lexer: fix parsing with disabled block left stripping

When a template was parsed with global block left stripping disabled, then
any text preceding an expression or statement block start tag was incorrectly
prepended to the first token value of the block, leading to syntax errors in
the compiler.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

2 files changed, 26 insertions, 3 deletions

diff --git a/lexer.c b/lexer.c
index aae3e2f..5be8ece 100644
--- a/lexer.c
+++ b/lexer.c
@@ -887,9 +887,12 @@ lex_step(uc_lexer_t *lex, FILE *fp)
 				buf_consume(lex, 1);
 			}
 
-			/* global block lstrip */
-			else if (lex->config && lex->config->lstrip_blocks) {
-				rv = lookbehind_to_text(lex, lex->source->off, TK_TEXT, " \t\v\f\r");
+			/* put out text leading up to the opening tag and potentially
+			 * strip trailing white space from it depending on the global
+			 * block lstrip setting */
+			else {
+				rv = lookbehind_to_text(lex, lex->source->off, TK_TEXT,
+					(lex->config && lex->config->lstrip_blocks) ? " \t\v\f\r" : NULL);
 			}
 		}
 		else {
diff --git a/tests/custom/04_bugs/40_lexer_bug_on_lstrip_off b/tests/custom/04_bugs/40_lexer_bug_on_lstrip_off
new file mode 100644
index 0000000..dc4f8dd
--- /dev/null
+++ b/tests/custom/04_bugs/40_lexer_bug_on_lstrip_off
@@ -0,0 +1,20 @@
+When a template was parsed with global block left stripping disabled,
+then any text preceding an expression or statement block start tag was
+incorrectly prepended to the first token value of the block, leading
+to syntax errors in the compiler.
+
+-- Testcase --
+{% for (let x in [1, 2, 3]): %}
+{{ x }}
+{% endfor %}
+-- End --
+
+-- Args --
+-Tno-lstrip
+-- End --
+
+-- Expect stdout --
+1
+2
+3
+-- End --