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Rewrite
transform-block-scoping plugin (#15200)
* Add test for `const` with `tdz` * Rewrite block-scoping plugin * Update block-scoping fixtures * Update other fixtures * Fix `let` shadowing variable read in a sibling scope * Update fixtures * Update Babel 8 fixtures * Add minNodeVersion * Fix block scoped vars shadowing globals * Review by JLHwung * minNodeVersion to class fields test
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127
packages/babel-plugin-transform-block-scoping/src/annex-B_3_3.ts
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,127 @@ | ||
| import { types as t } from "@babel/core"; | ||
| import type { NodePath, Visitor, Scope } from "@babel/traverse"; | ||
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| // Whenever a function declaration in a nested block scope | ||
| // doesn't conflict with a block-scoped binding from an outer | ||
| // scope, we transform it to a variable declaration. | ||
| // | ||
| // This implements the Annex B.3.3 behavior. | ||
| // | ||
| // TODO(Babel 8): Figure out how this should interact with | ||
| // the transform-block-scoped functions plugin (it feels | ||
| // wrong to handle this transform here), and what we want | ||
| // to do with Anned B behavior in general. | ||
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| // To avoid confusing block-scoped variables transformed to | ||
| // var with original vars, this transformation happens in two | ||
| // different places: | ||
| // 1. For functions that "conflict" with var-variables, in | ||
| // the VariableDeclaration visitor. | ||
| // 2. For functions that don't conflict with any variable, | ||
| // in the FunctionDeclaration visitor. | ||
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| export const annexB33FunctionsVisitor: Visitor = { | ||
| VariableDeclaration(path) { | ||
| if (isStrict(path)) return; | ||
| if (path.node.kind !== "var") return; | ||
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| const varScope = | ||
| path.scope.getFunctionParent() || path.scope.getProgramParent(); | ||
| // eslint-disable-next-line @typescript-eslint/no-use-before-define | ||
| varScope.path.traverse(functionsToVarVisitor, { | ||
| names: Object.keys(path.getBindingIdentifiers()), | ||
| }); | ||
| }, | ||
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| // NOTE: These two visitors target the same nodes as the | ||
| // block-scoped-functions plugin | ||
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| BlockStatement(path) { | ||
| if (isStrict(path)) return; | ||
| if (t.isFunction(path.parent, { body: path.node })) return; | ||
| transformStatementList(path.get("body")); | ||
| }, | ||
|
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| SwitchCase(path) { | ||
| if (isStrict(path)) return; | ||
| transformStatementList(path.get("consequent")); | ||
| }, | ||
| }; | ||
|
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| function transformStatementList(paths: NodePath<t.Statement>[]) { | ||
| outer: for (const path of paths) { | ||
| if (!path.isFunctionDeclaration()) continue; | ||
| // Annex B.3.3 only applies to plain functions. | ||
| if (path.node.async || path.node.generator) return; | ||
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| const { scope } = path.parentPath; | ||
| if (isVarScope(scope)) return; | ||
|
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| const { name } = path.node.id; | ||
| let currScope = scope; | ||
| do { | ||
| if (currScope.parent.hasOwnBinding(name)) continue outer; | ||
| currScope = currScope.parent; | ||
| } while (!isVarScope(currScope)); | ||
|
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| maybeTransformBlockScopedFunction(path); | ||
| } | ||
| } | ||
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| function maybeTransformBlockScopedFunction( | ||
| path: NodePath<t.FunctionDeclaration>, | ||
| ) { | ||
| const { | ||
| node, | ||
| parentPath: { scope }, | ||
| } = path; | ||
|
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| const { id } = node; | ||
| scope.removeOwnBinding(id.name); | ||
| node.id = null; | ||
|
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| const varNode = t.variableDeclaration("var", [ | ||
| t.variableDeclarator(id, t.toExpression(node)), | ||
| ]); | ||
| // @ts-expect-error undocumented property | ||
| varNode._blockHoist = 2; | ||
|
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| const [varPath] = path.replaceWith(varNode); | ||
| scope.registerDeclaration(varPath); | ||
| } | ||
|
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| const functionsToVarVisitor: Visitor<{ names: string[] }> = { | ||
| Scope(path, { names }) { | ||
| for (const name of names) { | ||
| const binding = path.scope.getOwnBinding(name); | ||
| if (binding && binding.kind === "hoisted") { | ||
| maybeTransformBlockScopedFunction( | ||
| binding.path as NodePath<t.FunctionDeclaration>, | ||
| ); | ||
| } | ||
| } | ||
| }, | ||
| "Expression|Declaration"(path) { | ||
| path.skip(); | ||
| }, | ||
| }; | ||
|
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| export function isVarScope(scope: Scope) { | ||
| return scope.path.isFunctionParent() || scope.path.isProgram(); | ||
| } | ||
|
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| function isStrict(path: NodePath) { | ||
| return !!path.find(({ node }) => { | ||
| if (t.isProgram(node)) { | ||
| if (node.sourceType === "module") return true; | ||
| } else if (t.isClass(node)) { | ||
| return true; | ||
| } else if (!t.isBlockStatement(node)) { | ||
| return false; | ||
| } | ||
|
|
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| return node.directives?.some( | ||
| directive => directive.value.value === "use strict", | ||
| ); | ||
| }); | ||
| } |
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