Bun.Transpiler: default autoImportJSX to true for the automatic runtime

docs/runtime/transpiler.mdx

@@ -34,6 +34,7 @@ const result = transpiler.transformSync(code);
 ````
 
 ```ts output
+import { jsxDEV as jsxDEV_7x81h0kn } from "react/jsx-dev-runtime";
 import * as whatever from "./whatever.ts";
 export function Home(props) {
   return jsxDEV_7x81h0kn("p", {
@@ -216,6 +217,11 @@ interface TranspilerOptions {
   // Default: false
   trimUnusedImports?: boolean,
 
+  // Whether to prepend the automatic JSX runtime import
+  // (`import { jsx } from "react/jsx-runtime"`) when JSX is used
+  // Default: true
+  autoImportJSX?: boolean,
+
   // Whether to enable a set of JSX optimizations
   // jsxOptimizationInline ...,
 

packages/bun-types/bun.d.ts

@@ -2462,6 +2462,15 @@ declare module "bun" {
      */
     macro?: MacroMap;
 
+    /**
+     * When the automatic JSX runtime is in use, prepend an import for the
+     * bindings the transformed output actually uses (some of `jsx`, `jsxs`,
+     * `Fragment` from `"<jsxImportSource>/jsx-runtime"`, or `jsxDEV` from
+     * `jsx-dev-runtime`) so the output can run standalone. Set `false` to
+     * suppress the import.
+     *
+     * @default true
+     */
     autoImportJSX?: boolean;
     allowBunRuntime?: boolean;
     exports?: {

src/js_parser/parse/parse_entry.rs

@@ -480,28 +480,23 @@
             }
         }
 
-        // Symbol use counts are unavailable
-        // So we say "did we parse any JSX?"
-        // if yes, just automatically add the import so that .bun knows to include the file.
-        if p.options.jsx.parse && p.needs_jsx_import {
+        // Symbol use counts are unavailable, so "any JSX parsed?" is the proxy.
+        // Mirror the full-parse auto-import gate so scanImports() and scan()
+        // agree on the injected JSX runtime import.
+        if p.options.jsx.parse
+            && p.needs_jsx_import
+            && p.options.features.auto_import_jsx
+            && p.options.jsx.runtime == options::JSX::Runtime::Automatic
+        {
             // `add_import_record` requires `&'a [u8]`, but borrowing
             // `p.options` would conflict with `&mut p`, so copy into the arena.
             let arena = p.arena;
             let import_source: &'a [u8] = arena.alloc_slice_copy(p.options.jsx.import_source());
-            let classic_import_source: &'a [u8] =
-                arena.alloc_slice_copy(&p.options.jsx.classic_import_source);
             let _ = p.add_import_record(
-                bun_ast::ImportKind::Require,
+                bun_ast::ImportKind::Stmt,
                 bun_ast::Loc { start: 0 },
                 import_source,
             );
-            // Ensure we have both classic and automatic
-            // This is to handle cases where they use fragments in the automatic runtime
-            let _ = p.add_import_record(
-                bun_ast::ImportKind::Require,
-                bun_ast::Loc { start: 0 },
-                classic_import_source,
-            );
         }
 
         scan_pass.approximate_newline_count = p.lexer.approximate_newline_count;

src/runtime/api/JSTranspiler.rs

@@ -97,6 +97,7 @@ impl Default for Config {
             log: bun_ast::Log::default(), // overwritten at construction
             runtime: Runtime::Features {
                 top_level_await: true,
+                auto_import_jsx: true,
                 ..Default::default()
             },
             tree_shaking: false,
@@ -1743,6 +1744,7 @@ impl JSTranspiler {
         };
 
         let mut opts = bun_js_parser::ParserOptions::init(jsx, loader);
+        opts.features.auto_import_jsx = self.transpiler.get().options.auto_import_jsx;
         // SAFETY: see `transpiler_mut`. The `&mut Transpiler` is reborrowed
         // disjointly for `macro_context` (stored in `opts`) and `options.define`
         // (raw-addr read) below; both end when `opts` is consumed by `scan()`.

test/bundler/transpiler/transpiler.test.js

@@ -2086,6 +2086,7 @@ export default <>hi</>
         "process.env.NODE_ENV": JSON.stringify("development"),
       },
       logLevel: "error",
+      autoImportJSX: false,
     });
 
     expect(bun.transformSync("console.log(<div key={() => {}} points={() => {}}></div>);")).toBe(
@@ -2193,6 +2194,124 @@ console.log(<div {...obj} key="after" />);`),
     }
   });
 
+  // https://github.com/oven-sh/bun/issues/7499
+  describe("autoImportJSX defaults to true for the automatic runtime", () => {
+    it("no-arg constructor", () => {
+      expect(new Bun.Transpiler().transformSync("export default <div/>;")).toMatch(
+        /^import \{ jsx(?:DEV)? as (\w+) \} from "react\/jsx-(?:dev-)?runtime";\nexport default \1\("div",/,
+      );
+    });
+
+    it("development", () => {
+      const out = new Bun.Transpiler({
+        loader: "tsx",
+        define: { "process.env.NODE_ENV": JSON.stringify("development") },
+      }).transformSync("export default function App() { return <><div>hi</div></>; }");
+      expect(out).toMatch(
+        /^import { jsxDEV as (\w+), Fragment as (\w+) } from "react\/jsx-dev-runtime";\nexport default function App\(\) {\n  return \1\(\2,/,
+      );
+    });
+
+    it("async .transform() also emits the import", async () => {
+      const out = await new Bun.Transpiler({
+        loader: "tsx",
+        define: { "process.env.NODE_ENV": JSON.stringify("development") },
+      }).transform("export default <div>hi</div>;");
+      expect(out).toMatch(/^import { jsxDEV as (\w+) } from "react\/jsx-dev-runtime";\nexport default \1\("div",/);
+    });
+
+    it("production", () => {
+      const out = new Bun.Transpiler({
+        loader: "tsx",
+        tsconfig: { compilerOptions: { jsx: "react-jsx" } },
+      }).transformSync("export default <div>hi</div>;");
+      expect(out).toMatch(/^import { jsx as (\w+) } from "react\/jsx-runtime";\nexport default \1\("div",/);
+    });
+
+    it("respects jsxImportSource", () => {
+      const out = new Bun.Transpiler({
+        loader: "tsx",
+        tsconfig: { compilerOptions: { jsx: "react-jsx", jsxImportSource: "preact" } },
+      }).transformSync("export default <div>hi</div>;");
+      expect(out).toMatch(/^import { jsx as (\w+) } from "preact\/jsx-runtime";\nexport default \1\("div",/);
+    });
+
+    it("key-after-spread emits createElement with an import", () => {
+      const out = new Bun.Transpiler({
+        loader: "tsx",
+        define: { "process.env.NODE_ENV": JSON.stringify("development") },
+        logLevel: "error",
+      }).transformSync(`export default <div {...obj} key="after" />;`);
+      expect(out).toMatch(/^import { createElement as (\w+) } from "react";\nexport default \1\("div",/);
+    });
+
+    it("does not affect the classic runtime", () => {
+      const out = new Bun.Transpiler({
+        loader: "tsx",
+        tsconfig: { compilerOptions: { jsx: "react" } },
+      }).transformSync("export default <div>hi</div>;");
+      expect(out).toBe('export default React.createElement("div", null, "hi");\n');
+    });
+
+    it("can still be disabled", () => {
+      const out = new Bun.Transpiler({
+        loader: "tsx",
+        define: { "process.env.NODE_ENV": JSON.stringify("development") },
+        autoImportJSX: false,
+      }).transformSync("export default <div>hi</div>;");
+      expect(out).not.toContain("import");
+      expect(out).toContain("jsxDEV");
+    });
+
+    it("surfaces the runtime import through .scan()", () => {
+      const opts = { loader: "tsx", define: { "process.env.NODE_ENV": JSON.stringify("development") } };
+
+      expect(new Bun.Transpiler(opts).scan("export default <div/>;").imports).toEqual([
+        { kind: "import-statement", path: "react/jsx-dev-runtime" },
+      ]);
+      expect(new Bun.Transpiler({ ...opts, autoImportJSX: false }).scan("export default <div/>;").imports).toEqual([]);
+      expect(new Bun.Transpiler(opts).scan("export const x = 1;").imports).toEqual([]);
+    });
+
+    // scanImports() used to unconditionally add a `require-call` record for
+    // `<importSource>/jsx-dev-runtime` *and* a second one for the classic
+    // source, regardless of auto_import_jsx or the configured JSX runtime.
+    // It now mirrors the full-parse gate so it agrees with scan().
+    describe(".scanImports() agrees with .scan() on the injected JSX runtime import", () => {
+      const dev = { loader: "tsx", define: { "process.env.NODE_ENV": JSON.stringify("development") } };
+      const jsxDevRuntime = [{ kind: "import-statement", path: "react/jsx-dev-runtime" }];
+
+      it.each([
+        ["automatic (dev)", dev, "export default <div/>;", jsxDevRuntime],
+        ["automatic + fragment", dev, "export default <><div/></>;", jsxDevRuntime],
+        [
+          "automatic (prod)",
+          { loader: "tsx", tsconfig: { compilerOptions: { jsx: "react-jsx" } } },
+          "export default <div/>;",
+          [{ kind: "import-statement", path: "react/jsx-runtime" }],
+        ],
+        [
+          "automatic + jsxImportSource",
+          { loader: "tsx", tsconfig: { compilerOptions: { jsx: "react-jsx", jsxImportSource: "preact" } } },
+          "export default <div/>;",
+          [{ kind: "import-statement", path: "preact/jsx-runtime" }],
+        ],
+        ["autoImportJSX: false", { ...dev, autoImportJSX: false }, "export default <div/>;", []],
+        [
+          "classic runtime",
+          { loader: "tsx", tsconfig: { compilerOptions: { jsx: "react" } } },
+          "export default <div/>;",
+          [],
+        ],
+        ["no JSX", dev, "export const x = 1;", []],
+      ])("%s", (_, opts, src, expected) => {
+        const t = new Bun.Transpiler(opts);
+        expect(t.scanImports(src)).toEqual(expected);
+        expect(t.scan(src).imports).toEqual(expected);
+      });
+    });
+  });
+
   it("JSX bare key prop followed by key with a value does not crash", async () => {
     await using proc = Bun.spawn({
       cmd: [
@@ -2203,6 +2322,7 @@ console.log(<div {...obj} key="after" />);`),
             loader: "jsx",
             define: { "process.env.NODE_ENV": JSON.stringify("development") },
             logLevel: "error",
+            autoImportJSX: false,
           });
           process.stdout.write(t.transformSync('console.log(<div key key="duplicate"></div>);'));
           process.stdout.write(t.transformSync('console.log(<div key className="x" key="duplicate"></div>);'));
@@ -2344,6 +2464,7 @@ console.log(<div {...obj} key="after" />);`),
       define: {
         "process.env.NODE_ENV": JSON.stringify("development"),
       },
+      autoImportJSX: false,
     });
     expect(bun.transformSync("export var foo = <div>{...a}b</div>")).toBe(
       `export var foo = jsxDEV_7x81h0kn("div", {