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Support TypeScript const enums #13324

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merged 6 commits into from
Aug 3, 2021
Merged

Support TypeScript const enums #13324

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933ba59
Compile `const enum` as normal enums
nicolo-ribaudo May 17, 2021
9f709ff
[ts] Introduce `optimizeConstEnums` option to inline const enums
nicolo-ribaudo May 17, 2021
2d82724
Add option to the preset
nicolo-ribaudo May 17, 2021
e37c002
Update test
nicolo-ribaudo May 17, 2021
3301a7c
Update packages/babel-preset-typescript/test/normalize-options.spec.js
nicolo-ribaudo May 17, 2021
2831419
Move option validation
nicolo-ribaudo May 17, 2021
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89 changes: 89 additions & 0 deletions packages/babel-plugin-transform-typescript/src/const-enum.ts
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@@ -0,0 +1,89 @@
import type * as t from "@babel/types";
import type { NodePath } from "@babel/traverse";

import { translateEnumValues } from "./enum";

export default function transpileConstEnum(
path: NodePath<t.TSEnumDeclaration & { const: true }>,
t: typeof import("@babel/types"),
) {
const { name } = path.node.id;

const parentIsExport = path.parentPath.isExportNamedDeclaration();
let isExported = parentIsExport;
if (!isExported && t.isProgram(path.parent)) {
isExported = path.parent.body.some(
stmt =>
t.isExportNamedDeclaration(stmt) &&
!stmt.source &&
stmt.specifiers.some(
spec => t.isExportSpecifier(spec) && spec.local.name === name,
),
);
}

const entries = translateEnumValues(path, t);

if (isExported) {
const obj = t.objectExpression(
entries.map(([name, value]) =>
t.objectProperty(
t.isValidIdentifier(name)
? t.identifier(name)
: t.stringLiteral(name),
value,
),
),
);

if (path.scope.hasOwnBinding(name)) {
(parentIsExport ? path.parentPath : path).replaceWith(
t.expressionStatement(
t.callExpression(
t.memberExpression(t.identifier("Object"), t.identifier("assign")),
[path.node.id, obj],
),
),
);
} else {
path.replaceWith(
t.variableDeclaration("var", [t.variableDeclarator(path.node.id, obj)]),
);
path.scope.registerDeclaration(path);
}

return;
}

const entriesMap = new Map(entries);

// TODO: After fixing https://github.com/babel/babel/pull/11065, we can
// use path.scope.getBinding(name).referencePaths rather than doing
// a full traversal.
path.scope.path.traverse({
Scope(path) {
if (path.scope.hasOwnBinding(name)) path.skip();
},
MemberExpression(path) {
if (!t.isIdentifier(path.node.object, { name })) return;

let key: string;
if (path.node.computed) {
if (t.isStringLiteral(path.node.property)) {
key = path.node.property.value;
} else {
return;
}
} else if (t.isIdentifier(path.node.property)) {
key = path.node.property.name;
} else {
return;
}
if (!entriesMap.has(key)) return;

path.replaceWith(t.cloneNode(entriesMap.get(key)));
},
});

path.remove();
}
8 changes: 4 additions & 4 deletions packages/babel-plugin-transform-typescript/src/enum.ts
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Expand Up @@ -5,9 +5,6 @@ import type { NodePath } from "@babel/traverse";

export default function transpileEnum(path, t) {
const { node } = path;
if (node.const) {
throw path.buildCodeFrameError("'const' enums are not supported.");
}

if (node.declare) {
path.remove();
Expand Down Expand Up @@ -105,7 +102,10 @@ type PreviousEnumMembers = {
[name: string]: number | string;
};

function translateEnumValues(path, t) {
export function translateEnumValues(
path: NodePath<t.TSEnumDeclaration>,
t: typeof import("@babel/types"),
): Array<[name: string, value: t.Expression]> {
const seen: PreviousEnumMembers = Object.create(null);
// Start at -1 so the first enum member is its increment, 0.
let prev: number | typeof undefined = -1;
Expand Down
8 changes: 7 additions & 1 deletion packages/babel-plugin-transform-typescript/src/index.ts
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Expand Up @@ -3,6 +3,7 @@ import syntaxTypeScript from "@babel/plugin-syntax-typescript";
import { types as t, template } from "@babel/core";
import { injectInitialization } from "@babel/helper-create-class-features-plugin";

import transpileConstEnum from "./const-enum";
import transpileEnum from "./enum";
import transpileNamespace from "./namespace";
import type { NodePath } from "@babel/traverse";
Expand Down Expand Up @@ -56,6 +57,7 @@ export default declare((api, opts) => {
jsxPragma = "React.createElement",
jsxPragmaFrag = "React.Fragment",
onlyRemoveTypeImports = false,
optimizeConstEnums = false,
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Can we default it to true in next minor? I know we have onlyRemoveTypeImports default to true in Babel 8, but supporting new language features should be opt-in by default, like we did for other ES features.

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I'm not sure we should.

In TypeScript with --isolatedModules, code like this works and logs x:

const enum A {
  x
}

// @ts-expect-error
console.log(A[A.x]);

export {};

However, with optimizeConstEnums it stops working because we don't ignore const anymore.

For the default behavior, I'd prefer to match --isolatedModules as closely as possible where it's easy to do so.

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Interesting, I think it should be a TS issue, they could have optimized the const enums here.

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TypeScript docs mentions why ambient const enums (ie. declare const enum) don't work with isolatedModules.

When isolatedModules: false, it seems const enum and declare const enum function the same.

When isolatedModules: true, it seems const enum transpiles as if it was just enum since you get the reverse-mapped object. declare const enum transpiles into the usual empty output, because it's expected to be inlined. However, the isolatedModules: true will produce error:

Cannot access ambient const enums when the '--isolatedModules' flag is provided.(2748)

No idea why they only document declare const enum and not const enum. But I assume their reasoning of converting const enum to just enum is to have it work across modules. And I guess they treat declare const enum as an error since you are explicitly saying it is ambient.

Anyway, @nicolo-ribaudo. I'm not familiar with babel code, but did you make sure you also support declare const enum when optimizeConstEnums: true? When isolatedModules: false, declare const enum seems to function the same as const enum, so you can just strip the declare.

Also, if we want to copy TypeScript functionality with isolatedModules: true and optimizeConstEnums: false, should we transpile const enum by treating it as enum ie. transpile it to the reverse-mapped object instead of throwing an error?

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The default Babel behavior is to match --isolatedModules (as mentioned in our docs at the 4th caveat).

Thus, this PR makes it so that by default const enums are compiled to "normal" enums, which also matches the default behavior of your babel-plugin-const-enum plugin. It's implemented in 933ba59 (#13324).

With optimizeConstEnums: true the plugin seems to correctly work: https://github.com/babel/babel/pull/13324/files#diff-d0d0efefe2a94935f80a8f399bbca77e2a0fbbc8e7a3ba2a1a2f07eff7bcb0de. When optimizeConstEnums: false, it produces some broken output:

declare const enum Animal {
  Dog,
  Cat
}
let x: Animal = Animal.Dog;

// becomes

let x = Animal.Dog;

however, I'm not too much concerned about it because:

  • It's exactly the same output that TS generates with --isolatedMoudles
  • TypeScript will report a type-checking error saying that declare const enum are not supported.

} = opts;

if (!process.env.BABEL_8_BREAKING) {
Expand Down Expand Up @@ -420,7 +422,11 @@ export default declare((api, opts) => {
},

TSEnumDeclaration(path) {
transpileEnum(path, t);
if (optimizeConstEnums && path.node.const) {
transpileConstEnum(path, t);
} else {
transpileEnum(path, t);
}
},

TSImportEqualsDeclaration(path) {
Expand Down
1 change: 0 additions & 1 deletion ...ages/babel-plugin-transform-typescript/test/fixtures/declarations/const-enum/options.json
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3 changes: 3 additions & 0 deletions ...babel-plugin-transform-typescript/test/fixtures/declarations/export-declare-enum/input.ts
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export declare enum A {}

;
3 changes: 3 additions & 0 deletions ...l-plugin-transform-typescript/test/fixtures/declarations/export-declare-enum/options.json
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{
"sourceType": "module"
}
1 change: 1 addition & 0 deletions ...bel-plugin-transform-typescript/test/fixtures/declarations/export-declare-enum/output.mjs
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;
3 changes: 2 additions & 1 deletion packages/babel-plugin-transform-typescript/test/fixtures/enum/const/input.ts
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@@ -1 +1,2 @@
const enum E {}
// With --isolatedModules, TSC ignores the "const" modifier when compiling enums
const enum E {}
1 change: 0 additions & 1 deletion packages/babel-plugin-transform-typescript/test/fixtures/enum/const/options.json
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4 changes: 4 additions & 0 deletions packages/babel-plugin-transform-typescript/test/fixtures/enum/const/output.js
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// With --isolatedModules, TSC ignores the "const" modifier when compiling enums
var E;

(function (E) {})(E || (E = {}));
11 changes: 11 additions & 0 deletions ...n-transform-typescript/test/fixtures/optimize-const-enums/custom-values-exported/input.ts
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export const enum A {
x = 3,
y = "f",
z = 4 << 2,
w = y
}

A.x;
A.y;
A.z;
A.w;
10 changes: 10 additions & 0 deletions ...transform-typescript/test/fixtures/optimize-const-enums/custom-values-exported/output.mjs
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export var A = {
x: 3,
y: "f",
z: 16,
w: "f"
};
A.x;
A.y;
A.z;
A.w;
11 changes: 11 additions & 0 deletions ...bel-plugin-transform-typescript/test/fixtures/optimize-const-enums/custom-values/input.ts
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const enum A {
x = 3,
y = "f",
z = 4 << 2,
w = y
}

A.x;
A.y;
A.z;
A.w;
4 changes: 4 additions & 0 deletions ...l-plugin-transform-typescript/test/fixtures/optimize-const-enums/custom-values/output.mjs
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3;
"f";
16;
"f";
3 changes: 3 additions & 0 deletions ...ges/babel-plugin-transform-typescript/test/fixtures/optimize-const-enums/declare/input.ts
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declare const enum A { x }

A.x;
1 change: 1 addition & 0 deletions ...s/babel-plugin-transform-typescript/test/fixtures/optimize-const-enums/declare/output.mjs
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0;
3 changes: 3 additions & 0 deletions ...plugin-transform-typescript/test/fixtures/optimize-const-enums/export-const-enum/input.ts
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export const enum A { y }

let x = A.y;
4 changes: 4 additions & 0 deletions ...ugin-transform-typescript/test/fixtures/optimize-const-enums/export-const-enum/output.mjs
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export var A = {
y: 0
};
let x = A.y;
5 changes: 5 additions & 0 deletions ...es/babel-plugin-transform-typescript/test/fixtures/optimize-const-enums/exported/input.ts
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const enum A { y }

let x = A.y;

export { A };
5 changes: 5 additions & 0 deletions .../babel-plugin-transform-typescript/test/fixtures/optimize-const-enums/exported/output.mjs
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var A = {
y: 0
};
let x = A.y;
export { A };
8 changes: 8 additions & 0 deletions ...el-plugin-transform-typescript/test/fixtures/optimize-const-enums/local-shadowed/input.ts
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const enum A { x }

{
let A = {};
A.x;
}

A.x;
5 changes: 5 additions & 0 deletions ...-plugin-transform-typescript/test/fixtures/optimize-const-enums/local-shadowed/output.mjs
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{
let A = {};
A.x;
}
0;
8 changes: 8 additions & 0 deletions packages/babel-plugin-transform-typescript/test/fixtures/optimize-const-enums/local/input.ts
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const enum A {
x, y
}

A.x;
A["y"];
A.z;
A;
4 changes: 4 additions & 0 deletions ...ges/babel-plugin-transform-typescript/test/fixtures/optimize-const-enums/local/output.mjs
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0;
1;
A.z;
A;
13 changes: 13 additions & 0 deletions ...l-plugin-transform-typescript/test/fixtures/optimize-const-enums/merged-exported/input.ts
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export const enum A {
x, y
}

export const enum A {
z
}

A.x;
A["y"];
A.z;
A.w;
A;
12 changes: 12 additions & 0 deletions ...plugin-transform-typescript/test/fixtures/optimize-const-enums/merged-exported/output.mjs
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export var A = {
x: 0,
y: 1
};
Object.assign(A, {
z: 0
});
A.x;
A["y"];
A.z;
A.w;
A;
13 changes: 13 additions & 0 deletions ...ages/babel-plugin-transform-typescript/test/fixtures/optimize-const-enums/merged/input.ts
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const enum A {
x, y
}

const enum A {
z
}

A.x;
A["y"];
A.z;
A.w;
A;
5 changes: 5 additions & 0 deletions ...es/babel-plugin-transform-typescript/test/fixtures/optimize-const-enums/merged/output.mjs
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0;
1;
0;
A.w;
A;
4 changes: 4 additions & 0 deletions packages/babel-plugin-transform-typescript/test/fixtures/optimize-const-enums/options.json
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{
"plugins": [["transform-typescript", { "optimizeConstEnums": true }]],
"sourceType": "module"
}
3 changes: 3 additions & 0 deletions packages/babel-preset-typescript/src/index.js
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Expand Up @@ -12,6 +12,7 @@ export default declare((api, opts) => {
jsxPragma,
jsxPragmaFrag,
onlyRemoveTypeImports,
optimizeConstEnums,
} = normalizeOptions(opts);

const pluginOptions = process.env.BABEL_8_BREAKING
Expand All @@ -21,6 +22,7 @@ export default declare((api, opts) => {
jsxPragma,
jsxPragmaFrag,
onlyRemoveTypeImports,
optimizeConstEnums,
})
: isTSX => ({
allowDeclareFields: opts.allowDeclareFields,
Expand All @@ -29,6 +31,7 @@ export default declare((api, opts) => {
jsxPragma,
jsxPragmaFrag,
onlyRemoveTypeImports,
optimizeConstEnums,
});

return {
Expand Down
14 changes: 13 additions & 1 deletion packages/babel-preset-typescript/src/normalize-options.js
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Expand Up @@ -2,7 +2,12 @@ import { OptionValidator } from "@babel/helper-validator-option";
const v = new OptionValidator("@babel/preset-typescript");

export default function normalizeOptions(options = {}) {
let { allowNamespaces = true, jsxPragma, onlyRemoveTypeImports } = options;
let {
allowNamespaces = true,
jsxPragma,
onlyRemoveTypeImports,
optimizeConstEnums,
} = options;

if (process.env.BABEL_8_BREAKING) {
const TopLevelOptions = {
Expand All @@ -12,6 +17,7 @@ export default function normalizeOptions(options = {}) {
jsxPragma: "jsxPragma",
jsxPragmaFrag: "jsxPragmaFrag",
onlyRemoveTypeImports: "onlyRemoveTypeImports",
optimizeConstEnums: "optimizeConstEnums",
};
v.validateTopLevelOptions(options, TopLevelOptions);
allowNamespaces = v.validateBooleanOption(
Expand All @@ -29,6 +35,11 @@ export default function normalizeOptions(options = {}) {
options.onlyRemoveTypeImports,
true,
);
optimizeConstEnums = v.validateBooleanOption(
TopLevelOptions.optimizeConstEnums,
options.optimizeConstEnums,
true,
);
}

const jsxPragmaFrag = v.validateStringOption(
Expand Down Expand Up @@ -56,5 +67,6 @@ export default function normalizeOptions(options = {}) {
jsxPragma,
jsxPragmaFrag,
onlyRemoveTypeImports,
optimizeConstEnums,
};
}
3 changes: 3 additions & 0 deletions packages/babel-preset-typescript/test/fixtures/opts/optimizeConstEnums/input.ts
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const enum A { x }

A.x;
1 change: 1 addition & 0 deletions packages/babel-preset-typescript/test/fixtures/opts/optimizeConstEnums/output.js
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0;
3 changes: 3 additions & 0 deletions packages/babel-preset-typescript/test/fixtures/opts/options.json
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{
"presets": [["typescript", { "optimizeConstEnums": true }]]
}