feat: support embedded import map expansion (#111)

This supports the embedded import map expansion feature from Deno 1.40: https://deno.com/blog/v1.40#simpler-imports-in-denojson

mod_test.ts

@@ -674,6 +674,33 @@ Deno.test("bundle config ref import map", async (t) => {
   });
 });
 
+Deno.test("bundle config inline import map with expansion", async (t) => {
+  await testLoader(t, LOADERS, async (esbuild, loader) => {
+    const configPath = join(
+      Deno.cwd(),
+      "testdata",
+      "config_inline_expansion.json",
+    );
+    const res = await esbuild.build({
+      ...DEFAULT_OPTS,
+      plugins: [
+        ...denoPlugins({ configPath, loader }),
+      ],
+      bundle: true,
+      platform: "neutral",
+      entryPoints: ["./testdata/mapped_jsr.js"],
+    });
+    assertEquals(res.warnings, []);
+    assertEquals(res.errors, []);
+    assertEquals(res.outputFiles.length, 1);
+    const output = res.outputFiles[0];
+    assertEquals(output.path, "<stdout>");
+    const dataURL = `data:application/javascript;base64,${btoa(output.text)}`;
+    const ns = await import(dataURL);
+    assertEquals(ns.join("a", "b"), join("a", "b"));
+  });
+});
+
 const COMPUTED_PLUGIN: esbuild.Plugin = {
   name: "computed",
   setup(build) {

src/plugin_deno_resolver.ts

@@ -7,7 +7,11 @@ import {
   SpecifierMap,
   toFileUrl,
 } from "../deps.ts";
-import { readDenoConfig, urlToEsbuildResolution } from "./shared.ts";
+import {
+  expandEmbeddedImportMap,
+  readDenoConfig,
+  urlToEsbuildResolution,
+} from "./shared.ts";
 
 export type { ImportMap, Scopes, SpecifierMap };
 
@@ -76,6 +80,7 @@ export function denoResolverPlugin(
               imports: config.imports,
               scopes: config.scopes,
             } as ImportMap;
+            expandEmbeddedImportMap(configImportMap);
             importMap = resolveImportMap(
               configImportMap,
               toFileUrl(options.configPath),

src/shared.ts

@@ -1,4 +1,11 @@
-import { esbuild, extname, fromFileUrl, JSONC, toFileUrl } from "../deps.ts";
+import {
+  esbuild,
+  extname,
+  fromFileUrl,
+  ImportMap,
+  JSONC,
+  toFileUrl,
+} from "../deps.ts";
 import { MediaType } from "./deno.ts";
 
 export interface Loader {
@@ -325,3 +332,27 @@ export function parseJsrSpecifier(specifier: URL): JsrSpecifier {
     path: pathStartIndex === path.length ? null : path.slice(pathStartIndex),
   };
 }
+
+// For all pairs in `imports` where the specifier does not end in a /, and the
+// target starts with `jsr:` or `npm:`, and no entry exists for `${specifier}/`,
+// add an entry for `${specifier}/` pointing to the target with a / appended,
+// and a `/` appended to the scheme, if none is present there.
+export function expandEmbeddedImportMap(importMap: ImportMap) {
+  if (importMap.imports !== undefined) {
+    const newImports: [string, string | null][] = [];
+    for (const [specifier, target] of Object.entries(importMap.imports)) {
+      newImports.push([specifier, target]);
+      if (
+        !specifier.endsWith("/") && target &&
+        (target.startsWith("jsr:") || target.startsWith("npm:")) &&
+        !importMap.imports[specifier + "/"]
+      ) {
+        const newSpecifier = specifier + "/";
+        const newTarget = target.slice(0, 4) + "/" +
+          target.slice(target[4] === "/" ? 5 : 4) + "/";
+        newImports.push([newSpecifier, newTarget]);
+      }
+    }
+    importMap.imports = Object.fromEntries(newImports);
+  }
+}

src/shared_test.ts

@@ -1,10 +1,12 @@
 import {
+  expandEmbeddedImportMap,
   NpmSpecifier,
   parseJsrSpecifier,
   parseNpmSpecifier,
 } from "./shared.ts";
 import { assertEquals, assertThrows } from "../test_deps.ts";
 import { JsrSpecifier } from "./shared.ts";
+import { ImportMap } from "../deps.ts";
 
 interface NpmSpecifierTestCase extends NpmSpecifier {
   specifier: string;
@@ -190,3 +192,30 @@ Deno.test("parseJsrSpecifier", async (t) => {
     });
   }
 });
+
+Deno.test("expandEmbeddedImportMap", () => {
+  const importMap: ImportMap = {
+    imports: {
+      "@std/path": "jsr:@std/[email protected]",
+      "preact": "npm:preact@^10.0.0",
+      "preact2": "npm:/preact2@^10.0.0",
+
+      "preact-render-to-string": "jsr:preact-render-to-string",
+      "preact-render-to-string/": "jsr:preact-render-to-string2/",
+    },
+  };
+  expandEmbeddedImportMap(importMap);
+  assertEquals(importMap, {
+    imports: {
+      "@std/path": "jsr:@std/[email protected]",
+      "@std/path/": "jsr:/@std/[email protected]/",
+      "preact": "npm:preact@^10.0.0",
+      "preact/": "npm:/preact@^10.0.0/",
+      "preact2": "npm:/preact2@^10.0.0",
+      "preact2/": "npm:/preact2@^10.0.0/",
+
+      "preact-render-to-string": "jsr:preact-render-to-string",
+      "preact-render-to-string/": "jsr:preact-render-to-string2/",
+    },
+  });
+});

testdata/config_inline_expansion.json

@@ -0,0 +1,6 @@
+{
+  "lock": "./jsr/deno.lock",
+  "imports": {
+    "@std/path": "jsr:@std/path@^0.213"
+  }
+}

testdata/mapped_jsr.js

@@ -0,0 +1 @@
+export * from "@std/path/join";