parser: fix crash with trailing comma (#551)

fix crash with trailing comma:

```sql
select a, from t;
```

would get stuck at the comma, now we report an error:

```
error[syntax-error]: unexpected trailing comma
 --> stdin:1:9
  |
1 | select a, from t;
  |         ^
  |
```

Author: sbdchd

crates/squawk_parser/src/grammar.rs

@@ -4510,6 +4510,8 @@ const TARGET_FOLLOW: TokenSet = TokenSet::new(&[
     R_PAREN,
     R_BRACK,
     RETURNING_KW,
+    SEMICOLON,
+    EOF,
 ])
 .union(COMPOUND_SELECT_FIRST);
 
@@ -4567,7 +4569,7 @@ fn opt_target_list(p: &mut Parser) -> Option<CompletedMarker> {
     let m = p.start();
     while !p.at(EOF) && !p.at(SEMICOLON) {
         if opt_target_el(p).is_some() {
-            if p.at(COMMA) && matches!(p.nth(1), SEMICOLON | EOF) {
+            if p.at(COMMA) && p.nth_at_ts(1, TARGET_FOLLOW) {
                 p.err_and_bump("unexpected trailing comma");
                 break;
             }
@@ -4584,6 +4586,8 @@ fn opt_target_list(p: &mut Parser) -> Option<CompletedMarker> {
                     break;
                 }
             }
+        } else {
+            break;
         }
     }
     Some(m.complete(p, TARGET_LIST))

crates/squawk_parser/tests/data/err/select.sql

@@ -29,5 +29,8 @@ select numeric 1234;
 -- warns about a missing semicolon
 select select;
 
+-- extra comma
+select a, from t;
+
 -- trailing comma at EOF
 select 1,

crates/squawk_parser/tests/snapshots/tests__select_err.snap

@@ -223,6 +223,27 @@ SOURCE_FILE
       SELECT_KW "select"
   SEMICOLON ";"
   WHITESPACE "\n\n"
+  COMMENT "-- extra comma"
+  WHITESPACE "\n"
+  SELECT
+    SELECT_CLAUSE
+      SELECT_KW "select"
+      WHITESPACE " "
+      TARGET_LIST
+        TARGET
+          NAME_REF
+            IDENT "a"
+        ERROR
+          COMMA ","
+    WHITESPACE " "
+    FROM_CLAUSE
+      FROM_KW "from"
+      WHITESPACE " "
+      FROM_ITEM
+        NAME_REF
+          IDENT "t"
+  SEMICOLON ";"
+  WHITESPACE "\n\n"
   COMMENT "-- trailing comma at EOF"
   WHITESPACE "\n"
   SELECT
@@ -248,4 +269,5 @@ ERROR@396: expected expression
 ERROR@397: expected expression
 ERROR@520: missing comma
 ERROR@646: expected SEMICOLON
-ERROR@689: unexpected trailing comma
+ERROR@679: unexpected trailing comma
+ERROR@723: unexpected trailing comma