Flow: add support for inexact tuple types

changelog_unreleased/flow/16271.md

@@ -0,0 +1,15 @@
+#### Support Flow's inexact tuple types (#16271 by @gkz)
+
+Adds support for Flow's inexact tuple types.
+
+<!-- prettier-ignore -->
+```jsx
+// Input
+type T = [number, ...];
+
+// Prettier stable
+type T = [number];
+
+// Prettier main
+type T = [number, ...];
+```

src/language-js/print/array.js

@@ -29,11 +29,13 @@ import { printTypeAnnotationProperty } from "./type-annotation.js";
 
 function printEmptyArrayElements(path, options, openBracket, closeBracket) {
   const { node } = path;
+  const inexact = node.inexact ? "..." : "";
   if (!hasComment(node, CommentCheckFlags.Dangling)) {
-    return [openBracket, closeBracket];
+    return [openBracket, inexact, closeBracket];
   }
   return group([
     openBracket,
+    inexact,
     printDanglingComments(path, options, { indent: true }),
     softline,
     closeBracket,
@@ -68,7 +70,8 @@ function printArray(path, options, print) {
     );
   } else {
     const lastElem = elements.at(-1);
-    const canHaveTrailingComma = lastElem?.type !== "RestElement";
+    const canHaveTrailingComma =
+      lastElem?.type !== "RestElement" && !node.inexact;
 
     // JavaScript allows you to have empty elements in an array which
     // changes its length based on the number of commas. The algorithm
@@ -129,7 +132,13 @@ function printArray(path, options, print) {
             shouldUseConciseFormatting
               ? printArrayElementsConcisely(path, options, print, trailingComma)
               : [
-                  printArrayElements(path, options, elementsProperty, print),
+                  printArrayElements(
+                    path,
+                    options,
+                    elementsProperty,
+                    node.inexact,
+                    print,
+                  ),
                   trailingComma,
                 ],
             printDanglingComments(path, options),
@@ -183,13 +192,13 @@ function isLineAfterElementEmpty({ node }, { originalText: text }) {
   return isNextLineEmptyAfterIndex(text, skipToComma(locEnd(node)));
 }
 
-function printArrayElements(path, options, elementsProperty, print) {
+function printArrayElements(path, options, elementsProperty, inexact, print) {
   const parts = [];
 
   path.each(({ node, isLast }) => {
     parts.push(node ? group(print()) : "");
 
-    if (!isLast) {
+    if (!isLast || inexact) {
       parts.push([
         ",",
         line,
@@ -198,6 +207,10 @@ function printArrayElements(path, options, elementsProperty, print) {
     }
   }, elementsProperty);
 
+  if (inexact) {
+    parts.push("...");
+  }
+
   return parts;
 }
 

tests/format/flow/tuples/__snapshots__/format.test.js.snap

@@ -1,5 +1,33 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`inexact.js [babel-flow] format 1`] = `
+"Unexpected token (1:15)
+> 1 | type Empty = [...];
+    |               ^
+  2 |
+  3 | type One = [number, ...];
+  4 |
+Cause: Unexpected token (1:14)"
+`;
+
+exports[`inexact.js format 1`] = `
+====================================options=====================================
+parsers: ["flow"]
+printWidth: 80
+                                                                                | printWidth
+=====================================input======================================
+type Empty = [...];
+
+type One = [number, ...];
+
+=====================================output=====================================
+type Empty = [...];
+
+type One = [number, ...];
+
+================================================================================
+`;
+
 exports[`labeled.js [babel-flow] format 1`] = `
 "Unexpected token, expected "," (1:12)
 > 1 | type T = [a: string, b: number];

tests/format/flow/tuples/inexact.js

@@ -0,0 +1,3 @@
+type Empty = [...];
+
+type One = [number, ...];