# Adding a new language

If you want to add a new language to the site, you should follow this steps:

* Add the new language to the exported `languages` variable in `lib/languages.js`:
    - The syntax is as follows:
  ```js
  'language-key': {
    name: YOUR_LANGUAGE_DISPLAY_NAME,
    monaco: MONACO_MODE_ID,
    extensions: ARRAY_OF_FILE_EXTENSIONS_OF_YOUR_LANGUAGE,
    alias: [], // Leave empty unless needed
  }
  ```
    - If the language is supported by Monaco Editor (You can find the
      list [here](https://github.com/microsoft/monaco-languages/tree/main/src)), you should add it to the list of
      languages inside the `MonacoEditorWebpackPlugin` config in `webpack.config.js`
    - If not, you should implement your own language mode; see `static/modes/asm-mode.js` as an example. Don't forget
      to *require* your mode file in `static/modes/_all.js`, in alphabetical order
    - `language-key` is how your language will be referred internally by the code. In the rest of this document,
      replace `{language-key}` by the corresponding value in the real files.

* Add a `lib/compilers/{language-key}.js` file using the template below:
    ```js
    import { BaseCompiler } from '../base-compiler';

    export class LanguageCompiler extends BaseCompiler {
        static get key() { return 'language'; }
    }
    ```
    - The value returned by `key` above corresponds to the `compilerType` value
      in `etc/config/{language-key}.defaults.properties` (Explained below). This is usually `{language-key}`, but you
      can use whatever fits best
    - Override the `OptionsForFilter` method from the base class
    - Comment out the line saying `fs.remove(result.dirPath);` in base-compiler.js, so the latest CE compile attempt
      remains on disk for you to review
        - Remember to undo this change before opening a PR!
    - For reference, the basic behaviour of BaseCompiler is:
        - make a random temporary folder
        - save example.extension to the new folder, the full path to this is the `inputFilename`
        - the `outputFilename` is determined by the `getOutputFilename()` method
        - execute the compiler.exe with the arguments from `OptionsForFilter()` and adding `inputFilename`
        - be aware that the language class is only instanced once, so storing state is not possible
    - If the compiler has problems with the defaults, you will have to override the `runCompiler()` method too. When
      overriding it, here are some ideas
        - set `execOptions.customCwd` parameter if the working directory needs to be somewhere else
        - set `execOptions.env` parameter if the compiler requires special environment variables
        - manipulate `options`, but make sure the user can still add their own arguments in CE

* Add your `LanguageCompiler` to `lib/compilers/_all.js`, in alphabetical order

* Add a `etc/config/{language-key}.local.properties` file:
    - The syntax for its basic contents is documented in [AddingACompiler.md](AddingACompiler.md)
    - This file is ignored by Git, so that you can test the config locally
    - You should add 1 compiler for the language you want to test
    - Test the command line options of the language compilers outside CE

* Add a new file `etc/config/{language-key}.defaults.properties`. This is where a default configuration will live.
    - Usually, this loads default compilers from their usual paths on a normal installation 
      (Check `etc/config/c++.defaults.properties` for an example)

* Of important note, for both files, is to properly define `compilerType` property in the newly added compilers. This
  should equal the value returned by your `LanguageCompiler.key` function

* Running `make dev EXTRA_ARGS="--debug --language {language-key}"` to tell CE to only load your new language

* You can check http://127.0.0.1:10240/api/compilers to be sure your language and compilers are there

* Make an installer in the [infra](https://github.com/compiler-explorer/infra) repository

* Add your language files (`{language-key}.*.properties` and `lib/compilers/{language-key}.js`) to the list
  in `.github/labeler.yml`
