Add subpath imports "markdownlint-imports-browser" and "markdownlint-…

…imports-node" for overriding "browser"/"default" behavior in bundlers like webpack.

package.json

@@ -16,6 +16,8 @@
   },
   "imports": {
     "#node-imports": {
+      "markdownlint-imports-browser": "./lib/node-imports-browser.mjs",
+      "markdownlint-imports-node": "./lib/node-imports-node.mjs",
       "browser": "./lib/node-imports-browser.mjs",
       "default": "./lib/node-imports-node.mjs"
     }
@@ -99,6 +101,7 @@
     "markdown-it-sub": "2.0.0",
     "markdown-it-sup": "2.0.0",
     "markdownlint-rule-extended-ascii": "0.1.0",
+    "nano-spawn": "0.2.0",
     "npm-run-all": "4.1.5",
     "terser-webpack-plugin": "5.3.11",
     "toml": "3.0.0",

test/markdownlint-test.mjs

@@ -13,6 +13,7 @@ import pluginInline from "markdown-it-for-inline";
 import pluginSub from "markdown-it-sub";
 import pluginSup from "markdown-it-sup";
 import test from "ava";
+import spawn from "nano-spawn";
 import { getVersion } from "markdownlint";
 import { lint as lintAsync } from "markdownlint/async";
 import { lint as lintPromise } from "markdownlint/promise";
@@ -1398,3 +1399,29 @@ for (const [ exportName, exportPath ] of exportMappings) {
     t.is(importExportName, importExportPath);
   });
 }
+
+test("subpathImports", async(t) => {
+  t.plan(8);
+  const scenarios = [
+    { "conditions": "browser", "throws": true },
+    { "conditions": "default", "throws": false },
+    { "conditions": "markdownlint-imports-browser", "throws": true },
+    { "conditions": "markdownlint-imports-node", "throws": false }
+  ];
+  for (const scenario of scenarios) {
+    const { conditions, throws } = scenario;
+    try {
+      // eslint-disable-next-line no-await-in-loop
+      await spawn("node", [ `--conditions=${conditions}`, "./standalone.mjs" ], { "cwd": "./example" });
+      t.true(!throws, conditions);
+    } catch {
+      t.true(throws, conditions);
+    }
+  }
+  // Fake "100%" coverage for node-imports-browser.mjs
+  const { "fs": browserFs } = await import("../lib/node-imports-browser.mjs");
+  t.throws(() => browserFs.access());
+  t.throws(() => browserFs.accessSync());
+  t.throws(() => browserFs.readFile());
+  t.throws(() => browserFs.readFileSync());
+});