DRAFT: Completions for cabal.project files, hls-cabal-project-plugin

.github/actions/setup-build/action.yml

@@ -23,6 +23,9 @@ inputs:
 runs:
   using: "composite"
   steps:
+    - name: Init submodules
+      run: git submodule update --init
+
     - name: Workaround runner image issue
       if: runner.os == 'Linux'
       # https://github.com/actions/runner-images/issues/7061

.github/workflows/test.yml

@@ -92,6 +92,9 @@ jobs:
     steps:
       - uses: actions/checkout@v3
 
+      - name: Init submodules
+        run: git submodule update --init
+
       - uses: ./.github/actions/setup-build
         with:
           ghc: ${{ matrix.ghc }}
@@ -238,6 +241,10 @@ jobs:
         name: Test hls-cabal-plugin test suite
         run: cabal test hls-cabal-plugin-tests || cabal test hls-cabal-plugin-tests
 
+      - if: matrix.test
+        name: Test hls-cabal-project-plugin test suite
+        run: cabal test hls-cabal-project-plugin-tests || cabal test hls-cabal-project-plugin-tests
+
       # TODO enable when it supports 9.10
       - if: matrix.test && matrix.ghc != '9.10' && matrix.ghc != '9.12'
         name: Test hls-retrie-plugin test suite

.gitmodules

@@ -8,3 +8,7 @@
 #     Commit git commit -m "Removed submodule <name>"
 #     Delete the now untracked submodule files
 #     rm -rf path_to_submodule
+
+[submodule "vendor/cabal"]
+	path = vendor/cabal
+	url = https://github.com/rm41339/cabal.git

cabal.project

@@ -5,7 +5,27 @@ packages:
          ./ghcide
          ./hls-plugin-api
          ./hls-test-utils
+         ./vendor/cabal/Cabal
+         ./vendor/cabal/Cabal-syntax
+         ./vendor/cabal/cabal-install
+         ./vendor/cabal/cabal-install-solver
+         ./vendor/cabal/Cabal-described
+         ./vendor/cabal/Cabal-tree-diff
 
+source-repository-package
+   type:     git
+   location: https://github.com/fendor/cabal-add/
+   tag: 3ae65c28bfc6eff66a7a05bb9547665f62a35b63
+
+source-repository-package
+   type:     git
+   location: https://github.com/fendor/haskell-ci/
+   tag: e3e68f064f9610267bb47ea6404ccaa6924c2201
+   subdir: cabal-install-parsers
+
+package cabal-install
+  tests: False
+  benchmarks: False
 
 index-state: 2025-08-08T12:31:54Z
 
@@ -50,6 +70,10 @@ constraints:
 -- cabal-add depends on cabal-install-parsers.
 allow-newer:
   cabal-install-parsers:Cabal-syntax,
+  *:Cabal-syntax,
+  *:cabal-install,
+  *:Cabal
+  rere:QuickCheck
 
 if impl(ghc >= 9.11)
   benchmarks: False

docs/configuration.md

@@ -443,22 +443,20 @@ This will install `eglot` and enable it by default in `haskell-mode`.
 To configure `haskell-language-server` we use the `eglot-workspace-configuration` variable.
 With `M-x eglot-show-workspace-configuration` you can see the JSON that `eglot` will send to `haskell-language-server`.
 See <https://joaotavora.github.io/eglot/#Customizing-Eglot> for more information.
-As an example, the setting below will disable the `stan` plugin.
+As an example, the setting below will disable the `stan` plugin and use `fourmolu` for formatting:
 
 ```emacs-lisp
 (use-package eglot
   :ensure t
   :config
-  (add-hook 'haskell-mode-hook 'eglot-ensure)
+  (add-hook 'haskell-mode-hook 'eglot-ensure) ; start eglot automatically in haskell projects
   :config
   (setq-default eglot-workspace-configuration
-                '((haskell
-                   (plugin
-                    (stan
-                     (globalOn . :json-false))))))  ;; disable stan
+                '(:haskell (:plugin (:stan (:globalOn :json-false)) ; disable stan
+                            :formattingProvider "fourmolu")))       ; use fourmolu instead of ormolu
   :custom
-  (eglot-autoshutdown t)  ;; shutdown language server after closing last file
-  (eglot-confirm-server-initiated-edits nil)  ;; allow edits without confirmation
+  (eglot-autoshutdown t)  ; shutdown language server after closing last file
+  (eglot-confirm-server-initiated-edits nil)  ; allow edits without confirmation
   )
 ```
 

ghcide/session-loader/Development/IDE/Session.hs

@@ -14,6 +14,7 @@
   ,retryOnException
   ,Log(..)
   ,runWithDb
+  , cacheDir
   ) where
 
 -- Unfortunately, we cannot use loadSession with ghc-lib since hie-bios uses
@@ -629,7 +630,7 @@
                  [] -> error $ "GHC version could not be parsed: " <> version
                  ((runTime, _):_)
                    | compileTime == runTime -> do
                      atomicModifyIORef' cradle_files (\xs -> (cfp:xs,()))
                      session (hieYaml, toNormalizedFilePath' cfp, opts, libDir)
                    | otherwise -> return (([renderPackageSetupException cfp GhcVersionMismatch{..}], Nothing),[])
              -- Failure case, either a cradle error or the none cradle
@@ -896,7 +897,7 @@
             x <- map errMsgDiagnostic closure_errs
             DriverHomePackagesNotClosed us <- pure x
             pure us
         isBad ci = (homeUnitId_ (componentDynFlags ci)) `OS.member` bad_units
     -- Whenever we spin up a session on Linux, dynamically load libm.so.6
     -- in. We need this in case the binary is statically linked, in which
     -- case the interactive session will fail when trying to load

haskell-language-server.cabal

@@ -322,6 +322,90 @@ test-suite hls-cabal-plugin-tests
     , lsp-types
     , text
 
+-----------------------------
+-- cabal project plugin
+-----------------------------
+
+flag cabalProject
+  description: Enable cabalProject plugin
+  default:     True
+  manual:      True
+
+common cabalProject
+  if flag(cabalProject)
+    build-depends: haskell-language-server:hls-cabal-project-plugin
+    cpp-options: -Dhls_cabal_project
+
+library hls-cabal-project-plugin
+  import:           defaults, pedantic, warnings
+  if !flag(cabalProject)
+    buildable: False
+  exposed-modules:
+    Ide.Plugin.CabalProject
+    Ide.Plugin.CabalProject.Parse
+    Ide.Plugin.CabalProject.Diagnostics
+    Ide.Plugin.CabalProject.Types
+    Ide.Plugin.CabalProject.Completion.Completions
+    Ide.Plugin.CabalProject.Completion.Data
+
+  build-depends:
+    , bytestring
+    , Cabal-syntax          >= 3.7
+    , containers
+    , deepseq
+    , directory
+    , filepath
+    , extra                 >=1.7.4
+    , ghcide                == 2.11.0.0
+    , hashable
+    , hls-plugin-api        == 2.11.0.0
+    , hls-graph             == 2.11.0.0
+    , lens
+    , lsp                   ^>=2.7
+    , lsp-types             ^>=2.3
+    , regex-tdfa            ^>=1.3.1
+    , text
+    , text-rope
+    , transformers
+    , unordered-containers  >=0.2.10.0
+    , containers
+    , process
+    , aeson
+    , Cabal
+    , pretty
+    , cabal-install
+    , cabal-install-solver
+    , haskell-language-server:hls-cabal-plugin
+    , base16-bytestring
+    , cryptohash-sha1
+
+  hs-source-dirs:   plugins/hls-cabal-project-plugin/src
+
+test-suite hls-cabal-project-plugin-tests
+  import:           defaults, pedantic, test-defaults, warnings
+  if !flag(cabalProject)
+    buildable: False
+  type:             exitcode-stdio-1.0
+  hs-source-dirs:   plugins/hls-cabal-project-plugin/test
+  main-is:          Main.hs
+  other-modules:
+    Completer
+    Utils
+  build-depends:
+    , bytestring
+    , Cabal-syntax          >= 3.7
+    , extra
+    , filepath
+    , ghcide
+    , haskell-language-server:hls-cabal-project-plugin
+    , hls-test-utils    == 2.11.0.0
+    , lens
+    , lsp-types
+    , text
+    , hls-plugin-api
+    , cabal-install
+    , haskell-language-server:hls-cabal-plugin
+
 -----------------------------
 -- class plugin
 -----------------------------
@@ -1847,6 +1931,7 @@ library
                   , pedantic
                   -- plugins
                   , cabal
+                  , cabalProject
                   , callHierarchy
                   , cabalfmt
                   , cabalgild

hls-plugin-api/src/Ide/Types.hs

@@ -14,7 +14,7 @@
 {-# LANGUAGE UndecidableInstances  #-}
 {-# LANGUAGE ViewPatterns          #-}
 module Ide.Types
-( PluginDescriptor(..), defaultPluginDescriptor, defaultCabalPluginDescriptor
+( PluginDescriptor(..), defaultPluginDescriptor, defaultCabalPluginDescriptor, defaultCabalProjectPluginDescriptor
 , defaultPluginPriority
 , describePlugin
 , IdeCommand(..)
@@ -1077,6 +1077,21 @@ defaultCabalPluginDescriptor plId desc =
     Nothing
     [".cabal"]
 
+defaultCabalProjectPluginDescriptor :: PluginId -> T.Text -> PluginDescriptor ideState
+defaultCabalProjectPluginDescriptor plId desc =
+  PluginDescriptor
+    plId
+    desc
+    defaultPluginPriority
+    mempty
+    mempty
+    mempty
+    defaultConfigDescriptor
+    mempty
+    mempty
+    Nothing
+    [".project"]
+
 newtype CommandId = CommandId T.Text
   deriving (Show, Read, Eq, Ord)
 instance IsString CommandId where

plugins/hls-cabal-plugin/src/Ide/Plugin/Cabal/Diagnostics.hs

@@ -5,6 +5,8 @@ module Ide.Plugin.Cabal.Diagnostics
 , warningDiagnostic
 , positionFromCabalPosition
 , fatalParseErrorDiagnostic
+, toBeginningOfNextLine
+, mkDiag
   -- * Re-exports
 , FileDiagnostic
 , Diagnostic(..)

plugins/hls-cabal-plugin/test/testdata/completer.cabal

@@ -11,4 +11,4 @@ be
 library
     lib
 
-co
+co