[Mesa-dev] [PATCH 22/23] glsl/glcpp: Add a catch-all rule for unexpected characters.

Carl Worth cworth at cworth.org
Thu Jun 26 15:19:22 PDT 2014

In some of the recent glcpp bug-fixing, we found that glcpp was emitting
unrecognized characters from the input source file to stdout, and dropping
them from the source passed onto the compiler proper.

This was obviously confusing, and totally undesired.

The bogus behavior comes from an implicit default rule in flex, which is
that any unmatched character is implicitly matched and printed to stdout.

To avoid this implicit matching and printing, here we add an explicit
catch-all rule. If this rule ever matches it prints an internal compiler
error. The correct response for anyt such error is fixing glcpp to handle
the unexpected character in the correct way.
 src/glsl/glcpp/glcpp-lex.l | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/glsl/glcpp/glcpp-lex.l b/src/glsl/glcpp/glcpp-lex.l
index 3d32cf4..721d8ae 100644
--- a/src/glsl/glcpp/glcpp-lex.l
+++ b/src/glsl/glcpp/glcpp-lex.l
@@ -161,6 +161,10 @@ glcpp_lex_update_state_per_token (glcpp_parser_t *parser, int token)
 %option stack
 %option never-interactive
+	/* Note: When adding any start conditions to this list, you must also
+	 * update the "Internal compiler error" catch-all rule near the end of
+	 * this file. */
 SPACE		[[:space:]]
@@ -534,6 +538,15 @@ HEXADECIMAL_INTEGER	0[xX][0-9a-fA-F]+[uU]?
+	/* This is a catch-all to avoid the annoying default flex action which
+	 * matches any character and prints it. If any input ever matches this
+	 * rule, then we have made a mistake above and need to fix one or more
+	 * of the preceding patterns to match that input. */
+	glcpp_error(yylloc, yyextra, "Internal compiler error: Unexpected character: %s", yytext);
 	/* We don't actually use the UNREACHABLE start condition. We
 	only have this action here so that we can pretend to call some
 	generated functions, (to avoid "defined but not used"

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