[Mesa-dev] [PATCH] glcpp: Rewrite line-continuation support to act globally.

[Carl Worth]

Previously, we were only supporting line-continuation backslash characters
within lines of pre-processor directives, (as per the specification). With
OpenGL 4.3, line continuations are now supported anywhere within a shader.

While changing this, also fix a bug where the preprocessor was ignoring line
continuation characters when a line ended in multiple backslash characters.

The new code is also more efficient than the old. Previously, we would perform
a ralloc copy at each newline. We now perform copies only at each occurrence
of a line-continuation.
---
 src/glsl/glcpp/pp.c |  108 ++++++++++++++++++++-------------------------------
 1 file changed, 42 insertions(+), 66 deletions(-)

diff --git a/src/glsl/glcpp/pp.c b/src/glsl/glcpp/pp.c
index 11b2941..1135570 100644
--- a/src/glsl/glcpp/pp.c
+++ b/src/glsl/glcpp/pp.c
@@ -70,82 +70,58 @@ glcpp_warning (YYLTYPE *locp, glcpp_parser_t *parser, const char *fmt, ...)
 				     &parser->info_log_length, "\n");
 }
 
-/* Searches backwards for '^ *#' from a given starting point. */
-static int
-in_directive(const char *shader, const char *ptr)
-{
-	assert(ptr >= shader);
-
-	/* Search backwards for '#'. If we find a \n first, it doesn't count */
-	for (; ptr >= shader && *ptr != '#'; ptr--) {
-		if (*ptr == '\n')
-			return 0;
-	}
-	if (ptr >= shader) {
-		/* Found '#'...look for spaces preceded by a newline */
-		for (ptr--; ptr >= shader && isblank(*ptr); ptr--);
-		// FIXME: I don't think the '\n' case can happen
-		if (ptr < shader || *ptr == '\n')
-			return 1;
-	}
-	return 0;
-}
-
-/* Remove any line continuation characters in preprocessing directives.
- * However, ignore any in GLSL code, as "There is no line continuation
- * character" (1.30 page 9) in GLSL.
+/* Remove any line continuation characters in the shader, (whether in
+ * preprocessing directives or in GLSL code).
  */
 static char *
 remove_line_continuations(glcpp_parser_t *ctx, const char *shader)
 {
-	int in_continued_line = 0;
-	int extra_newlines = 0;
 	char *clean = ralloc_strdup(ctx, "");
-	const char *search_start = shader;
-	const char *newline;
-	while ((newline = strchr(search_start, '\n')) != NULL) {
-		const char *backslash = NULL;
-
-		/* # of characters preceding the newline. */
-		int n = newline - shader;
-
-		/* Find the preceding '\', if it exists */
-		if (n >= 1 && newline[-1] == '\\')
-			backslash = newline - 1;
-		else if (n >= 2 && newline[-1] == '\r' && newline[-2] == '\\')
-			backslash = newline - 2;
-
-		/* Double backslashes don't count (the backslash is escaped) */
-		if (backslash != NULL && backslash[-1] == '\\') {
-			backslash = NULL;
-		}
-
-		if (backslash != NULL) {
-			/* We found a line continuation, but do we care? */
-			if (!in_continued_line) {
-				if (in_directive(shader, backslash)) {
-					in_continued_line = 1;
-					extra_newlines = 0;
-				}
-			}
-			if (in_continued_line) {
-				/* Copy everything before the \ */
-				ralloc_strncat(&clean, shader, backslash - shader);
+	const char *backslash, *newline;
+	int collapsed_newlines = 0;
+
+	while (1) {
+		backslash = strchr(shader, '\\');
+
+		/* If we have previously collapsed any
+		 * line-continuations, then we want to insert
+		 * additional newlines at the next occurrence of a
+		 * newline character to avoid changing any line
+		 * numbers. */
+		if (collapsed_newlines) {
+			newline = strchr(shader, '\n');
+			if (newline &&
+			    (backslash == NULL || newline < backslash))
+			{
+				ralloc_strncat(&clean, shader,
+					       newline - shader + 1);
+				while (collapsed_newlines--)
+					ralloc_strcat(&clean, "\n");
 				shader = newline + 1;
-				extra_newlines++;
 			}
-		} else if (in_continued_line) {
-			/* Copy everything up to and including the \n */
-			ralloc_strncat(&clean, shader, newline - shader + 1);
-			shader = newline + 1;
-			/* Output extra newlines to make line numbers match */
-			for (; extra_newlines > 0; extra_newlines--)
-				ralloc_strcat(&clean, "\n");
-			in_continued_line = 0;
 		}
-		search_start = newline + 1;
+
+		if (backslash == NULL)
+			break;
+
+		/* At each line continuation, (backslash followed by a
+		 * newline), copy all preceding text to the output,
+		 * then advance the shader pointer to the character
+		 * after the newline. */
+		if (backslash[1] == '\n' ||
+		    (backslash[1] == '\r' && backslash[2] == '\n'))
+		{
+			collapsed_newlines++;
+			ralloc_strncat(&clean, shader, backslash - shader);
+			if (backslash[1] == '\n')
+				shader = backslash + 2;
+			else
+				shader = backslash + 3;
+		}
 	}
+
 	ralloc_strcat(&clean, shader);
+
 	return clean;
 }
 
-- 
1.7.10