Improve traverse typings

packages/babel-core/src/transformation/normalize-file.ts

@@ -107,9 +107,9 @@ const EXTERNAL_SOURCEMAP_REGEX =
 
 function extractCommentsFromList(
   regex: RegExp,
-  comments: ReadonlyArray<t.Comment>,
+  comments: t.Comment[],
   lastComment: string | null,
-): [ReadonlyArray<t.Comment>, string | null] {
+): [t.Comment[], string | null] {
   if (comments) {
     comments = comments.filter(({ value }) => {
       if (regex.test(value)) {

packages/babel-generator/src/generators/methods.ts

@@ -37,13 +37,7 @@ export function _parameters(
 
 export function _param(
   this: Printer,
-  parameter:
-    | t.Function["params"][number]
-    | t.TSIndexSignature["parameters"][number]
-    | t.TSDeclareMethod["params"][number]
-    | t.TSDeclareFunction["params"][number]
-    | t.TSFunctionType["parameters"][number]
-    | t.TSConstructorType["parameters"][number],
+  parameter: t.Identifier | t.RestElement | t.Pattern | t.TSParameterProperty,
   parent?:
     | t.Function
     | t.TSIndexSignature

packages/babel-generator/src/generators/statements.ts

@@ -50,22 +50,14 @@ export function IfStatement(this: Printer, node: t.IfStatement) {
 }
 
 // Recursively get the last statement.
-function getLastStatement(
-  statement: Exclude<t.Statement, t.BreakStatement>,
-): t.Statement {
-  if (
-    !isStatement(
-      // @ts-ignore body is not in BreakStatement
-      statement.body,
-    )
-  ) {
+function getLastStatement(statement: t.Statement): t.Statement {
+  // @ts-ignore: If statement.body is empty or not a Node, isStatement will return false
+  const { body } = statement;
+  if (isStatement(body) === false) {
     return statement;
   }
 
-  return getLastStatement(
-    // @ts-ignore body is not in BreakStatement
-    statement.body,
-  );
+  return getLastStatement(body);
 }
 
 export function ForStatement(this: Printer, node: t.ForStatement) {

packages/babel-generator/src/generators/typescript.ts

@@ -239,9 +239,10 @@ export function tsPrintFunctionOrConstructorType(
 ) {
   const { typeParameters } = node;
   const parameters = process.env.BABEL_8_BREAKING
-    ? // @ts-expect-error Babel 8 AST shape
+    ? // @ts-ignore Babel 8 AST shape
       node.params
-    : node.parameters;
+    : // @ts-ignore Babel 7 AST shape
+      node.parameters;
   this.print(typeParameters, node);
   this.token("(");
   this._parameters(parameters, node);
@@ -250,9 +251,10 @@ export function tsPrintFunctionOrConstructorType(
   this.token("=>");
   this.space();
   const returnType = process.env.BABEL_8_BREAKING
-    ? // @ts-expect-error Babel 8 AST shape
+    ? // @ts-ignore Babel 8 AST shape
       node.returnType
-    : node.typeAnnotation;
+    : // @ts-ignore Babel 7 AST shape
+      node.typeAnnotation;
   this.print(returnType.typeAnnotation, node);
 }
 

packages/babel-generator/src/printer.ts

@@ -669,9 +669,8 @@ class Printer {
   _printComment(comment: t.Comment, skipNewLines?: boolean) {
     if (!this.format.shouldPrintComment(comment.value)) return;
 
-    // Some plugins use this to mark comments as removed using the AST-root 'comments' property,
+    // Some plugins (such as flow-strip-types) use this to mark comments as removed using the AST-root 'comments' property,
     // where they can't manually mutate the AST node comment lists.
-    // @ts-ignore todo: which plugin?
     if (comment.ignore) return;
 
     if (this._printedComments.has(comment)) return;

packages/babel-helper-create-class-features-plugin/src/fields.ts

@@ -107,6 +107,7 @@ interface PrivateNameVisitorState {
 function privateNameVisitorFactory<S>(
   visitor: Visitor<PrivateNameVisitorState & S>,
 ) {
+  // @ts-ignore Fixme: TS complains _exploded: boolean does not satisfy visitor functions
   const privateNameVisitor: Visitor<PrivateNameVisitorState & S> = {
     ...visitor,
 

packages/babel-helper-module-transforms/src/normalize-and-load-metadata.ts

@@ -580,7 +580,9 @@ function removeModuleDeclarations(programPath: NodePath<t.Program>) {
       ) {
         // @ts-expect-error todo(flow->ts): avoid mutations
         declaration._blockHoist = child.node._blockHoist;
-        child.replaceWith(declaration);
+        child.replaceWith(
+          declaration as NodePath<t.FunctionDeclaration | t.ClassDeclaration>,
+        );
       } else {
         // These should have been removed by the nameAnonymousExports() call.
         throw declaration.buildCodeFrameError(

packages/babel-helper-split-export-declaration/src/index.ts

@@ -51,7 +51,7 @@ export default function splitExportDeclaration(
     }
 
     const updatedDeclaration = standaloneDeclaration
-      ? declaration
+      ? declaration.node
       : variableDeclaration("var", [
           variableDeclarator(
             cloneNode(id),

packages/babel-helper-transform-fixture-test-runner/src/index.ts

@@ -33,14 +33,16 @@ type Module = {
 };
 
 if (!process.env.BABEL_8_BREAKING) {
-  // Introduced in Node.js 8
+  // Introduced in Node.js 10
   if (!assert.rejects) {
     assert.rejects = async function (block, validateError) {
       try {
-        await block();
+        await (typeof block === "function" ? block() : block);
         return Promise.reject(new Error("Promise not rejected"));
       } catch (error) {
-        if (!validateError(error)) {
+        // @ts-ignore Fixme: validateError can be a string | object
+        // see https://nodejs.org/api/assert.html#assertrejectsasyncfn-error-message
+        if (typeof validateError === "function" && !validateError(error)) {
           return Promise.reject(
             new Error("Promise rejected with invalid error"),
           );

packages/babel-plugin-proposal-async-generator-functions/src/index.ts

@@ -3,7 +3,7 @@ import remapAsyncToGenerator from "@babel/helper-remap-async-to-generator";
 import syntaxAsyncGenerators from "@babel/plugin-syntax-async-generators";
 import { types as t } from "@babel/core";
 import type { PluginPass } from "@babel/core";
-import type { Visitor } from "@babel/traverse";
+import type { NodePath, Visitor } from "@babel/traverse";
 import rewriteForAwait from "./for-await";
 
 export default declare(api => {
@@ -29,7 +29,7 @@ export default declare(api => {
       path.skip();
     },
 
-    ForOfStatement(path, { file }) {
+    ForOfStatement(path: NodePath<t.ForOfStatement>, { file }) {
       const { node } = path;
       if (!node.await) return;
 
@@ -49,7 +49,7 @@ export default declare(api => {
       }
 
       // push the rest of the original loop body onto our new body
-      block.body.push(...(node.body as t.BlockStatement).body);
+      block.body.push(...path.node.body.body);
 
       t.inherits(loop, node);
       t.inherits(loop.body, node.body);

packages/babel-plugin-proposal-decorators/src/transformer-2021-12.ts

@@ -143,7 +143,10 @@ function replaceClassWithVar(
       t.sequenceExpression([newClassExpr, varId]),
     );
 
-    return [t.cloneNode(varId), newPath.get("expressions.0")];
+    return [
+      t.cloneNode(varId),
+      newPath.get("expressions.0") as NodePath<t.ClassExpression>,
+    ];
   }
 }
 

packages/babel-plugin-proposal-destructuring-private/src/index.ts

@@ -10,7 +10,8 @@ import { convertFunctionParams } from "@babel/plugin-transform-parameters";
 import { unshiftForXStatementBody } from "@babel/plugin-transform-destructuring";
 
 import type { PluginPass } from "@babel/core";
-import type { Visitor } from "@babel/traverse";
+import type { NodePath, Visitor } from "@babel/traverse";
+import type * as t from "@babel/types";
 
 export default declare(function ({ assertVersion, assumption, types: t }) {
   assertVersion("^7.17.0");
@@ -51,7 +52,10 @@ export default declare(function ({ assertVersion, assumption, types: t }) {
       const { params: transformedParams, variableDeclaration } =
         buildVariableDeclarationFromParams(paramsAfterIndex, scope);
 
-      path.get("body").unshiftContainer("body", variableDeclaration);
+      (path.get("body") as NodePath<t.BlockStatement>).unshiftContainer(
+        "body",
+        variableDeclaration,
+      );
       params.push(...transformedParams);
       // preserve function.length
       // (b, p1) => {}

packages/babel-plugin-proposal-object-rest-spread/src/index.ts

@@ -540,7 +540,7 @@ export default declare((api, opts: Options) => {
       },
 
       // taken from transform-destructuring/src/index.js#visitor
-      ForXStatement(path) {
+      ForXStatement(path: NodePath<t.ForXStatement>) {
         const { node, scope } = path;
         const leftPath = path.get("left");
         const left = node.left;
@@ -558,7 +558,7 @@ export default declare((api, opts: Options) => {
           ]);
 
           path.ensureBlock();
-          const body = node.body as t.BlockStatement;
+          const body = path.node.body;
 
           if (body.body.length === 0 && path.isCompletionRecord()) {
             body.body.unshift(

packages/babel-plugin-transform-block-scoping/src/index.ts

@@ -62,12 +62,12 @@ export default declare((api, opts: Options) => {
         }
       },
 
-      Loop(path, state) {
+      Loop(path: NodePath<t.Loop>, state) {
         const { parent, scope } = path;
         path.ensureBlock();
         const blockScoping = new BlockScoping(
           path,
-          path.get("body") as NodePath<t.BlockStatement>,
+          path.get("body"),
           parent,
           scope,
           throwIfClosureRequired,
@@ -534,6 +534,7 @@ class BlockScoping {
             ]),
           );
         } else if (violation.isForXStatement()) {
+          // @ts-expect-error TS requires explicit annotation of "violation"
           violation.ensureBlock();
           violation
             .get("left")

packages/babel-plugin-transform-destructuring/src/index.ts

@@ -8,6 +8,7 @@ import {
   type DestructuringTransformerNode,
 } from "./util";
 export { buildObjectExcludingKeys, unshiftForXStatementBody } from "./util";
+import type { NodePath } from "@babel/traverse";
 
 /**
  * Test if a VariableDeclaration's declarations contains any Patterns.
@@ -68,7 +69,7 @@ export default declare((api, options: Options) => {
         path.scope.crawl();
       },
 
-      ForXStatement(path) {
+      ForXStatement(path: NodePath<t.ForXStatement>) {
         const { node, scope } = path;
         const left = node.left;
 
@@ -82,7 +83,7 @@ export default declare((api, options: Options) => {
           ]);
 
           path.ensureBlock();
-          const statementBody = (node.body as t.BlockStatement).body;
+          const statementBody = path.node.body.body;
           const nodes = [];
           // todo: the completion of a for statement can only be observed from
           // a do block (or eval that we don't support),

packages/babel-plugin-transform-modules-amd/src/index.ts

@@ -32,9 +32,9 @@ function injectWrapper(
   const { body, directives } = path.node;
   path.node.directives = [];
   path.node.body = [];
-  const amdFactoryCall = (
-    path.pushContainer("body", wrapper)[0] as NodePath<t.ExpressionStatement>
-  ).get("expression") as NodePath<t.CallExpression>;
+  const amdFactoryCall = path
+    .pushContainer("body", wrapper)[0]
+    .get("expression") as NodePath<t.CallExpression>;
   const amdFactoryCallArgs = amdFactoryCall.get("arguments");
   const amdFactory = (
     amdFactoryCallArgs[

packages/babel-plugin-transform-modules-umd/src/index.ts

@@ -264,7 +264,7 @@ export default declare((api, options: Options) => {
           ])[0] as NodePath<t.ExpressionStatement>;
           const umdFactory = (
             umdWrapper.get("expression.arguments")[1] as NodePath<t.Function>
-          ).get("body");
+          ).get("body") as NodePath<t.BlockStatement>;
           umdFactory.pushContainer("directives", directives);
           umdFactory.pushContainer("body", body);
         },

packages/babel-plugin-transform-parameters/src/params.ts

@@ -1,25 +1,25 @@
 import { template, types as t } from "@babel/core";
 import type { NodePath, Scope, Visitor } from "@babel/traverse";
 
-const buildDefaultParam = template(`
+const buildDefaultParam = template.statement(`
   let VARIABLE_NAME =
     arguments.length > ARGUMENT_KEY && arguments[ARGUMENT_KEY] !== undefined ?
       arguments[ARGUMENT_KEY]
     :
       DEFAULT_VALUE;
 `);
 
-const buildLooseDefaultParam = template(`
+const buildLooseDefaultParam = template.statement(`
   if (ASSIGNMENT_IDENTIFIER === UNDEFINED) {
     ASSIGNMENT_IDENTIFIER = DEFAULT_VALUE;
   }
 `);
 
-const buildLooseDestructuredDefaultParam = template(`
+const buildLooseDestructuredDefaultParam = template.statement(`
   let ASSIGNMENT_IDENTIFIER = PARAMETER_NAME === UNDEFINED ? DEFAULT_VALUE : PARAMETER_NAME ;
 `);
 
-const buildSafeArgumentsAccess = template(`
+const buildSafeArgumentsAccess = template.statement(`
   let $0 = arguments.length > $1 ? arguments[$1] : undefined;
 `);
 
@@ -238,7 +238,7 @@ export default function convertFunctionParams(
     // throws, it must reject asynchronously.
     path.node.generator = false;
   } else {
-    path.get("body").unshiftContainer("body", body as t.Statement[]);
+    path.get("body").unshiftContainer("body", body);
   }
 
   return true;

packages/babel-preset-env/src/normalize-options.ts

@@ -1,5 +1,8 @@
 import semver, { type SemVer } from "semver";
 import corejs2Polyfills from "@babel/compat-data/corejs2-built-ins";
+// @ts-ignore Fixme: TS can not infer types from ../data/core-js-compat.js
+// but we can't import core-js-compat/data.json because JSON imports does
+// not work on Node 14
 import corejs3Polyfills from "../data/core-js-compat";
 import { plugins as pluginsList } from "./plugins-compat-data";
 import moduleTransformations from "./module-transformations";

packages/babel-standalone/src/index.ts

@@ -106,7 +106,7 @@ export function transform(code: string, options: InputOptions) {
 }
 
 export function transformFromAst(
-  ast: Parameters<typeof babelTransformFromAst>[0],
+  ast: Parameters<typeof babelTransformFromAstSync>[0],
   code: string,
   options: InputOptions,
 ) {