glcpp: Only warn for macro names containing __

Section 3.3 (Preprocessor) of the GLSL 1.30 spec (and later) and the
GLSL ES spec (all versions) say:

    "All macro names containing two consecutive underscores ( __ ) are
    reserved for future use as predefined macro names. All macro names
    prefixed with "GL_" ("GL" followed by a single underscore) are also
    reserved."

The intention is that names containing __ are reserved for internal use
by the implementation, and names prefixed with GL_ are reserved for use
by Khronos.  Since every extension adds a name prefixed with GL_ (i.e.,
the name of the extension), that should be an error.  Names simply
containing __ are dangerous to use, but should be allowed.  In similar
cases, the C++ preprocessor specification says, "no diagnostic is
required."

Per the Khronos bug mentioned below, a future version of the GLSL
specification will clarify this.

Signed-off-by: Ian Romanick <[email protected]>
Cc: "9.2 10.0 10.1" <[email protected]>
Reviewed-by: Kenneth Graunke <[email protected]>
Tested-by: Kenneth Graunke <[email protected]>
Reviewed-by: Anuj Phogat <[email protected]>
Tested-by: Darius Spitznagel <[email protected]>
Cc: Tapani Pälli <[email protected]>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=71870
Bugzilla: Khronos #11702

2 files changed, 21 insertions, 5 deletions

diff --git a/src/glsl/glcpp/glcpp-parse.y b/src/glsl/glcpp/glcpp-parse.y
index 5bb2891c475..bdc598f31b8 100644
--- a/src/glsl/glcpp/glcpp-parse.y
+++ b/src/glsl/glcpp/glcpp-parse.y
@@ -1770,11 +1770,27 @@ static void
 _check_for_reserved_macro_name (glcpp_parser_t *parser, YYLTYPE *loc,
 				const char *identifier)
 {
-	/* According to the GLSL specification, macro names starting with "__"
-	 * or "GL_" are reserved for future use.  So, don't allow them.
+	/* Section 3.3 (Preprocessor) of the GLSL 1.30 spec (and later) and
+	 * the GLSL ES spec (all versions) say:
+	 *
+	 *     "All macro names containing two consecutive underscores ( __ )
+	 *     are reserved for future use as predefined macro names. All
+	 *     macro names prefixed with "GL_" ("GL" followed by a single
+	 *     underscore) are also reserved."
+	 *
+	 * The intention is that names containing __ are reserved for internal
+	 * use by the implementation, and names prefixed with GL_ are reserved
+	 * for use by Khronos.  Since every extension adds a name prefixed
+	 * with GL_ (i.e., the name of the extension), that should be an
+	 * error.  Names simply containing __ are dangerous to use, but should
+	 * be allowed.
+	 *
+	 * A future version of the GLSL specification will clarify this.
 	 */
 	if (strstr(identifier, "__")) {
-		glcpp_error (loc, parser, "Macro names containing \"__\" are reserved.\n");
+		glcpp_warning(loc, parser,
+			      "Macro names containing \"__\" are reserved "
+			      "for use by the implementation.\n");
 	}
 	if (strncmp(identifier, "GL_", 3) == 0) {
 		glcpp_error (loc, parser, "Macro names starting with \"GL_\" are reserved.\n");
diff --git a/src/glsl/glcpp/tests/086-reserved-macro-names.c.expected b/src/glsl/glcpp/tests/086-reserved-macro-names.c.expected
index d8aa9f0a648..5ca42a983a4 100644
--- a/src/glsl/glcpp/tests/086-reserved-macro-names.c.expected
+++ b/src/glsl/glcpp/tests/086-reserved-macro-names.c.expected
@@ -1,8 +1,8 @@
-0:1(10): preprocessor error: Macro names containing "__" are reserved.
+0:1(10): preprocessor warning: Macro names containing "__" are reserved for use by the implementation.
 
 0:2(9): preprocessor error: Macro names starting with "GL_" are reserved.
 
-0:3(9): preprocessor error: Macro names containing "__" are reserved.
+0:3(9): preprocessor warning: Macro names containing "__" are reserved for use by the implementation.