Re: [PATCH] lib: test_scanf: Add explicit type cast to result initialization in test_number_prefix()

From: Andy Shevchenko
Date: Fri Aug 04 2023 - 00:25:12 EST


On Thu, Aug 03, 2023 at 11:14:42AM -0700, Nathan Chancellor wrote:
> A recent change in clang allows it to consider more expressions as
> compile time constants, which causes it to point out an implicit
> conversion in the scanf tests:
>
> lib/test_scanf.c:661:2: warning: implicit conversion from 'int' to 'unsigned char' changes value from -168 to 88 [-Wconstant-conversion]
> 661 | test_number_prefix(unsigned char, "0xA7", "%2hhx%hhx", 0, 0xa7, 2, check_uchar);
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> lib/test_scanf.c:609:29: note: expanded from macro 'test_number_prefix'
> 609 | T result[2] = {~expect[0], ~expect[1]}; \
> | ~ ^~~~~~~~~~
> 1 warning generated.
>
> The result of the bitwise negation is the type of the operand after
> going through the integer promotion rules, so this truncation is
> expected but harmless, as the initial values in the result array get
> overwritten by _test() anyways. Add an explicit cast to the expected
> type in test_number_prefix() to silence the warning. There is no
> functional change, as all the tests still pass with GCC 13.1.0 and clang
> 18.0.0.

> do { \
> const T expect[2] = { expect0, expect1 }; \
> - T result[2] = {~expect[0], ~expect[1]}; \
> + T result[2] = {(T)~expect[0], (T)~expect[1]}; \

Can we add spaces as above, while at it?

T result[2] = { (T)~expect[0], (T)~expect[1] }; \

> _test(fn, &expect, str, scan_fmt, n_args, &result[0], &result[1]); \
> } while (0)

--
With Best Regards,
Andy Shevchenko