1 files changed, 34 insertions, 14 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;
 }