New IO interface to scan for Gentoo eclass vars

Uses the `portageq` command to scan for repositories, which in turn are
scanned for eclasses, which are then scanned for eclass variables.

The variables are scanned using a heuristic which looks for

    "# @ECLASS_VARIABLE: "

at the start of each line, which means only properly documented
variables will be found.

Signed-off-by: hololeap <hololeap@users.noreply.github.com>

ShellCheck.cabal

@@ -97,6 +97,7 @@ library
       ShellCheck.Regex
     other-modules:
       Paths_ShellCheck
+      ShellCheck.PortageVariables
       ShellCheck.PortageAutoInternalVariables
     default-language: Haskell98
 

src/ShellCheck/PortageVariables.hs

@@ -0,0 +1,158 @@
+
+module ShellCheck.PortageVariables
+    ( RepoName
+    , RepoPath
+    , EclassVar
+    , Repository(..)
+    , Eclass(..)
+    , portageVariables
+    , scanRepos
+    ) where
+
+import Control.Applicative
+import Control.Monad
+import Control.Monad.Trans.Class
+import Control.Monad.Trans.Maybe
+import Data.Map (Map)
+import qualified Data.Map as M
+import System.Directory (listDirectory)
+import System.Exit (ExitCode(..))
+import System.FilePath
+import System.Process -- (readProcessWithExitCode)
+import Text.Parsec hiding ((<|>))
+import Text.Parsec.String
+
+type RepoName = String
+type RepoPath = FilePath
+type EclassVar = String
+
+data Repository = Repository
+    { repositoryName :: RepoName
+    , repositoryLocation :: RepoPath
+    , repositoryEclasses :: [Eclass]
+    } deriving (Show, Eq, Ord)
+
+data Eclass = Eclass
+    { eclassName :: String
+    , eclassVars :: [EclassVar]
+    } deriving (Show, Eq, Ord)
+
+portageVariables :: [Repository] -> Map String [EclassVar]
+portageVariables = foldMap $ foldMap go . repositoryEclasses
+  where
+    go e = M.singleton (eclassName e) (eclassVars e)
+
+-- | Run @portageq@ to gather a list of repo names and paths, then scan each
+--   one for eclasses and ultimately eclass metadata.
+scanRepos :: IO [Repository]
+scanRepos = do
+    let cmd = "/usr/bin/portageq"
+    let args = ["repos_config", "/"]
+    out <- runOrDie cmd args
+    case parse reposParser "scanRepos" out of
+        Left pe -> fail $ show pe
+        Right nps -> do
+            forM nps $ \(n,p) -> Repository n p <$> getEclasses p
+
+-- | Get the name of the repo and its path from blocks outputted by
+--   @portageq@. If the path doesn't exist, this will return @Nothing@.
+reposParser :: Parser [(RepoName, RepoPath)]
+reposParser =
+    choice
+        [ [] <$ eof
+        , repoName >>= repoBlock
+        ]
+  where
+    -- Get the name of the repo at the top of the block
+    repoName :: Parser RepoName
+    repoName
+        =  char '['
+        *> manyTill anyChar (try (char ']'))
+        <* endOfLine
+
+    -- Parse the block for location field
+    repoBlock :: RepoName -> Parser [(RepoName, RepoPath)]
+    repoBlock n = choice
+        [ try $ do
+            l <- string "location = " *> takeLine
+            -- Found the location, skip the rest of the block
+            skipMany miscLine *> endOfBlock
+            insert (n,l)
+          -- Did not find the location, keep trying
+        , try $ miscLine *> repoBlock n
+          -- Reached the end of the block, no location field
+        , endOfBlock *> ignore
+        ]
+
+    miscLine :: Parser ()
+    miscLine = skipNonEmptyLine
+
+    -- A block ends with an eol or eof
+    endOfBlock :: Parser ()
+    endOfBlock = void endOfLine <|> eof
+
+    insert :: (RepoName, RepoPath) -> Parser [(RepoName, RepoPath)]
+    insert r = (r:) <$> reposParser
+
+    ignore :: Parser [(RepoName, RepoPath)]
+    ignore = reposParser
+
+-- | Scan the repo path for @*.eclass@ files in @eclass/@, then run
+--   'eclassParser' on each of them to produce @[Eclass]@.
+--
+--   If the @eclass/@ directory doesn't exist, the scan is skipped for that
+--   repo.
+getEclasses :: RepoPath -> IO [Eclass]
+getEclasses repoLoc = fmap (maybe [] id) $ runMaybeT $ do
+    let eclassDir = repoLoc </> "eclass"
+
+    -- Silently fail if the repo doesn't have an eclass dir
+    fs <- MaybeT $ Just <$> listDirectory eclassDir <|> pure Nothing
+    let fs' = filter (\(_,e) -> e == ".eclass") $ map splitExtensions fs
+
+    forM fs' $ \(n,e) -> do
+        evs <- lift $ parseFromFile eclassParser (eclassDir </> n <.> e)
+        case evs of
+            Left pe -> lift $ fail $ show pe
+            Right vs -> pure $ Eclass n vs
+
+eclassParser :: Parser [EclassVar]
+eclassParser = choice
+        [ -- cons the EclassVar to the list and continue
+          try $ liftA2 (:) eclassVar eclassParser
+          -- or skip the line and continue
+        , skipLine *> eclassParser
+          -- or end the list on eof
+        , [] <$ eof
+        ]
+  where
+    -- Scans for @ECLASS_VARIABLE comments rather than parsing the raw bash
+    eclassVar :: Parser EclassVar
+    eclassVar = string "# @ECLASS_VARIABLE: " *> takeLine
+
+takeLine :: Parser String
+takeLine = manyTill anyChar (try endOfLine)
+
+-- | Fails if next char is 'endOfLine'
+skipNonEmptyLine :: Parser ()
+skipNonEmptyLine = notFollowedBy endOfLine *> skipLine
+
+skipLine :: Parser ()
+skipLine = void takeLine
+
+-- | Run the command and return the full stdout string (stdin is ignored).
+--
+--   If the command exits with a non-zero exit code, this will throw an
+--   error including the captured contents of stdout and stderr.
+runOrDie :: FilePath -> [String] -> IO String
+runOrDie cmd args = do
+    (ec, o, e) <- readProcessWithExitCode cmd args ""
+    case ec of
+        ExitSuccess -> pure o
+        ExitFailure i -> fail $ unlines $ map unwords
+            $   [ [ show cmd ]
+                    ++ map show args
+                    ++ [ "failed with exit code", show i]
+                , [ "stdout:" ], [ o ]
+                , [ "stderr:" ], [ e ]
+                ]