Break long WHEN/THEN/ELSE clauses into separate lines

src/syntax/expr.ts

@@ -122,13 +122,18 @@ export const exprMap: CstToDocMap<AllExprNodes> = {
     print("endKw"),
   ],
   case_when: (print, node) => {
+    const whenThen = group([
+      group([print("whenKw"), indent([line, print("condition")])]),
+      line,
+      print("thenKw"),
+    ]);
     if (isProgram(node.result)) {
       return [
-        print.spaced(["whenKw", "condition", "thenKw"]),
+        whenThen,
         indent([hardline, stripTrailingHardline(print("result"))]),
       ];
     }
-    return print.spaced(["whenKw", "condition", "thenKw", "result"]);
+    return group([whenThen, indent([line, print("result")])]);
   },
   case_else: (print, node) => {
     if (isProgram(node.result)) {
@@ -137,7 +142,7 @@ export const exprMap: CstToDocMap<AllExprNodes> = {
         indent([hardline, stripTrailingHardline(print("result"))]),
       ];
     }
-    return print.spaced(["elseKw", "result"]);
+    return group([print("elseKw"), indent([line, print("result")])]);
   },
   member_expr: (print, node) =>
     isArraySubscript(node.property)

test/expr/expr.test.ts

@@ -192,6 +192,79 @@ describe("expr", () => {
           END
       `);
     });
+
+    it(`breaks long WHEN/THEN into separate lines`, async () => {
+      await test(
+        dedent`
+          SELECT
+            CASE
+              WHEN column_name = 1 THEN
+                result_name
+            END
+        `,
+        { printWidth: 40 },
+      );
+    });
+
+    it(`breaks multiple long WHEN/THEN clauses without blank lines between them`, async () => {
+      await test(
+        dedent`
+          SELECT
+            CASE
+              WHEN column_name = 1 THEN
+                result_name
+              WHEN column_name = 2 THEN
+                other_result
+              ELSE foo
+            END
+        `,
+        { printWidth: 40 },
+      );
+    });
+
+    it(`breaks long ELSE into separate lines`, async () => {
+      await test(
+        dedent`
+          SELECT
+            CASE
+              WHEN x = 1 THEN 'A'
+              ELSE
+                long_fallback_expression
+            END
+        `,
+        { printWidth: 25 },
+      );
+    });
+
+    it(`indents long multi-condition WHEN clauses`, async () => {
+      await test(
+        dedent`
+          SELECT
+            CASE
+              WHEN
+                column_name = 1
+                AND (other_name = 2 OR other_name = 3)
+              THEN
+                result_name
+            END
+        `,
+        { printWidth: 50 },
+      );
+    });
+
+    it(`indents long multi-expression THEN clauses`, async () => {
+      await test(
+        dedent`
+          SELECT
+            CASE
+              WHEN column_name = 1 THEN
+                result_name = 1
+                AND other_name = 2
+            END
+        `,
+        { printWidth: 45 },
+      );
+    });
   });
 
   it(`formats quantifier expressions`, async () => {

test/proc/case.test.ts

@@ -12,4 +12,21 @@ describe("case", () => {
       END CASE
     `);
   });
+
+  it(`breaks long WHEN/THEN clauses into separate lines`, async () => {
+    await testBigquery(
+      dedent`
+        CASE foo
+          WHEN
+            column_name = 1
+            AND (other_name = 2 OR other_name = 3)
+          THEN
+            SELECT CONCAT('Product one');
+          ELSE
+            SELECT CONCAT('Invalid product');
+        END CASE
+      `,
+      { printWidth: 50 },
+    );
+  });
 });