fix: add guard for import map with extraneous dist directory

node/bundler.test.ts

@@ -1,6 +1,7 @@
 import { promises as fs } from 'fs'
 import { join, resolve } from 'path'
 import process from 'process'
+import { pathToFileURL } from 'url'
 
 import { deleteAsync } from 'del'
 import tmp from 'tmp-promise'
@@ -345,3 +346,40 @@ test('Loads declarations and import maps from the deploy configuration', async (
 
   await cleanup()
 })
+
+test('Uses an absolute URL for the import map when the dist directory is not a child of the base path', async () => {
+  const { basePath, cleanup } = await useFixture('with_import_maps')
+  const { path: distPath } = await tmp.dir()
+  const declarations = [
+    {
+      function: 'func1',
+      path: '/func1',
+    },
+  ]
+  const sourceDirectory = join(basePath, 'functions')
+  const result = await bundle([sourceDirectory], distPath, declarations, {
+    basePath,
+    configPath: join(sourceDirectory, 'config.json'),
+  })
+  const generatedFiles = await fs.readdir(distPath)
+
+  expect(result.functions.length).toBe(1)
+
+  // ESZIP, manifest and import map.
+  expect(generatedFiles.length).toBe(3)
+
+  const manifestFile = await fs.readFile(resolve(distPath, 'manifest.json'), 'utf8')
+  const manifest = JSON.parse(manifestFile)
+  expect(() => validateManifest(manifest)).not.toThrowError()
+  const { bundles, import_map: importMapURL } = manifest
+
+  expect(bundles.length).toBe(1)
+  expect(bundles[0].format).toBe('eszip2')
+  expect(generatedFiles.includes(bundles[0].asset)).toBe(true)
+
+  const importMapPath = join(distPath, 'import_map.json')
+  expect(importMapURL).toBe(pathToFileURL(importMapPath).toString())
+
+  await cleanup()
+  await fs.rm(distPath, { recursive: true })
+})

node/formats/eszip.ts

@@ -69,8 +69,18 @@ const createUserImportMap = async (importMap: ImportMap, basePath: string, distD
 
   await importMap.writeToFile(destPath)
 
-  const relativePath = relative(basePath, destPath)
-  const importMapURL = new URL(relativePath, virtualRoot)
+  let virtualPath = relative(basePath, destPath)
+
+  // If the dist directory is not a child of the base path, we can't represent
+  // the relative path as a file URL (because something like 'file://../foo' is
+  // not valid). This should never happen, but it's best to leave the absolute
+  // path untransformed to avoid getting a build error due to a missing import
+  // map.
+  if (virtualPath.startsWith('..')) {
+    virtualPath = destPath
+  }
+
+  const importMapURL = new URL(virtualPath, virtualRoot)
 
   return importMapURL.toString()
 }