An Emacs mode for the Dart language
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README.md

dart-mode is a major mode for editing Dart files in Emacs.

Installation

  1. Add Marmalade to your package-archives if you don't already have it.

  2. Install dart-mode via:

    M-x package-refresh-contents [RET]
    M-x package-install [RET] dart-mode
    

General Configuration

The dart-sdk-path variable can be set to tell Emacs where to find the Dart SDK. This is used to run the Dart analysis server and the Dart formatter. By default, it's set by finding the dart executable on the system path.

Note that user code that wants to run Dart scripts can use the dart-executable-path function to locate the dart executable itself in the SDK's bin/ directory.

Dart Analyzer

dart-mode supports the Dart analysis server, which runs in the background and analyzes your Dart code to figure out what every identifier and method call refers to. It provides all sorts of useful features that aren't possible when your code is treated as plain text.

To enable analyzer support, add (setq dart-enable-analysis-server t) to your .emacs file.

Error Checking

The Dart analyzer can use Flycheck to notify you of errors and warnings in your Dart code. To enable this, just add (add-hook 'dart-mode-hook 'flycheck-mode) to your .emacs file. Don't worry about installing Flycheck—if you have dart-mode, you automatically have it as well!

Seeing Information

To see all the information the analyzer knows about a particular identifier, move your cursor onto it and press C-c ?. This will show the identifier's type and documentation in the echo area at the bottom of the editor, as well as some extra information if it's available.

Sometimes there's just too much documentation to fit down there, or you want to keep the documentation open as you're working. In that case, you can run C-u C-c ? instead to open the information in a new window to read at your leisure.

Navigation

When your cursor is on an identifier, you can press C-c C-g to go to the exact location that identifier was originally defined. This can even take you to the Dart SDK's sources, or to packages that your library imports. Be careful when you're there, though: any edits may corrupt your package cache!

Search

There are several ways to use the analyzer to search through your Dart code. All of these pop up a search results window listing every use with handy links to take you right to the code. Note that for large codebases, additional results may be added to these results pages as the analyzer finds them. But once you see the last "Found X results" line, you know for sure you're seeing everything!

  • You can search for all references to the identifier under your cursor by pressing C-c C-f. This will show you everywhere a method, getter, or setter is called; everywhere a class is used as a type, constructed, or has static methods called on it; everywhere a named argument is passed; and so on.

  • You can search for all member declarations with a given name by pressing C-c C-e. This will list all declarations within classes that have the name, but not any declarations at the top level.

  • If you want to search for top-level declarations instead, you can press C-c C-t.

  • If you want to find all references to members with a given name, you can press C-c C-r. This will show you everywhere a member with that name is called, even if it's in a dynamic context and the analyzer can't figure out what it's referring to.

Expansion

If you press M-/, the analyzer will try to expand whatever text you've already typed into a valid identifier. This uses the same logic that IDEs use for autocomplete, but the UI works like Emacs' dabbrev-expand command. You can press M-/ multiple times in a row to cycle through possible completions.

When you've selected an expansion that's a method call, you can press M-? (M-/ plus shift) to insert the parameter list. The first parameter will be selected, and anything you type will replace it. Once it's replaced, you can press M-? again to select the second parameter, and so on.

If the analysis server isn't enabled for the current buffer, this will fall back to whatever command is assigned to M-/ outside of Dart mode (dabbrev-expand in vanilla Emacs). This will usually pick up any custom key bindings, but if it doesn't you can manually choose a fallback by setting the `

Dart Formatter

Dart comes with a formatter that modifies Dart code's whitespace to make the formatting consistent and readable. You can press C-c C-o to format the current buffer.

Formatter Configuration

By default, dart-mode will use the version of the formatter that's bundled with the Dart SDK. However, you can customize this by setting dart-formatter-command-override. Note that if you want to access the formatter command from Elisp, you should call the dart-formatter-command function instead.

When formatting fails, usually because the buffer's Dart code couldn't be parsed, a buffer listing the errors will pop up by default. This behavior can be customized by setting dart-formatter-show-errors. It has three valid values:

  • 'buffer is the default, and pops up a buffer listing the errors.
  • 'echo shows the errors temporarily in the echo area at the bottom of the frame.
  • nil doesn't show the errors at all.

If you set the dart-format-on-save variable to t, the formatter will be run automatically before you save any Dart buffer. This can be helpful when working on codebases where formatting is required.