[PATCH] Fix bogus fix-it for FLT_MAX (PR c/89122)

[Richard Biener]

On Thu, Jan 31, 2019 at 12:09 AM David Malcolm <dmalcolm@redhat.com> wrote:
>
> PR c/89122 reports that we emit a bogus fix-it hint for the case where
> the code uses FLT_MAX, but has included <limits.h> rather than <float.h>:
>
> x.c:3:11: error: 'FLT_MAX' undeclared here (not in a function); did you
>   mean 'INT_MAX'?
>     3 | float f = FLT_MAX;
>       |           ^~~~~~~
>       |           INT_MAX
>
> This patch adds some knowledge of <float.h> (and <cfloat>) to
> known-headers.cc, fixing the issue:
>
> x.c:3:11: error: 'FLT_MAX' undeclared here (not in a function)
>     3 | float f = FLT_MAX;
>       |           ^~~~~~~
> x.c:2:1: note: 'FLT_MAX' is defined in header '<float.h>'; did you forget
>   to '#include <float.h>'?
>     1 | #include <limits.h>
>   +++ |+#include <float.h>
>     2 |
>
> Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu.
>
> Is this OK for trunk in stage 4? (presumably very low risk)

What does it not say for

  int i = FLT_MAX;

?  Hopefully it doesn't suggest to include float.h but suggests
to include limits.h and INT_MAX?

> gcc/c-family/ChangeLog:
>         PR c/89122
>         * known-headers.cc (get_stdlib_header_for_name): Add
>         {FLT|DBL|LDBL}_{MAX|MIN} to "hints" array.
>
> gcc/testsuite/ChangeLog:
>         PR c/89122
>         * g++.dg/spellcheck-stdlib.C (test_FLT_MAX): New test.
>         * gcc.dg/spellcheck-stdlib.c (test_FLT_MAX): New test.
> ---
>  gcc/c-family/known-headers.cc            | 8 ++++++++
>  gcc/testsuite/g++.dg/spellcheck-stdlib.C | 5 +++++
>  gcc/testsuite/gcc.dg/spellcheck-stdlib.c | 5 +++++
>  3 files changed, 18 insertions(+)
>
> diff --git a/gcc/c-family/known-headers.cc b/gcc/c-family/known-headers.cc
> index e3dcf73..c222f30 100644
> --- a/gcc/c-family/known-headers.cc
> +++ b/gcc/c-family/known-headers.cc
> @@ -84,6 +84,14 @@ get_stdlib_header_for_name (const char *name, enum stdlib lib)
>      {"ULONG_MAX", {"<limits.h>", "<climits>"} },
>      {"USHRT_MAX", {"<limits.h>", "<climits>"} },
>
> +    /* <float.h> and <cfloat>.  */
> +    {"DBL_MAX", {"<float.h>", "<cfloat>"} },
> +    {"DBL_MIN", {"<float.h>", "<cfloat>"} },
> +    {"FLT_MAX", {"<float.h>", "<cfloat>"} },
> +    {"FLT_MIN", {"<float.h>", "<cfloat>"} },
> +    {"LDBL_MAX", {"<float.h>", "<cfloat>"} },
> +    {"LDBL_MIN", {"<float.h>", "<cfloat>"} },
> +
>      /* <stdarg.h> and <cstdarg>.  */
>      {"va_list", {"<stdarg.h>", "<cstdarg>"} },
>
> diff --git a/gcc/testsuite/g++.dg/spellcheck-stdlib.C b/gcc/testsuite/g++.dg/spellcheck-stdlib.C
> index 11a4e3e..31e91fe 100644
> --- a/gcc/testsuite/g++.dg/spellcheck-stdlib.C
> +++ b/gcc/testsuite/g++.dg/spellcheck-stdlib.C
> @@ -77,6 +77,11 @@ int test_INT_MAX (void)
>    // { dg-message "'INT_MAX' is defined in header '<climits>'; did you forget to '#include <climits>'?" "" { target *-*-* } INT_MAX_line }
>  }
>
> +/* Missing <cfloat>.  */
> +float test_FLT_MAX = FLT_MAX; // { dg-line FLT_MAX_line }
> +// { dg-error "'FLT_MAX' was not declared" "" { target *-*-* } FLT_MAX_line }
> +// { dg-message "'FLT_MAX' is defined in header '<cfloat>'; did you forget to '#include <cfloat>'?" "" { target *-*-* } FLT_MAX_line }
> +
>  /* Missing <cstring>.  */
>
>  void test_cstring (char *dest, char *src)
> diff --git a/gcc/testsuite/gcc.dg/spellcheck-stdlib.c b/gcc/testsuite/gcc.dg/spellcheck-stdlib.c
> index 7474c9a..1ae3b5e 100644
> --- a/gcc/testsuite/gcc.dg/spellcheck-stdlib.c
> +++ b/gcc/testsuite/gcc.dg/spellcheck-stdlib.c
> @@ -62,3 +62,8 @@ int test_INT_MAX (void)
>    /* { dg-bogus "__INT_MAX__" "" { target *-*-* } INT_MAX_line } */
>    /* { dg-message "'INT_MAX' is defined in header '<limits.h>'; did you forget to '#include <limits.h>'?" "" { target *-*-* } INT_MAX_line } */
>  }
> +
> +/* Missing <float.h>.  */
> +float test_FLT_MAX = FLT_MAX; /* { dg-line FLT_MAX_line } */
> +/* { dg-error "'FLT_MAX' undeclared" "" { target *-*-* } FLT_MAX_line } */
> +/* { dg-message "'FLT_MAX' is defined in header '<float.h>'; did you forget to '#include <float.h>'?" "" { target *-*-* } FLT_MAX_line } */
> --
> 1.8.5.3
>