Add typedefs for dotenv and dotenv-expand

flow-libs/dotenv-expand.js.flow

@@ -0,0 +1,7 @@
+// @flow strict-local
+
+declare module 'dotenv-expand' {
+  import type {DotenvConfigOutput} from 'dotenv';
+
+  declare module.exports: (config: DotenvConfigOutput) => DotenvConfigOutput;
+}

flow-libs/dotenv.js.flow

@@ -0,0 +1,30 @@
+// @flow strict-local
+
+// Derived from and sections taken from
+// https://github.com/motdotla/dotenv/blob/03a891554c49915fe919c649f51b3adcae662a84/lib/main.js
+// and https://github.com/flow-typed/flow-typed/blob/9b8ade1b0dd93ae110a5612cce80d81d0c34a00e/definitions/npm/dotenv_v4.x.x/flow_v0.34.x-/dotenv_v4.x.x.js
+// both of which are MIT licensed (see roots of their respective repos)
+declare module 'dotenv' {
+  declare type DotenvParseOptions = {|
+    debug?: boolean
+  |};
+
+  // keys and values from src
+  declare type DotenvParseOutput = {[string]: string};
+
+  declare type DotenvConfigOptions = {|
+    path?: string, // path to .env file
+    encoding?: string, // encoding of .env file
+    debug?: string // turn on logging for debugging purposes
+  |};
+
+  declare type DotenvConfigOutput = {|
+    parsed?: DotenvParseOutput,
+    error?: Error
+  |};
+
+  declare module.exports: {
+    config(options: ?DotenvConfigOptions): DotenvConfigOutput,
+    parse(src: string | Buffer, options: ?DotenvParseOptions): DotenvParseOutput
+  };
+}