <hash_map>
> using namespace std; using namespace __gnu_cxx; template <typename KeyType,
> typename ValueType> void MapTest(hash_map<KeyType, ValueType> map) { for
> (hash_map<KeyType, ValueType>::const_iterator it = map.begin(); it !=
> map.end(); it++) { }
> }
>
>
> without this patch produces:
>
> z.cc:6:53: error: expected ';' in 'for' statement specifier
> for (hash_map<KeyType, ValueType>::const_iterator it = map.begin(); ... ^
> z.cc:6:53: error: use of undeclared identifier 'it'
> z.cc:6:71: error: use of undeclared identifier 'it'
> for (hash_map<KeyType, ValueType>::const_iterator it = map.begin(); it ... ^
> z.cc:6:86: error: expected ')'
> ...ValueType>::const_iterator it = map.begin(); it != map.end(); it++) {
> ^
> z.cc:6:7: note: to match this '('
> for (hash_map<KeyType, ValueType>::const_iterator it = map.begin(); ... ^
> z.cc:6:88: error: use of undeclared identifier 'it'
> ...ValueType>::const_iterator it = map.begin(); it != map.end(); it++) {
> ^
>
>
> but with this patch produces:
>
> z.cc:6:8: error: missing 'typename' prior to dependent type name
> 'hash_map<KeyType, ValueType>::const_iterator'
> for (hash_map<KeyType, ValueType>::const_iterator it = map.begin(); ...
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> typename
>
> Same patch attached again. Please review!
>
>
> Nick
>
>
>
> On 20 January 2012 17:54, Nick Lewycky <nlewycky at google.com> wrote:
>
>
>> The attached patch fixes PR11358:
>>
>>
>> pr11358.cc:11:5: error: missing 'typename' prior to dependent type name
>> 'Container::iterator'
>> Container::iterator i = c.begin();
>> ^~~~~~~~~~~~~~~~~~~
>> typename
>>
>> It works by teaching Parser::isCXXDeclarationSpecifier() to, in the event
>> of a cxxscope annotation followed by an identifier, ("Container::" and
>> "iterator" in the above example), look at the next token. Yes, this means
>> doing two-tokens of look-ahead. If that next token is an identifier or
>> cvr-qualifier, we conclude that this can't possibly be an expression and
>> return a parse error.
>>
>> This is pretty important because some developers don't seem to understand
>> the rule for where they need to put typename, and Clang has exacerbated this
>> by teaching them that they only need to put typename where the compiler
>> tells them to put typename. Consequently, when we don't tell them to put
>> typename there, that isn't one of the things they'll try any more.
>>
>> The condition under which we'll do an extra token of look-ahead is when we
>> see a dependent nested-name-specifier followed by an identifier while doing
>> the tentative parse to determine whether the statement is a declaration or
>> an expression. This is reasonably rare. Here's some build times of boost:
>>
>> run of "bootstrap" with patch: 0m26.460s 0m26.530s without patch: 0m25.510s
>> 0m26.110s
>> run of "b2" with patch: 13m12.050s 12m58.670s without patch: 12m26.260s
>> 13m9.030s
>>
>>
>> So we conclude that my testing machine is crazy noisy, but at least the
>> patch doesn't cause a horrible performance regression. To give you another
>> statistic, the number of times we need to look ahead by one more token is
>> slightly less than 250,000 times across all translation units in an
>> llvm+clang build. I haven't checked how many of those are unique.
>>
>> Please review!
>>
>>
>> Nick
>>
>>
>>
>