packages/babel-helper-module-transforms/src/rewrite-live-references.js
import assert from "assert";
import * as t from "@babel/types";
import template from "@babel/template";
import simplifyAccess from "@babel/helper-simple-access";
import type { ModuleMetadata } from "./";
export default function rewriteLiveReferences(
programPath: NodePath,
metadata: ModuleMetadata,
) {
const imported = new Map();
const exported = new Map();
const requeueInParent = path => {
// Manualy re-queue `exports.default =` expressions so that the ES3
// transform has an opportunity to convert them. Ideally this would
// happen automatically from the replaceWith above. See #4140 for
// more info.
programPath.requeue(path);
};
for (const [source, data] of metadata.source) {
for (const [localName, importName] of data.imports) {
imported.set(localName, [source, importName, null]);
}
for (const localName of data.importsNamespace) {
imported.set(localName, [source, null, localName]);
}
}
for (const [local, data] of metadata.local) {
let exportMeta = exported.get(local);
if (!exportMeta) {
exportMeta = [];
exported.set(local, exportMeta);
}
exportMeta.push(...data.names);
}
// Rewrite initialization of bindings to update exports.
programPath.traverse(rewriteBindingInitVisitor, {
metadata,
requeueInParent,
scope: programPath.scope,
exported, // local name => exported name list
});
simplifyAccess(
programPath,
// NOTE(logan): The 'Array.from' calls are to make this code with in loose mode.
new Set([...Array.from(imported.keys()), ...Array.from(exported.keys())]),
);
// Rewrite reads/writes from imports and exports to have the correct behavior.
programPath.traverse(rewriteReferencesVisitor, {
seen: new WeakSet(),
metadata,
requeueInParent,
scope: programPath.scope,
imported, // local / import
exported, // local name => exported name list
buildImportReference: ([source, importName, localName], identNode) => {
const meta = metadata.source.get(source);
if (localName) {
if (meta.lazy) identNode = t.callExpression(identNode, []);
return identNode;
}
let namespace = t.identifier(meta.name);
if (meta.lazy) namespace = t.callExpression(namespace, []);
return t.memberExpression(namespace, t.identifier(importName));
},
});
}
/**
* A visitor to inject export update statements during binding initialization.
*/
const rewriteBindingInitVisitor = {
Scope(path) {
path.skip();
},
ClassDeclaration(path) {
const { requeueInParent, exported, metadata } = this;
const { id } = path.node;
if (!id) throw new Error("Expected class to have a name");
const localName = id.name;
const exportNames = exported.get(localName) || [];
if (exportNames.length > 0) {
const statement = t.expressionStatement(
buildBindingExportAssignmentExpression(
metadata,
exportNames,
t.identifier(localName),
),
);
statement._blockHoist = path.node._blockHoist;
requeueInParent(path.insertAfter(statement)[0]);
}
},
VariableDeclaration(path) {
const { requeueInParent, exported, metadata } = this;
Object.keys(path.getOuterBindingIdentifiers()).forEach(localName => {
const exportNames = exported.get(localName) || [];
if (exportNames.length > 0) {
const statement = t.expressionStatement(
buildBindingExportAssignmentExpression(
metadata,
exportNames,
t.identifier(localName),
),
);
statement._blockHoist = path.node._blockHoist;
requeueInParent(path.insertAfter(statement)[0]);
}
});
},
};
const buildBindingExportAssignmentExpression = (
metadata,
exportNames,
localExpr,
) => {
return (exportNames || []).reduce((expr, exportName) => {
// class Foo {} export { Foo, Foo as Bar };
// as
// class Foo {} exports.Foo = exports.Bar = Foo;
return t.assignmentExpression(
"=",
t.memberExpression(
t.identifier(metadata.exportName),
t.identifier(exportName),
),
expr,
);
}, localExpr);
};
const buildImportThrow = localName => {
return template.expression.ast`
(function() {
throw new Error('"' + '${localName}' + '" is read-only.');
})()
`;
};
const rewriteReferencesVisitor = {
ReferencedIdentifier(path) {
const {
seen,
buildImportReference,
scope,
imported,
requeueInParent,
} = this;
if (seen.has(path.node)) return;
seen.add(path.node);
const localName = path.node.name;
const localBinding = path.scope.getBinding(localName);
const rootBinding = scope.getBinding(localName);
// redeclared in this scope
if (rootBinding !== localBinding) return;
const importData = imported.get(localName);
if (importData) {
const ref = buildImportReference(importData, path.node);
// Preserve the binding location so that sourcemaps are nicer.
ref.loc = path.node.loc;
if (
(path.parentPath.isCallExpression({ callee: path.node }) ||
path.parentPath.isOptionalCallExpression({ callee: path.node }) ||
path.parentPath.isTaggedTemplateExpression({ tag: path.node })) &&
t.isMemberExpression(ref)
) {
path.replaceWith(t.sequenceExpression([t.numericLiteral(0), ref]));
} else if (path.isJSXIdentifier() && t.isMemberExpression(ref)) {
const { object, property } = ref;
path.replaceWith(
t.JSXMemberExpression(
t.JSXIdentifier(object.name),
t.JSXIdentifier(property.name),
),
);
} else {
path.replaceWith(ref);
}
requeueInParent(path);
// The path could have been replaced with an identifier that would
// otherwise be re-visited, so we skip processing its children.
path.skip();
}
},
AssignmentExpression: {
exit(path) {
const {
scope,
seen,
imported,
exported,
requeueInParent,
buildImportReference,
} = this;
if (seen.has(path.node)) return;
seen.add(path.node);
const left = path.get("left");
// No change needed
if (left.isMemberExpression()) return;
if (left.isIdentifier()) {
// Simple update-assign foo += 1; export { foo };
// => exports.foo = (foo += 1);
const localName = left.node.name;
// redeclared in this scope
if (scope.getBinding(localName) !== path.scope.getBinding(localName)) {
return;
}
const exportedNames = exported.get(localName);
const importData = imported.get(localName);
if (exportedNames?.length > 0 || importData) {
assert(path.node.operator === "=", "Path was not simplified");
const assignment = path.node;
if (importData) {
assignment.left = buildImportReference(importData, assignment.left);
assignment.right = t.sequenceExpression([
assignment.right,
buildImportThrow(localName),
]);
}
path.replaceWith(
buildBindingExportAssignmentExpression(
this.metadata,
exportedNames,
assignment,
),
);
requeueInParent(path);
}
} else {
const ids = left.getOuterBindingIdentifiers();
const programScopeIds = Object.keys(ids).filter(
localName =>
scope.getBinding(localName) === path.scope.getBinding(localName),
);
const id = programScopeIds.find(localName => imported.has(localName));
if (id) {
path.node.right = t.sequenceExpression([
path.node.right,
buildImportThrow(id),
]);
}
// Complex ({a, b, c} = {}); export { a, c };
// => ({a, b, c} = {}), (exports.a = a, exports.c = c);
const items = [];
programScopeIds.forEach(localName => {
const exportedNames = exported.get(localName) || [];
if (exportedNames.length > 0) {
items.push(
buildBindingExportAssignmentExpression(
this.metadata,
exportedNames,
t.identifier(localName),
),
);
}
});
if (items.length > 0) {
let node = t.sequenceExpression(items);
if (path.parentPath.isExpressionStatement()) {
node = t.expressionStatement(node);
node._blockHoist = path.parentPath.node._blockHoist;
}
const statement = path.insertAfter(node)[0];
requeueInParent(statement);
}
}
},
},
"ForOfStatement|ForInStatement"(path) {
const { scope, node } = path;
const { left } = node;
const { exported, scope: programScope } = this;
if (!t.isVariableDeclaration(left)) {
let didTransform = false;
const bodyPath = path.get("body");
const loopBodyScope = bodyPath.scope;
for (const name of Object.keys(t.getOuterBindingIdentifiers(left))) {
if (
exported.get(name) &&
programScope.getBinding(name) === scope.getBinding(name)
) {
didTransform = true;
if (loopBodyScope.hasOwnBinding(name)) {
loopBodyScope.rename(name);
}
}
}
if (!didTransform) {
return;
}
const newLoopId = scope.generateUidIdentifierBasedOnNode(left);
bodyPath.unshiftContainer(
"body",
t.expressionStatement(t.assignmentExpression("=", left, newLoopId)),
);
path
.get("left")
.replaceWith(
t.variableDeclaration("let", [t.variableDeclarator(newLoopId)]),
);
scope.registerDeclaration(path.get("left"));
}
},
};