parser: fix select select causing a panic (#499)

Author: sbdchd

crates/squawk_parser/src/grammar.rs

@@ -4211,7 +4211,7 @@ fn opt_as_col_label(p: &mut Parser<'_>) -> bool {
 }
 
 fn opt_target_list(p: &mut Parser) -> Option<CompletedMarker> {
-    if !p.at_ts(TARGET_LIST_START) {
+    if !p.at_ts(TARGET_LIST_START) || p.at(SELECT_KW) {
         return None;
     }
     let m = p.start();

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

@@ -25,5 +25,9 @@ select 1 in c;
 -- type cast must use a string literal
 select numeric 1234;
 
+-- regression test: this would cause the parser to get stuck & panic, now it
+-- warns about a missing semicolon
+select select;
+
 -- trailing comma at EOF
 select 1,

crates/squawk_parser/tests/snapshots/tests__select_err.snap

@@ -1,7 +1,6 @@
 ---
 source: crates/squawk_parser/tests/tests.rs
 input_file: crates/squawk_parser/tests/data/err/select.sql
-snapshot_kind: text
 ---
 SOURCE_FILE
   COMMENT "--- via https://duckdb.org/docs/stable/sql/dialect/friendly_sql.html#trailing-commas"
@@ -209,6 +208,19 @@ SOURCE_FILE
             INT_NUMBER "1234"
   SEMICOLON ";"
   WHITESPACE "\n\n"
+  COMMENT "-- regression test: this would cause the parser to get stuck & panic, now it"
+  WHITESPACE "\n"
+  COMMENT "-- warns about a missing semicolon"
+  WHITESPACE "\n"
+  SELECT
+    SELECT_CLAUSE
+      SELECT_KW "select"
+  WHITESPACE " "
+  SELECT
+    SELECT_CLAUSE
+      SELECT_KW "select"
+  SEMICOLON ";"
+  WHITESPACE "\n\n"
   COMMENT "-- trailing comma at EOF"
   WHITESPACE "\n"
   SELECT
@@ -233,4 +245,5 @@ ERROR@395: expected expression
 ERROR@396: expected expression
 ERROR@397: expected expression
 ERROR@520: missing comma
-ERROR@561: unexpected trailing comma
+ERROR@646: expected SEMICOLON
+ERROR@689: unexpected trailing comma