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coc-metals

coc-metals npm code style: prettier Gitter

coc-metals is the recommended coc.nvim extension for Metals, the Scala language server. coc-metals offers automated Metals installation, easy configuration, Metals-specific commands, an embedded doctor, implementation of the decoration protocol, and many other small features.

NOTE: The readme is up-to-date with the main branch, so not all features will be available if you're using the latest stable release. The vim page on the Metals site is synced with the latest stable release

Table of Contents

Requirements

coc-metals works with both Vim and Neovim, but we recommend neovim for a smoother experience and extra features such as the decoration protocol.

  • coc.nvim - There are detailed instructions in their repo on how to get set up and running quickly.
  • Java 8 or 11 provided by OpenJDK or Oracle. Eclipse OpenJ9 is not supported, please make sure the JAVA_HOME environment variable points to a valid Java 8 or 11 installation.
  • Node >= 10 in order for coc.nvim to work correctly.
  • coc.nvim doesn't come with a default mapping for LSP commands, so you need to configure this in order for any of the commands to work. You can find an example configuration and instructions here

Installing coc-metals

Once you have coc.nvim installed, you can then install Metals a few different ways, but the easiest is by running.

:CocInstall coc-metals

If you install this way and are using the latest stable of coc.nvim, then daily your extensions will get checked to see if they are up to date. However, this is changing and has already changed in main. So in that case, you'll need to issue the :CocUpdate to update your extensions. If you install with this method youc an also see the version of your extensions by doing a :CocList extensions.

If you'd like to use the latest changes on main, but manage it using a plugin manager to download the extension, then if you are using vim-plug for example, enter the following into where you manage your plugins:

Plug 'scalameta/coc-metals', {'do': 'yarn install --frozen-lockfile'}

Then, issue a :PlugInstall to install the extension, and regularly a :PlugUpdate to update it and pull in the latest changes.

*** Keep in mind that if you are installing directly from the repo via :CocInstall with the repository url or through a plugin manager, remove coc-metals with :CocUninstall coc-metals before you add it in with one of the other methods to not conflict with one another.

Importing a build

The first time you open Metals in a new workspace it prompts you to import the build. Click "Import build" to start the installation step.

Build Import

  • "Not now" disables this prompt for 2 minutes.
  • "Don't show again" disables this prompt indefinitely. If you'd like to get this choice again, execute the metals.reset-choice command which will interactively allow you to reset choices that you've made for various things.
  • Use tail -f .metals/metals.log to watch the build import progress.
  • Behind the scenes, Metals uses Bloop to import sbt builds, but you don't need Bloop installed on your machine to run this step.

Once the import step completes, compilation starts for your open *.scala files.

Once the sources have compiled successfully, you can navigate the codebase with goto definition.

Custom sbt launcher

By default, Metals runs an embedded sbt-launch.jar launcher that respects .sbtopts and .jvmopts. However, the environment variables SBT_OPTS and JAVA_OPTS are not respected.

Update the metals.sbtScript setting to use a custom sbt script instead of the default Metals launcher if you need further customizations like reading environment variables.

sbt-launcher

Speeding up import

The "Import build" step can take a long time, especially the first time you run it in a new build. The exact time depends on the complexity of the build and if library dependencies need to be downloaded. For example, this step can take everything from 10 seconds in small cached builds up to 10-15 minutes in large uncached builds.

Consult the Bloop documentation to learn how to speed up build import.

Importing changes

When you change build.sbt or sources under project/, you will be prompted to re-import the build.

Build Re-Import

Configure Java version

The coc-metals extension uses by default the JAVA_HOME environment variable (via find-java-home) to locate the java executable.

No Java Home

If no JAVA_HOME is detected you can then Open Settings by following the instructions or do it at a later time by using :CocConfig or :CocConfigLocal which will open up your configuration where you can manually enter your JAVA_HOME location.

java-home

coc.nvim uses jsonc as a configuration file format. It's basically json with comment support.

In order to get comment highlighting, please add:

autocmd FileType json syntax match Comment +\/\/.\+$+

Using latest Metals SNAPSHOT

Update the "Server Version" setting to try out the latest pending Metals features.

After updating the version, you'll be triggered to reload the window. This will be necessary before the new version will be downloaded and used.

Update Metals Version

List all workspace compile errors

To list all compilation errors and warnings in the workspace, run the following command.

:CocList diagnostics

Or use the default recommended mapping <space> a.

This is helpful to see compilation errors in different files from your current open buffer.

Diagnostics

If you'd like to get all of the workspace diagnostics in your statusBar since by default you will only see the diagnostics for the buffer, you can find a section here in the wiki explaing how to do it.

Run doctor

To troubleshoot problems with your build workspace, open your coc commands by either using :CocCommand or the recommend mapping <space> c. This will open your command window allowing you to search for metals.doctor-run command.

Run Doctor Command

This command opens an embedded doctor in your preview window. If you're not familiar with having multiple windows, you can use <C-w> + w to jump into it.

Embedded Doctor

Worksheets

Metals allows users to create a *.worksheet.sc file and see evaluations right in their file. In Vim, this is done using comments that are inserted which will allow you to hover on them to expand. In Neovim, this is done using Neovim's virtual text to implement Metal's Decoration Protocol. If using Neovim, make sure to have the following line included in your .vimrc along with your coc.nvim mappings. Also keep in mind that the worksheet needs to be created inside of your project to have access to your dependencies etc. If you create them in the root of your project for example, your worksheet will only have access to the standard lib.

nmap <Leader>ws <Plug>(coc-metals-expand-decoration)

Then, when on the line that you'd like to expand the decoration to get the hover information, execute a <leader>ws in order to see the expanded text for that line.

Decorations with worksheets

NOTE Keep in mind that you can also directly import dependencies is your worksheet just like you would in an Ammonite script. This is a great way to try something out without changing your build definition.

Tree View Protocol

Tree View Protocol

coc-metals has a built-in implementation of the Tree View Protocol. If you have the recommended mappings copied, you'll notice that in the bottom you'll have some TVP related settings. You can start by opening the TVP panel by using the default <space> t. Once open, you'll see there are three parts to the panel. The first being the MetalsCompile window where you can see ongoing compilations, the second is the MetalsPackages window where you are able to see a tree view of all your packages, and finally the metalsBuild window where you have build related commands.

You are able to trigger the commands while being on top of the option you are attempting to trigger and pressing r. You can change this default in the settings. You can find all the relevant TVP settings below in the Available Configuration Options.

Goto Super Method

Depending on whether you're using Vim or Neovim, you'll have a slightly different behavior with this feature. If you're using Neovim, you'll want to ensure that you have codeLens.enable set to true in your Coc Config since you'll be able to quickly see via code lenses which members are overridden. Then, you'll be able to simply trigger a code lens action on the line of the member that is overridden. The default mapping for this is <leader> cl.

If you're using Vim, you'll still have access to this functionality, but you'll have to infer which members are overridden and utilize the metals.go-to-super-method command.

There is also a metals.super-method-hierarchy command which will show you the entire hierarchy of the overridden method.

Goto super method

If you don't utilize this feature you can disable it by setting metals.superMethodLensesEnabled to false.

All Available Commands

You can see a list of all the available Metals server commands on the Metals Website.

You can also view these by toggling the CocList commands, which is <space>c with the default mappings.

Show document symbols

Run :CocList outline to show a symbol outline for the current file or use the default mapping <space> o.

Document Symbols

Available Configuration Options

The following configuration options are currently available. The easiest way to set these configurations is to enter :CocConfig or :CocLocalConfig to set your global or local configuration settings respectively.

If you'd like to get autocompletion help for the configuration values you can install coc-json.

Configuration Option Description
metals.enable Enable the coc-metals extension (default true)
metals.serverVersion The version of the Metals server artifact. Requires reloading the window.
metals.serverProperties Optional list of properties to pass along to the Metals server. By default, the environment variable JAVA_OPTS and .jvmopts file are respected.
metals.ammoniteJvmProperties Optional list of JVM properties to pass along to the Ammonite server. Each property needs to be a separate item. Example: -Xmx1G or -Xms100M
metals.javaHome Optional path to the Java home directory. Requires reloading the window. Defaults to the most recent Java 8 version computed by the locate-java-home npm package.
metals.sbtScript Optional absolute path to an sbt executable to use for running sbt bloopInstall. By default, Metals uses java -jar sbt-launch.jar with an embedded launcher while respecting .jvmopts and .sbtopts. Update this setting if your sbt script requires more customizations like using environment variables.
metals.millScript Optional absolute path to a mill executable to use for running mill mill.contrib.Bloop/install. By default, Metals uses an embedded millw script while respecting .mill-version file. Update this setting if your mill script requires more customizations.
metals.mavenScript Optional absolute path to a mvn executable to use for running mvn ch.epfl.scala:maven-bloop_2.10:<bloop_version>:bloopInstall. By default, Metals uses an embedded mvnw script. Update this setting if your mvn script requires more customizations.
metals.gradleScript Optional absolute path to a gradle executable to use for running gradle bloopInstall. By default, Metals uses an embedded gradlew script. Update this setting if your gradle script requires more customizations.
metals.scalafmtConfigPath Optional custom path to the .scalafmt.conf file. Should be an absolute path and use forward slashes / for file separators (even on Windows).
metals.scalafixConfigPath Optional custom path to the .scalafix.conf file. Should be an absolute path and use forward slashes / for file separators (even on Windows).
metals.customRepositories Optional list of custom resolvers passed to Coursier when fetching metals dependencies. For documentation on accepted values see the Coursier documentation. The extension will pass these to Coursier using the COURSIER_REPOSITORIES environment variable after joining the custom repositories with a pipe character (
metals.bloopVersion This version will be used for the Bloop build tool plugin, for any supported build tool,while importing in Metals as well as for running the embedded server
metals.bloopSbtAlreadyInstalled If true, Metals will not generate a project/metals.sbt file under the assumption that sbt-bloop is already manually installed in the sbt build. Build import will fail with a 'not valid command bloopInstall' error in case Bloop is not manually installed in the build when using this option.
metals.statusBarEnabled Turn on usage of the statusBar integration. Note: You need to ensure you are adding something like %{coc#status()} in order to display it, or use a plugin that includes a status integration.
metals.superMethodLensesEnabled Enable/disable goto super method code lens (default is true)
metals.enableStripMarginOnTypeFormatting When enabled, if you press the return key from the first line of a multiline string containing a pipe, it will automatically add .stripMargin. (default is true)
metals.excludedPackages List of packages you'd like to be left out of completions, symbol searches, and code actions. Ex. akka.actor.typed.javadsl will ensure nothing in the javadsl package gets recommended to you. You can find the list of default exclusions here on the Metals website. If you need to remove one of the defaults, you can simply include it and preface it with --.
metals.showInferredType When this option is enabled, each method that has infered types have those types displayed as extra info in the hover window.
metals.showImplicitArguments When this option is enabled, each method that has implicit arguments have those aruments displayed as extra info in the hover window.
metals.showImplicitConversionsAndClasses When this option is enabled, each implicit method and class is displayed as extra info in the hover window.
metals.treeviews.toggleNode Expand / Collapse tree node (default <CR>)
metals.treeviews.initialWidth Initial Tree Views panels (default 40)
metals.treeviews.initialViews Initial views that the Tree View Panel Displays. Don't mess with this unless you know what you're doing.
metals.treeviews.gotoLastChild Go to the last child Node (defalt J)
metals.treeviews.gotoParentNode Go to parent Node (default p)
metals.treeviews.gotoFirstChild Go to first child Node (default K)
metals.treeviews.executeCommand Execute command for node (default r)
metals.treeviews.gotoPrevSibling Go to prev sibling (default <C-k>)
metals.treeviews.gotoNextSibling Go to next sibling (default <C-j>)
metals.treeviews.forceChildrenReload Force the reloading of the children of this node. May be useful when the wrong result is cached and tree contains invalid data. (default f)
metals.treeviews.executeCommandAndOpenTab Execute command and open node under cursor in tab (if node is class, trait and so on) (default t)
metals.treeviews.executeCommandAndOpenSplit Execute command and open node under cursor in horizontal split (if node is class, trait and so on) (default s)
metals.treeviews.executeCommandAndOpenVSplit Execute command and open node under cursor in horizontal split (if node is class, trait and so on) (default v)

Enable on type formatting for multiline string formatting

on-type

To properly support different multiline string formatting options like adding | in your multiline string we use the onTypeFormatting LSP functionality. To enable the functionality you need to enable coc.preferences.formatOnType setting.

coc-preferences-formatOnType

Shut down the language server

The Metals server is shutdown when you exit vim as you normally would.

:wq

This step clean ups resources that are used by the server.

Statusline integration

It's recommended to use a statusline integration with coc-metals in order to allow messages to be displayed in your status line rather than as a message. This will allow for a better experience as you can continue to get status information while entering a command or responding to a prompt. However, we realize that not everyone by default will have this setup, and since the user needs to see messages about the status of their build, the following is defaulted to false.

"metals.statusBarEnabled": true

Again, it's recommended to make this active, and use a statusline plugin, or manually add the coc status information into your statusline. coc.nvim has multiple ways to integrate with various statusline plugins. You can find instructions for each of them located here. If you're unsure of what to use, vim-airline is a great minimal choice that will work out of the box.

With vim-airline, you'll notice two noteworthy things. The first will be that you'll have diagnostic information on the far right of your screen.

Diagnostic statusline

You'll also have metals status information in your status bar.

Status bar info

Without a statusline integration, you'll get messages like you see below.

No status line

If you don't use a statusline plugin, but would still like to see this information, the easiest way is to make sure you have the following in your .vimrc.

set statusline^=%{coc#status()}%{get(b:,'coc_current_function','')}

Formatting on save

If you'd like to have :w format using Metals + Scalafmt, then make sure you have the following in your :CocConfig.

"coc.preferences.formatOnSaveFiletypes": ["scala"]

Analyzing Stacktraces

analyze-stacktrace

NOTE: Only available in Neovim since this needs virtual text.

To utilize the analyze stacktrace command you'll want to copy your your stacktrace to your register. Once copied, simply execute the metals.analyze-stacktrace command. This should create a .metals/stacktrace.scala file which will have code lenses which will allow you to jump to the part of your codebase listed in the stacktrace. Keep in mind that in order to utilize this feature you'll want to make sure you have "codeLens.enable": true in your config.

Debugging

coc-metals provides easy integration with the great vimspector plugin that allows you to run a Debug Adapter Server and debug your application with minimum manual steps.

Requirements:

  • *This is only currently available for Neovim +0.4.3 for now until the the launch.json Metals expects can be mapped to match the .vimspector.json file that vimspector uses. For now, you'll need to trigger the run or debug with code lenses provided by Neovim.

  • vimspector plugin - Basically you just need to add vimspector into vim's runtimepath, for example, if you are using vim-plug then add this line in .vimrc

Plug 'puremourning/vimspector'

Configuration:

The vimspector documentation is quite robust, so please make sure to read through it.

There are multiple ways to have you base configuration for vimspector to work with Metals. You can either set this up globally to work with all of your Scala projects or for an individual project.

Global Example:

Put your coc-metals.json file in the following directory: /path/to/vimspector/configurations/{os}/scala (where os is linux, macos or windows) with following content:

{
  "configurations": {
    "coc-metals": {
      "adapter": {
        "port": "${port}",
        "variables": {
        }
      },
      "configuration": {
        "request": "launch"
      },
      "breakpoints": {
        "exception": {
          "caught": "N",
          "uncaught": "N"
        }
      }
    }
  }
}

You can also just place the same contents above in the root of your local project in a .vimspector.json file, and it will work the same way.

With these configuration parameters the codeLens 'run' and 'debug' appear against runnable classes (applications or tests) of your project. Then, you will be able to trigger these codeLens actions (default mapping is <leader> cl) and start Debug Adapter Server. Once Debug Adapter Server is started coc-metals will transfer necessary information to vimspector to activate debugging.

For now both actions 'run' and 'debug' start vimspector in debug mode. This may be improved in next versions.

Gitignore

The Metals server places logs and other files in the .metals/ directory. The Bloop compile server places logs and compilation artifacts in the .bloop directory. A Bloop plugin that generates Bloop configuration is added in the project/metals.sbt file. If you are editing Ammonite scripts, you'll also see an .ammonite directory created for Ammonite. It's recommended to ignore these directories and file from version control systems like git.

# ~/.gitignore
.metals/
.bloop/
project/metals.sbt
.ammonite/

Troubleshooting

If you have any questions or issues with coc-metals, please submit an issue in this repo if it pertains to the extension. If the issues is general to Metals, please submit it in the Metals issue repo. If you have any feature requests, we also have a feature request issue repo. There is also a section in the wiki for Commonly Asked Questions. Fee free to peruse that to potentially find an answer you may be looking for.

Contributing

If you're interested in contributing, please visit the CONTRIBUTING guide for help on getting started.

Theme

The screen shots are in Neovim. The theme is onedark. The status bar is vim-airline, and all being ran in iTerm2.


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