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fix(2.0): niche cases for DCE #2161

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fix(2.0): niche cases for DCE #2161

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21 changes: 18 additions & 3 deletions packages/start/src/directives/remove-unused-variables.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,20 @@ import type * as babel from "@babel/core";
import * as t from "@babel/types";
import { isPathValid } from "./paths.ts";

function isInvalidForRemoval(path: babel.NodePath) {
if (isPathValid(path, t.isCatchClause)) {
// This case is for `catch (error)` blocks
return true;
}

// This one is for destructured variables
let target = path;
if (isPathValid(path, t.isVariableDeclarator)) {
target = path.get('id');
}
return isPathValid(target, t.isObjectPattern) || isPathValid(target, t.isArrayPattern);
}

export function removeUnusedVariables(program: babel.NodePath<t.Program>) {
// TODO(Alexis):
// This implementation is simple but slow
Expand All @@ -24,17 +38,18 @@ export function removeUnusedVariables(program: babel.NodePath<t.Program>) {
case "hoisted":
case "module":
if (binding.references === 0 && !binding.path.removed) {
if (isPathValid(binding.path.parentPath, t.isImportDeclaration)) {
const parent = binding.path.parentPath;
if (isPathValid(parent, t.isImportDeclaration)) {
if (parent.node.specifiers.length === 1) {
parent.remove();
} else {
binding.path.remove();
}
} else {
dirty = true;
} else if (!(isInvalidForRemoval(binding.path))) {
binding.path.remove();
dirty = true;
}
dirty = true;
}
break;
case "local":
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