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

[David Malcolm]

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)

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