diff --git a/.gitignore b/.gitignore
index 150b05c88..d72d73737 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,7 @@
 dist/
 dist-newstyle/
 .stack-work/
-stack.yaml
-stack.yaml.lock
+tests/projects/**/stack*.yaml
+tests/projects/**/stack*.yaml.lock
 cabal.project.local*
 .vscode/
diff --git a/README.md b/README.md
index 741565879..1a6ed7d6f 100644
--- a/README.md
+++ b/README.md
@@ -73,6 +73,16 @@ cradle:
 
 This configuration suffices if your whole project can be loaded by the command `stack repl`. As a rule of thumb, this works if the project consists of only one executable, one library and one test-suite.
 
+Some projects have multiple `stack-*.yaml` files for multiple versions of ghc/resolvers. In this case you
+can specify an alternate relative file to use by using the `stackYaml` option. The path is relative to the
+configuration file.
+
+```yaml
+cradle:
+  stack:
+    stackYaml: "./stack-8.8.3.yaml"
+```
+
 If your project is more complicated, you need to specify which [components](https://docs.haskellstack.org/en/stable/build_command/#components) you want to load. A component is, roughly speaking, a library/executable/test-suite or benchmark in `stack`. You can view the components/targets of a stack project by executing the command:
 ``` sh
 $ stack ide targets
@@ -126,6 +136,26 @@ Here you can see two important features:
 
 This way we specified which component needs to be compiled given a source file for our whole project.
 
+If you use both, multiple components and an alternate `stack.yaml` file, there is a way to specify defaults
+for the path-specific configurations.
+
+```yaml
+cradle:
+  stack:
+    stackYaml: "stack-8.3.3.yaml"
+    components:
+    - path: "./src"
+      component: "hie-bios:lib"
+    - path: "./exe"
+      component: "hie-bios:exe:hie-bios"
+    - path: "./tests/BiosTests.hs"
+      component: "hie-bios:test:hie-bios"
+    - path: "./tests/ParserTests.hs"
+      component: "hie-bios:test:parser-tests"
+```
+
+A word of warning: Due to current restrictions in the language server, as mentioned in [this bug report](https://github.com/haskell/haskell-language-server/issues/268#issuecomment-667640809) all referenced stack.yaml files must specify the same version of GHC, as only one version of ghcide is loaded at a time per workspace root. This restriction might be lifted in the future.
+
 #### Debugging a `stack` cradle
 
 If you find that `hie-bios` can't load a certain component or file, run `stack repl` and `stack repl <component name>` to see if `stack` succeeds in building your project. Chances are that there is a problem in your project and if you fix that, `hie-bios` will succeed to load it.
@@ -267,6 +297,25 @@ Here you can see two important features:
   * The filepath can be a file.
     * This is convenient if components are overlapping.
 
+Similarly to `multi-stack` configurations, you can also specify multiple components using a `components` subkey.
+While this is currently not used for anything, this syntax gives you a place to put defaults, directly under
+the `cabal` entry.
+
+```yaml
+cradle:
+  cabal:
+    # Reserved for future default options
+    components:
+    - path: "./src"
+      component: "lib:hie-bios"
+    - path: "./exe"
+      component: "exe:hie-bios"
+    - path: "./tests/BiosTests.hs"
+      component: "test:hie-bios"
+    - path: "./tests/ParserTests.hs"
+      component: "test:parser-tests"
+```
+
 This way we specified which component needs to be compiled given a certain source file for our whole project.
 
 #### Debugging a `cabal` cradle
diff --git a/hie-bios.cabal b/hie-bios.cabal
index f632df98d..c1b279716 100644
--- a/hie-bios.cabal
+++ b/hie-bios.cabal
@@ -31,12 +31,16 @@ Extra-Source-Files:     ChangeLog.md
                         tests/configs/direct.yaml
                         tests/configs/multi.yaml
                         tests/configs/multi-ch.yaml
+                        tests/configs/multi-stack-with-yaml.yaml
+                        tests/configs/keys-not-unique-fails.yaml
                         tests/configs/nested-cabal-multi.yaml
                         tests/configs/nested-stack-multi.yaml
                         tests/configs/none.yaml
                         tests/configs/obelisk.yaml
                         tests/configs/stack-config.yaml
                         tests/configs/stack-multi.yaml
+                        tests/configs/stack-with-both.yaml
+                        tests/configs/stack-with-yaml.yaml
                         tests/projects/symlink-test/a/A.hs
                         tests/projects/symlink-test/hie.yaml
                         tests/projects/multi-direct/A.hs
@@ -145,7 +149,18 @@ Extra-Source-Files:     ChangeLog.md
                         tests/projects/implicit-stack-multi/other-package/Setup.hs
                         tests/projects/implicit-stack-multi/other-package/other-package.cabal
                         tests/projects/implicit-stack-multi/other-package/Main.hs
-
+                        tests/projects/multi-stack-with-yaml/appA/Setup.hs
+                        tests/projects/multi-stack-with-yaml/appA/appA.cabal
+                        tests/projects/multi-stack-with-yaml/appA/src/Lib.hs
+                        tests/projects/multi-stack-with-yaml/appB/Setup.hs
+                        tests/projects/multi-stack-with-yaml/appB/appB.cabal
+                        tests/projects/multi-stack-with-yaml/appB/src/Lib.hs
+                        tests/projects/multi-stack-with-yaml/hie.yaml
+                        tests/projects/stack-with-yaml/Setup.hs
+                        tests/projects/stack-with-yaml/app/Main.hs
+                        tests/projects/stack-with-yaml/hie.yaml
+                        tests/projects/stack-with-yaml/stack-with-yaml.cabal
+                        tests/projects/stack-with-yaml/src/Lib.hs
 
 tested-with: GHC==8.10.1, GHC==8.8.3, GHC==8.6.5, GHC==8.4.4
 
@@ -216,6 +231,7 @@ test-suite parser-tests
       base,
       filepath,
       hie-bios,
+      hspec-expectations,
       tasty,
       tasty-hunit,
       text,
diff --git a/src/HIE/Bios/Config.hs b/src/HIE/Bios/Config.hs
index 84c6e8e3a..995d7b6d6 100644
--- a/src/HIE/Bios/Config.hs
+++ b/src/HIE/Bios/Config.hs
@@ -2,20 +2,46 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE TupleSections #-}
 {-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# LANGUAGE LambdaCase #-}
 -- | Logic and datatypes for parsing @hie.yaml@ files.
 module HIE.Bios.Config(
     readConfig,
     Config(..),
     CradleConfig(..),
+    CabalType,
+    pattern CabalType,
+    cabalComponent,
+    StackType,
+    pattern StackType,
+    stackComponent,
+    stackYaml,
     CradleType(..),
     Callable(..)
     ) where
 
+import Control.Exception
 import qualified Data.Text as T
 import qualified Data.Vector as V
 import qualified Data.HashMap.Strict as Map
+import           Data.Maybe (mapMaybe)
+import           Data.Semigroup
 import           Data.Foldable (foldrM)
+import           Data.Aeson (JSONPath)
 import           Data.Yaml
+import           Data.Yaml.Internal (Warning(..))
+
+type MLast a = Maybe (Last a)
+
+viewLast :: MLast a -> Maybe a
+viewLast (Just l) = Just $ getLast l
+viewLast Nothing = Nothing
+
+pattern MLast :: Maybe a -> MLast a
+pattern MLast m <- (viewLast -> m) where
+    MLast (Just l) = Just $ Last l
+    MLast Nothing = Nothing
 
 -- | Configuration that can be used to load a 'Cradle'.
 -- A configuration has roughly the following form:
@@ -43,11 +69,45 @@ data CradleConfig a =
 data Callable = Program FilePath | Command String
     deriving (Show, Eq)
 
+data CabalType
+    = CabalType_ { _cabalComponent :: !(MLast String) }
+    deriving (Eq)
+
+instance Semigroup CabalType where
+    CabalType_ cr <> CabalType_ cl = CabalType_ (cr <> cl)
+
+instance Monoid CabalType where
+    mempty = CabalType_ mempty
+
+pattern CabalType :: Maybe String -> CabalType
+pattern CabalType { cabalComponent } = CabalType_ (MLast cabalComponent)
+{-# COMPLETE CabalType #-}
+
+instance Show CabalType where
+  show = show . Cabal
+
+data StackType
+    = StackType_ { _stackComponent :: !(MLast String) , _stackYaml :: !(MLast String) }
+    deriving (Eq)
+
+instance Semigroup StackType where
+    StackType_ cr yr <> StackType_ cl yl = StackType_ (cr <> cl) (yr <> yl)
+
+instance Monoid StackType where
+    mempty = StackType_ mempty mempty
+
+pattern StackType :: Maybe String -> Maybe String -> StackType
+pattern StackType { stackComponent, stackYaml } = StackType_ (MLast stackComponent) (MLast stackYaml)
+{-# COMPLETE StackType #-}
+
+instance Show StackType where
+  show = show . Stack
+
 data CradleType a
-    = Cabal { component :: Maybe String }
-    | CabalMulti [ (FilePath, String) ]
-    | Stack { component :: Maybe String }
-    | StackMulti [ (FilePath, String) ]
+    = Cabal { cabalType :: !CabalType }
+    | CabalMulti { defaultCabal :: !CabalType, subCabalComponents :: [ (FilePath, CabalType) ] }
+    | Stack { stackType :: !StackType }
+    | StackMulti { defaultStack :: !StackType, subStackComponents :: [ (FilePath, StackType) ] }
 --  Bazel and Obelisk used to be supported but bit-rotted and no users have complained.
 --  They can be added back if a user
 --    | Bazel
@@ -73,10 +133,10 @@ instance FromJSON a => FromJSON (CradleType a) where
     parseJSON _ = fail "Not a known cradle type. Possible are: cabal, stack, bios, direct, default, none, multi"
 
 instance Show (CradleType a) where
-    show (Cabal comp) = "Cabal {component = " ++ show comp ++ "}"
-    show (CabalMulti a) = "CabalMulti " ++ show a
-    show (Stack comp) = "Stack {component = " ++ show comp ++ "}"
-    show (StackMulti a) = "StackMulti " ++ show a
+    show (Cabal comp) = "Cabal {component = " ++ show (cabalComponent comp) ++ "}"
+    show (CabalMulti d a) = "CabalMulti {defaultCabal = " ++ show d ++ ", subCabalComponents = " ++ show a ++ "}"
+    show (Stack comp) = "Stack {component = " ++ show (stackComponent comp) ++ ", stackYaml = " ++ show (stackYaml comp) ++ "}"
+    show (StackMulti d a) = "StackMulti {defaultStack = " ++ show d ++ ", subStackComponents = "  ++ show a ++ "}"
     show Bios { call, depsCall } = "Bios {call = " ++ show call ++ ", depsCall = " ++ show depsCall ++ "}"
     show (Direct args) = "Direct {arguments = " ++ show args ++ "}"
     show None = "None"
@@ -96,38 +156,61 @@ parseCradleType o
     | Just val  <- Map.lookup "other" o = Other <$> parseJSON val <*> pure val
 parseCradleType o = fail $ "Unknown cradle type: " ++ show o
 
-parseStackOrCabal
-  :: (Maybe String -> CradleType a)
-  -> ([(FilePath, String)] -> CradleType a)
+parseSingleOrMultiple
+  :: Monoid x
+  => (x -> CradleType a)
+  -> (x -> [(FilePath, x)] -> CradleType a)
+  -> (Map.HashMap T.Text Value -> Parser x)
   -> Value
   -> Parser (CradleType a)
-parseStackOrCabal singleConstructor _ (Object x)
-  | Map.size x == 1, Just (String stackComponent) <- Map.lookup "component" x
-  = return $ singleConstructor $ Just $ T.unpack stackComponent
-  | Map.null x
-  = return $ singleConstructor Nothing
-  | otherwise
-  = fail "Not a valid Configuration type, following keys are allowed: component"
-parseStackOrCabal _ multiConstructor (Array x) = do
-  let parseOne e
+parseSingleOrMultiple single multiple parse = doParse where
+    parseOne e
         | Object v <- e
         , Just (String prefix) <- Map.lookup "path" v
-        , Just (String comp) <- Map.lookup "component" v
-        , Map.size v == 2
-        = return (T.unpack prefix, T.unpack comp)
+        = (T.unpack prefix,) <$> parse (Map.delete "path" v)
         | otherwise
-        = fail "Expected an object with path and component keys"
-
-  xs <- foldrM (\v cs -> (: cs) <$> parseOne v) [] x
-  return $ multiConstructor xs
-parseStackOrCabal singleConstructor _ Null = return $ singleConstructor Nothing
-parseStackOrCabal _ _ _ = fail "Configuration is expected to be an object."
+        = fail "Expected an object with a path key"
+    parseArray = foldrM (\v cs -> (: cs) <$> parseOne v) []
+    doParse (Object v)
+        | Just (Array x) <- Map.lookup "components" v
+        = do
+            d <- parse (Map.delete "components" v)
+            xs <- parseArray x
+            return $ multiple d xs
+        | Just _ <- Map.lookup "components" v
+        = fail "Expected components to be an array of subcomponents"
+        | Nothing <- Map.lookup "components" v
+        = single <$> parse v
+    doParse (Array x)
+        = do
+            xs <- parseArray x
+            return $ multiple mempty xs
+    doParse Null = single <$> parse Map.empty
+    doParse _ = fail "Configuration is expected to be an object or an array of objects."
 
 parseStack :: Value -> Parser (CradleType a)
-parseStack = parseStackOrCabal Stack StackMulti
+parseStack = parseSingleOrMultiple Stack StackMulti $
+  \case x | Map.size x == 2
+          , Just (String component) <- Map.lookup "component" x
+          , Just (String syaml) <- Map.lookup "stackYaml" x
+          -> return $ StackType (Just $ T.unpack component) (Just $ T.unpack syaml)
+          | Map.size x == 1, Just (String component) <- Map.lookup "component" x
+          -> return $ StackType (Just $ T.unpack component) Nothing
+          | Map.size x == 1, Just (String syaml) <- Map.lookup "stackYaml" x
+          -> return $ StackType Nothing (Just $ T.unpack syaml)
+          | Map.null x
+          -> return $ StackType Nothing Nothing
+          | otherwise
+          -> fail "Not a valid Stack configuration, following keys are allowed: component, stackYaml"
 
 parseCabal :: Value -> Parser (CradleType a)
-parseCabal = parseStackOrCabal Cabal CabalMulti
+parseCabal = parseSingleOrMultiple Cabal CabalMulti $
+  \case x | Map.size x == 1, Just (String component) <- Map.lookup "component" x
+          -> return $ CabalType (Just $ T.unpack component)
+          | Map.null x
+          -> return $ CabalType Nothing
+          | otherwise
+          -> fail "Not a valid Cabal configuration, following keys are allowed: component"
 
 parseBios :: Value -> Parser (CradleType a)
 parseBios (Object x) =
@@ -206,4 +289,17 @@ instance FromJSON a => FromJSON (Config a) where
 -- If the contents of the file is not a valid 'Config a',
 -- an 'Control.Exception.IOException' is thrown.
 readConfig :: FromJSON a => FilePath -> IO (Config a)
-readConfig = decodeFileThrow
\ No newline at end of file
+readConfig fp = do
+    result <- decodeFileWithWarnings fp
+    either throwIO failOnAnyDuplicate result
+    where
+        failOnAnyDuplicate :: ([Warning], Config a) -> IO (Config a)
+        failOnAnyDuplicate (warnings, config) = do
+            _ <- case mapMaybe failOnDuplicate warnings of
+                    dups@(_:_) -> throwIO $ InvalidYaml $ Just $ YamlException
+                                          $ "Duplicate keys are not allowed, found: " ++ show dups
+                    _ -> return ()
+            return config
+        -- future proofing in case more warnings are added
+        failOnDuplicate :: Warning -> Maybe JSONPath
+        failOnDuplicate (DuplicateKey a) = Just a
diff --git a/src/HIE/Bios/Cradle.hs b/src/HIE/Bios/Cradle.hs
index b6558a0a6..ff9bee5f5 100644
--- a/src/HIE/Bios/Cradle.hs
+++ b/src/HIE/Bios/Cradle.hs
@@ -55,6 +55,7 @@ import qualified Data.Conduit.Combinators as C
 import qualified Data.Conduit as C
 import qualified Data.Conduit.Text as C
 import qualified Data.Text as T
+import qualified Data.HashMap.Strict as Map
 import           Data.Maybe (fromMaybe, maybeToList)
 import           GHC.Fingerprint (fingerprintString)
 
@@ -93,17 +94,17 @@ loadCradleWithOpts _copts buildCustomCradle wfile = do
 
 getCradle :: (b -> Cradle a) -> (CradleConfig b, FilePath) -> Cradle a
 getCradle buildCustomCradle (cc, wdir) = addCradleDeps cradleDeps $ case cradleType cc of
-    Cabal mc -> cabalCradle wdir mc
-    CabalMulti ms ->
+    Cabal CabalType{ cabalComponent = mc } -> cabalCradle wdir mc
+    CabalMulti dc ms ->
       getCradle buildCustomCradle $
         (CradleConfig cradleDeps
-          (Multi [(p, CradleConfig [] (Cabal (Just c))) | (p, c) <- ms])
+          (Multi [(p, CradleConfig [] (Cabal $ dc <> c)) | (p, c) <- ms])
         , wdir)
-    Stack mc -> stackCradle wdir mc
-    StackMulti ms ->
+    Stack StackType{ stackComponent = mc, stackYaml = syaml} -> stackCradle wdir mc (fromMaybe "stack.yaml" syaml)
+    StackMulti ds ms ->
       getCradle buildCustomCradle $
         (CradleConfig cradleDeps
-          (Multi [(p, CradleConfig [] (Stack (Just c))) | (p, c) <- ms])
+          (Multi [(p, CradleConfig [] (Stack $ ds <> c)) | (p, c) <- ms])
         , wdir)
  --   Bazel -> rulesHaskellCradle wdir
  --   Obelisk -> obeliskCradle wdir
@@ -143,8 +144,8 @@ implicitConfig' fp = (\wdir ->
          (Bios (Program $ wdir </> ".hie-bios") Nothing Nothing, wdir)) <$> biosWorkDir fp
   --   <|> (Obelisk,) <$> obeliskWorkDir fp
   --   <|> (Bazel,) <$> rulesHaskellWorkDir fp
-     <|> (stackExecutable >> (Stack Nothing,) <$> stackWorkDir fp)
-     <|> ((Cabal Nothing,) <$> cabalWorkDir fp)
+     <|> (stackExecutable >> (Stack $ StackType Nothing Nothing,) <$> stackWorkDir fp)
+     <|> ((Cabal $ CabalType Nothing,) <$> cabalWorkDir fp)
 
 
 yamlConfig :: FilePath ->  MaybeT IO FilePath
@@ -553,16 +554,16 @@ cabalWorkDir wdir =
 ------------------------------------------------------------------------
 -- | Stack Cradle
 -- Works for by invoking `stack repl` with a wrapper script
-stackCradle :: FilePath -> Maybe String -> Cradle a
-stackCradle wdir mc =
+stackCradle :: FilePath -> Maybe String -> FilePath -> Cradle a
+stackCradle wdir mc syaml =
   Cradle
     { cradleRootDir    = wdir
     , cradleOptsProg   = CradleAction
         { actionName = Types.Stack
-        , runCradle = stackAction wdir mc
+        , runCradle = stackAction wdir mc syaml
         , runGhcCmd = \args ->
             readProcessWithCwd
-              wdir "stack" (["exec", "--silent", "ghc", "--"] <> args) ""
+              wdir "stack" (["--stack-yaml", syaml, "exec", "--silent", "ghc", "--"] <> args) ""
         }
     }
 
@@ -575,32 +576,32 @@ stackCradle wdir mc =
 -- a '.cabal' file.
 --
 -- Found dependencies are relative to 'rootDir'.
-stackCradleDependencies :: FilePath -> FilePath -> IO [FilePath]
-stackCradleDependencies wdir componentDir = do
+stackCradleDependencies :: FilePath -> FilePath -> FilePath -> IO [FilePath]
+stackCradleDependencies wdir componentDir syaml = do
   let relFp = makeRelative wdir componentDir
   cabalFiles' <- findCabalFiles componentDir
   let cabalFiles = map (relFp </>) cabalFiles'
-  return $ map normalise $ cabalFiles ++ [relFp </> "package.yaml", "stack.yaml"]
+  return $ map normalise $ cabalFiles ++ [relFp </> "package.yaml", syaml]
 
-stackAction :: FilePath -> Maybe String -> LoggingFunction -> FilePath -> IO (CradleLoadResult ComponentOptions)
-stackAction work_dir mc l _fp = do
-  let ghcProcArgs = ("stack", ["exec", "ghc", "--"])
+stackAction :: FilePath -> Maybe String -> FilePath -> LoggingFunction -> FilePath -> IO (CradleLoadResult ComponentOptions)
+stackAction work_dir mc syaml l _fp = do
+  let ghcProcArgs = ("stack", ["--stack-yaml", syaml, "exec", "ghc", "--"])
   -- Same wrapper works as with cabal
   withCabalWrapperTool ghcProcArgs work_dir $ \wrapper_fp -> do
     (ex1, _stdo, stde, args) <-
       readProcessWithOutputFile l work_dir $
-        proc "stack" $ ["repl", "--no-nix-pure", "--with-ghc", wrapper_fp]
+        proc "stack" $ ["--stack-yaml", syaml, "repl", "--no-nix-pure", "--with-ghc", wrapper_fp]
                        ++ [ comp | Just comp <- [mc] ]
     (ex2, pkg_args, stdr, _) <-
       readProcessWithOutputFile l work_dir $
-        proc "stack" ["path", "--ghc-package-path"]
+        proc "stack" ["--stack-yaml", syaml, "path", "--ghc-package-path"]
     let split_pkgs = concatMap splitSearchPath pkg_args
         pkg_ghc_args = concatMap (\p -> ["-package-db", p] ) split_pkgs
     case processCabalWrapperArgs args of
         Nothing -> do
           -- Best effort. Assume the working directory is the
           -- the root of the component, so we are right in trivial cases at least.
-          deps <- stackCradleDependencies work_dir work_dir
+          deps <- stackCradleDependencies work_dir work_dir syaml
           pure $ CradleFail
                     (CradleError deps ex1 $
                       [ "Failed to parse result of calling stack" ]
@@ -609,7 +610,7 @@ stackAction work_dir mc l _fp = do
                     )
 
         Just (componentDir, ghc_args) -> do
-          deps <- stackCradleDependencies work_dir componentDir
+          deps <- stackCradleDependencies work_dir componentDir syaml
           pure $ makeCradleResult
                     ( combineExitCodes [ex1, ex2]
                     , stde ++ stdr, componentDir
@@ -736,6 +737,14 @@ findFile p dir = do
     getFiles = filter p <$> getDirectoryContents dir
     doesPredFileExist file = doesFileExist $ dir </> file
 
+-- Some environments (e.g. stack exec) include GHC_PACKAGE_PATH.
+-- Cabal v2 *will* complain, even though or precisely because it ignores them
+-- Unset them from the environment to sidestep this
+getCleanEnvironment :: IO [(String, String)]
+getCleanEnvironment = do
+  e <- getEnvironment
+  return $ Map.toList $ Map.delete "GHC_PACKAGE_PATH" $ Map.fromList e
+
 -- | Call a given process.
 -- * A special file is created for the process to write to, the process can discover the name of
 -- the file by reading the @HIE_BIOS_OUTPUT@ environment variable. The contents of this file is
@@ -749,7 +758,7 @@ readProcessWithOutputFile
   -> CreateProcess -- ^ Parameters for the process to be executed.
   -> IO (ExitCode, [String], [String], [String])
 readProcessWithOutputFile l work_dir cp = do
-  old_env <- getEnvironment
+  old_env <- getCleanEnvironment
 
   withHieBiosOutput old_env $ \output_file -> do
     -- Pipe stdout directly into the logger
@@ -797,7 +806,8 @@ runGhcCmdOnPath wdir args = readProcessWithCwd wdir "ghc" args ""
 -- | Wrapper around 'readCreateProcess' that sets the working directory
 readProcessWithCwd :: FilePath -> FilePath -> [String] -> String -> IO (CradleLoadResult String)
 readProcessWithCwd dir cmd args stdi = do
-  let createProc = (proc cmd args) { cwd = Just dir }
+  cleanEnv <- getCleanEnvironment
+  let createProc = (proc cmd args) { cwd = Just dir, env = Just cleanEnv }
   mResult <- optional $ readCreateProcessWithExitCode createProc stdi
   case mResult of
     Just (ExitSuccess, stdo, _) -> pure $ CradleSuccess stdo
diff --git a/tests/BiosTests.hs b/tests/BiosTests.hs
index 0e8093c71..99a53d6da 100644
--- a/tests/BiosTests.hs
+++ b/tests/BiosTests.hs
@@ -144,6 +144,12 @@ main = do
           , testCaseSteps "nested-stack2" $ testLoadCradleDependencies isStackCradle "./tests/projects/nested-stack" "MyLib.hs"
               (\deps -> deps `shouldMatchList` ["nested-stack.cabal", "package.yaml", "stack.yaml"]
               )
+          , testCaseSteps "stack-with-yaml" {- tests if both components can be loaded -}
+                        $  testDirectory isStackCradle "./tests/projects/stack-with-yaml" "app/Main.hs"
+                        >> testDirectory isStackCradle "./tests/projects/stack-with-yaml" "src/Lib.hs"
+          , testCaseSteps "multi-stack-with-yaml" {- tests if both components can be loaded -}
+                        $  testDirectory isStackCradle "./tests/projects/multi-stack-with-yaml" "appA/src/Lib.hs"
+                        >> testDirectory isStackCradle "./tests/projects/multi-stack-with-yaml" "appB/src/Lib.hs"
           ,
           -- Test for special characters in the path for parsing of the ghci-scripts.
           -- Issue https://github.com/mpickering/hie-bios/issues/162
@@ -338,18 +344,21 @@ copyDir src dst = do
 
 writeStackYamlFiles :: IO ()
 writeStackYamlFiles =
-  forM_ stackProjects $ \(proj, pkgs) ->
-    writeFile (proj </> "stack.yaml") (stackYaml stackYamlResolver pkgs)
+  forM_ stackProjects $ \(proj, syaml, pkgs) ->
+    writeFile (proj </> syaml) (stackYaml stackYamlResolver pkgs)
 
-stackProjects :: [(FilePath, [FilePath])]
+stackProjects :: [(FilePath, FilePath, [FilePath])]
 stackProjects =
-  [ ("tests" </> "projects" </> "multi-stack", ["."])
-  , ("tests" </> "projects" </> "failing-stack", ["."])
-  , ("tests" </> "projects" </> "simple-stack", ["."])
-  , ("tests" </> "projects" </> "nested-stack", [".", "./sub-comp"])
-  , ("tests" </> "projects" </> "space stack", ["."])
-  , ("tests" </> "projects" </> "implicit-stack", ["."])
-  , ("tests" </> "projects" </> "implicit-stack-multi", ["."])
+  [ ("tests" </> "projects" </> "multi-stack", "stack.yaml", ["."])
+  , ("tests" </> "projects" </> "failing-stack", "stack.yaml", ["."])
+  , ("tests" </> "projects" </> "simple-stack", "stack.yaml", ["."])
+  , ("tests" </> "projects" </> "nested-stack", "stack.yaml", [".", "./sub-comp"])
+  , ("tests" </> "projects" </> "space stack", "stack.yaml", ["."])
+  , ("tests" </> "projects" </> "implicit-stack", "stack.yaml", ["."])
+  , ("tests" </> "projects" </> "implicit-stack-multi", "stack.yaml", ["."])
+  , ("tests" </> "projects" </> "implicit-stack-multi", "stack.yaml", ["."])
+  , ("tests" </> "projects" </> "multi-stack-with-yaml", "stack-alt.yaml", ["appA", "appB"])
+  , ("tests" </> "projects" </> "stack-with-yaml", "stack-alt.yaml", ["."])
   ]
 
 stackYaml :: String -> [FilePath] -> String
diff --git a/tests/ParserTests.hs b/tests/ParserTests.hs
index a31eac57c..f4f60f73d 100644
--- a/tests/ParserTests.hs
+++ b/tests/ParserTests.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 module Main where
 
+import Test.Hspec.Expectations
 import Test.Tasty
 import Test.Tasty.HUnit
 import HIE.Bios.Config
@@ -10,6 +11,7 @@ import Data.Yaml
 import qualified Data.Text as T
 import System.FilePath
 import Control.Applicative ( (<|>) )
+import Control.Exception
 
 configDir :: FilePath
 configDir = "tests/configs"
@@ -17,36 +19,48 @@ configDir = "tests/configs"
 main :: IO ()
 main = defaultMain $
   testCase "Parser Tests" $ do
-    assertParser "cabal-1.yaml" (noDeps (Cabal (Just "lib:hie-bios")))
-    assertParser "stack-config.yaml" (noDeps (Stack Nothing))
+    assertParser "cabal-1.yaml" (noDeps (Cabal $ CabalType (Just "lib:hie-bios")))
+    assertParser "stack-config.yaml" (noDeps (Stack $ StackType Nothing Nothing))
     --assertParser "bazel.yaml" (noDeps Bazel)
     assertParser "bios-1.yaml" (noDeps (Bios (Program "program") Nothing Nothing))
     assertParser "bios-2.yaml" (noDeps (Bios (Program "program") (Just (Program "dep-program")) Nothing))
     assertParser "bios-3.yaml" (noDeps (Bios (Command "shellcommand") Nothing Nothing))
     assertParser "bios-4.yaml" (noDeps (Bios (Command "shellcommand") (Just (Command "dep-shellcommand")) Nothing))
     assertParser "bios-5.yaml" (noDeps (Bios (Command "shellcommand") (Just (Program "dep-program")) Nothing))
-    assertParser "dependencies.yaml" (Config (CradleConfig ["depFile"] (Cabal (Just "lib:hie-bios"))))
+    assertParser "dependencies.yaml" (Config (CradleConfig ["depFile"] (Cabal $ CabalType (Just "lib:hie-bios"))))
     assertParser "direct.yaml" (noDeps (Direct ["list", "of", "arguments"]))
     assertParser "none.yaml" (noDeps None)
     --assertParser "obelisk.yaml" (noDeps Obelisk)
-    assertParser "multi.yaml" (noDeps (Multi [("./src", CradleConfig [] (Cabal (Just "lib:hie-bios")))
-                                             , ("./test", CradleConfig [] (Cabal (Just "test")) ) ]))
+    assertParser "multi.yaml" (noDeps (Multi [("./src", CradleConfig [] (Cabal $ CabalType (Just "lib:hie-bios")))
+                                             ,("./test", CradleConfig [] (Cabal $ CabalType (Just "test")) ) ]))
 
-    assertParser "cabal-multi.yaml" (noDeps (CabalMulti [("./src", "lib:hie-bios")
-                                                    ,("./", "lib:hie-bios")]))
+    assertParser "cabal-multi.yaml" (noDeps (CabalMulti (CabalType Nothing)
+                                                        [("./src", CabalType $ Just "lib:hie-bios")
+                                                        ,("./", CabalType $ Just "lib:hie-bios")]))
 
-    assertParser "stack-multi.yaml" (noDeps (StackMulti [("./src", "lib:hie-bios")
-                                                    ,("./", "lib:hie-bios")]))
+    assertParser "stack-multi.yaml" (noDeps (StackMulti (StackType Nothing Nothing)
+                                                        [("./src", StackType (Just "lib:hie-bios") Nothing)
+                                                        ,("./", StackType (Just"lib:hie-bios") Nothing)]))
 
     assertParser "nested-cabal-multi.yaml" (noDeps (Multi [("./test/testdata", CradleConfig [] None)
                                                           ,("./", CradleConfig [] (
-                                                                    CabalMulti [("./src", "lib:hie-bios")
-                                                                               ,("./tests", "parser-tests")]))]))
+                                                                    CabalMulti (CabalType Nothing)
+                                                                               [("./src", CabalType $ Just "lib:hie-bios")
+                                                                               ,("./tests", CabalType $ Just "parser-tests")]))]))
 
     assertParser "nested-stack-multi.yaml" (noDeps (Multi [("./test/testdata", CradleConfig [] None)
                                                           ,("./", CradleConfig [] (
-                                                                    StackMulti [("./src", "lib:hie-bios")
-                                                                              ,("./tests", "parser-tests")]))]))
+                                                                    StackMulti (StackType Nothing Nothing)
+                                                                               [("./src", StackType (Just "lib:hie-bios") Nothing)
+                                                                               ,("./tests", StackType (Just "parser-tests") Nothing)]))]))
+    assertParser "stack-with-yaml.yaml"
+      (noDeps (Stack $ StackType Nothing (Just "stack-8.8.3.yaml")))
+    assertParser "stack-with-both.yaml"
+      (noDeps (Stack $ StackType (Just "hie-bios:hie") (Just "stack-8.8.3.yaml")))
+    assertParser "multi-stack-with-yaml.yaml"
+      (noDeps (StackMulti (StackType Nothing (Just "stack-8.8.3.yaml"))
+                          [("./src", StackType (Just "lib:hie-bios") Nothing)
+                          ,("./vendor", StackType (Just "parser-tests") Nothing)]))
 
     assertCustomParser "ch-cabal.yaml"
       (noDeps (Other CabalHelperCabal $ simpleCabalHelperYaml "cabal"))
@@ -56,9 +70,10 @@ main = defaultMain $
       (noDeps (Multi
         [ ("./src", CradleConfig [] (Other CabalHelperStack $ simpleCabalHelperYaml "stack"))
         , ("./input", CradleConfig [] (Other CabalHelperCabal $ simpleCabalHelperYaml "cabal"))
-        , ("./test", CradleConfig [] (Cabal (Just "test")))
+        , ("./test", CradleConfig [] (Cabal $ CabalType (Just "test")))
         , (".", CradleConfig [] None)
         ]))
+    assertParserFails "keys-not-unique-fails.yaml" invalidYamlException
 
 assertParser :: FilePath -> Config Void -> Assertion
 assertParser fp cc = do
@@ -67,6 +82,13 @@ assertParser fp cc = do
                            , "Expected: " ++ show cc
                            , "Actual: " ++ show conf ])
 
+invalidYamlException :: Selector ParseException
+invalidYamlException (InvalidYaml (Just _)) = True
+invalidYamlException _ = False
+
+assertParserFails :: Exception e => FilePath -> Selector e -> Assertion
+assertParserFails fp es = (readConfig (configDir </> fp) :: IO (Config Void)) `shouldThrow` es
+
 assertCustomParser :: FilePath -> Config CabalHelper -> Assertion
 assertCustomParser fp cc = do
   conf <- readConfig (configDir </> fp)
diff --git a/tests/configs/keys-not-unique-fails.yaml b/tests/configs/keys-not-unique-fails.yaml
new file mode 100644
index 000000000..7a99aa23b
--- /dev/null
+++ b/tests/configs/keys-not-unique-fails.yaml
@@ -0,0 +1,12 @@
+cradle:
+  cabal:
+    components:
+      - path: "./src"
+        component: "lib:hie-bios"
+      - path: "./"
+        component: "lib:hie-bios"
+    components:
+      - path: "./src"
+        component: "exe:hie-bios"
+      - path: "./"
+        component: "exe:hie-bios"
diff --git a/tests/configs/multi-stack-with-yaml.yaml b/tests/configs/multi-stack-with-yaml.yaml
new file mode 100644
index 000000000..8c83efbef
--- /dev/null
+++ b/tests/configs/multi-stack-with-yaml.yaml
@@ -0,0 +1,8 @@
+cradle:
+  stack:
+    stackYaml: "stack-8.8.3.yaml"
+    components:
+      - path: "./src"
+        component: "lib:hie-bios"
+      - path: "./vendor"
+        component: "parser-tests" 
diff --git a/tests/configs/stack-with-both.yaml b/tests/configs/stack-with-both.yaml
new file mode 100644
index 000000000..202d67661
--- /dev/null
+++ b/tests/configs/stack-with-both.yaml
@@ -0,0 +1,4 @@
+cradle:
+  stack:
+    stackYaml: "stack-8.8.3.yaml"
+    component: "hie-bios:hie"
diff --git a/tests/configs/stack-with-yaml.yaml b/tests/configs/stack-with-yaml.yaml
new file mode 100644
index 000000000..8155c9fa3
--- /dev/null
+++ b/tests/configs/stack-with-yaml.yaml
@@ -0,0 +1,3 @@
+cradle:
+  stack:
+    stackYaml: "stack-8.8.3.yaml"
diff --git a/tests/projects/multi-stack-with-yaml/appA/Setup.hs b/tests/projects/multi-stack-with-yaml/appA/Setup.hs
new file mode 100644
index 000000000..9a994af67
--- /dev/null
+++ b/tests/projects/multi-stack-with-yaml/appA/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/tests/projects/multi-stack-with-yaml/appA/appA.cabal b/tests/projects/multi-stack-with-yaml/appA/appA.cabal
new file mode 100644
index 000000000..edc2ea3bf
--- /dev/null
+++ b/tests/projects/multi-stack-with-yaml/appA/appA.cabal
@@ -0,0 +1,12 @@
+cabal-version:       >=2.0
+name:                appA
+version:             0.1.0.0
+build-type:          Simple
+
+library
+  exposed-modules: Lib
+  -- other-modules:
+  -- other-extensions:
+  build-depends:       base >=4.10 && < 5, filepath
+  hs-source-dirs:      src
+  default-language:    Haskell2010
diff --git a/tests/projects/multi-stack-with-yaml/appA/src/Lib.hs b/tests/projects/multi-stack-with-yaml/appA/src/Lib.hs
new file mode 100644
index 000000000..6d85a26fe
--- /dev/null
+++ b/tests/projects/multi-stack-with-yaml/appA/src/Lib.hs
@@ -0,0 +1 @@
+module Lib where
diff --git a/tests/projects/multi-stack-with-yaml/appB/Setup.hs b/tests/projects/multi-stack-with-yaml/appB/Setup.hs
new file mode 100644
index 000000000..9a994af67
--- /dev/null
+++ b/tests/projects/multi-stack-with-yaml/appB/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/tests/projects/multi-stack-with-yaml/appB/appB.cabal b/tests/projects/multi-stack-with-yaml/appB/appB.cabal
new file mode 100644
index 000000000..e9b261c94
--- /dev/null
+++ b/tests/projects/multi-stack-with-yaml/appB/appB.cabal
@@ -0,0 +1,12 @@
+cabal-version:       >=2.0
+name:                appB
+version:             0.1.0.0
+build-type:          Simple
+
+library
+  exposed-modules: Lib
+  -- other-modules:
+  -- other-extensions:
+  build-depends:       base >=4.10 && < 5, filepath
+  hs-source-dirs:      src
+  default-language:    Haskell2010
diff --git a/tests/projects/multi-stack-with-yaml/appB/src/Lib.hs b/tests/projects/multi-stack-with-yaml/appB/src/Lib.hs
new file mode 100644
index 000000000..6d85a26fe
--- /dev/null
+++ b/tests/projects/multi-stack-with-yaml/appB/src/Lib.hs
@@ -0,0 +1 @@
+module Lib where
diff --git a/tests/projects/multi-stack-with-yaml/hie.yaml b/tests/projects/multi-stack-with-yaml/hie.yaml
new file mode 100644
index 000000000..46cbb53df
--- /dev/null
+++ b/tests/projects/multi-stack-with-yaml/hie.yaml
@@ -0,0 +1,16 @@
+cradle:
+  multi:
+    - path: "appA"
+      config:
+        cradle:
+          stack:
+            - path: appA/src
+              component: appA:lib
+              stackYaml: stack-alt.yaml
+    - path: "appB"
+      config:
+        cradle:
+          stack:
+            - path: appB/src
+              component: appB:lib
+              stackYaml: stack-alt.yaml
diff --git a/tests/projects/multi-stack/multi-stack.cabal b/tests/projects/multi-stack/multi-stack.cabal
index c55b7c1bb..b6eb67fdf 100644
--- a/tests/projects/multi-stack/multi-stack.cabal
+++ b/tests/projects/multi-stack/multi-stack.cabal
@@ -20,4 +20,4 @@ executable multi-stack
   build-depends:       base >=4.10 && < 5, directory
   -- hs-source-dirs:
   default-language:    Haskell2010
-  ghc-options:         +RTS -A1m -N -RTS -Wall
\ No newline at end of file
+  ghc-options:         +RTS -A1m -N -RTS -Wall
diff --git a/tests/projects/stack-with-yaml/Setup.hs b/tests/projects/stack-with-yaml/Setup.hs
new file mode 100644
index 000000000..9a994af67
--- /dev/null
+++ b/tests/projects/stack-with-yaml/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/tests/projects/stack-with-yaml/app/Main.hs b/tests/projects/stack-with-yaml/app/Main.hs
new file mode 100644
index 000000000..0efdb0b52
--- /dev/null
+++ b/tests/projects/stack-with-yaml/app/Main.hs
@@ -0,0 +1,4 @@
+
+import System.Directory (getCurrentDirectory)
+
+main = return ()
diff --git a/tests/projects/stack-with-yaml/hie.yaml b/tests/projects/stack-with-yaml/hie.yaml
new file mode 100644
index 000000000..a5f7431f6
--- /dev/null
+++ b/tests/projects/stack-with-yaml/hie.yaml
@@ -0,0 +1,9 @@
+cradle:
+  stack:
+    stackYaml: "stack-alt.yaml"
+    components:
+    - path: ./src
+      component: "stack-with-yaml:lib"
+
+    - path: ./app
+      component: "stack-with-yaml:exe:stack-with-yaml"
diff --git a/tests/projects/stack-with-yaml/src/Lib.hs b/tests/projects/stack-with-yaml/src/Lib.hs
new file mode 100644
index 000000000..a709c5ea9
--- /dev/null
+++ b/tests/projects/stack-with-yaml/src/Lib.hs
@@ -0,0 +1,5 @@
+module Lib where
+
+import System.FilePath ((</>))
+
+foo = "test" </> "me"
diff --git a/tests/projects/stack-with-yaml/stack-with-yaml.cabal b/tests/projects/stack-with-yaml/stack-with-yaml.cabal
new file mode 100644
index 000000000..538314132
--- /dev/null
+++ b/tests/projects/stack-with-yaml/stack-with-yaml.cabal
@@ -0,0 +1,23 @@
+cabal-version:       >=2.0
+name:                stack-with-yaml
+version:             0.1.0.0
+build-type:          Simple
+
+library
+  exposed-modules: Lib
+  -- other-modules:
+  -- other-extensions:
+  build-depends:       base >=4.10 && < 5, filepath
+  hs-source-dirs:      src
+  default-language:    Haskell2010
+
+
+
+executable stack-with-yaml
+  main-is:              app/Main.hs
+  -- other-modules:
+  -- other-extensions:
+  build-depends:       base >=4.10 && < 5, directory
+  -- hs-source-dirs:
+  default-language:    Haskell2010
+  ghc-options:         +RTS -A1m -N -RTS -Wall