Re: [PATCH] restore CFString handling in attribute format (PR 88638)

[Iain Sandoe <idsandoe@googlemail.com>]

> On 5 Jan 2019, at 17:39, Martin Sebor <msebor@gmail.com> wrote:
> 
> On 1/5/19 3:31 AM, Iain Sandoe wrote:
>> Hi Martin,
>>> On 4 Jan 2019, at 22:30, Mike Stump <mikestump@comcast.net> wrote:
>>> 
>>> On Jan 4, 2019, at 2:03 PM, Martin Sebor <msebor@gmail.com> wrote:
>>>> 
>>>> The improved handling of attribute positional arguments added
>>>> in r266195 introduced a regression on Darwin where attribute
>>>> format with the CFString archetype accepts CFString* parameter
>>>> types in positions where only char* would otherwise be allowed.
>>> 
>>> You didn't ask Ok?  I'll assume you want a review...  The darwin bits and the testsuite bits look fine.
>>>> 
>>>> Index: gcc/doc/extend.texi
>>>> ===================================================================
>>>> --- gcc/doc/extend.texi	(revision 267580)
>>>> +++ gcc/doc/extend.texi	(working copy)
>>>> @@ -22368,10 +22368,12 @@ bit-fields.  See the Solaris man page for @code{cm
>>>>  @node Darwin Format Checks
>>>>  @subsection Darwin Format Checks
>>>>  -Darwin targets support the @code{CFString} (or @code{__CFString__}) in the format
>>>> -attribute context.  Declarations made with such attribution are parsed for correct syntax
>>>> -and format argument types.  However, parsing of the format string itself is currently undefined
>>>> -and is not carried out by this version of the compiler.
>>>> +In addition to the full set of archetypes, Darwin targets also support
>>>> +the @code{CFString} (or @code{__CFString__}) archetype in the @code{format}
>>>> +attribute.  Declarations with this archetype are parsed for correct syntax
>>>> +and argument types.  However, parsing of the format string itself and
>>>> +validating arguments against it in calls to such functions is currently
>>>> +not performed.
>>>>    Additionally, @code{CFStringRefs} (defined by the @code{CoreFoundation} headers) may
>>>>  also be used as format arguments.  Note that the relevant headers are only likely to be
>>>> 
>> I find “archetype(s)” to be an usual (and possibly unfamiliar to many) word for this context.
>> how about:
>> s/archetype in/variant for the/
>> and then
>>  s/with this archetype/with this variant/
>> in the following sentence.
>> However, just 0.02GBP .. (fixing the fails is more important than bikeshedding the wording).
> 
> Thanks for chiming in!  I used archetype because that's the term
> used in the attribute format specification to describe the first
> argument.  I do tend to agree that archetype alone may not be
> sufficiently familiar to all users.  I'm happy to add text to
> make that clear.  Would you find the following better?
> 
>  In addition to the full set of format archetypes (attribute
>  format style arguments such as @code{printf}, @code{scanf},
>  @code{strftime}, and @code{strfmon}), Darwin targets also
>  support the @code{CFString} (or @code{__CFString__}) archetype…

Yes, that makes is clearer

(as an aside, I think that to many people the meaning of archetype - as ‘generic’  or ‘root example’
  etc  tends to come to mind before the ‘template/mold’ meaning … however couldn’t think of 
 a better term that’s not already overloaded).

> FWIW, I wanted to figure out how the CFString attribute made it
> possible to differentiate between printf and scanf (and the other)
> kinds of functions, for example, so I could add new tests for it,
> but I couldn't tell that from the manual.  So I'm trying to update
> the text to make it clear that although CFString is just like
> the sprintf and scanf format arguments/archetypes, beyond
> validating declarations that use it, the attribute serves no
> functional purpose, so the printf/scanf distinction is moot.

The CFString container** is more general than our implementation, e.g. it should be able
to contain a variety of string formats (e.g. UTF etc.).   AFAIR at the time I implemented
it for FSF GCC (it was originally in the Apple Local branch), we didn’t have sufficient parsing
support for such things (and the support in the Apple-local branch didn’t look applicable).

If we do more sophisitcated checks, we probably need to take cognisance of the fact that a
fully-implemented CFString impl can have non-ascii payload.   I suspect (although honestly
it’s been a while, I maybe mis-remember) that was the reason I didn’t try to implement the
inspection at the time (if so, there’s probably a code comment to that effect).

> Out of curiosity, is the attribute used for function call
> validation by compilers other than GCC?  I couldn't find
> anything online.

It used to be used for the platform GCC, when that was the “system compiler" (last edition
 apple 4.2.1) and I therefore assume it’s used by clang - but actually haven’t double-checked
at the time we added it - it was relevant.

Let’s revisit this in 10, and see if we can’t sync up with the platform expectations from the clang impl.

thanks for taking care of this,

Iain

** it’s actually a simple ObjectiveC object that happens to be supported by the CoreFoundation (C) 
classes as well as ObjectiveC .. making it possible to pass around general string containers between
the languages.