IntelliJ plugin for Haskell

When I was learning Haskell, I missed the nice features of IntelliJ IDEA. My first approach was to use default way of creating an IntelliJ plugin by defining a grammar and a lexer according to Haskell report. That didn't work out because I could not define all the recursion. Then I decided to use grammar and lexer definitions only for tokenizing and parsing Haskell code, and not for syntax checking the code. This is needed for syntax highlighting, all kinds of navigation and so on. Further Haskell language support is provided with the support of external tools: ghc-mod and haskell-docs.

This plugin is written mainly in Scala and is not meant to support GHC/Cabal directly. It supports sandbox projects and expects that Cabal init/install/build is done on the command line.

Any feedback is welcome!!

Features

Syntax highlighting (which can be customized);
Error/warning highlighting;
Find usages of identifiers;
Resolve references to identifiers (also to library code if library source code is added to project and resolves inside import declaration);
Code completion by resolving references;
In-place rename identifiers (in which global rename first shows preview so refactoring scope can be adjusted).
View type info from (selected) expression;
View expression info;
View quick documentation;
View quick definition;
Structure view;
Navigate to declaration (called Class in IntelliJ menu);
Navigate to identifier (called Symbol in IntelliJ menu);
Code completion by looking to import declarations;
Simple form of code formatting;
Inspection by HLint;
Quick fixes for HLint suggestions;
View error, action to view formatted message from ghc-mod. Especially useful in case message consists of multiple lines (Ctrl-F10, Meta-F10 on Mac OSX);
Intention actions (suggested by ghc-mod);

A lot of features are with the help of ghc-mod(i)!!

Getting started:

Cabal install latest versions of ghc-mod and haskell-docs;
Set file paths to ghc-mod, ghc-modi, hlint, cabal and haskell-docs in the menu Settings/Other Settings/Haskell.
Be sure in Editor/Filetypes that Haskell language file is registered with pattern *.hs and Literate Haskell language file with pattern *.lhs;
First install and build your project in a Cabal sandbox. (Make sure that Haddock documentation is generated, see haskell-docs).
After the project is built in the sandbox, create a Haskell project in IntelliJ by using File/New/Project... from the IntelliJ menu;
In the New Project wizard select Haskell module and check Haskell in Additional Libraries and Frameworks;
In next page of wizard create GHC SDK by selecting path to GHC binaries, e.g. /usr/local/bin;
In last page of wizard select path to root of project;
Add Content Root to Haskell module in Project structure/Project Settings/Modules/Sources by selecting root folder of Haskell sandbox project;
Select in Project structure/Project settings/Modules which folders to exclude (like .cabal-sandbox and dist) and which folders are Source and Test (normally src and test).
Use Tools/Add Haskell package dependencies to download all sources of dependencies. They will be added as source libraries to module. If you use Cabal 1.22 also test dependencies will be downloaded. This option gives you nice navigation features through libraries. Sources are downloaded to folder ideaHaskellLib inside root of project

Remarks

~~ghc-mod does not support GHC < 7.10 and Cabal 1.22. See for more info the ghc-mod wiki. So in case you are using for example GHC 7.8.4, you will have to use Cabal 1.20.x~~ ;
In Navigation dialog dots can not be used. Workaround is by using spaces instead of dots, so when you want to go to Control.Lens, type Control Lens;
IntelliJ has a nice terminal plugin, useful for executing the Cabal commands;
ghc-mod can not help in library files and if Haskell source file contains not completely valid Haskell (e.g. while typing). In that case I try to solve request by using AST-tree (IntelliJ calls it PSI-tree).
Because of ghc-mod issue #275 ghc-mod is used (instead of ghc-modi) for checking syntax of Haskell file;
Because of ghc-mod issue #362 ghc-mod is used (instead of ghc-modi) for getting symbols of module using browse command. Performance for code completion will probably improve if I can use ghc-modi for browse;
It would be nice if ghc-mod issue #303 would be solved. That would made it possible to get support from ghc-mod while type/syntax errors exist. For example, while typing.
~~Created workaround for this issue: https://youtrack.jetbrains.com/issue/IDEA-130894.~~
Developed plugin on Ubuntu;
During testing on Mac OSX Yosemite Beta I noticed problem with ghc-modi: PATH environment variable asked from within IntelliJ was not the same as the global one. I had to create workaround only for Mac OSX :-( This workaround will add path of GHC SDK to PATH environment variable which is passed to ghc-modi process. Other solutions are welcome!
Windows is not supported. Maybe it will work okay but I can not test it;
Created workaround for ghc-mod issue #432;
~~I found an issue in IntelliJ 14.1, see https://youtrack.jetbrains.com/issue/IDEA-138236. Hopefully they will fix it soon;~~
When you get an error like NG BUG: GMECabalCompAssignment [(Left "lib/directory-1.2.1.0/System/Directory.hs",fromList [])], add the source root (in this example lib/directory-1.2.1.0) to Project Settings/Libraries because ghc-mod(i) does not support Haskell files which are not part of project itself;
Be sure all module names are directly or indirectly listed in Cabal file;

How to build project

Clone this project;
Go to root of project and start sbt;
Run task updateIdea from the sbt console;
Run task compile from the sbt console;
Install/enable the following plugins in IntelliJ: Plugin Devkit, Grammar-Kit and PsiViewer;
Import this project as an sbt project in IntelliJ;
Select Build/Make project;

How to prepare plugin for deployment

Right click on top of intellij-haskell.iml inside intellij-haskell folder;
Select Import module;
Be sure unmanaged-jars dependency is set to provided inside Project structure/Project settings/Modules/Dependencies (btw, setting provided inside sbt file gives error);
Right click on top of intellij-haskell plugin module and select Prepare Plugin Module 'intellij-haskell' for deployment;

How to run/debug plugin inside IntelliJ

Set Plugin SDK settings right inside Project structure/Platform settings/SDKs. For example to, set SDK home path to idea/142.5239.7 inside project root folder;
Set Module-SDK right for intellij-haskell plugin module inside Project structure/Project structure/Project settings/Modules;
To run plugin inside IntelliJ, first run configuration has to be created. Navigate to Run/Edit configurations and create plugin configuration for intellij-haskell;

Development remarks

After making changes to _HaskellLexer.flex, run Run Flex Generator. This will generate _HaskellLexer.java;
After making changes to haskell.bnf, run Generate Parser Code. This will generate parser Java files in gen directory;
Add sources.zip inside idea/[idea build #] to Project structure/Project settings/Modules/Dependencies/unmanaged-jars to see IntelliJ sources;

sannysanoff / intellij-haskell