c-family: add hints for strerror

Add proper hints for implicit declaration of strerror.

The results could be confusing depending on the other included headers.
These example messages are from compiling a trivial program to print the
string for an errno value. It only includes stdio.h (cstdio for C++).

Before:
$ /tmp/gcc-master/bin/gcc test.c -o test_c
test.c: In function ‘main’:
test.c:4:20: warning: implicit declaration of function ‘strerror’; did you mean ‘perror’? [-Wimplicit-function-declaration]
    4 |     printf("%s\n", strerror(0));
      |                    ^~~~~~~~
      |                    perror

$ /tmp/gcc-master/bin/g++ test.cpp -o test_cpp
test.cpp: In function ‘int main()’:
test.cpp:4:20: error: ‘strerror’ was not declared in this scope; did you mean ‘stderr’?
    4 |     printf("%s\n", strerror(0));
      |                    ^~~~~~~~
      |                    stderr

After:
$ /tmp/gcc-known-headers/bin/gcc test.c -o test_c
test.c: In function ‘main’:
test.c:4:20: warning: implicit declaration of function ‘strerror’ [-Wimplicit-function-declaration]
    4 |     printf("%s\n", strerror(0));
      |                    ^~~~~~~~
test.c:2:1: note: ‘strerror’ is defined in header ‘<string.h>’; this is probably fixable by adding ‘#include <string.h>’
    1 | #include <stdio.h>
  +++ |+#include <string.h>
    2 |

$ /tmp/gcc-known-headers/bin/g++ test.cpp -o test_cpp
test.cpp: In function ‘int main()’:
test.cpp:4:20: error: ‘strerror’ was not declared in this scope
    4 |     printf("%s\n", strerror(0));
      |                    ^~~~~~~~
test.cpp:2:1: note: ‘strerror’ is defined in header ‘<cstring>’; this is probably fixable by adding ‘#include <cstring>’
    1 | #include <cstdio>
  +++ |+#include <cstring>
    2 |

gcc/c-family/ChangeLog:

	* known-headers.cc (get_stdlib_header_for_name): Add strerror.

gcc/testsuite/ChangeLog:

	* g++.dg/spellcheck-stdlib.C: Add check for strerror.
	* gcc.dg/spellcheck-stdlib-2.c: New test.

Signed-off-by: Oskari Pirhonen <xxc3ncoredxx@gmail.com>

3 files changed, 11 insertions, 0 deletions

diff --git a/gcc/c-family/known-headers.cc b/gcc/c-family/known-headers.cc
index dbc42ea..871fd71 100644
--- a/gcc/c-family/known-headers.cc
+++ b/gcc/c-family/known-headers.cc
@@ -182,6 +182,7 @@ get_stdlib_header_for_name (const char *name, enum stdlib lib)
     {"strchr", {"<string.h>", "<cstring>"} },
     {"strcmp", {"<string.h>", "<cstring>"} },
     {"strcpy", {"<string.h>", "<cstring>"} },
+    {"strerror", {"<string.h>", "<cstring>"} },
     {"strlen", {"<string.h>", "<cstring>"} },
     {"strncat", {"<string.h>", "<cstring>"} },
     {"strncmp", {"<string.h>", "<cstring>"} },
diff --git a/gcc/testsuite/g++.dg/spellcheck-stdlib.C b/gcc/testsuite/g++.dg/spellcheck-stdlib.C
index fd0f3a9..33718b8 100644
--- a/gcc/testsuite/g++.dg/spellcheck-stdlib.C
+++ b/gcc/testsuite/g++.dg/spellcheck-stdlib.C
@@ -104,6 +104,8 @@ void test_cstring (char *dest, char *src)
   // { dg-message "'#include <cstring>'" "" { target *-*-* } .-1 }
   strcpy(dest, "test"); // { dg-error "was not declared" }
   // { dg-message "'#include <cstring>'" "" { target *-*-* } .-1 }
+  strerror(0); // { dg-error "was not declared" }
+  // { dg-message "'#include <cstring>'" "" { target *-*-* } .-1 }
   strlen("test"); // { dg-error "was not declared" }
   // { dg-message "'#include <cstring>'" "" { target *-*-* } .-1 }
   strncat(dest, "test", 3); // { dg-error "was not declared" }
diff --git a/gcc/testsuite/gcc.dg/spellcheck-stdlib-2.c b/gcc/testsuite/gcc.dg/spellcheck-stdlib-2.c
new file mode 100644
index 0000000..4762e2d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/spellcheck-stdlib-2.c
@@ -0,0 +1,8 @@
+/* { dg-options "-Wimplicit-function-declaration" } */
+
+/* Missing <string.h>.  */
+void test_string_h (void)
+{
+  strerror (0); /* { dg-error "implicit declaration of function 'strerror'" } */
+  /* { dg-message "'strerror' is defined in header '<string.h>'" "" { target *-*-* } .-1 } */
+}