feat: Support simple cabal projects without a project.cabal file

lua/neotest-haskell/cabal.lua

@@ -12,6 +12,19 @@ local function get_package_file(package_root)
   end
 end
 
+--- A 'simple' cabal project is a haskell project without project.cabal file
+--- that contains a '*.cabal' file.
+---@async
+function cabal.build_command_simple(pos)
+  logger.debug('Building spec for simple Cabal project...')
+  local command = {
+    'cabal',
+    'test',
+  }
+  local test_opts = hspec.get_cabal_test_opts(pos)
+  return test_opts and vim.list_extend(command, test_opts) or command
+end
+
 ---@async
 function cabal.build_command(package_root, pos)
   logger.debug('Building spec for Cabal project...')

lua/neotest-haskell/init.lua

@@ -59,12 +59,16 @@ function HaskellNeotestAdapter.build_spec(args)
   end
 
   local package_root = base.match_package_root_pattern(pos.path)
-  local project_root = base.match_project_root_pattern(pos.path)
+  -- If this isn't a stack project or a multi-package cabal project,
+  -- then the root is also where the package (i.e. '*.cabal' file) is.
+  local project_root = base.match_project_root_pattern(pos.path) or package_root
 
   if lib.files.exists(project_root .. '/cabal.project') then
     return mkCommand(cabal.build_command(package_root, pos))
   elseif lib.files.exists(project_root .. '/stack.yaml') and vim.fn.executable('stack') == 1 then
     return mkCommand(stack.build_command(project_root, package_root, pos))
+  elseif lib.files.match_root_pattern('*.cabal')(project_root) then
+    return mkCommand(cabal.build_command_simple(pos))
   end
 
   logger.error('Project is neither a Cabal nor a Stack project.')

tests/fixtures/hspec/cabal/simple/simple.cabal

@@ -0,0 +1,16 @@
+cabal-version:      3.0
+name:               simple
+version:            0.1.0.0
+build-type:         Simple
+common warnings
+    ghc-options: -Wall
+
+test-suite simple-test
+    import:           warnings
+    default-language: Haskell2010
+    type:             exitcode-stdio-1.0
+    hs-source-dirs:   test
+    main-is:          Spec.hs
+    build-depends:    base >=4.9 && < 5
+                    , hspec ==2.*
+                    , hspec-discover

tests/fixtures/hspec/cabal/simple/test/FirstSpec.hs

@@ -0,0 +1,15 @@
+module FirstSpec where
+
+import Test.Hspec
+
+spec :: Spec
+spec = do
+  describe "section 1" $ do
+    it "is a tautology" $ do
+      True `shouldBe` True
+    it "assumes that 2 is 1" $ do
+      2 `shouldBe` (1 :: Integer)
+
+  describe "section 2" $ do
+    it "only contains one test" $ do
+      sum [1..17] `shouldBe` ((17 * 18) `div` 2 :: Integer)

tests/fixtures/hspec/cabal/simple/test/Spec.hs

@@ -0,0 +1 @@
+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}