py/lexer: Wrap in parenthesis all f-string arguments passed to format.

This is important for literal tuples, e.g.

    f"{a,b,}, {c}" --> "{}".format((a,b), (c),)

which would otherwise result in either a syntax error or the wrong result.

Fixes issue #9635.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/py/lexer.c b/py/lexer.c
index 39e9662f6..e7d0e8144 100644
--- a/py/lexer.c
+++ b/py/lexer.c
@@ -356,6 +356,9 @@ STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw, bool is_fstring)
                     vstr_add_byte(&lex->vstr, '{');
                     next_char(lex);
                 } else {
+                    // wrap each argument in (), e.g.
+                    // f"{a,b,}, {c}" --> "{}".format((a,b), (c),)
+                    vstr_add_byte(&lex->fstring_args, '(');
                     // remember the start of this argument (if we need it for f'{a=}').
                     size_t i = lex->fstring_args.len;
                     // extract characters inside the { until we reach the
@@ -382,7 +385,9 @@ STATIC void parse_string_literal(mp_lexer_t *lex, bool is_raw, bool is_fstring)
                         // remove the trailing '='
                         lex->fstring_args.len--;
                     }
-                    // comma-separate args
+                    // close the paren-wrapped arg to .format().
+                    vstr_add_byte(&lex->fstring_args, ')');
+                    // comma-separate args to .format().
                     vstr_add_byte(&lex->fstring_args, ',');
                 }
                 vstr_add_byte(&lex->vstr, '{');