feat(haskell): Add Haskell module (#3587)

* feat(haskell): add haskell module and implement ghc version detection

* feat(haskell): implement stack resolver version detection

* fix(haskell): handle more complex resolvers

* fix(haskell): rename resolver_version to snapshot

* fix(haskell): change default color to bold purple

* feat(haskell): add tests

* fix(haskell): format

* fix(haskell): replace incorrect `or` with `or_else`

* fix(haskell): use write_all instead of write

* fix(haskell): λ as Haskell icon by default

* fix(haskell): fix tests and add a real stack.yaml testcase

* fix(haskell): make clippy happy

docs/.vuepress/public/presets/toml/bracketed-segments.toml

@@ -49,6 +49,9 @@ format = '([\[$all_status$ahead_behind\]]($style))'
 [golang]
 format = '\[[$symbol($version)]($style)\]'
 
+[haskell]
+format = '\[[$symbol($version)]($style)\]'
+
 [helm]
 format = '\[[$symbol($version)]($style)\]'
 

docs/.vuepress/public/presets/toml/nerd-font-symbols.toml

@@ -28,6 +28,9 @@ symbol = " "
 [golang]
 symbol = " "
 
+[haskell]
+symbol = " "
+
 [hg_branch]
 symbol = " "
 

docs/config/README.md

@@ -217,6 +217,7 @@ $elixir\
 $elm\
 $erlang\
 $golang\
+$haskell\
 $helm\
 $java\
 $julia\
@@ -1672,6 +1673,39 @@ By default the module will be shown if any of the following conditions are met:
 format = "via [🏎💨 $version](bold cyan) "
 ```
 
+## Haskell
+
+The `haskell` module finds the current selected GHC version and/or the selected Stack snapshot.
+
+By default the module will be shown if any of the following conditions are met:
+
+- The current directory contains a `stack.yaml` file
+- The current directory contains any `.hs`, `.cabal`, or `.hs-boot` file
+
+### Options
+
+| Option              | Default                              | Description                                        |
+| ------------------- | ------------------------------------ | -------------------------------------------------- |
+| `format`            | `"via [$symbol($version )]($style)"` | The format for the module.                         |
+| `symbol`            | `"λ "`                               | A format string representing the symbol of Haskell |
+| `detect_extensions` | `["hs", "cabal", "hs-boot"]`         | Which extensions should trigger this module.       |
+| `detect_files`      | `["stack.yaml", "cabal.project"]`    | Which filenames should trigger this module.        |
+| `detect_folders`    | `[]`                                 | Which folders should trigger this module.          |
+| `style`             | `"bold purple"`                      | The style for the module.                          |
+| `disabled`          | `false`                              | Disables the `haskell` module.                     |
+
+### Variables
+
+| Variable     | Example     | Description                                                                             |
+| ------------ | ----------- | --------------------------------------------------------------------------------------- |
+| version      |             | `ghc_version` or `snapshot` depending on whether the current project is a Stack project |
+| snapshot     | `lts-18.12` | Currently selected Stack snapshot                                                       |
+| ghc\_version | `9.2.1`     | Currently installed GHC version                                                         |
+| symbol       |             | Mirrors the value of option `symbol`                                                    |
+| style\*      |             | Mirrors the value of option `style`                                                     |
+
+*: This variable can only be used as a part of a style string
+
 ## Helm
 
 The `helm` module shows the currently installed version of [Helm](https://helm.sh/).