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This repo implements a LSIF indexed for Haskell source files.

It relies on HIE files which will be released in GHC 8.8.

What works:

  1. References and definitions
  2. Indexing for a single complete project
  3. Hover to show types

Things which are not implemented yet and their status are:

  1. Cross-project references (because I don't understand the spec) microsoft/language-server-protocol#680
  2. textDocument/documentSymbol just TODO
  3. textDocument/foldingRange - This is easy when you decide what the folding ranges should be. I just don't really like the feature so haven't done it yet.
  4. textDocument/documentLink - I'm not sure how you would implement this.
  5. Work out what the difference between definition/declaration is
  6. Work out how type definition is different to just normal definition.
  7. Work out how implementation is different to declaration to definition.

Other improvements that have to be made.

  1. It might be good to try to compress the JSON output, the JSON output for the groups example is about 25000 lines long for a 100 line text file. This will surely be a problem when trying to index a big project. This can be done by inlining certain edges but I thought the whole point was not to buffer anything.

  2. Switch to Zubin's encoding. This will make it easier to generate the right thing and also make 1. easier probably.

  3. Set up a nix example which turns on -fwrite-interface-file and then generates the lsif.json file for the project.

  4. Integrate LSIF generation into hadrian.

Instructions about how to use

The integration is not very good yet but if you're brave... The instructions are mainly here so that I can make them simpler.

Pre-requestite: A suffifiently new version of GHC (anything called 8.7 will probably work), I use ghc-artefact-nix to enter a shell with a recent enough version.

You will need to generate some .hie files by compiling a file with the -fwrite-ide-info command.

Then running cabal new-run exe:hie-lsif will produce a file called test.json. This is the LSIF file.

Commandline arguments

hie-lsif accepts the following arguments

  • --root <dir>: specify the directory all the paths in the hie files are to be considered relative too. This is usually the root directory of your project, or the working directory of ghc when it is used to generate the hie files

    Defaults to the current working directory

  • --hie <dir>: the location of the directory where the hie files are stored

    Defaults to the current working directory

  • --include-contents: flag which controls whether the contents of the haskell source files(as stored in .hie files) should be included in the generated lsif file.

Using the file

First, copy the test.json file to the root of the project you want to use it with. Rename it to lsif.json.

You probably should open the file and check the paths are correct in it to the source file as the language server will not do anything unless they are right. All the paths will be at the start of the file.

Then, you have to install the LSIF language server from my fork so that it starts up with Haskell files. There are instructions in the README there on how to do that.

Once that is installed, in vscode, open the folder where the source files and the lsif.json files are located.

Things to note about the language server:

  1. It only reads the lsif.json file once on startup. If you change the lsif.json file you have to close and reopen the folder for it to read the new changes.
  2. You can't use a symlink for the lsif.json file.

It can be useful to open the debugging pane to see what the language server is doing, if anything.

Using the file in the editor

If you hover over an identifier now, it should show you the type of the identifier. If you right click on an identifier you should be able to find all references, jump to definition and so on.


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