@let: allow trailing comma.HEADmaster

We allow forms like @let(x,) and @let(x, y=1,) with the
trailing comma. This is helpful for code generators and macros,
which can then treat temporary variables as comma-terminated
items.

* awkgram.y (let_var_list_opt): Add a production which matches a
trailing comma after let_var_list.

* test/let1.awk, test/let1.ok: Test cases.

* doc/gawkt.texi, doc/gawktexi.in:  Trailing comma documented.

* awkgram.c: Regenerated with Bison 3.8.

1 files changed, 2 insertions, 0 deletions

diff --git a/awkgram.y b/awkgram.y
index 4f568e22..fc35100d 100644
--- a/awkgram.y
+++ b/awkgram.y
@@ -1603,6 +1603,8 @@ let_var_list_opt
 	  { $$ = NULL; }
 	| let_var_list
 	  { $$ = $1; }
+	| let_var_list comma
+	  { $$ = $1; }
 	;
 
 let_var_list