feat: detect install command

Author: tpluscode

README.md

@@ -38,7 +38,7 @@ The inputs this action uses are:
 | `NETLIFY_DEPLOY_MESSAGE` | `false` | '' | An optional deploy message |
 | `build_directory` | `false` | `'build'` | The directory where your files are built |
 | `functions_directory` | `false` | N/A | The (optional) directory where your Netlify functions are stored |
-| `install_command` | `false` | `npm i` | The (optional) command to install dependencies |
+| `install_command` | `false` | Auto-detected | The (optional) command to install dependencies. Runs `yarn` when `yarn.lock` is found; `npm i` otherwise |
 | `build_command` | `false` | `npm run build` | The (optional) command to build static website |
 | `deploy_alias` | `false` | '' | (Optional) [Deployed site alias](https://cli.netlify.com/commands/deploy) |
 

action.yml

@@ -36,7 +36,7 @@ inputs:
   install_command:
     description: 'Command to install dependencies'
     required: false
-    default: 'npm i'
+    default: ''
 
   build_command:
     description: 'Command to build static website'

entrypoint.sh

@@ -12,7 +12,15 @@ BUILD_COMMAND=$7
 DEPLOY_ALIAS=$8
 
 # Install dependencies
-eval ${INSTALL_COMMAND:-"npm i"}
+if [[ -n $INSTALL_COMMAND ]]
+then
+	eval $INSTALL_COMMAND
+elif [[ -f yarn.lock ]]
+then
+	yarn
+else
+	npm i
+fi
 
 # Build project
 eval ${BUILD_COMMAND:-"npm run build"}