Prettier 2.3. In which assignments are consistent, short keys non-breaking, and Handlebars official

This release focuses on fixing long-standing issues in the JavaScript printer. Be warned that, unfortunately, reformatting a project with the new version might result in quite a big diff. If you don’t use ignoreRevsFile to hide such wholesale changes from git blame, it might be about time.

A remarkable milestone is the long-awaited release of the Ember / Handlebars formatter. It’s supposed to be the last formatter included directly in the core library. In the future, for sustainability, languages should be added only by plugins.

We are grateful to our financial contributors: Salesforce, Indeed, Frontend Masters, Airbnb, Shogun Labs, Skyscanner, Konstantin Pschera, and many others who help us keep going. If you enjoy Prettier and would like to support our work, head to our OpenCollective. Please consider also supporting the projects Prettier depends on, such as typescript-eslint, remark, and Babel.

Most of the changes in this release are thanks to the hard work of Fisker Cheung, Georgii Dolzhykov, and Sosuke Suzuki, along with many other contributors.

And just a reminder, when Prettier is installed or updated, it’s strongly recommended to specify the exact version in package.json: "2.3.0", not "^2.3.0".

Highlights

JavaScript

Format assignments more consistently (#10222, #10643, #10672 by @thorn0; #10158 by @sosukesuzuki)

Previously, Prettier had a lot of trouble with figuring out how to break lines in assignments. E.g., long right-hand sides often stayed unbroken. Not anymore.

// Prettier 2.2
aParticularlyLongAndObnoxiousNameForIllustrativePurposes = anotherVeryLongNameForIllustrativePurposes;

aParticularlyLongAndObnoxiousNameForIllustrativePurposes = "a very long string for illustrative purposes"
  .length;

someReallyLongThingStoredInAMapWithAReallyBigName[
  pageletID
] = _someVariableThatWeAreCheckingForFalsiness
  ? Date.now() - _someVariableThatWeAreCheckingForFalsiness
  : 0;

class x {
  private readonly rawConfigFromFile$: BehaviorSubject<any> = new BehaviorSubject(
    notRead
  );
}

// Prettier 2.3
aParticularlyLongAndObnoxiousNameForIllustrativePurposes =
  anotherVeryLongNameForIllustrativePurposes;

aParticularlyLongAndObnoxiousNameForIllustrativePurposes =
  "a very long string for illustrative purposes".length;

someReallyLongThingStoredInAMapWithAReallyBigName[pageletID] =
  _someVariableThatWeAreCheckingForFalsiness
    ? Date.now() - _someVariableThatWeAreCheckingForFalsiness
    : 0;

class x {
  private readonly rawConfigFromFile$: BehaviorSubject<any> =
    new BehaviorSubject(notRead);
}

Prevent wrapping object properties with short keys (#10335 by @thorn0)

Line breaks after short property names in object literals often look unnatural. Even when such a line break yields a line length benefit of 1 or 2 characters, it rarely looks justified. Prettier 2.3 avoids line breaks after property names shorter than tabWidth + 3 – for example, 5 characters in the default configuration, or 7 characters with tabWidth: 4. This heuristic may be revised in future versions.

// Prettier 2.2
const importantLink = {
  url:
    "https://prettier.io/docs/en/rationale.html#what-prettier-is-concerned-about",
  gitHubUrl:
    "https://github.com/prettier/prettier/blob/main/docs/rationale.md#what-prettier-is-concerned-about",
};

// Prettier 2.3
const importantLink = {
  url: "https://prettier.io/docs/en/rationale.html#what-prettier-is-concerned-about",
  gitHubUrl:
    "https://github.com/prettier/prettier/blob/main/docs/rationale.md#what-prettier-is-concerned-about",
};

Ember / Handlebars

Move Handlebars support out of alpha to release (#10290 by @dcyriller & @thorn0)

This started in 2017. Handlebars support has been in Prettier for a while, but it wasn’t released officially as it wasn’t really ready. Its status went from “alpha” to “experimental” to “beta” and then, if you checked older release notes, you can see that after “beta” somehow it was “alpha” again…

Well, anyway, it finally is happening: Prettier can now officially format HTML templates with Handlebars! 🎉

It uses Glimmer, Ember’s Handlebars parser, so it should be compliant with the HTML spec thanks to the Ember team.

The --html-whitespace-sensitivity option is supported and defaults to strict, which means that Prettier will always respect the presence or absence of whitespace around tags and consider it unsafe to add whitespace where there were none and vice versa as this can affect how the document is rendered in the browser. The css value is not yet supported (treated as strict for now).

The feature is called “Ember / Handlebars” and not just “Handlebars” because Glimmer doesn’t support some syntax and use cases of Handlebars. This is mostly due to the fact that Handlebars, being a template engine (a preprocessor), doesn’t care about the underlying syntax of the content it processes whereas Glimmer parses two syntaxes – HTML and Handlebars – at the same time and combines the result into a single tree, which Prettier can print. This means Prettier won’t format Handlebars files that can’t be parsed into such a tree, either because the underlying syntax isn’t HTML or because template directives and tags overlap in a way that can’t be represented in a tree (e.g., {{#if foo}}<div>{{/if}). Even with these restrictions, the formatter still seems to be useful enough to non-Ember Handlebars users. As for the syntax unsupported by Ember, there is a good chance to see support for it in future versions of Prettier as Glimmer uses a full-fledged Handlebars parser under the hood.

Files with the extensions .hbs and .handlebars are recognized as Handlebars by default. For other extensions, the --parser option with the value glimmer has to be specified – for example, using command line or, better yet, configuration overrides.

See the formatter in action on the playground!

Formatting Improvements

JavaScript

Refine formatting of curried arrow functions (#9992, #10543 by @sosukesuzuki & @thorn0)

// Prettier 2.2
const currying = (argument1) => (argument2) => (argument3) => (argument4) => (
  argument5
) => (argument6) => foo;

// Prettier 2.3
const currying =
  (argument1) =>
  (argument2) =>
  (argument3) =>
  (argument4) =>
  (argument5) =>
  (argument6) =>
    foo;

Improve formatting for React Hooks calls (#10238 by @sosukesuzuki)

// Prettier 2.2
const { firstName, lastName } = useMemo(() => parseFullName(fullName), [
  fullName,
]);

// Prettier 2.3
const { firstName, lastName } = useMemo(
  () => parseFullName(fullName),
  [fullName]
);

Improve visual separation between header and body in classes with multiline headers (#10085 by @sosukesuzuki)

// Prettier 2.2
class loooooooooooooooooooong
  extends looooooooooooooooooong
  implements loooooooooooooooooooong {
  property: string;
}

// Prettier 2.3
class loooooooooooooooooooong
  extends looooooooooooooooooong
  implements loooooooooooooooooooong
{
  property: string;
}

Concise formatting of number-only arrays (#10106, #10160 by @thorn0)

While in general, Prettier avoids this kind of formatting because it's not diff-friendly, in this special case we decided that the benefits outweigh the risks.

If at least one element has a trailing single-line (// ...) comment on the same line, the concise formatting isn't applied. On the other hand, single-line comments placed on separate lines don't have such an effect and – as well as empty lines – can be used for logical grouping.

jsx

// Input
const lazyCatererNumbers  =  [1, 2, 4, 7, 11, 16, 22, 29, 37, 46,

// n > 10
56, 67, 79, 92, 106, 121, 137, 154, 172, 191, 211, 232, 254, 277, 301, 326, 352, 379, 407, 436, 466,
497, 529, 562, 596, 631, 667, 704, 742, 781,
// n > 40
821, 862, 904, 947, 991, 1036, 1082, 1129, 1177, 1226, 1276, 1327, 1379];

// Prettier 2.2
const lazyCatererNumbers = [
  1,
  2,
  4,
  7,
  11,
  16,
  22,
  29,
  37,
  // ... ✂ 46 lines ✂ ...
  1379,
];

// Prettier 2.3
const lazyCatererNumbers = [
  1, 2, 4, 7, 11, 16, 22, 29, 37, 46,

  // n > 10
  56, 67, 79, 92, 106, 121, 137, 154, 172, 191, 211, 232, 254, 277, 301, 326,
  352, 379, 407, 436, 466, 497, 529, 562, 596, 631, 667, 704, 742, 781,
  // n > 40
  821, 862, 904, 947, 991, 1036, 1082, 1129, 1177, 1226, 1276, 1327, 1379,
];

Improve formatting for nested await expressions in heads of member and call expressions (#10342 by @thorn0)

Even though Prettier tries to be helpful here, please don't write code like this. Have mercy upon your teammates and use intermediate variables.

jsx

// Input
const getAccountCount = async () =>
  (await
    (await (
      await focusOnSection(BOOKMARKED_PROJECTS_SECTION_NAME)
    ).findItem("My bookmarks")).getChildren()
  ).length

// Prettier 2.2
const getAccountCount = async () =>
  (
    await (
      await (await focusOnSection(BOOKMARKED_PROJECTS_SECTION_NAME)).findItem(
        "My bookmarks"
      )
    ).getChildren()
  ).length;

// Prettier 2.3
const getAccountCount = async () =>
  (
    await (
      await (
        await focusOnSection(BOOKMARKED_PROJECTS_SECTION_NAME)
      ).findItem("My bookmarks")
    ).getChildren()
  ).length;

Improve formatting for `do` expressions in function calls (#10693 by @sosukesuzuki)

“do expressions” are a stage 1 ECMAScript proposal.

// Prettier 2.2
expect(
  do {
    var bar = "foo";
    bar;
  }
).toBe("foo");

// Prettier 2.3
expect(do {
  var bar = "foo";
  bar;
}).toBe("foo");

Consistent indentation for conditional operators (#10187, #10266 by @sosukesuzuki)

// Prettier 2.2
const dotNotationMemberExpression = (callNode.parent?.type ===
AST_NODE_TYPES.ChainExpression
  ? callNode.parent.parent
  : callNode.parent
).TSESTree.BinaryExpression;

const computedMemberExpression = (callNode.parent?.type ===
AST_NODE_TYPES.ChainExpression
  ? callNode.parent.parent
  : callNode.parent)[TSESTree.BinaryExpression];

const callExpressionCallee = (callNode.parent?.type ===
  AST_NODE_TYPES.ChainExpression
  ? callNode.parent.parent
  : callNode.parent)(TSESTree.BinaryExpression);

const typeScriptAsExpression = (callNode.parent?.type ===
AST_NODE_TYPES.ChainExpression
  ? callNode.parent.parent
  : callNode.parent) as TSESTree.BinaryExpression;

// Prettier 2.3
const dotNotationMemberExpression = (
  callNode.parent?.type === AST_NODE_TYPES.ChainExpression
    ? callNode.parent.parent
    : callNode.parent
).TSESTree.BinaryExpression;

const computedMemberExpression = (
  callNode.parent?.type === AST_NODE_TYPES.ChainExpression
    ? callNode.parent.parent
    : callNode.parent
)[TSESTree.BinaryExpression];

const callExpressionCallee = (
  callNode.parent?.type === AST_NODE_TYPES.ChainExpression
    ? callNode.parent.parent
    : callNode.parent
)(TSESTree.BinaryExpression);

const typeScriptAsExpression = (
  callNode.parent?.type === AST_NODE_TYPES.ChainExpression
    ? callNode.parent.parent
    : callNode.parent
) as TSESTree.BinaryExpression;

HTML

Prefix-based multiline formatting for the `class` attribute (#7865 by @thorn0)

Formatting of HTML class names will now keep classes on one line until the line length limit is reached; at that point, consecutive classes with the same prefix will be grouped together on each line. For layout frameworks such as Bootstrap and Tailwind CSS, which add many classes to an element, this is important for readability and maintainability vs. the previous behavior (keeping all classes on one line) or e.g. putting each class on its own line.

html

<!-- Prettier 2.2 -->
<div
  class="SomeComponent__heading-row d-flex flex-column flex-lg-row justify-content-start justify-content-lg-between align-items-start align-items-lg-center"
></div>

<!-- Prettier 2.3 -->
<div
  class="
    SomeComponent__heading-row
    d-flex
    flex-column flex-lg-row
    justify-content-start justify-content-lg-between
    align-items-start align-items-lg-center
  "
></div>

Other Changes

JavaScript

Fix unstable multiple comments on the same line (#9672 by @fisker)

// Input
a;
/*1*//*2*/
/*3*/
b;

// Prettier 2.2
a; /*2*/
/*1*/ /*3*/
b;

// Prettier 2.2 (second format)
a; /*2*/ /*3*/
/*1*/ b;

// Prettier 2.3
a;
/*1*/ /*2*/
/*3*/
b;

Don’t format nodes that end just before `rangeStart` (#9704 by @fisker)

Previously, when range formatting was performed, such nodes were considered part of the range, now they're excluded. This affects other languages that the range formatting feature supports, not only JavaScript.

// Input
foo = 1.0000;bar = 1.0000;baz=1.0000;
             ^^^^^^^^^^^^^ Range

// Prettier 2.2
foo = 1.0;
bar = 1.0;baz=1.0000;

// Prettier 2.3
foo = 1.0000;bar = 1.0;baz=1.0000;

Fix comments inside JSX end tag (#9711 by @fisker)

jsx

// Input
<a><// comment
/a>;

// Prettier 2.2
<a></// comment
a>;

// Prettier 2.3
<a></
  // comment
  a
>;

Fix inconsistent language comment detection (#9743 by @fisker)

An /* HTML */ comment should directly precede a template literal for the latter to be recognized as HTML-in-JS. Previously, the comment was erroneously recognized is some other locations.

jsx

// Input
foo /* HTML */ = `<DIV>
</DIV>`;

// Prettier 2.2 (--parser=babel)
foo /* HTML */ = `<div></div>`;

// Prettier 2.2 (--parser=meriyah)
foo /* HTML */ = `<DIV>
</DIV>`;

// Prettier 2.3 (All JavaScript parsers)
foo /* HTML */ = `<DIV>
</DIV>`;

Fix extra semicolon added to ignored directives (#9850 by @fisker)

// Input
// prettier-ignore
'use strict';

function foo() {
// prettier-ignore
"use strict";;
}

// Prettier 2.2
// prettier-ignore
'use strict';;

function foo() {
  // prettier-ignore
  "use strict";;
}

// Prettier 2.3
// prettier-ignore
'use strict';

function foo() {
  // prettier-ignore
  "use strict";
}

Fix unstable JSX formatting with U+3000 (#9866 by @fisker)

// Input
<p>
  <span />　{this.props.data.title}　<span />
  //----- ^ U+3000 --------------- ^ U+3000
</p>

// Prettier 2.2
<p>
  <span />
  　{this.props.data.title}　<span />
  //----- ^ U+3000 --------------- ^ U+3000
</p>;

// Prettier 2.2 (second format)
<p>
  <span />　{this.props.data.title}　<span />
  //----- ^ U+3000 --------------- ^ U+3000
</p>;

// Prettier 2.3
<p>
  <span />　{this.props.data.title}　<span />
  //----- ^ U+3000 --------------- ^ U+3000
</p>;

Fix error thrown on expressions like `a(b => c => function (){})` (#10278 by @thorn0)

Regression from v2.2.0.

jsx

// Input
a(b => c => function (){})

// Prettier 2.2
TypeError: Cannot read property 'length' of undefined

// Prettier 2.3
a((b) => (c) => function () {});

Improve formatting for inline decorators (#10296 by @fisker)

jsx

// Input
class Foo {
  @decorator([]) bar() {}
  @decorator(
    []
  ) baz() {}
}

// Prettier 2.2
class Foo {
  @decorator([]) bar() {}
  @decorator([])
  baz() {}
}

// Prettier 2.3
class Foo {
  @decorator([]) bar() {}
  @decorator([]) baz() {}
}

Fix ASI protection for private fields (#10334 by @thorn0)

jsx

// Input
class C {
  #field = 'value';
  ["method"]() {}
}

// Prettier 2.2 (with --no-semi)
class C {
  #field = "value"
  ["method"]() {}
}

// Prettier 2.3 (with --no-semi)
class C {
  #field = "value";
  ["method"]() {}
}

Support Module Blocks proposal (#10417 by @sosukesuzuki, @thorn0)

Support formatting for Module Blocks Stage 2 proposal.

// Input
module { export let foo = "foo"; };

// Prettier 2.2
SyntaxError: Unexpected token, expected ";"

// Prettier 2.3
module {
  export let foo = "foo";
};

Fix missing parentheses for `yield` in a pipeline (#10446 by @fisker)

jsx

// Input
function* f() {
  return x |> (yield #);
}

// Prettier 2.2
function* f() {
  return x |> yield #;
}

// Prettier 2.3
function* f() {
  return x |> (yield #);
}

Make Babel’s error recovery more selective (#10495 by @fisker, #9787 by @sosukesuzuki, #10065, #10322 by @thorn0)

Previously, because of the error recovery, the Babel parser was too permissive, which lead to all kinds of AST shapes that Prettier couldn’t print. Prettier 2.3 lets Babel recover only from a few harmless types of errors – for example, multiple const declarations with the same name. Anything else is reported as syntax errors.

// Input
foo("a", , "b");

// Prettier 2.2
TypeError: Cannot read property 'type' of null

// Prettier 2.3
[error] stdin: SyntaxError: Argument expression expected. (1:10)
[error] > 1 | foo("a", , "b");
[error]     |          ^

// Input
const \u{20} = 1

// Prettier 2.2
const   = 1;

// Prettier 2.3
[error] stdin: SyntaxError: Invalid Unicode escape (1:7)
[error] > 1 | const \u{20} = 1
[error]     |       ^         ^

Avoid last-argument hugging for number-only arrays (#10517 by @thorn0)

Another special case for number-only arrays.

jsx

// Input
instantiate(game, [
  transform([-0.7, 0.5, 0]),
  render_colored_diffuse(game.MaterialDiffuse, game.Meshes["monkey_flat"], [1, 1, 0.3, 1]),
]);

// Prettier 2.2
instantiate(game, [
  transform([-0.7, 0.5, 0]),
  render_colored_diffuse(game.MaterialDiffuse, game.Meshes["monkey_flat"], [
    1,
    1,
    0.3,
    1,
  ]),
]);

// Prettier 2.3
instantiate(game, [
  transform([-0.7, 0.5, 0]),
  render_colored_diffuse(
    game.MaterialDiffuse,
    game.Meshes["monkey_flat"],
    [1, 1, 0.3, 1]
  ),
]);

Improve detection of AMD `define` (#10528 by @thorn0)

Prettier special-cases AMD define calls to avoid unexpected line breaks in them. We now only format define calls if they are at the top level of a function or program and are passed arguments in the way AMD expects.

jsx

// Prettier 2.2
const someVariable = define("some string literal", anotherVariable, yetAnotherVariable);

// Prettier 2.3
const someVariable = define(
  "some string literal",
  anotherVariable,
  yetAnotherVariable
);

Fix duplicated `prettier-ignore` comments (#10666 by @fisker)

jsx

// Input
foo = a.
  // prettier-ignore
  b;

// Prettier 2.2
foo =
  // prettier-ignore
  a.
  // prettier-ignore
  b;

// Prettier 2.3
foo = a.
  // prettier-ignore
  b;

Process conditional groups in `mapDoc` (#10695 by @thorn0)

In particular, this fixes broken substitutions in HTML-in-JS.

jsx

// Input
export default function include_photoswipe(
	gallery_selector = ".my-gallery"
): string {
	return /* HTML */ `
		<script>
			window.addEventListener("load", () =>
				initPhotoSwipeFromDOM("${gallery_selector}")
			);
		</script>`;
}

// Prettier 2.2
export default function include_photoswipe(
  gallery_selector = ".my-gallery"
): string {
  return /* HTML */ ` <script>
    window.addEventListener("load", () =>
      initPhotoSwipeFromDOM("PRETTIER_HTML_PLACEHOLDER_0_13_IN_JS")
    );
  </script>`;
}

// Prettier 2.3
export default function include_photoswipe(
  gallery_selector = ".my-gallery"
): string {
  return /* HTML */ ` <script>
    window.addEventListener("load", () =>
      initPhotoSwipeFromDOM("${gallery_selector}")
    );
  </script>`;
}

Avoid arg expansion that leads to broken code (#10712 by @thorn0)

jsx

// Input
glimseGlyphsHazardNoopsTieTie(({ a, b = () => {
  console.log();
}}) => averredBathersBoxroomBuggyNurl());

// Prettier 2.2
glimseGlyphsHazardNoopsTieTie(({ a, b = () => {
    console.log();
  } }) => averredBathersBoxroomBuggyNurl());

// Prettier 2.3
glimseGlyphsHazardNoopsTieTie(
  ({
    a,
    b = () => {
      console.log();
    },
  }) => averredBathersBoxroomBuggyNurl()
);

Fix missing parentheses around `async` in `for-of` (#10781 by @fisker)

See https://github.com/tc39/ecma262/issues/2034

jsx

// Input
for ((async) of []);

// Prettier 2.2
for (async of []);

// Prettier 2.2 (second format)
SyntaxError: Unexpected token, expected "=>" (1:15)
> 1 | for (async of []);

// Prettier 2.3
for ((async) of []);

Support `async do` expressions proposal (#10813 by @sosukesuzuki)

See https://github.com/tc39/proposal-async-do-expressions

// Input
const x = async do {
  await requestAPI().json();
};

// Prettier 2.2
SyntaxError: Unexpected token, expected ";" (1:17)

// Prettier 2.3
const x = async do {
  await requestAPI().json();
};

TypeScript

Fix missing comments in `MethodDefinition` (#9872 by @fisker)

typescript parser only, babel-ts doesn't have this issue.

// Input
class Foo {
  bar() /* bat */;
}

// Prettier 2.2
Error: Comment "bat" was not printed. Please report this error!

// Prettier 2.3
class Foo {
  bar /* bat */();
}

Fix unnecessary line breaks in method type declaration parameters (#10024 by @sosukesuzuki, #10357 by @thorn0)

// Input
type Foo = {
  method(foo: "foo"): `
  `
};

// Prettier 2.2
type Foo = {
  method(
    foo: "foo"
  ): `
  `;
};

// Prettier 2.3
type Foo = {
  method(foo: "foo"): `
  `;
};

Print trailing commas in type parameters (#10109 by @sosukesuzuki, #10353 by @thorn0)

TypeScript has been supporting trailing commas in type parameters since TypeScript 2.7 released in January 2018. Prettier 2.3 prints them if the trailingComma option is set to all. Keep this option at the more conservative default value es5 if compatibility with TypeScript 2.7 or older is needed. Note that TypeScript still doesn't support trailing commas in type arguments (type parameter instantiations).

// Input
export class BaseSingleLevelProfileTargeting<
	T extends ValidSingleLevelProfileNode,
> {
  // ...
}

// Prettier 2.2
export class BaseSingleLevelProfileTargeting<
  T extends ValidSingleLevelProfileNode
> {
  // ...
}

// Prettier 2.3 with --trailling-comma=all
export class BaseSingleLevelProfileTargeting<
  T extends ValidSingleLevelProfileNode,
> {
  // ...
}

Allow hugging arguments that are non-concise arrow functions with return type annotations (#10316 by @thorn0)

// Prettier 2.2
users.map(
  (user: User): User => {
    return user;
  }
);

// Prettier 2.3
users.map((user: User): User => {
  return user;
})

Correct parentheses for non-null assertions (#10337 by @thorn0)

Necessary parentheses sometimes weren't printed in expressions containing non-null assertions. This has been fixed.

// Input
const myFunction2 = (key: string): number =>
  ({
    a: 42,
    b: 42,
  }[key]!)

// Prettier 2.2 (invalid syntax)
const myFunction2 = (key: string): number =>
  {
    a: 42,
    b: 42,
  }[key]!;

// Prettier 2.3
const myFunction2 = (key: string): number =>
  ({
    a: 42,
    b: 42,
  }[key]!);

Indent type assertions in heads of member and call expressions (#10341 by @thorn0)

// Input
const accountCount = (findItemInSection(BOOKMARKED_PROJECTS_SECTION_NAME,
  "My bookmarks") as TreeItem).getChildren().length;

// Prettier 2.2
const accountCount = (findItemInSection(
  BOOKMARKED_PROJECTS_SECTION_NAME,
  "My bookmarks"
) as TreeItem).getChildren().length;

// Prettier 2.3
const accountCount = (
  findItemInSection(
    BOOKMARKED_PROJECTS_SECTION_NAME,
    "My bookmarks"
  ) as TreeItem
).getChildren().length;

Support intrinsic keyword (#10390 by @sosukesuzuki)

// Input
type Uppercase<S extends string> = intrinsic;

// Prettier 2.2
Error: unknown type: "TSIntrinsicKeyword"

// Prettier 2.3
type Uppercase<S extends string> = intrinsic;

Support TypeScript 4.2 (#10418, #10466, #10546, #10589 by @sosukesuzuki)

`abstract` Construct Signatures

// Input
type T = abstract new () => void;

// Prettier 2.2
SyntaxError: Unexpected token, expected ";" (1:19)

// Prettier 2.3
type T = abstract new () => void;

Type imports in import require declaration

// Input
import type A = require("A");

// Prettier 2.2
SyntaxError: Only ECMAScript imports may use 'import type'.

// Prettier 2.3
import type A = require("A");

Fix misplaced comments in unions and intersections (#10457 by @thorn0)

// Input
type Foo = "1" | "2" /* two */ | "3";

// Prettier 2.2
type Foo = "1" | "2" | /* two */ "3";

// Prettier 2.3
type Foo = "1" | "2" /* two */ | "3";

Don’t print parens around nested type assertions (#10702 by @thorn0)

// Input
foo as unknown as Bar

// Prettier 2.2
(foo as unknown) as Bar;

// Prettier 2.3
foo as unknown as Bar;

Support TypeScript 4.3 via `babel-ts` (#10811 by @sosukesuzuki)

`override` modifiers in class elements

class Foo extends  {
  override method() {}
}

static index signatures (`[key: KeyType]: ValueType`) in classes

class Foo {
  static [key: string]: Bar;
}

`get` / `set` in type declarations

interface Foo {
  set foo(value);
  get foo(): string;
}

Flow

Fix missing semicolon in `declare export * from …` (#9767 by @fisker)

jsx

// Input
declare export * from "ES6_ExportAllFrom_Source2";

// Prettier 2.2
declare export * from "ES6_ExportAllFrom_Source2"

// Prettier 2.3
declare export * from "ES6_ExportAllFrom_Source2";

Support `this` type annotation in functions via `babel-flow` (#10397 by @sosukesuzuki)

this type annotation is supported since Babel 7.13.

// Input
var foo: (this: boolean) => void;

// Prettier 2.2
SyntaxError: Unexpected token, expected ")" (1:15)

// Prettier 2.3
var foo: (this: boolean) => void;

Fix range formatting issues (#10505 by @thorn0)

Prettier had trouble formatting some ranges in function declarations. SyntaxError was thrown. Prettier 2.3 formats these cases without errors. Examples of problematic ranges are shown below:

jsx

declare export function graphql<Props, Variables, Component: React$ComponentType<Props>>
  //                            ^^^^^ range 1
  (query: GQLDocument, config?: Config<Props, QueryConfigOptions<Variables>>):
  (Component: Component) => React$ComponentType<$Diff<React$ElementConfig<Component>, {
    data: Object|void,
    //           ^^^^ range 2
    mutate: Function|void
  }>>

Support for Flow's indexed access type (#10594 by @gkz)

// Input
const x: Obj['foo'] = 1;

// Prettier 2.2
// Error: unsupported node type "IndexedAccessType"

// Prettier 2.3
const x: Obj["foo"] = 1;

Support for Flow's optional indexed access type (#10788 by @gkz)

// Input
type T = Obj?.['foo'];

// Prettier 2.2
// Error: unsupported node type "OptionalIndexedAccessType"

// Prettier 2.3
type T = Obj?.['foo'];

JSON

Don't use smart quotes for JSON5 with `--quote-props=preserve` (#10323 by @thorn0)

With the quoteProps option set to preserve and singleQuotes to false (default), double quotes are always used for printing strings, including situations like "bla\"bla". This effectively allows using --parser json5 for "JSON with comments and trailing commas".

// Input
{
  "char": "\"",
}

// Prettier 2.2
{
  "char": '"',
}

// Prettier 2.3
{
  "char": "\"",
}

Stricter JSON parser (#10346, #10443, #10456, #10434 by @fisker)

Prettier internally uses a JavaScript expression parser to parse JSON. That's why the json and json5 parsers used to be very forgiving and allowed all kinds of JavaScript expressions. Now they are much stricter, although some simple non-standard syntax is still allowed (e.g., JSON6 is supported, except for multiple minus signs: ----123).

// Input
[1, 2, 1 + 2]

// Prettier 2.2
[1, 2, 1 + 2]

// Prettier 2.3
SyntaxError: BinaryExpression is not allowed in JSON. (1:8)
> 1 | [1, 2, 1 + 2]
    |        ^

Improve error message (#10433 by @fisker)

// Input
{key: "foo" + "bar"}

// Prettier 2.2 (--parser=json-stringify)
SyntaxError: BinaryExpression is not allowed in JSON. (1:7)
> 1 | {key: "foo" + "bar"}
    |       ^

// Prettier 2.3
SyntaxError: BinaryExpression is not allowed in JSON. (1:7)
> 1 | {key: "foo" + "bar"}
    |       ^^^^^^^^^^^^^

Fix syntax error on JSON range formatting (#10497 by @fisker)

// Input
[{ a: 1.0000}, {"b":   2.0000 }]
//                 ^^^^^^^^^^^ range

// Prettier 2.2
SyntaxError: Unexpected token (1:4)
> 1 | "b":   2.0000
    |    ^

// Prettier 2.3
[{ a: 1.0000}, { "b": 2.0 }]

CSS

Fix absolute path in custom CSS `-custom-url()` calls (#9966 by @vjeux)

The CSS parser is parsing this as ["division", "absolute/path"] instead of a single "/absolute/path" token unless you are in a url() call. Because we put space after division, it results in an incorrect path. The fix was to avoid printing a space if a division is the first token of a call, which hopefully should be safe.

css

/* Input */
-custom-url(/absolute/path)

/* Prettier 2.2 */
-custom-url(/ absolute/path)

/* Prettier 2.3 */
-custom-url(/absolute/path)

Exclude `@keyframes` params from being parsed as a Less variable (#10773 by @tmazeika)

css

/* Input */
@keyframes :global(spin) {
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(360deg);
  }
}

/* Prettier 2.2 */
@keyframes: global(spin){
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(360deg);
  }
};

/* Prettier 2.3 */
@keyframes :global(spin) {
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(360deg);
  }
}

SCSS

Fix broken comment inside parens (#9710 by @fisker)

scss

// Input
.simplification {
  foo: (
    calc() // not a comment anymore
  );
}

// Prettier 2.2
.simplification {
  foo: (calc() // not a comment anymore);
}

// Prettier 2.3
.simplification {
  foo: (
    calc() // not a comment anymore
  );
}

Fix maps with keys that are lists or maps (#10005 by @fisker)

scss

// Input
$map: (
  ('my list'): 'hello world',
);

// Prettier 2.2
TypeError: Cannot read property 'length' of undefined

// Prettier 2.3
$map: (
  ("my list"): "hello world",
);

Ember / Handlebars

Preserve tilde comments (#9082 by @kangax, @fisker)

hbs

{{!-- Input --}}
{{~! Comment }}
{{! Comment ~}}
{{~! Comment ~}}

{{!-- Prettier 2.2 --}}
{{! Comment }}
{{! Comment }}
{{! Comment }}

{{!-- Prettier 2.3 --}}
{{~! Comment }}
{{! Comment ~}}
{{~! Comment ~}}

Add a whitespace sensitive mode (#9885 by @dcyriller)

--html-whitespace-sensitivity strict

hbs

{{!-- Input --}}
<span>123 {{mustache}}</span>
<span>
123 {{mustache}}</span>
<span>123 {{mustache}}
</span>
<span>
123 {{mustache}}
</span>

{{!-- Prettier 2.2 --}}
<span>
  123 {{mustache}}
</span>
<span>
  123 {{mustache}}
</span>
<span>
  123 {{mustache}}
</span>
<span>
  123 {{mustache}}
</span>

{{!-- Prettier 2.3 --}}
<span>123 {{mustache}}</span>
<span>
  123
  {{mustache}}</span>
<span>123
  {{mustache}}
</span>
<span>
  123
  {{mustache}}
</span>

Print final `blockParam` on its own line (#9978 by @dcyriller)

hbs

{{!-- Input --}}
<MyComponent @prop={{true}} @prop2={{true}} @prop3={{true}} @prop4={{true}} as |thing|></MyComponent>
{{#block param hashKey=hashValue hashKey=hashValue hashKey=hashValue as |blockParam|}}
  Hello
{{/block}}

{{!-- Prettier 2.2 --}}
<MyComponent
  @prop={{true}}
  @prop2={{true}}
  @prop3={{true}}
  @prop4={{true}} as |thing|
/>
{{#block
  param
  hashKey=hashValue
  hashKey=hashValue
  hashKey=hashValue as |blockParam|
}}
  Hello
{{/block}}

{{!-- Prettier 2.3 --}}
<MyComponent
  @prop={{true}}
  @prop2={{true}}
  @prop3={{true}}
  @prop4={{true}}
  as |thing|
/>
{{#block
  param
  hashKey=hashValue
  hashKey=hashValue
  hashKey=hashValue
  as |blockParam|
}}
  Hello
{{/block}}

Fix formatting of attributes (#10145 by @thorn0)

fix escaping of {{ in attributes and text
fix the choice between ' and " for attributes with interpolations
fix the bug with [object Object] printed in the class attribute
implement simple formatting for the class attribute, like Prettier formatted it in HTML before v2.3.0

hbs

{{!-- Input --}}
<div class="
foo"></div>
<div bar='"{{expr}}"'></div>
<div baz="\{{ non-expression }}"></div>

{{!-- Prettier 2.2 --}}
<div class="[object Object],foo"></div>
<div bar=""{{expr}}""></div>
<div baz="{{ non-expression }}"></div>

{{!-- Prettier 2.3 --}}
<div class="foo"></div>
<div bar='"{{expr}}"'></div>
<div baz="\{{ non-expression }}"></div>

Split text content on multiple lines (#10179 by @dcyriller)

handlebars

{{!-- Input --}}
<div>
  A long enough string to trigger a line break that would prevent wrapping more and more.
</div>

{{!-- Prettier 2.2 --}}
<div>
  A long enough string to trigger a line break that would prevent wrapping more and more.
</div>

{{!-- Prettier 2.3 --}}
<div>
  A long enough string to trigger a line break that would prevent wrapping more
  and more.
</div>

Preserve numeric character references (#10550 by @rwjblue and @thorn0)

hbs

{{! Input }}
<span class="stampFont" style="font-family: 'stampfont'">&#xf000;</span>

{{! Prettier 2.2 }}
<span class="stampFont" style="font-family: 'stampfont'"></span>

{{! Prettier 2.3 }}
<span class="stampFont" style="font-family: 'stampfont'">&#xf000;</span>

Do not break opening mustache and path (#10586 by @dcyriller)

handlebars

{{!-- Input --}}
<GlimmerComponent
  @errors={{or this.aVeryLongProperty (and this.aProperty (v-get bike "number" "message"))}}
  data-test-beneficiary-account-number
/>
<GlimmerComponent
  @progress={{aPropertyEngdingAfterEightiethColumnToHighlightAWeirdClosingParenIssue}}
/>

{{!-- Prettier 2.2 --}}
<GlimmerComponent
  @errors={{
    or
    this.aVeryLongProperty
    (and this.aProperty (v-get bike "number" "message"))
  }}
  data-test-beneficiary-account-number
/>
<GlimmerComponent
  @progress={{
    aPropertyEngdingAfterEightiethColumnToHighlightAWeirdClosingParenIssue
  }}
/>

{{!-- Prettier 2.3 --}}
<GlimmerComponent
  @errors={{or
    this.aLongProperty
    (and this.aProperty (v-get bike "number" "message"))
  }}
  data-test-beneficiary-account-number
/>
<GlimmerComponent
  @progress={{aPropertyEngdingAfterEightiethColumnToHighlightAWeirdClosingParenIssue}}
/>

GraphQL

Fix missing space after keyword in anonymous operations (#10689 by @patriscus)

graphql

# Input
query ($unnamed: String) {
  id
}

# Prettier 2.2
query($unnamed: String) {
  id
}

# Prettier 2.3
query ($unnamed: String) {
  id
}

Markdown

Fix extra newline at the end of JavaScript fenced code block with string literal (#9736 by @fisker)

markdown

<!-- Input -->
Markdown

```js
"· "
```

<!-- Prettier 2.2 -->
Markdown

```js
"· ";

```

<!-- Prettier 2.3 -->
Markdown

```js
"· ";
```

Fix empty front matter formatting (#9791 by @fisker)

markdown

<!-- Input -->
---
---

# Title

a|b|c|
|:--|:-:|--:|
|d|e|f|

---

text

<!-- Prettier 2.2 -->
---
---
# Title

a|b|c|
|:--|:-:|--:|
|d|e|f|
---

text

<!-- Prettier 2.3 -->
---
---

# Title

| a   |  b  |   c |
| :-- | :-: | --: |
| d   |  e  |   f |

---

text

Support YAML document end marker in front matter (#9878 by @michaelbeaumont)

Add the ability to delimit the end of front matter with ....

markdown

<!-- Input -->
---
title: Hello
slug: home
...

Markdown

<!-- Prettier 2.2 -->
---

title: Hello
slug: home
...

Markdown

<!-- Prettier 2.3 -->
---
title: Hello
slug: home
...

Markdown

YAML

Fix SyntaxError incorrectly thrown on anchors followed by empty lines (#10516 by @eemeli & @thorn0)

Prettier couldn't parse this valid YAML. Thanks to Eemeli Aro for fixing this bug in the underlying parser.

yaml

# Input
key1: &default

  subkey1: value1

key2:
  <<: *default

# Prettier 2.2
SyntaxError: Nested mappings are not allowed in compact mappings (1:7)

# Prettier 2.3
key1: &default
  subkey1: value1

key2:
  <<: *default

API

Treat `.prettierrc` as YAML when formatting it (#8105 by @fisker)

The .prettierrc file can be written in either JSON or YAML. Previously, when Prettier formatted it, the parser was inferred to be json, which lead to a SyntaxError thrown if the content was YAML. Now it’s treated as a YAML file. However, if it's JSON, it will be formatted as JSON (not as JSON-like YAML).

Use arrays instead of `concat` (#9733 by @fisker, @thorn0)

To simplify the code of AST printers, the data structure for the concatenation command has been changed from { type: 'concat', parts: Doc[] } to Doc[]. The old format is deprecated, but for compatibility, the doc printer still supports it, and doc.builders.concat (as well as some other builder functions) will keep using it until the next major version of Prettier.

If you're a plugin author, this change should only concern you if your plugin introspects or modifies composed docs. If it happens to be the case, please make your plugin compatible with future versions of Prettier by tweaking the introspecting code to support the new format. There also is an off-chance where this change can break things, namely if a plugin calls another plugin to print an embedded language and then introspects the returned doc. There seems to be no reason for plugins to do that though.

To replace concat(…) calls in your plugins, you can try auto-fix by this ESLint rule prettier-doc/no-concat.

jsx

// Prettier 2.2
myDoc = group(concat(["foo", line, "bar"]));

// Prettier 2.3
myDoc = group(["foo", line, "bar"]);

Fix `lineSuffixBoundary` IR command (#10122 by @thorn0)

There was a bug in the implementation of the lineSuffixBoundary command that significantly limited its usefulness: the printer algorithm didn't correctly consider it a potential line break. Now that the bug has been fixed, we urge plugin authors to give this command another try and see if it can help them simplify printing of trailing comments.

jsx

// Input
group([
  "let foo = [",
  indent([
    softline,
    [lineSuffixBoundary, "item1,"],
    line,
    [lineSuffixBoundary, "item2,", lineSuffix(" // comment")],
    line,
    [lineSuffixBoundary, "item3"],
  ]),
  softline,
  "];",
])

// Prettier 2.2
let foo = [item1, item2,  // comment
  item3];

// Prettier 2.3
let foo = [
  item1,
  item2, // comment
  item3
];

Add `indentIfBreak` IR command (#10221 by @thorn)

indentIfBreak(doc, { groupId }) is an optimized version of ifBreak(indent(doc), doc, { groupId }).

Simplified `print` callback (#10557 by @fisker)

The third argument of the print method of plugin printers (the print callback) has been updated. Its first argument can be a string or an array of strings now.

To print the current node, call print without arguments:

diff

 function print(path, options, print) {
   const parts = [];
   path.each((childPath) => {
-    parts.push(print(childPath));
+    parts.push(print());
   }, "children");
   return parts;
 }

To print a property of the current node, use "property" or ["property"]:

diff

 function print(path, options, print) {
-  return path.call(print, "property");
+  return print("property");
 }

To print a sub-property of the current node, use ["property1", "property2"]:

diff

 function print(path, options, print) {
   // print `node.child.child`
-  return path.call(print, "child", "child");
+  return print(["child", "child"]);
 }

CLI

Add CLI option to prevent errors on unmatched pattern (#10058 by @daronmcintosh)

The Prettier CLI will no longer display an error when no files match the glob pattern passed as input.

# Prettier 2.2
$ npx prettier --check "prettier/docs/*.yaml"
Checking formatting...
[error] No files matching the pattern were found: "prettier/docs/*.yaml".
All matched files use Prettier code style!

# Prettier 2.3
$ npx prettier --check --no-error-on-unmatched-pattern "prettier/docs/*.yaml"
Checking formatting...
All matched files use Prettier code style!

Add CLI flag for debugging comment attachment issues (#10124 by @thorn0)

A new --debug-print-comments CLI flag and corresponding functionality for the Playground.

Round-trippable `--debug-print-doc` (#10169, #10177 by @thorn0)

The idea is to make the output of --debug-print-doc closer to actual code for generating docs (Prettier's intermediate representation). Ideally, it should be possible for it to work without modification after copy-pasting into a JS file. That ideal hasn't probably been reached by this PR, but it's pretty close. This is going to make --debug-print-doc and the corresponding part of the Playground a bit more useful.

Print an error message when `--find-config-path` can't find config file (#10208 by @fisker)

console

# Prettier 2.2
$ prettier --find-config-path /prettier.js
# Silently failed

# Prettier 2.3
$ prettier --find-config-path /prettier.js
[error] Can not find configure file for "/prettier.js"

Clear printed long filenames of formatting file (#10217 by @fisker)

console

# Prettier 2.2
$ prettier tests/flow-repo/config_module_system_node_resolve_dirname --check
Checking formatting...
tests\flow-repo\config_module_system_node_resolve_dirname\custom_resolve_dir\tes
tests\flow-repo\config_module_system_node_resolve_dirname\custom_resolve_dir\tes
tests\flow-repo\config_module_system_node_resolve_dirname\subdir\custom_resolve_
All matched files use Prettier code style!

# Prettier 2.3
$ prettier tests/flow-repo/config_module_system_node_resolve_dirname --check
Checking formatting...
All matched files use Prettier code style!

Don't skip file paths containing special words like `constructor` (#10256 by @ashlkv)

Directories whose names happened to coincide with the properties of Object.prototype were ignored by Prettier CLI because of a classic bug (introduced in Prettier 2.0.0) with object properties not being checked for being own.

console

# Prettier 2.2
$ prettier "js/constructor/*.js" --write
[error] No matching files. Patterns: js/constructor/*.js

# Prettier 2.3
$ prettier "js/constructor/*.js" --write
js/constructor/test.js 42ms

Highlights

JavaScript

Format assignments more consistently (#10222, #10643, #10672 by @thorn0; #10158 by @sosukesuzuki)

Prevent wrapping object properties with short keys (#10335 by @thorn0)

Ember / Handlebars

Move Handlebars support out of alpha to release (#10290 by @dcyriller & @thorn0)

Formatting Improvements

JavaScript

Refine formatting of curried arrow functions (#9992, #10543 by @sosukesuzuki & @thorn0)

Improve formatting for React Hooks calls (#10238 by @sosukesuzuki)

Improve visual separation between header and body in classes with multiline headers (#10085 by @sosukesuzuki)

Concise formatting of number-only arrays (#10106, #10160 by @thorn0)

Improve formatting for nested await expressions in heads of member and call expressions (#10342 by @thorn0)

Improve formatting for do expressions in function calls (#10693 by @sosukesuzuki)

Consistent indentation for conditional operators (#10187, #10266 by @sosukesuzuki)

HTML

Prefix-based multiline formatting for the class attribute (#7865 by @thorn0)

Other Changes

JavaScript

Fix unstable multiple comments on the same line (#9672 by @fisker)

Don’t format nodes that end just before rangeStart (#9704 by @fisker)

Fix comments inside JSX end tag (#9711 by @fisker)

Fix inconsistent language comment detection (#9743 by @fisker)

Fix extra semicolon added to ignored directives (#9850 by @fisker)

Fix unstable JSX formatting with U+3000 (#9866 by @fisker)

Fix error thrown on expressions like a(b => c => function (){}) (#10278 by @thorn0)

Improve formatting for inline decorators (#10296 by @fisker)

Fix ASI protection for private fields (#10334 by @thorn0)

Support Module Blocks proposal (#10417 by @sosukesuzuki, @thorn0)

Fix missing parentheses for yield in a pipeline (#10446 by @fisker)

Make Babel’s error recovery more selective (#10495 by @fisker, #9787 by @sosukesuzuki, #10065, #10322 by @thorn0)

Avoid last-argument hugging for number-only arrays (#10517 by @thorn0)

Improve detection of AMD define (#10528 by @thorn0)

Fix duplicated prettier-ignore comments (#10666 by @fisker)

Process conditional groups in mapDoc (#10695 by @thorn0)

Avoid arg expansion that leads to broken code (#10712 by @thorn0)

Fix missing parentheses around async in for-of (#10781 by @fisker)

Support async do expressions proposal (#10813 by @sosukesuzuki)

TypeScript

Fix missing comments in MethodDefinition (#9872 by @fisker)

Fix unnecessary line breaks in method type declaration parameters (#10024 by @sosukesuzuki, #10357 by @thorn0)

Print trailing commas in type parameters (#10109 by @sosukesuzuki, #10353 by @thorn0)

Allow hugging arguments that are non-concise arrow functions with return type annotations (#10316 by @thorn0)

Correct parentheses for non-null assertions (#10337 by @thorn0)

Indent type assertions in heads of member and call expressions (#10341 by @thorn0)

Support intrinsic keyword (#10390 by @sosukesuzuki)

Support TypeScript 4.2 (#10418, #10466, #10546, #10589 by @sosukesuzuki)

abstract Construct Signatures

Type imports in import require declaration

Fix misplaced comments in unions and intersections (#10457 by @thorn0)

Don’t print parens around nested type assertions (#10702 by @thorn0)

Support TypeScript 4.3 via babel-ts (#10811 by @sosukesuzuki)

override modifiers in class elements

static index signatures ([key: KeyType]: ValueType) in classes

get / set in type declarations

Flow

Fix missing semicolon in declare export * from … (#9767 by @fisker)

Support this type annotation in functions via babel-flow (#10397 by @sosukesuzuki)

Fix range formatting issues (#10505 by @thorn0)

Support for Flow's indexed access type (#10594 by @gkz)

Support for Flow's optional indexed access type (#10788 by @gkz)

JSON

Don't use smart quotes for JSON5 with --quote-props=preserve (#10323 by @thorn0)

Stricter JSON parser (#10346, #10443, #10456, #10434 by @fisker)

Improve error message (#10433 by @fisker)

Fix syntax error on JSON range formatting (#10497 by @fisker)

CSS

Fix absolute path in custom CSS -custom-url() calls (#9966 by @vjeux)

Exclude @keyframes params from being parsed as a Less variable (#10773 by @tmazeika)

SCSS

Fix broken comment inside parens (#9710 by @fisker)

Fix maps with keys that are lists or maps (#10005 by @fisker)

Ember / Handlebars

Preserve tilde comments (#9082 by @kangax, @fisker)

Add a whitespace sensitive mode (#9885 by @dcyriller)

Print final blockParam on its own line (#9978 by @dcyriller)

Fix formatting of attributes (#10145 by @thorn0)

Split text content on multiple lines (#10179 by @dcyriller)

Preserve numeric character references (#10550 by @rwjblue and @thorn0)

Improve formatting for `do` expressions in function calls (#10693 by @sosukesuzuki)

Prefix-based multiline formatting for the `class` attribute (#7865 by @thorn0)

Don’t format nodes that end just before `rangeStart` (#9704 by @fisker)

Fix error thrown on expressions like `a(b => c => function (){})` (#10278 by @thorn0)

Fix missing parentheses for `yield` in a pipeline (#10446 by @fisker)

Improve detection of AMD `define` (#10528 by @thorn0)

Fix duplicated `prettier-ignore` comments (#10666 by @fisker)

Process conditional groups in `mapDoc` (#10695 by @thorn0)

Fix missing parentheses around `async` in `for-of` (#10781 by @fisker)

Support `async do` expressions proposal (#10813 by @sosukesuzuki)

Fix missing comments in `MethodDefinition` (#9872 by @fisker)

`abstract` Construct Signatures

Support TypeScript 4.3 via `babel-ts` (#10811 by @sosukesuzuki)

`override` modifiers in class elements

static index signatures (`[key: KeyType]: ValueType`) in classes

`get` / `set` in type declarations

Fix missing semicolon in `declare export * from …` (#9767 by @fisker)

Support `this` type annotation in functions via `babel-flow` (#10397 by @sosukesuzuki)

Don't use smart quotes for JSON5 with `--quote-props=preserve` (#10323 by @thorn0)

Fix absolute path in custom CSS `-custom-url()` calls (#9966 by @vjeux)

Exclude `@keyframes` params from being parsed as a Less variable (#10773 by @tmazeika)

Print final `blockParam` on its own line (#9978 by @dcyriller)

Treat `.prettierrc` as YAML when formatting it (#8105 by @fisker)

Use arrays instead of `concat` (#9733 by @fisker, @thorn0)

Fix `lineSuffixBoundary` IR command (#10122 by @thorn0)

Add `indentIfBreak` IR command (#10221 by @thorn)

Simplified `print` callback (#10557 by @fisker)

Round-trippable `--debug-print-doc` (#10169, #10177 by @thorn0)

Print an error message when `--find-config-path` can't find config file (#10208 by @fisker)

Don't skip file paths containing special words like `constructor` (#10256 by @ashlkv)