C: hints for missing stdlib includes for macros and types

The C frontend already "knows" about many common functions in
the C standard library:

  test.c: In function 'test':
  test.c:3:3: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
     printf ("hello world\n");
     ^~~~~~
  test.c:3:3: warning: incompatible implicit declaration of built-in function 'printf'
  test.c:3:3: note: include '<stdio.h>' or provide a declaration of 'printf'

and which header file they are in.

However it doesn't know about various types and macros:

test.c:1:13: error: 'NULL' undeclared here (not in a function)
 void *ptr = NULL;
             ^~~~

This patch uses the name_hint/deferred_diagnostic machinery to
add hints for missing C standard library headers for some of the
most common type and macro names.

For example, the above becomes:
test.c:1:13: error: 'NULL' undeclared here (not in a function)
 void *ptr = NULL;
             ^~~~
test.c:1:13: note: 'NULL' is defined in header '<stddef.h>'; did you forget to '#include <stddef.h>'?

gcc/c/ChangeLog:
	* c-decl.c (get_c_name_hint): New function.
	(class suggest_missing_header): New class.
	(lookup_name_fuzzy): Call get_c_name_hint and use it to
	suggest missing headers to the user.

gcc/testsuite/ChangeLog:
	* gcc.dg/spellcheck-stdlib.c: New test case.

From-SVN: r254979

1 files changed, 7 insertions, 0 deletions

diff --git a/gcc/c/ChangeLog b/gcc/c/ChangeLog
index 6e19393..b60a8e7 100644
--- a/gcc/c/ChangeLog
+++ b/gcc/c/ChangeLog
@@ -1,5 +1,12 @@
 2017-11-20  David Malcolm  <dmalcolm@redhat.com>
 
+	* c-decl.c (get_c_name_hint): New function.
+	(class suggest_missing_header): New class.
+	(lookup_name_fuzzy): Call get_c_name_hint and use it to
+	suggest missing headers to the user.
+
+2017-11-20  David Malcolm  <dmalcolm@redhat.com>
+
 	* c-decl.c: Define INCLUDE_UNIQUE_PTR before including system.h.
 	Include "c-family/name-hint.h"
 	(implicit_decl_warning): Convert "hint" from