Fix #if-skipping to *really* skip the skipped group.

Previously we were avoiding printing within a skipped group, but we
were still evluating directives such as #define and #undef and still
emitting diagnostics for things such as macro calls with the wrong
number of arguments.

Add a test for this and fix it with a high-priority rule in the lexer
that consumes the skipped content.

4 files changed, 44 insertions, 25 deletions

diff --git a/glcpp-lex.l b/glcpp-lex.l
index 52269c6b30..a51d9e185f 100644
--- a/glcpp-lex.l
+++ b/glcpp-lex.l
@@ -47,39 +47,58 @@ HEXADECIMAL_INTEGER	0[xX][0-9a-fA-F]+[uU]?
 
 %%
 
-{HASH}define{HSPACE}+/{IDENTIFIER}"(" {
+{HASH}if/.*\n {
+	yyextra->lexing_if = 1;
 	yyextra->space_tokens = 0;
-	return HASH_DEFINE_FUNC;
+	return HASH_IF;
 }
 
-{HASH}define {
+{HASH}elif/.*\n {
+	yyextra->lexing_if = 1;
 	yyextra->space_tokens = 0;
-	return HASH_DEFINE_OBJ;
+	return HASH_ELIF;
 }
 
-{HASH}undef {
+{HASH}else/.*\n {
 	yyextra->space_tokens = 0;
-	return HASH_UNDEF;
+	return HASH_ELSE;
 }
 
-{HASH}if {
+{HASH}endif/.*\n {
 	yyextra->space_tokens = 0;
-	return HASH_IF;
+	return HASH_ENDIF;
 }
 
-{HASH}elif {
+	/* When skipping (due to an #if 0 or similar) consume anything
+	 * up to a newline. We do this less priroty than any
+	 * #if-related directive (#if, #elif, #else, #endif), but with
+	 * more priority than any other directive or token to avoid
+	 * any side-effects from skipped content.
+	 *
+	 * We use the lexing_if flag to avoid skipping any part of an
+	 * if conditional expression. */
+[^\n]+/\n {
+	if (yyextra->lexing_if ||
+	    yyextra->skip_stack == NULL ||
+	    yyextra->skip_stack->type == SKIP_NO_SKIP)
+	{
+		REJECT;
+	}
+}
+
+{HASH}define{HSPACE}+/{IDENTIFIER}"(" {
 	yyextra->space_tokens = 0;
-	return HASH_ELIF;
+	return HASH_DEFINE_FUNC;
 }
 
-{HASH}else {
+{HASH}define {
 	yyextra->space_tokens = 0;
-	return HASH_ELSE;
+	return HASH_DEFINE_OBJ;
 }
 
-{HASH}endif {
+{HASH}undef {
 	yyextra->space_tokens = 0;
-	return HASH_ENDIF;
+	return HASH_UNDEF;
 }
 
 {HASH} {
@@ -163,6 +182,7 @@ HEXADECIMAL_INTEGER	0[xX][0-9a-fA-F]+[uU]?
 }
 
 \n {
+	yyextra->lexing_if = 0;
 	return NEWLINE;
 }
 
diff --git a/glcpp-parse.y b/glcpp-parse.y
index f4c834e038..dd8e133f55 100644
--- a/glcpp-parse.y
+++ b/glcpp-parse.y
@@ -159,19 +159,11 @@ input:
 
 line:
 	control_line {
-		if (parser->skip_stack == NULL ||
-		    parser->skip_stack->type == SKIP_NO_SKIP)
-		{
-			printf ("\n");
-		}
+		printf ("\n");
 	}
 |	text_line {
-		if (parser->skip_stack == NULL ||
-		    parser->skip_stack->type == SKIP_NO_SKIP)
-		{
-			_glcpp_parser_print_expanded_token_list (parser, $1);
-			printf ("\n");
-		}
+		_glcpp_parser_print_expanded_token_list (parser, $1);
+		printf ("\n");
 		talloc_free ($1);
 	}
 |	expanded_line
@@ -889,6 +881,7 @@ glcpp_parser_create (void)
 	parser->defines = hash_table_ctor (32, hash_table_string_hash,
 					   hash_table_string_compare);
 	parser->active = _string_list_create (parser);
+	parser->lexing_if = 0;
 	parser->space_tokens = 1;
 	parser->newline_as_space = 0;
 	parser->in_control_line = 0;
diff --git a/glcpp.h b/glcpp.h
index 5c8c304a9c..41fc2043d1 100644
--- a/glcpp.h
+++ b/glcpp.h
@@ -127,6 +127,7 @@ struct glcpp_parser {
 	yyscan_t scanner;
 	struct hash_table *defines;
 	string_list_t *active;
+	int lexing_if;
 	int space_tokens;
 	int newline_as_space;
 	int in_control_line;
diff --git a/tests/062-if-0-skips-garbage.c b/tests/062-if-0-skips-garbage.c
new file mode 100644
index 0000000000..d9e439bb89
--- /dev/null
+++ b/tests/062-if-0-skips-garbage.c
@@ -0,0 +1,5 @@
+#define foo(a,b)
+#if 0
+foo(bar)
+foo(
+#endif