Add addPath to core (#13)

* Add add-path

* Format

* lint

packages/core/__tests__/lib.test.ts

@@ -1,5 +1,6 @@
 import {ExitCode} from '@actions/exit'
 import * as os from 'os'
+import * as path from 'path'
 import * as core from '../src/core'
 
 /* eslint-disable @typescript-eslint/unbound-method */
@@ -11,6 +12,7 @@ const testEnvVars = {
   'my secret': '',
   'special char secret \r\n];': '',
   'my secret2': '',
+  PATH: `path1${path.delimiter}path2`,
 
   // Set inputs
   INPUT_MY_INPUT: 'val',
@@ -78,6 +80,14 @@ describe('@actions/core', () => {
     ])
   })
 
+  it('prependPath produces the correct commands and sets the env', () => {
+    core.addPath('myPath')
+    expect(process.env['PATH']).toBe(
+      `myPath${path.delimiter}path1${path.delimiter}path2`
+    )
+    assertWriteCalls([`##[add-path]myPath${os.EOL}`])
+  })
+
   it('getInput gets non-required input', () => {
     expect(core.getInput('my input')).toBe('val')
   })

packages/core/src/core.ts

@@ -1,6 +1,8 @@
 import {ExitCode} from '@actions/exit'
 import {issue, issueCommand} from './command'
 
+import * as path from 'path'
+
 /**
  * Interface for getInput options
  */
@@ -33,6 +35,15 @@ export function exportSecret(name: string, val: string): void {
   issueCommand('set-secret', {}, val)
 }
 
+/**
+ * Prepends inputPath to the PATH (for this action and future actions)
+ * @param inputPath
+ */
+export function addPath(inputPath: string): void {
+  issueCommand('add-path', {}, inputPath)
+  process.env['PATH'] = `${inputPath}${path.delimiter}${process.env['PATH']}`
+}
+
 /**
  * Gets the value of an input.  The value is also trimmed.
  *