glsl/glcpp: Fix glcpp to catch garbage after #if 1 ... #else

Previously, a line such as:

	#else garbage

would flag an error if it followed "#if 0", but not if it followed "#if 1".

We fix this by setting a new bit of state (lexing_else) that allows the lexer
to defer switching to the <SKIP> start state until after the NEWLINE following
the #else directive.

A new test case is added for:

	#if 1
	#else garbage
	#endif

which was untested before, (and did not generate the desired error).

This fixes the following Khronos GLES3 CTS tests:

	tokens_after_else_vertex
        tokens_after_else_fragment

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>

src/glsl/glcpp/glcpp-lex.l

@@ -137,14 +137,15 @@ HEXADECIMAL_INTEGER	0[xX][0-9a-fA-F]+[uU]?
 	 *	2. The skip_stack is NULL meaning that we've reached
 	 *	   the last #endif.
 	 *
-	 *	3. The lexing_if bit is set. This indicates that we
-	 *	   are lexing the expression following an "#if" of
-	 *	   "#elif". Even inside an "#if 0" we need to lex this
-	 *	   expression so the parser can correctly update the
-	 *	   skip_stack state.
+	 *	3. The lexing_directive bit is set. This indicates that we are
+	 *	   lexing a pre-processor directive, (such as #if, #elif, or
+	 *	   #else). For the #if and #elif directives we always need to
+	 *	   parse the conditions, (even if otherwise within an #if
+	 *	   0). And for #else, we want to be able to generate an error
+	 *	   if any garbage follows #else.
 	 */
 	if (YY_START == INITIAL || YY_START == SKIP) {
-		if (parser->lexing_if ||
+		if (parser->lexing_directive ||
 		    parser->skip_stack == NULL ||
 		    parser->skip_stack->type == SKIP_NO_SKIP)
 		{
@@ -193,25 +194,25 @@ HEXADECIMAL_INTEGER	0[xX][0-9a-fA-F]+[uU]?
 
 <SKIP,INITIAL>{
 {HASH}ifdef {
-	yyextra->lexing_if = 1;
+	yyextra->lexing_directive = 1;
 	yyextra->space_tokens = 0;
 	return HASH_IFDEF;
 }
 
 {HASH}ifndef {
-	yyextra->lexing_if = 1;
+	yyextra->lexing_directive = 1;
 	yyextra->space_tokens = 0;
 	return HASH_IFNDEF;
 }
 
 {HASH}if/[^_a-zA-Z0-9] {
-	yyextra->lexing_if = 1;
+	yyextra->lexing_directive = 1;
 	yyextra->space_tokens = 0;
 	return HASH_IF;
 }
 
 {HASH}elif/[^_a-zA-Z0-9] {
-	yyextra->lexing_if = 1;
+	yyextra->lexing_directive = 1;
 	yyextra->space_tokens = 0;
 	return HASH_ELIF;
 }
@@ -348,7 +349,7 @@ HEXADECIMAL_INTEGER	0[xX][0-9a-fA-F]+[uU]?
 	if (parser->commented_newlines) {
 		BEGIN NEWLINE_CATCHUP;
 	}
-	yyextra->lexing_if = 0;
+	yyextra->lexing_directive = 0;
 	yylineno++;
 	yycolumn = 0;
 	return NEWLINE;
@@ -357,7 +358,7 @@ HEXADECIMAL_INTEGER	0[xX][0-9a-fA-F]+[uU]?
 	/* Handle missing newline at EOF. */
 <INITIAL><<EOF>> {
 	BEGIN DONE; /* Don't keep matching this rule forever. */
-	yyextra->lexing_if = 0;
+	yyextra->lexing_directive = 0;
 	return NEWLINE;
 }
 

src/glsl/glcpp/glcpp-parse.y

@@ -364,7 +364,7 @@ control_line:
 			glcpp_warning(& @1, parser, "ignoring illegal #elif without expression");
 		}
 	}
-|	HASH_ELSE {
+|	HASH_ELSE { parser->lexing_directive = 1; } NEWLINE {
 		if (parser->skip_stack &&
 		    parser->skip_stack->has_else)
 		{
@@ -376,7 +376,7 @@ control_line:
 			if (parser->skip_stack)
 				parser->skip_stack->has_else = true;
 		}
-	} NEWLINE
+	}
 |	HASH_ENDIF {
 		_glcpp_parser_skip_stack_pop (parser, & @1);
 	} NEWLINE
@@ -1211,7 +1211,7 @@ glcpp_parser_create (const struct gl_extensions *extensions, gl_api api)
 	parser->defines = hash_table_ctor (32, hash_table_string_hash,
 					   hash_table_string_compare);
 	parser->active = NULL;
-	parser->lexing_if = 0;
+	parser->lexing_directive = 0;
 	parser->space_tokens = 1;
 	parser->newline_as_space = 0;
 	parser->in_control_line = 0;

src/glsl/glcpp/glcpp.h

@@ -168,7 +168,7 @@ struct glcpp_parser {
 	yyscan_t scanner;
 	struct hash_table *defines;
 	active_list_t *active;
-	int lexing_if;
+	int lexing_directive;
 	int space_tokens;
 	int newline_as_space;
 	int in_control_line;

src/glsl/glcpp/tests/123-garbage-after-else-1.c

@@ -0,0 +1,3 @@
+#if 1
+#else garbage
+#endif

src/glsl/glcpp/tests/123-garbage-after-else-1.c.expected

@@ -0,0 +1,4 @@
+0:2(7): preprocessor error: syntax error, unexpected IDENTIFIER, expecting NEWLINE
+0:1(7): preprocessor error: Unterminated #if
+
+