assert.h: allow gcc to detect assert(a = 1) errors
Commit Message
On Fri, Nov 25, 2016 at 10:14 PM, Jim Meyering <jim@meyering.net> wrote:
> On Wed, Nov 23, 2016 at 11:36 PM, Florian Weimer <fweimer@redhat.com> wrote:
>> On 11/24/2016 03:21 AM, Jim Meyering wrote:
>>
>>> We *do* need that __STRICT_ANSI__ disjunct.
>>> Otherwise, this would evoke no warning:
>>>
>>> $ gcc -isystem. -I. -Werror=pedantic k.c
>>> In file included from k.c:1:0:
>>> k.c: In function ‘main’:
>>> k.c:2:23: warning: ISO C forbids braced-groups within expressions
>>> [-Wpedantic]
>>> int main() { assert ( ({1;}) ); return 0; }
>>
>>
>> Agreed.
>>
>>> Tests I ran manually in a directory with the new assert.h file:
>>
>>
>>> Do you require a test suite addition for these? If so, would a single
>>> bourne shell script be acceptable?
>>
>>
>> We currently lack the machinery for that. It's not just that it would need
>> a shell script. We also do not compile tests with headers as system
>> headers.
>>
>> The patch looks good to me, but it needs a ChangeLog entry.
>
> Thanks for the review.
> Here's a proposed ChangeLog entry:
>
> 2016-11-25 Jim Meyering <meyering@fb.com>
>
> Let gcc detect assert(a = 1) errors.
> * assert/assert.h (assert): Rewrite assert's definition so that a
> s/==/=/ typo, e.g., assert(errno = ENOENT) is not hidden from
> gcc's -Wparentheses by assert-added parentheses. The new
> definition uses "if (expr) /* empty */; else __assert_fail...",
> so gcc -Wall will now detect that type of error in an assert, too.
> The __STRICT_ANSI__ disjunct is to avoid the warning that -Wpedantic
> would otherwise issue for the use of ({...}). I would have preferred
> to use __extension__ to mark that, but doing so would mistakenly
> suppress warnings about any extension in the user-supplied "expr".
> E.g., "assert ( ({1;}) )" must continue to evoke a warning.
> https://bugzilla.redhat.com/1105335
Here's the complete, rebased patch. Ok to push, presuming I still have
commit access?
From 0954feae6411cc0de5f5cb6c7e007b972388139f Mon Sep 17 00:00:00 2001
From: Jim Meyering <meyering@fb.com>
Date: Thu, 5 Jun 2014 10:42:05 -0700
Subject: [PATCH] assert.h: allow gcc to detect assert(a = 1) errors
* assert/assert.h (assert): Rewrite assert's definition so that
a s/==/=/ typo, e.g., assert(errno = ENOENT) is not hidden from
gcc's -Wparentheses by assert-added parentheses. The new definition
uses "if (expr) /* empty */; else __assert_fail...", so
gcc -Wall will now detect that type of error in an assert, too.
The __STRICT_ANSI__ disjunct is to avoid the warning that -Wpedantic
would otherwise issue for the use of ({...}). I would have preferred
to use __extension__ to mark that, but doing so would mistakenly
suppress warnings about any extension in the user-supplied "expr".
E.g., "assert ( ({1;}) )" must continue to evoke a warning.
---
ChangeLog | 15 +++++++++++++++
assert/assert.h | 21 +++++++++++++++++----
2 files changed, 32 insertions(+), 4 deletions(-)
Comments
On Thu, Dec 8, 2016 at 7:17 PM, Jim Meyering <jim@meyering.net> wrote:
> On Fri, Nov 25, 2016 at 10:14 PM, Jim Meyering <jim@meyering.net> wrote:
>> On Wed, Nov 23, 2016 at 11:36 PM, Florian Weimer <fweimer@redhat.com> wrote:
>>> On 11/24/2016 03:21 AM, Jim Meyering wrote:
>>>
>>>> We *do* need that __STRICT_ANSI__ disjunct.
>>>> Otherwise, this would evoke no warning:
>>>>
>>>> $ gcc -isystem. -I. -Werror=pedantic k.c
>>>> In file included from k.c:1:0:
>>>> k.c: In function ‘main’:
>>>> k.c:2:23: warning: ISO C forbids braced-groups within expressions
>>>> [-Wpedantic]
>>>> int main() { assert ( ({1;}) ); return 0; }
>>>
>>>
>>> Agreed.
>>>
>>>> Tests I ran manually in a directory with the new assert.h file:
>>>
>>>
>>>> Do you require a test suite addition for these? If so, would a single
>>>> bourne shell script be acceptable?
>>>
>>>
>>> We currently lack the machinery for that. It's not just that it would need
>>> a shell script. We also do not compile tests with headers as system
>>> headers.
>>>
>>> The patch looks good to me, but it needs a ChangeLog entry.
>>
>> Thanks for the review.
>> Here's a proposed ChangeLog entry:
>>
>> 2016-11-25 Jim Meyering <meyering@fb.com>
>>
>> Let gcc detect assert(a = 1) errors.
>> * assert/assert.h (assert): Rewrite assert's definition so that a
>> s/==/=/ typo, e.g., assert(errno = ENOENT) is not hidden from
>> gcc's -Wparentheses by assert-added parentheses. The new
>> definition uses "if (expr) /* empty */; else __assert_fail...",
>> so gcc -Wall will now detect that type of error in an assert, too.
>> The __STRICT_ANSI__ disjunct is to avoid the warning that -Wpedantic
>> would otherwise issue for the use of ({...}). I would have preferred
>> to use __extension__ to mark that, but doing so would mistakenly
>> suppress warnings about any extension in the user-supplied "expr".
>> E.g., "assert ( ({1;}) )" must continue to evoke a warning.
>> https://bugzilla.redhat.com/1105335
>
> Here's the complete, rebased patch. Ok to push, presuming I still have
> commit access?
Friendly pre-holiday ping?
@@ -1,3 +1,18 @@
+2016-11-25 Jim Meyering <meyering@fb.com>
+
+ Let gcc detect assert(a = 1) errors.
+ * assert/assert.h (assert): Rewrite assert's definition so that a
+ s/==/=/ typo, e.g., assert(errno = ENOENT) is not hidden from
+ gcc's -Wparentheses by assert-added parentheses. The new
+ definition uses "if (expr) /* empty */; else __assert_fail...",
+ so gcc -Wall will now detect that type of error in an assert, too.
+ The __STRICT_ANSI__ disjunct is to avoid the warning that -Wpedantic
+ would otherwise issue for the use of ({...}). I would have preferred
+ to use __extension__ to mark that, but doing so would mistakenly
+ suppress warnings about any extension in the user-supplied "expr".
+ E.g., "assert ( ({1;}) )" must continue to evoke a warning.
+ https://bugzilla.redhat.com/1105335
+
2016-12-08 Joseph Myers <joseph@codesourcery.com>
* Rules [$(run-built-tests) != no] (tests-expected): Add
@@ -82,10 +82,23 @@ extern void __assert (const char *__assertion, const char *__file, int __line)
__END_DECLS
-# define assert(expr) \
- ((expr) \
- ? __ASSERT_VOID_CAST (0) \
- : __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))
+/* When possible, define assert so that it does not add extra
+ parentheses around EXPR. Otherwise, those added parentheses would
+ suppress warnings we'd expect to be detected by gcc's -Wparentheses. */
+# if !defined __GNUC__ || defined __STRICT_ANSI__
+# define assert(expr) \
+ ((expr) \
+ ? __ASSERT_VOID_CAST (0) \
+ : __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION))
+# else
+# define assert(expr) \
+ ({ \
+ if (expr) \
+ ; /* empty */ \
+ else \
+ __assert_fail (#expr, __FILE__, __LINE__, __ASSERT_FUNCTION); \
+ })
+# endif
# ifdef __USE_GNU
# define assert_perror(errnum) \