c: Add support for __FILE_NAME__ macro (PR c/42579)

The toolchain provided by ST for stm32 has had support for
__FILENAME__ for a while, but clang/llvm has recently implemented
support for __FILE_NAME__, so it seems better to use the same macro
name in GCC.

It happens that the ST patch is similar to the one proposed in PR
c/42579.

Given these input files:
::::::::::::::
mydir/myinc.h
::::::::::::::
char* mystringh_file = __FILE__;
char* mystringh_filename = __FILE_NAME__;
char* mystringh_base_file = __BASE_FILE__;
::::::::::::::
mydir/mysrc.c
::::::::::::::

char* mystring_file = __FILE__;
char* mystring_filename = __FILE_NAME__;
char* mystring_base_file = __BASE_FILE__;

we produce:
$ gcc mydir/mysrc.c -I . -E
char* mystringh_file = "./mydir/myinc.h";
char* mystringh_filename = "myinc.h";
char* mystringh_base_file = "mydir/mysrc.c";

char* mystring_file = "mydir/mysrc.c";
char* mystring_filename = "mysrc.c";
char* mystring_base_file = "mydir/mysrc.c";

2021-05-20  Christophe Lyon  <christophe.lyon@linaro.org>
	    Torbjörn Svensson  <torbjorn.svensson@st.com>

	PR c/42579
	libcpp/
	* include/cpplib.h (cpp_builtin_type): Add BT_FILE_NAME entry.
	* init.c (builtin_array): Likewise.
	* macro.c (_cpp_builtin_macro_text): Add support for BT_FILE_NAME.

	gcc/
	* doc/cpp.texi (Common Predefined Macros): Document __FILE_NAME__.

	gcc/testsuite/
	* c-c++-common/spellcheck-reserved.c: Add tests for __FILE_NAME__.
	* c-c++-common/cpp/file-name-1.c: New test.

gcc/doc/cpp.texi

@@ -2005,6 +2005,13 @@ This macro expands to the name of the main input file, in the form
 of a C string constant.  This is the source file that was specified
 on the command line of the preprocessor or C compiler.
 
+@item __FILE_NAME__
+This macro expands to the basename of the current input file, in the
+form of a C string constant.  This is the last path component by which
+the preprocessor opened the file.  For example, processing
+@code{"/usr/local/include/myheader.h"} would set this
+macro to @code{"myheader.h"}.
+
 @item __INCLUDE_LEVEL__
 This macro expands to a decimal integer constant that represents the
 depth of nesting in include files.  The value of this macro is

gcc/testsuite/c-c++-common/cpp/file-name-1.c

@@ -0,0 +1,22 @@
+/* { dg-do preprocess } */
+/* { dg-additional-options -Wno-pedantic } */
+
+main-1 __FILE_NAME__
+
+# 7 "inner.h" 1
+inner-1 __FILE_NAME__
+# 9 "subdir/inside.h" 1
+inside-1 __FILE_NAME__
+inside-2 __FILE__
+# 11 "" 2
+inner-2 __FILE_NAME__
+#13 "" 2
+main-2 __FILE_NAME__
+
+
+/* { dg-final { scan-file file-name-1.i "main-1 \"\[^\n]*file-name-1.c\"\n" } } */
+/* { dg-final { scan-file file-name-1.i "main-2 \"\[^\n]*file-name-1.c\"\n" } } */
+/* { dg-final { scan-file file-name-1.i "inner-1 \"inner.h\"\n" } } */
+/* { dg-final { scan-file file-name-1.i "inner-2 \"inner.h\"\n" } } */
+/* { dg-final { scan-file file-name-1.i "inside-1 \"inside.h\"\n" } } */
+/* { dg-final { scan-file file-name-1.i "inside-2 \"subdir/inside.h\"\n" } } */

gcc/testsuite/c-c++-common/spellcheck-reserved.c

@@ -50,3 +50,21 @@ const char * test_3 (void)
   /* { dg-error "did you mean '__FILE__'" "" { target c } misspelled__FILE_ } */
   /* { dg-error "'__FILE_' was not declared in this scope; did you mean '__FILE__'\\?"  "" { target c++ } misspelled__FILE_ } */
 }
+
+/* Verify that we can correct "__FILE_NAME_" to "__FILE_NAME__".  */
+
+const char * test_4 (void)
+{
+  return __FILE_NAME_; /* { dg-line misspelled__FILE_NAME_ } */
+  /* { dg-error "did you mean '__FILE_NAME__'" "" { target c } misspelled__FILE_NAME_ } */
+  /* { dg-error "'__FILE_NAME_' was not declared in this scope; did you mean '__FILE_NAME__'\\?"  "" { target c++ } misspelled__FILE_NAME_ } */
+}
+
+/* Verify that we can correct "__FILENAME__" to "__FILE_NAME__".  */
+
+const char * test_5 (void)
+{
+  return __FILENAME__; /* { dg-line misspelled__FILENAME__ } */
+  /* { dg-error "did you mean '__FILE_NAME__'" "" { target c } misspelled__FILENAME__ } */
+  /* { dg-error "'__FILENAME__' was not declared in this scope; did you mean '__FILE_NAME__'\\?"  "" { target c++ } misspelled__FILENAME__ } */
+}

libcpp/include/cpplib.h

@@ -886,6 +886,7 @@ enum cpp_builtin_type
   BT_SPECLINE = 0,		/* `__LINE__' */
   BT_DATE,			/* `__DATE__' */
   BT_FILE,			/* `__FILE__' */
+  BT_FILE_NAME,			/* `__FILE_NAME__' */
   BT_BASE_FILE,			/* `__BASE_FILE__' */
   BT_INCLUDE_LEVEL,		/* `__INCLUDE_LEVEL__' */
   BT_TIME,			/* `__TIME__' */

libcpp/init.c

@@ -405,6 +405,7 @@ static const struct builtin_macro builtin_array[] =
   B("__TIME__",		 BT_TIME,          false),
   B("__DATE__",		 BT_DATE,          false),
   B("__FILE__",		 BT_FILE,          false),
+  B("__FILE_NAME__",	 BT_FILE_NAME,     false),
   B("__BASE_FILE__",	 BT_BASE_FILE,     false),
   B("__LINE__",		 BT_SPECLINE,      true),
   B("__INCLUDE_LEVEL__", BT_INCLUDE_LEVEL, true),

libcpp/macro.c

@@ -531,15 +531,21 @@ _cpp_builtin_macro_text (cpp_reader *pfile, cpp_hashnode *node,
       }
       break;
     case BT_FILE:
+    case BT_FILE_NAME:
     case BT_BASE_FILE:
       {
 	unsigned int len;
 	const char *name;
 	uchar *buf;
-	
+
-	if (node->value.builtin == BT_FILE)
+	if (node->value.builtin == BT_FILE
-	  name = linemap_get_expansion_filename (pfile->line_table,
+	    || node->value.builtin == BT_FILE_NAME)
-						 pfile->line_table->highest_line);
+	  {
+	    name = linemap_get_expansion_filename (pfile->line_table,
+						   pfile->line_table->highest_line);
+	    if ((node->value.builtin == BT_FILE_NAME) && name)
+	      name = lbasename (name);
+	  }
 	else
 	  {
 	    name = _cpp_get_file_name (pfile->main_file);