pre-commit · asottile · Jul 22, 2023 · Jul 19, 2023
diff --git a/.github/workflows/languages.yaml b/.github/workflows/languages.yaml
@@ -63,6 +63,8 @@ jobs:
         echo 'C:\Strawberry\c\bin' >> "$GITHUB_PATH"
       shell: bash
       if: matrix.os == 'windows-latest' && matrix.language == 'perl'
+    - uses: haskell/actions/setup@v2
+      if: matrix.language == 'haskell'
 
     - name: install deps
       run: python -mpip install -e . -r requirements-dev.txt

diff --git a/pre_commit/all_languages.py b/pre_commit/all_languages.py
@@ -9,6 +9,7 @@
 from pre_commit.languages import dotnet
 from pre_commit.languages import fail
 from pre_commit.languages import golang
+from pre_commit.languages import haskell
 from pre_commit.languages import lua
 from pre_commit.languages import node
 from pre_commit.languages import perl
@@ -31,6 +32,7 @@
     'dotnet': dotnet,
     'fail': fail,
     'golang': golang,
+    'haskell': haskell,
     'lua': lua,
     'node': node,
     'perl': perl,

diff --git a/pre_commit/languages/haskell.py b/pre_commit/languages/haskell.py
@@ -0,0 +1,56 @@
+from __future__ import annotations
+
+import contextlib
+import os.path
+from typing import Generator
+from typing import Sequence
+
+from pre_commit import lang_base
+from pre_commit.envcontext import envcontext
+from pre_commit.envcontext import PatchesT
+from pre_commit.envcontext import Var
+from pre_commit.errors import FatalError
+from pre_commit.prefix import Prefix
+
+ENVIRONMENT_DIR = 'hs_env'
+get_default_version = lang_base.basic_get_default_version
+health_check = lang_base.basic_health_check
+run_hook = lang_base.basic_run_hook
+
+
+def get_env_patch(target_dir: str) -> PatchesT:
+    bin_path = os.path.join(target_dir, 'bin')
+    return (('PATH', (bin_path, os.pathsep, Var('PATH'))),)
+
+
+@contextlib.contextmanager
+def in_env(prefix: Prefix, version: str) -> Generator[None, None, None]:
+    envdir = lang_base.environment_dir(prefix, ENVIRONMENT_DIR, version)
+    with envcontext(get_env_patch(envdir)):
+        yield
+
+
+def install_environment(
+    prefix: Prefix,
+    version: str,
+    additional_dependencies: Sequence[str],
+) -> None:
+    lang_base.assert_version_default('haskell', version)
+    envdir = lang_base.environment_dir(prefix, ENVIRONMENT_DIR, version)
+
+    pkgs = [*prefix.star('.cabal'), *additional_dependencies]
+    if not pkgs:
+        raise FatalError('Expected .cabal files or additional_dependencies')
+
+    bindir = os.path.join(envdir, 'bin')
+    os.makedirs(bindir, exist_ok=True)
+    lang_base.setup_cmd(prefix, ('cabal', 'update'))
+    lang_base.setup_cmd(
+        prefix,
+        (
+            'cabal', 'install',
+            '--install-method', 'copy',
+            '--installdir', bindir,
+            *pkgs,
+        ),
+    )
diff --git a/tests/languages/haskell_test.py b/tests/languages/haskell_test.py
@@ -0,0 +1,50 @@
+from __future__ import annotations
+
+import pytest
+
+from pre_commit.errors import FatalError
+from pre_commit.languages import haskell
+from pre_commit.util import win_exe
+from testing.language_helpers import run_language
+
+
+def test_run_example_executable(tmp_path):
+    example_cabal = '''\
+cabal-version:      2.4
+name:               example
+version:            0.1.0.0
+
+executable example
+    main-is:          Main.hs
+
+    build-depends:    base >=4
+    default-language: Haskell2010
+'''
+    main_hs = '''\
+module Main where
+
+main :: IO ()
+main = putStrLn "Hello, Haskell!"
+'''
+    tmp_path.joinpath('example.cabal').write_text(example_cabal)
+    tmp_path.joinpath('Main.hs').write_text(main_hs)
+
+    result = run_language(tmp_path, haskell, 'example')
+    assert result == (0, b'Hello, Haskell!\n')
+
+    # should not symlink things into environments
+    exe = tmp_path.joinpath(win_exe('hs_env-default/bin/example'))
+    assert exe.is_file()
+    assert not exe.is_symlink()
+
+
+def test_run_dep(tmp_path):
+    result = run_language(tmp_path, haskell, 'hello', deps=['hello'])
+    assert result == (0, b'Hello, World!\n')
+
+
+def test_run_empty(tmp_path):
+    with pytest.raises(FatalError) as excinfo:
+        run_language(tmp_path, haskell, 'example')
+    msg, = excinfo.value.args
+    assert msg == 'Expected .cabal files or additional_dependencies'