parser: fix parsing insert select on conflict

crates/squawk_parser/src/grammar.rs

@@ -3456,7 +3456,7 @@ fn join(p: &mut Parser<'_>) {
     if !opt_from_item(p) {
         p.error("expected from_item");
     }
-    if p.at(ON_KW) {
+    if p.at(ON_KW) && !p.nth_at(1, CONFLICT_KW) {
         on_clause(p);
     } else if p.at(USING_KW) {
         join_using_clause(p);

crates/squawk_parser/tests/data/ok/insert.sql

@@ -91,3 +91,12 @@ INSERT INTO distributors (did, dname) VALUES (10, 'Conrad International')
 
 -- with schema
 insert into s.t (c) values (1);
+
+
+-- regression check for issue #718
+-- we were parsing the `on conflict` as the start of a `join on`
+INSERT INTO t
+SELECT *
+FROM t
+CROSS JOIN f
+ON CONFLICT DO NOTHING;

crates/squawk_parser/tests/snapshots/tests__insert_ok.snap

@@ -1463,4 +1463,55 @@ SOURCE_FILE
             INT_NUMBER "1"
           R_PAREN ")"
   SEMICOLON ";"
+  WHITESPACE "\n\n\n"
+  COMMENT "-- regression check for issue #718"
+  WHITESPACE "\n"
+  COMMENT "-- we were parsing the `on conflict` as the start of a `join on`"
+  WHITESPACE "\n"
+  INSERT
+    INSERT_KW "INSERT"
+    WHITESPACE " "
+    INTO_KW "INTO"
+    WHITESPACE " "
+    PATH
+      PATH_SEGMENT
+        NAME_REF
+          IDENT "t"
+    WHITESPACE "\n"
+    SELECT
+      SELECT_CLAUSE
+        SELECT_KW "SELECT"
+        WHITESPACE " "
+        TARGET_LIST
+          TARGET
+            STAR "*"
+      WHITESPACE "\n"
+      FROM_CLAUSE
+        FROM_KW "FROM"
+        WHITESPACE " "
+        JOIN_EXPR
+          FROM_ITEM
+            NAME_REF
+              IDENT "t"
+          WHITESPACE "\n"
+          JOIN
+            JOIN_CROSS
+              CROSS_KW "CROSS"
+              WHITESPACE " "
+              JOIN_KW "JOIN"
+            WHITESPACE " "
+            FROM_ITEM
+              NAME_REF
+                IDENT "f"
+    WHITESPACE "\n"
+    ON_CONFLICT_CLAUSE
+      ON_KW "ON"
+      WHITESPACE " "
+      CONFLICT_KW "CONFLICT"
+      WHITESPACE " "
+      CONFLICT_DO_NOTHING
+        DO_KW "DO"
+        WHITESPACE " "
+        NOTHING_KW "NOTHING"
+  SEMICOLON ";"
   WHITESPACE "\n"