Implement virtual module support in `Bun.plugin` (#6167)

* Add support for `build.module` in `Bun.plugin`

* Another test

* Update docs

* Update isBuiltinModule.cpp

---------

Co-authored-by: Jarred Sumner <709451+Jarred-Sumner@users.noreply.github.com>
Co-authored-by: Dylan Conway <dylan.conway567@gmail.com>

3 files changed, 139 insertions, 0 deletions

diff --git a/test/bundler/bun-build-api.test.ts b/test/bundler/bun-build-api.test.ts
index 3c2308d94..d1f1a10b8 100644
--- a/test/bundler/bun-build-api.test.ts
+++ b/test/bundler/bun-build-api.test.ts
@@ -290,4 +290,27 @@ describe("Bun.build", () => {
     // depends on the ws package in the test/node_modules.
     expect(content).toContain("var websocket = __toESM(require_websocket(), 1);");
   });
+
+  test("module() throws error", async () => {
+    expect(() =>
+      Bun.build({
+        entrypoints: [join(import.meta.dir, "./fixtures/trivial/bundle-ws.ts")],
+        plugins: [
+          {
+            name: "test",
+            setup: b => {
+              b.module("ad", () => {
+                return {
+                  exports: {
+                    hello: "world",
+                  },
+                  loader: "object",
+                };
+              });
+            },
+          },
+        ],
+      }),
+    ).toThrow();
+  });
 });
diff --git a/test/js/bun/plugin/module-plugins.ts b/test/js/bun/plugin/module-plugins.ts
new file mode 100644
index 000000000..d6034c5df
--- /dev/null
+++ b/test/js/bun/plugin/module-plugins.ts
@@ -0,0 +1,38 @@
+import { plugin } from "bun";
+plugin({
+  name: "i am virtual!",
+  setup(builder) {
+    builder.module("my-virtual-module-async", async () => {
+      // check
+      await Bun.sleep(1);
+      return {
+        exports: {
+          hello: "world",
+        },
+        loader: "object",
+      };
+    });
+
+    builder.module("my-virtual-module-sync", () => {
+      return {
+        exports: {
+          hello: "world",
+        },
+        loader: "object",
+      };
+    });
+
+    builder.onLoad({ filter: /.*/, namespace: "rejected-promise" }, async ({ path }) => {
+      throw new Error("Rejected Promise");
+    });
+
+    builder.onResolve({ filter: /.*/, namespace: "rejected-promise2" }, ({ path }) => ({
+      namespace: "rejected-promise2",
+      path,
+    }));
+
+    builder.onLoad({ filter: /.*/, namespace: "rejected-promise2" }, ({ path }) => {
+      return Promise.reject(new Error("Rejected Promise"));
+    });
+  },
+});
diff --git a/test/js/bun/plugin/plugins.test.ts b/test/js/bun/plugin/plugins.test.ts
index c2827f600..2d3cfa1fa 100644
--- a/test/js/bun/plugin/plugins.test.ts
+++ b/test/js/bun/plugin/plugins.test.ts
@@ -185,6 +185,7 @@ plugin({
 
 // This is to test that it works when imported from a separate file
 import "../../third_party/svelte";
+import "./module-plugins";
 
 describe("require", () => {
   it("SSRs `<h1>Hello world!</h1>` with Svelte", () => {
@@ -210,6 +211,83 @@ describe("require", () => {
   });
 });
 
+describe("module", () => {
+  it("throws with require()", () => {
+    expect(() => require("my-virtual-module-async")).toThrow();
+  });
+
+  it("async module works with async import", async () => {
+    // @ts-expect-error
+    const { hello } = await import("my-virtual-module-async");
+
+    expect(hello).toBe("world");
+    delete require.cache["my-virtual-module-async"];
+  });
+
+  it("sync module module works with require()", async () => {
+    const { hello } = require("my-virtual-module-sync");
+
+    expect(hello).toBe("world");
+    delete require.cache["my-virtual-module-sync"];
+  });
+
+  it("sync module module works with require.resolve()", async () => {
+    expect(require.resolve("my-virtual-module-sync")).toBe("my-virtual-module-sync");
+    delete require.cache["my-virtual-module-sync"];
+  });
+
+  it("sync module module works with import", async () => {
+    // @ts-expect-error
+    const { hello } = await import("my-virtual-module-sync");
+
+    expect(hello).toBe("world");
+    delete require.cache["my-virtual-module-sync"];
+  });
+
+  it("modules are overridable", async () => {
+    // @ts-expect-error
+    let { hello, there } = await import("my-virtual-module-sync");
+    expect(there).toBeUndefined();
+    expect(hello).toBe("world");
+
+    Bun.plugin({
+      setup(builder) {
+        builder.module("my-virtual-module-sync", () => ({
+          exports: {
+            there: true,
+          },
+          loader: "object",
+        }));
+      },
+    });
+
+    {
+      const { there, hello } = require("my-virtual-module-sync");
+      expect(there).toBe(true);
+      expect(hello).toBeUndefined();
+    }
+
+    Bun.plugin({
+      setup(builder) {
+        builder.module("my-virtual-module-sync", () => ({
+          exports: {
+            yo: true,
+          },
+          loader: "object",
+        }));
+      },
+    });
+
+    {
+      // @ts-expect-error
+      const { there, hello, yo } = await import("my-virtual-module-sync");
+      expect(yo).toBe(true);
+      expect(hello).toBeUndefined();
+      expect(there).toBeUndefined();
+    }
+  });
+});
+
 describe("dynamic import", () => {
   it("SSRs `<h1>Hello world!</h1>` with Svelte", async () => {
     const { default: App }: any = await import("./hello.svelte");