allow specifying the version as lts to install the latest LTS version

for now, this just hardcodes the LTS version in the source (similar to how juliaup does it) since the latest LTS is not available in `versions.json`. Since the LTS is updated so rarely this might be ok for now.

.github/workflows/example-builds.yml

@@ -19,7 +19,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        julia-version: ['1.0.5', '1.2', '^1.5.0-beta1', '1']
+        julia-version: ['1.0.5', '1.2', '^1.5.0-beta1', '1', 'lts']
         julia-arch: [x64, x86]
         os: [ubuntu-latest, macOS-latest, windows-latest]
         # 32-bit Julia binaries are not available on macOS

README.md

@@ -109,6 +109,7 @@ You can either specify specific Julia versions or version ranges. If you specify
 - `'~1.3.0-rc1'` is a **tilde** version range that includes pre-releases of `1.3.0` starting at `rc1`. It matches all versions `≥ 1.3.0-rc1` and `< 1.4.0`.
 - `'^1.3.0-0'` is a **caret** version range that includes _all_ pre-releases of `1.3.0`. It matches all versions `≥ 1.3.0-` and `< 2.0.0`.
 - `'~1.3.0-0'` is a **tilde** version range that includes _all_ pre-releases of `1.3.0`. It matches all versions `≥ 1.3.0-` and `< 1.4.0`.
+- `'lts'` will install the latest LTS build.
 - `'nightly'` will install the latest nightly build.
 - `'1.7-nightly'` will install the latest nightly build for the upcoming 1.7 release. This version will only be available during certain phases of the Julia release cycle.
 

__tests__/installer.test.ts

@@ -55,6 +55,11 @@ describe('version matching tests', () => {
             expect(installer.getJuliaVersion([], 'nightly')).toEqual('nightly')
             expect(installer.getJuliaVersion(testVersions, 'nightly')).toEqual('nightly')
         })
+
+        it('LTS', () => {
+            // Update test when LTS is updated
+            expect(installer.getJuliaVersion(testVersions, 'lts')).toEqual(installer.getJuliaVersion(testVersions, '1.6'))
+        })
     })
 
     describe('version ranges', () => {

src/installer.ts

@@ -10,6 +10,8 @@ import retry = require('async-retry')
 
 import * as semver from 'semver'
 
+const LTS_VERSION = '1.6'
+
 // Translations between actions input and Julia arch names
 const osMap = {
     'win32': 'winnt',
@@ -82,6 +84,10 @@ export function getJuliaVersion(availableReleases: string[], versionInput: strin
         return versionInput
     }
 
+    if (versionInput == 'lts') {
+        return getJuliaVersion(availableReleases, LTS_VERSION, includePrerelease)
+    }
+
     // Use the highest available version that matches versionInput
     let version = semver.maxSatisfying(availableReleases, versionInput, {includePrerelease})
     if (version == null) {

src/setup-julia.ts

@@ -1,5 +1,4 @@
 import * as core from '@actions/core'
-import * as exec from '@actions/exec'
 import * as tc from '@actions/tool-cache'
 
 import * as fs from 'fs'