fix: Types containing comments generate invalid code

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

@@ -11,15 +11,7 @@ export function _params(
   this._parameters(node.params, node);
   this.token(")");
 
-  if (node.returnType) {
-    if (node.type === "ArrowFunctionExpression") {
-      this._noLineTerminator = true;
-      this.print(node.returnType, node);
-      this._noLineTerminator = false;
-    } else {
-      this.print(node.returnType, node);
-    }
-  }
+  this.print(node.returnType, node);
 }
 
 export function _parameters(

packages/babel-generator/src/printer.ts

@@ -1,7 +1,6 @@
 import Buffer from "./buffer";
 import type { Loc } from "./buffer";
 import * as n from "./node";
-import { isProgram, isFile, isEmptyStatement } from "@babel/types";
 import type * as t from "@babel/types";
 import type {
   RecordAndTuplePluginOptions,
@@ -507,42 +506,45 @@ class Printer {
   print(node: t.Node | null, parent?: t.Node) {
     if (!node) return;
 
-    const oldConcise = this.format.concise;
+    const nodeType = node.type;
+    const format = this.format;
+
+    const oldConcise = format.concise;
     if (
       // @ts-expect-error document _compact AST properties
       node._compact
     ) {
-      this.format.concise = true;
+      format.concise = true;
     }
 
     const printMethod =
       this[
-        node.type as Exclude<
+        nodeType as Exclude<
           t.Node["type"],
           // removed
           | "Noop"
           // renamed
           | t.DeprecatedAliases["type"]
         >
       ];
-    if (!printMethod) {
+    if (printMethod === undefined) {
       throw new ReferenceError(
         `unknown node of type ${JSON.stringify(
-          node.type,
-        )} with constructor ${JSON.stringify(node?.constructor.name)}`,
+          nodeType,
+        )} with constructor ${JSON.stringify(node.constructor.name)}`,
       );
     }
 
     this._printStack.push(node);
 
     const oldInAux = this._insideAux;
-    this._insideAux = !node.loc;
+    this._insideAux = node.loc == undefined;
     this._maybeAddAuxComment(this._insideAux && !oldInAux);
 
     let shouldPrintParens: boolean;
     if (
-      this.format.retainFunctionParens &&
-      node.type === "FunctionExpression" &&
+      format.retainFunctionParens &&
+      nodeType === "FunctionExpression" &&
       node.extra &&
       node.extra.parenthesized
     ) {
@@ -552,20 +554,30 @@ class Printer {
     }
     if (shouldPrintParens) this.token("(");
 
+    let noLineTerminator;
+    if (nodeType === "TSTypeAnnotation" || nodeType === "TypeAnnotation") {
+      noLineTerminator = this._noLineTerminator;
+      this._noLineTerminator = true;
+    }
+
     this._printLeadingComments(node);
 
-    const loc = isProgram(node) || isFile(node) ? null : node.loc;
+    const loc = nodeType === "Program" || nodeType === "File" ? null : node.loc;
 
     this.withSource("start", loc, printMethod.bind(this, node, parent));
 
     this._printTrailingComments(node);
 
+    if (noLineTerminator !== undefined) {
+      this._noLineTerminator = noLineTerminator;
+    }
+
     if (shouldPrintParens) this.token(")");
 
     // end
     this._printStack.pop();
 
-    this.format.concise = oldConcise;
+    format.concise = oldConcise;
     this._insideAux = oldInAux;
   }
 
@@ -667,7 +679,7 @@ class Printer {
   printBlock(parent: Extract<t.Node, { body: t.Statement }>) {
     const node = parent.body;
 
-    if (!isEmptyStatement(node)) {
+    if (node.type !== "EmptyStatement") {
       this.space();
     }
 

packages/babel-generator/test/fixtures/typescript/types-arrow-return-with-comment/input.js → packages/babel-generator/test/fixtures/flow/type-with-comment/input.js

@@ -1 +1,3 @@
 export default (): void /* hi! */ => {};
+
+const foo: any /* Hi! */[] = [];

packages/babel-generator/test/fixtures/flow/type-with-comment/output.js

@@ -0,0 +1,2 @@
+export default ((): void /* hi! */ => {});
+const foo: any /* Hi! */[] = [];

packages/babel-generator/test/fixtures/typescript/type-with-comment/input.js

@@ -0,0 +1,3 @@
+export default (): void /* hi! */ => {};
+
+const foo: any /* Hi! */[] = [];

packages/babel-generator/test/fixtures/typescript/type-with-comment/output.js

@@ -0,0 +1,2 @@
+export default ((): void /* hi! */ => {});
+const foo: any /* Hi! */[] = [];