Add env var substitution

__tests__/envvars.test.ts

@@ -0,0 +1,27 @@
+import {
+	substituteValues
+} from '../src/envvars'
+
+describe('substituteValues', () => {
+	test('returns original string with no substitution placeholders', async () => {
+		const input = 'This is a test'
+		const result = await substituteValues(input)
+		expect(result).toBe(input)
+	})
+
+	test('Handles \'env\' substitution placeholders', async () => {
+		process.env.TEST_ENV1='TestEnvValue1'
+		process.env.TEST_ENV2='TestEnvValue2'
+		const input = 'TEST_ENV1: ${env:TEST_ENV1}, TEST_ENV2: ${env:TEST_ENV2}'
+		const result = await substituteValues(input)
+		expect(result).toBe('TEST_ENV1: TestEnvValue1, TEST_ENV2: TestEnvValue2')
+	})
+
+	test('ignores substitution placeholders that it doesn\'t understand', async () => {
+		const input = 'TEST_ENV: ${nothingToSee:TEST_ENV}'
+		const result = await substituteValues(input)
+		expect(result).toBe(input)
+	})
+
+})
+

__tests__/inputs.test.ts

@@ -1,4 +1,3 @@
-import parse from 'csv-parse'
 import {
 	parseInputAsList,
 	parseInputAsRecord

src/config.ts

@@ -16,6 +16,7 @@ export interface DevContainerConfig {
 		args?: Record<string, string>
 	}
 	runArgs?: string[]
+	mounts?: string[]
 }
 
 export async function loadFromFile(

src/docker.ts

@@ -3,6 +3,7 @@ import * as core from '@actions/core'
 import * as config from './config'
 import {exec, execWithOptions} from './exec'
 import {getAbsolutePath} from './file'
+import {substituteValues} from './envvars'
 
 export async function isDockerBuildXInstalled(): Promise<boolean> {
 	const r = await exec('docker', 'buildx', '--help')
@@ -43,7 +44,7 @@ export async function buildImage(
 
 	const buildArgs = devcontainerConfig.build?.args
 	for (const argName in buildArgs) {
-		const argValue = buildArgs[argName]
+		const argValue = substituteValues(buildArgs[argName])
 		args.push('--build-arg', `${argName}=${argValue}`)
 	}
 
@@ -98,7 +99,10 @@ export async function runContainer(
 	args.push('--workdir', workspaceFolder)
 	args.push('--user', remoteUser)
 	if (devcontainerConfig.runArgs) {
-		args.push(...devcontainerConfig.runArgs)
+		const subtitutedRunArgs = devcontainerConfig.runArgs.map(a =>
+			substituteValues(a)
+		)
+		args.push(...subtitutedRunArgs)
 	}
 	if (envs) {
 		for (const env of envs) {

src/envvars.ts

@@ -0,0 +1,26 @@
+export function substituteValues(input: string): string {
+	// Find all `${...}` entries and substitute
+	// Note the non-greedy `.+?` match to avoid matching the start of
+	// one placeholder up to the end of another when multiple placeholders are present
+	return input.replace(/\$\{(.+?)\}/g, getSubstitutionValue)
+}
+
+function getSubstitutionValue(regexMatch: string, placeholder: string): string {
+	// Substitution values are in TYPE:KEY form
+	// e.g. env:MY_ENV
+
+	const parts = placeholder.split(':')
+	if (parts.length === 2) {
+		const type = parts[0]
+		const key = parts[1]
+		switch (type) {
+			case 'env':
+			case 'localenv':
+				return process.env[key] ?? ''
+		}
+	}
+
+	// if we can't process the format then return the original string
+	// as having it present in any output will likely make issues more obvious
+	return regexMatch
+}