syntax: recognize single-char escapes in regex literals again

Ensure that the single char escapes `\a`, `\b`, `\e`, `\f`, `\n`,
`\r`, `\t` and `\v` keep working. Since they're not part of the POSIX
extended regular expression spec, they're not handled by the RE engine
so we need to substitute them by their actual byte value while parsing
the literal.

Fixes: ac5cb87 ("syntax: fix string and regex literal parsing quirks")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

2 files changed, 15 insertions, 13 deletions

diff --git a/lexer.c b/lexer.c
index 21a3b3a..5e2e7e8 100644
--- a/lexer.c
+++ b/lexer.c
@@ -394,23 +394,13 @@ parse_string(struct uc_state *s)
 		/* continuation of escape sequence */
 		if (s->lex.is_escape) {
 			if (s->lex.esclen == 0) {
-				/* regex mode => do not interprete escapes */
-				if (q == '/') {
-					s->lex.is_escape = false;
-					lookbehind_append(s, "\\", 1);
-					lookbehind_append(s, ptr, 1);
-					buf_consume(s, (ptr + 1) - s->lex.bufstart);
-
-					continue;
-				}
-
 				/* non-unicode escape following a lead surrogate, emit replacement... */
 				if (s->lex.lead_surrogate && *ptr != 'u') {
 					append_utf8(s, 0xFFFD);
 					s->lex.lead_surrogate = 0;
 				}
 
-				switch (*ptr) {
+				switch ((q == '/') ? 0 : *ptr) {
 				case 'u':
 				case 'x':
 					s->lex.esc[s->lex.esclen++] = *ptr;
@@ -444,8 +434,20 @@ parse_string(struct uc_state *s)
 				default:
 					s->lex.is_escape = false;
 					c = strchr("a\ab\be\ef\fn\nr\rt\tv\v", *ptr);
-					lookbehind_append(s, (c && *c >= 'a') ? c + 1 : ptr, 1);
+
+					if (c && *c >= 'a') {
+						lookbehind_append(s, c + 1, 1);
+					}
+					else {
+						/* regex mode => retain backslash */
+						if (q == '/')
+							lookbehind_append(s, "\\", 1);
+
+						lookbehind_append(s, ptr, 1);
+					}
+
 					buf_consume(s, (ptr + 1) - s->lex.bufstart);
+
 					break;
 				}
 			}
diff --git a/tests/00_syntax/21_regex_literals b/tests/00_syntax/21_regex_literals
index bbb78fb..4aef33f 100644
--- a/tests/00_syntax/21_regex_literals
+++ b/tests/00_syntax/21_regex_literals
@@ -4,7 +4,7 @@ within regular expression literals is subject of the underlying
 regular expression engine.
 
 -- Expect stdout --
-[ "/Hello world/", "/test/gis", "/test/g", "/test1 \\\/ test2/", "/\\x31\\n\\.\\a\\b\\c\\u2600\\\\/" ]
+[ "/Hello world/", "/test/gis", "/test/g", "/test1 \\\/ test2/", "/\\x31\n\\.\u0007\b\\c\\u2600\\\\/" ]
 -- End --
 
 -- Testcase --