Improve type safety in dot-env module

src/utils/dev.ts

@@ -172,7 +172,6 @@ const getEnvSourceName = (source) => {
 // @ts-expect-error TS(7031) FIXME: Binding element 'devConfig' implicitly has an 'any... Remove this comment to see the full error message
 export const getDotEnvVariables = async ({ devConfig, env, site }): Promise<EnvironmentVariables> => {
   const dotEnvFiles = await loadDotEnvFiles({ envFiles: devConfig.envFiles, projectDir: site.root })
-  // @ts-expect-error TS(2339) FIXME: Property 'env' does not exist on type '{ warning: ... Remove this comment to see the full error message
   dotEnvFiles.forEach(({ env: fileEnv, file }) => {
     const newSourceName = `${file} file`
 

src/utils/dot-env.ts

@@ -7,26 +7,53 @@ import { isFileAsync } from '../lib/fs.js'
 
 import { warn } from './command-helpers.js'
 
-// @ts-expect-error TS(7031) FIXME: Binding element 'envFiles' implicitly has an 'any'... Remove this comment to see the full error message
-export const loadDotEnvFiles = async function ({ envFiles, projectDir }) {
+interface DotEnvFile {
+  file: string
+  env: Record<string, string>
+}
+
+interface DotEnvWarning {
+  warning: string
+}
+
+type LoadedDotEnvFile = DotEnvFile | DotEnvWarning | undefined
+
+const isDefined = <T>(value: T): value is NonNullable<T> => value !== undefined && value !== null
+const isWarning = (result: LoadedDotEnvFile): result is DotEnvWarning => isDefined(result) && 'warning' in result
+const isDotEnvFile = (result: LoadedDotEnvFile): result is DotEnvFile =>
+  isDefined(result) && 'file' in result && 'env' in result
+
+interface LoadDotEnvFilesOptions {
+  envFiles: string[]
+  projectDir: string
+}
+
+export const loadDotEnvFiles = async function ({
+  envFiles,
+  projectDir,
+}: LoadDotEnvFilesOptions): Promise<DotEnvFile[]> {
   const response = await tryLoadDotEnvFiles({ projectDir, dotenvFiles: envFiles })
 
-  // @ts-expect-error TS(2532) FIXME: Object is possibly 'undefined'.
-  const filesWithWarning = response.filter((el) => el.warning)
+  const filesWithWarning = response.filter(isWarning)
   filesWithWarning.forEach((el) => {
-    // @ts-expect-error TS(2532) FIXME: Object is possibly 'undefined'.
     warn(el.warning)
   })
 
-  // @ts-expect-error TS(2532) FIXME: Object is possibly 'undefined'.
-  return response.filter((el) => el.file && el.env)
+  return response.filter(isDotEnvFile)
 }
 
 // in the user configuration, the order is highest to lowest
 const defaultEnvFiles = ['.env.development.local', '.env.local', '.env.development', '.env']
 
-// @ts-expect-error TS(7031) FIXME: Binding element 'projectDir' implicitly has an 'an... Remove this comment to see the full error message
-export const tryLoadDotEnvFiles = async ({ dotenvFiles = defaultEnvFiles, projectDir }) => {
+interface TryLoadDotEnvFilesOptions {
+  projectDir: string
+  dotenvFiles?: string[]
+}
+
+export const tryLoadDotEnvFiles = async ({
+  dotenvFiles = defaultEnvFiles,
+  projectDir,
+}: TryLoadDotEnvFilesOptions): Promise<LoadedDotEnvFile[]> => {
   const results = await Promise.all(
     dotenvFiles.map(async (file) => {
       const filepath = path.resolve(projectDir, file)
@@ -37,8 +64,7 @@ export const tryLoadDotEnvFiles = async ({ dotenvFiles = defaultEnvFiles, projec
         }
       } catch (error) {
         return {
-          // @ts-expect-error TS(2571) FIXME: Object is of type 'unknown'.
-          warning: `Failed reading env variables from file: ${filepath}: ${error.message}`,
+          warning: `Failed reading env variables from file: ${filepath}: ${error instanceof Error ? error.message : error}`,
         }
       }
       const content = await readFile(filepath, 'utf-8')
@@ -48,5 +74,5 @@ export const tryLoadDotEnvFiles = async ({ dotenvFiles = defaultEnvFiles, projec
   )
 
   // we return in order of lowest to highest priority
-  return results.filter(Boolean).reverse()
+  return results.filter(isDefined).reverse()
 }