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An emacs mode for interacting with scala sbt and projects
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README.md

The mode provides basic functionality required for successfully interacting with sbt inside emacs. The core functionality includes:

  • interacting with sbt shell and scala console
  • compiling code and navigating to errors

See also (emacs-scala-mode)[https://github.com/hvesalai/emacs-scala-mode].

Installation

The preferred mechanism is via MELPA and use-package as per our Learning Emacs guide:

(use-package sbt-mode
  :commands sbt-start sbt-command
  :config
  ;; WORKAROUND: allows using SPACE when in the minibuffer
  (substitute-key-definition
   'minibuffer-complete-word
   'self-insert-command
   minibuffer-local-completion-map))

Start an sbt session with M-x sbt-start or send a command to the current sbt process with M-x sbt-command.

You might also want to customize some sbt-mode variables (run M-x customize-mode RET sbt-mode).

For example you can play with variable sbt:scroll-to-bottom-on-output. If set to t (which is a default value) sbt output buffer scrolls automatically to the last line if there is some new output. Setting this variable to nil will cause point remain on it's current position in a buffer when there is some new output. If set to nil and point is on the last line, it scrolls automaticaly with new output, but if there is compilation error (line beginning [error] - ...) it will stop on that line.

sbt 1.0

Although sbt 1.0 is supported, there are some niggles. Pull requests are always welcome to enhance the mode.

Related Customizations

To work efficiently with sbt-mode, you may wish to customise your workflow with the built-in Emacs compile support:

  • customise compilation-skip-threshold
  • locally bind a key to comint-bol
  • locally bind a key to comint-accumulate
  • locally bind a key to next-error

A more daring customisation is to use prettify-symbols-mode to replace long repetitive strings with symbols. For example

(add-hook 'sbt-mode-hook
          (lambda ()
            (setq prettify-symbols-alist
                  `((,(expand-file-name (directory-file-name default-directory)) . ?⌂)
                    (,(expand-file-name "~") . ?~)))
            (prettify-symbols-mode t)))

will replace occurrences of the project's root directory with the UTF-8 symbol for "house" and any long-form occurrences of your home directory with tilde.

Tasks

Searching

Most users may prefer to use projectile for these features, but sbt-mode provides also grep-based commands for searching things.

A special version of the rgrep command is available with sbt-mode.

  • M-x sbt-grep greps files in the sbt project
  • M-x sbt-find-definitions will search for the definition of the thing at point from the project .scala and .java files.
  • M-x sbt-find-usages will search for occurrences of the id at point from the project .scala and .java files.

Scala console

It is also possible to drop into an sbt console session using sbt-mode.

It is advised when typing multi-line code snippets, use comint-accumulate instead of RET for newlines. This way, if you need to modify the code, you can use M-p to recall the whole snippet for reworking.

You can also send a region of code from an other buffer in the same project. First set the mark to the other end of the region to send and the point (cursor) the other. Then run the M-x sbt-send-region command. sbt-paste-region will enter :paste mode of Scala REPL, so that multiline statement/expression will work as expected.

Compiling

The simplest way to compile the code you are working on in emacs by binding the sbt-run-previous-command to a key. For example (local-set-key (kbd "C-x '") 'sbt-run-previous-command). By default, this will run test:compile (see sbt:default-command customization variable).

Triggered execution

Triggered execution in sbt, the ~compile or ~test commands (when sbt is waiting with the message "press enter to interrupt"), can be interrupted by typing C-c C-j in sbt-mode (and C-c C-b C-j anywhere else). Hitting just RET in an sbt buffer doesn't interrupt sbt because there isn't a recognized sbt prompt in sbt-mode. Instead, hitting RET in an sbt-mode buffer will cause Emacs to complain that "Text is read-only".

Hydra

sbt-mode also offers hydra to speed up sbt interaction. This is focused mainly on running usual sbt commands compile, test:compile, test, run etc. on multiproject build. Hydra allows to execute these commands on per project basis.

Basics

Run the M-x sbt-hydra command. This will start new sbt process in sbt buffer (if there is already sbt process running it will switch to it's buffer).

You will see message:

Please wait! sbt projects are loading. sbt Hydra will be ready soon.

while sbt is launching.

To generate hydra we need to get information about available projects. This is done by running projects command in sbt (this is done automatically as soon as sbt is ready). After this is done, you will see message:

Success hydra for projects (projectA, projectB, ...) created.

After you will see this message run M-x sbt-hydra command again and you will see hydra appearing at the bottom of the screen. By pressing h you can invoke help where you can learn more detais about Hydra features.

We recommend to bind sbt-hydra command to some convenient shortcut.

Recommended usage

Hydra remembers last command which was executed and it can run this command automatically again on a save of an edited file. Of course it would be undesirable to run 10 commands when saving 10 edited files by save-some-buffers command so for this reason last sbt command will be run again only on a save of last edited file.

To enable this feature add sbt-hydra:check-modified-buffers into before-save-hook. For example:

(add-hook 'sbt-mode-hook (lambda ()
                           (add-hook 'before-save-hook 'sbt-hydra:check-modified-buffers)))

To eliminate undesirable execution of last sbt command, there is customizable variable allowed-files-regexp containing regular expressions to detect files which when edited will cause executing last sbt command again. By default this variable contains two records: .*.scala$ and ^routes$.

Customization

There exists 3 Directory Local Variables which provides more customization for Hydra. They must be specified in .dir-locals.el file in the root of your sbt project.

1. sbt-hydra:projects

This variable allows to specify list of projects to include in the Hydra. By default Hydra includes all sbt projects, which in case there is lots of them make working with Hydra cumbersome. This variable, when set, allows to specify subset of all projects.

((sbt-mode
  (sbt-hydra:projects "api" "core" "foo" "jerky" "server" "swanky" "util")))

2. sbt-hydra:command-line-arguments

When using run sbt command we usually want to provide some command line arguments to the main method. This variable allows us to specify these arguments. We can provide different arguments for every projects. Example configuration looks like this:

((sbt-mode
  (sbt-hydra:command-line-arguments . (
    ("restApi" . "myconf.conf development")
    ("jobs" . "delivery_flag")
    ("identityManager" . "myconf.conf 9001")))))

Here we have 3 sbt projects restApi, jobs and identityManager. For example when we execute run command through r hydra key we provide myconf.conf development arguments to restApi project main method.

3. sbt-hydra:system-properties

When using run sbt command we may to set system variables for our program to use while running. This variable allows us to specify system variables without need to manipule environment variables. When set they will be provided to our main method by forking JVM and putting them into javaOptions before executing run itself.

((sbt-mode
  (sbt-hydra:system-properties . (
    ("macwire" . ("-Dconf.file=myconf.conf" "-Xmx1G"))
    ("reader" . ("-Dconf.file=myconf.conf" "-Xmx1G"))))))

Here we have 2 sbt projects macwire and reader. For example for macwire project there will be set two system variables -Dconf.file=myconf.conf and -Xmx1G.

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