Improve formatting for empty tuple types (#11884)

* Don't print trailing comma when tuple is empty * Add tests * Don't print softline * Add tests * Update tests * Add changelog * Update changelog_unreleased/typescript/11884.md Co-authored-by: fisker Cheung <lionkay@gmail.com> * Fix names Co-authored-by: fisker Cheung <lionkay@gmail.com>
prettier · Nov 30, 2021 · e17404e · e17404e
1 parent 62ede8b
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diff --git a/changelog_unreleased/typescript/11884.md b/changelog_unreleased/typescript/11884.md
@@ -0,0 +1,32 @@
+#### Improve formatting for empty tuple types (#11884 by @sosukesuzuki)
+
+<!-- prettier-ignore -->
+```tsx
+// Input
+type Foo =
+  Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends []
+    ? Foo3
+    : Foo4;
+
+// Prettier stable
+type Foo = Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends [
+
+]
+  ? Foo3
+  : Foo4;
+
+// Prettier stable (tailingCommma = all)
+// Invalid TypeScript code
+type Foo = Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends [
+  ,
+]
+  ? Foo3
+  : Foo4;
+
+// Prettier main
+type Foo =
+  Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends []
+    ? Foo3
+    : Foo4;
+
+```
diff --git a/src/language-js/print/type-annotation.js b/src/language-js/print/type-annotation.js
@@ -4,7 +4,7 @@ const {
   printComments,
   printDanglingComments,
 } = require("../../main/comments.js");
-const { getLast } = require("../../common/util.js");
+const { getLast, isNonEmptyArray } = require("../../common/util.js");
 const {
   builders: { group, join, line, softline, indent, align, ifBreak },
 } = require("../../document/index.js");
@@ -287,15 +287,21 @@ function printFunctionType(path, options, print) {
 function printTupleType(path, options, print) {
   const node = path.getValue();
   const typesField = node.type === "TSTupleType" ? "elementTypes" : "types";
-  const hasRest =
-    node[typesField].length > 0 &&
-    getLast(node[typesField]).type === "TSRestType";
+  const types = node[typesField];
+  const isNonEmptyTuple = isNonEmptyArray(types);
+  const hasRest = isNonEmptyTuple && getLast(types).type === "TSRestType";
+  const bracketsDelimiterLine = isNonEmptyTuple ? softline : "";
   return group([
     "[",
-    indent([softline, printArrayItems(path, options, typesField, print)]),
-    ifBreak(shouldPrintComma(options, "all") && !hasRest ? "," : ""),
+    indent([
+      bracketsDelimiterLine,
+      printArrayItems(path, options, typesField, print),
+    ]),
+    ifBreak(
+      isNonEmptyTuple && shouldPrintComma(options, "all") && !hasRest ? "," : ""
+    ),
     printDanglingComments(path, options, /* sameIndent */ true),
-    softline,
+    bracketsDelimiterLine,
     "]",
   ]);
 }

diff --git a/tests/format/typescript/tuple/__snapshots__/jsfmt.spec.js.snap b/tests/format/typescript/tuple/__snapshots__/jsfmt.spec.js.snap
@@ -208,6 +208,71 @@ export interface ShopQueryResult {
 ================================================================================
 `;
 
+exports[`trailing-comma-for-empty-tuples.ts - {"trailingComma":"all"} format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+trailingComma: "all"
+                                                                                | printWidth
+=====================================input======================================
+type Loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong = []
+
+type Foo = Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends [] ? Foo3 : Foo4;
+=====================================output=====================================
+type Loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong =
+  [];
+
+type Foo =
+  Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends []
+    ? Foo3
+    : Foo4;
+
+================================================================================
+`;
+
+exports[`trailing-comma-for-empty-tuples.ts - {"trailingComma":"none"} format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+trailingComma: "none"
+                                                                                | printWidth
+=====================================input======================================
+type Loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong = []
+
+type Foo = Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends [] ? Foo3 : Foo4;
+=====================================output=====================================
+type Loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong =
+  [];
+
+type Foo =
+  Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends []
+    ? Foo3
+    : Foo4;
+
+================================================================================
+`;
+
+exports[`trailing-comma-for-empty-tuples.ts format 1`] = `
+====================================options=====================================
+parsers: ["typescript"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+type Loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong = []
+
+type Foo = Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends [] ? Foo3 : Foo4;
+=====================================output=====================================
+type Loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong =
+  [];
+
+type Foo =
+  Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends []
+    ? Foo3
+    : Foo4;
+
+================================================================================
+`;
+
 exports[`tuple.ts - {"trailingComma":"all"} format 1`] = `
 ====================================options=====================================
 parsers: ["typescript"]

diff --git a/tests/format/typescript/tuple/trailing-comma-for-empty-tuples.ts b/tests/format/typescript/tuple/trailing-comma-for-empty-tuples.ts
@@ -0,0 +1,3 @@
+type Loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong = []
+
+type Foo = Foooooooooooooooooooooooooooooooooooooooooooooooooooooooooo extends [] ? Foo3 : Foo4;