parser: handle missing exprs in case expr (#749)

Author: sbdchd

crates/squawk_parser/src/grammar.rs

@@ -20,6 +20,14 @@ const EXPR_RECOVERY_SET: TokenSet = TokenSet::new(&[
     // which should be written as:
     //   select 1; select 2;
     SELECT_KW,
+    // select case when x then y else end;
+    //                               ^ missing expr
+    END_KW,
+    // select case when x then else z end;
+    //                        ^ missing expr
+    ELSE_KW, // select case when then y end;
+    //                          ^ missing expr
+    THEN_KW,
 ]);
 
 fn literal(p: &mut Parser<'_>) -> Option<CompletedMarker> {
@@ -208,8 +216,8 @@ fn opt_else_clause(p: &mut Parser<'_>) {
         return;
     }
     let m = p.start();
-    if p.eat(ELSE_KW) && expr(p).is_none() {
-        p.error("expected an expression");
+    if p.eat(ELSE_KW) {
+        expr(p);
     }
     m.complete(p, ELSE_CLAUSE);
 }
@@ -219,13 +227,9 @@ fn opt_else_clause(p: &mut Parser<'_>) {
 fn when_clause(p: &mut Parser<'_>) -> CompletedMarker {
     let m = p.start();
     p.expect(WHEN_KW);
-    if expr(p).is_none() {
-        p.error("expected an expression");
-    }
+    expr(p);
     p.expect(THEN_KW);
-    if expr(p).is_none() {
-        p.error("expected an expression");
-    }
+    expr(p);
     m.complete(p, WHEN_CLAUSE)
 }
 
@@ -2334,7 +2338,6 @@ fn postfix_dot_expr(
     })
 }
 
-#[must_use]
 fn expr(p: &mut Parser) -> Option<CompletedMarker> {
     expr_bp(p, 1, &Restrictions::default())
 }

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

@@ -55,5 +55,14 @@ select select;
 -- extra comma
 select a, from t;
 
+-- case missing then expr
+select case when 1 then end;
+
+-- case missing when expr
+select case when then x end;
+
+-- case missing else expr
+select case when 1 then 2 else end;
+
 -- trailing comma at EOF
 select 1,

crates/squawk_parser/tests/snapshots/tests__select_err.snap

@@ -610,6 +610,81 @@ SOURCE_FILE
           IDENT "t"
   SEMICOLON ";"
   WHITESPACE "\n\n"
+  COMMENT "-- case missing then expr"
+  WHITESPACE "\n"
+  SELECT
+    SELECT_CLAUSE
+      SELECT_KW "select"
+      WHITESPACE " "
+      TARGET_LIST
+        TARGET
+          CASE_EXPR
+            CASE_KW "case"
+            WHITESPACE " "
+            WHEN_CLAUSE_LIST
+              WHEN_CLAUSE
+                WHEN_KW "when"
+                WHITESPACE " "
+                LITERAL
+                  INT_NUMBER "1"
+                WHITESPACE " "
+                THEN_KW "then"
+            WHITESPACE " "
+            END_KW "end"
+  SEMICOLON ";"
+  WHITESPACE "\n\n"
+  COMMENT "-- case missing when expr"
+  WHITESPACE "\n"
+  SELECT
+    SELECT_CLAUSE
+      SELECT_KW "select"
+      WHITESPACE " "
+      TARGET_LIST
+        TARGET
+          CASE_EXPR
+            CASE_KW "case"
+            WHITESPACE " "
+            WHEN_CLAUSE_LIST
+              WHEN_CLAUSE
+                WHEN_KW "when"
+                WHITESPACE " "
+                THEN_KW "then"
+                WHITESPACE " "
+                NAME_REF
+                  IDENT "x"
+            WHITESPACE " "
+            END_KW "end"
+  SEMICOLON ";"
+  WHITESPACE "\n\n"
+  COMMENT "-- case missing else expr"
+  WHITESPACE "\n"
+  SELECT
+    SELECT_CLAUSE
+      SELECT_KW "select"
+      WHITESPACE " "
+      TARGET_LIST
+        TARGET
+          CASE_EXPR
+            CASE_KW "case"
+            WHITESPACE " "
+            WHEN_CLAUSE_LIST
+              WHEN_CLAUSE
+                WHEN_KW "when"
+                WHITESPACE " "
+                LITERAL
+                  INT_NUMBER "1"
+                WHITESPACE " "
+                THEN_KW "then"
+                WHITESPACE " "
+                LITERAL
+                  INT_NUMBER "2"
+            WHITESPACE " "
+            ELSE_CLAUSE
+              ELSE_KW "else"
+            WHITESPACE " "
+            END_KW "end"
+  SEMICOLON ";"
+  WHITESPACE "\n\n"
   COMMENT "-- trailing comma at EOF"
   WHITESPACE "\n"
   SELECT
@@ -649,4 +724,7 @@ ERROR@1047: unexpected comma
 ERROR@1079: unexpected trailing comma
 ERROR@1203: expected SEMICOLON
 ERROR@1236: unexpected trailing comma
-ERROR@1280: unexpected trailing comma
+ERROR@1296: expected an expression, found END_KW
+ERROR@1345: expected an expression, found THEN_KW
+ERROR@1415: expected an expression, found END_KW
+ERROR@1455: unexpected trailing comma