Graphviz export (#81)

* Preliminary --dot support

* Format

* Update README with the dot flag

README.md

@@ -31,7 +31,7 @@ nix run github:utdemir/nix-tree -- --help
 
 ```console
 $ nix-tree --help
-Usage: nix-tree [INSTALLABLE] [--store STORE] [--version] [--derivation] [--impure]
+Usage: nix-tree [INSTALLABLE] [--store STORE] [--version] [--derivation] [--impure] [--dot]
 
   Interactively browse dependency graphs of Nix derivations.
 
@@ -43,6 +43,7 @@ Available options:
   --version                Show the nix-tree version
   --derivation             Operate on the store derivation rather than its outputs
   --impure                 Allow access to mutable paths and repositories
+  --dot                    Print the dependency graph in dot format
   -h,--help                Show this help text
 
 Keybindings:

nix-tree.cabal

@@ -61,6 +61,7 @@ common common-options
                     , directory
                     , optparse-applicative
                     , microlens
+                    , dot
 
 executable nix-tree
   import:             common-options

src/NixTree/Main.hs

@@ -22,7 +22,8 @@ data Opts = Opts
     oStore :: String,
     oVersion :: Bool,
     oDerivation :: Bool,
-    oImpure :: Bool
+    oImpure :: Bool,
+    oDot :: Bool
   }
 
 optsParser :: Opts.ParserInfo Opts
@@ -65,6 +66,7 @@ optsParser =
         <*> Opts.switch (Opts.long "version" <> Opts.help "Show the nix-tree version")
         <*> Opts.switch (Opts.long "derivation" <> Opts.help "Operate on the store derivation rather than its outputs")
         <*> Opts.switch (Opts.long "impure" <> Opts.help "Allow access to mutable paths and repositories")
+        <*> Opts.switch (Opts.long "dot" <> Opts.help "Print the dependency graph in dot format")
 
     keybindingsHelp :: Opts.Doc
     keybindingsHelp =
@@ -123,7 +125,9 @@ main = do
       & chunks 50
       & mapConcurrently_ (mapM_ (\p -> evaluate (rnf p) >> incProgress bar 1))
 
-    run env
+    if opts & oDot
+      then putTextLn $ storeEnvToDot env
+      else run env
 
 chunks :: Int -> [a] -> [[a]]
 chunks _ [] = []

src/NixTree/StorePath.hs

@@ -15,6 +15,7 @@ module NixTree.StorePath
     seBottomUp,
     seFetchRefs,
     mkStoreName,
+    storeEnvToDot,
   )
 where
 
@@ -25,7 +26,9 @@ import Data.Aeson.Types (Parser)
 import qualified Data.ByteString.Lazy as BL
 import qualified Data.HashMap.Strict as HM
 import qualified Data.HashSet as HS
+import qualified Data.Set as Set
 import qualified Data.Text as T
+import qualified Dot
 import System.FilePath.Posix (addTrailingPathSeparator, splitDirectories, (</>))
 import System.IO (hPutStrLn)
 import System.Process.Typed (proc, readProcessStdout_)
@@ -319,6 +322,39 @@ seBottomUp f StoreEnv {sePaths, seRoots} =
 
 --------------------------------------------------------------------------------
 
+storeEnvToDot :: StoreEnv s a -> Text
+storeEnvToDot env =
+  seBottomUp go env
+    & seGetRoots
+    & toList
+    & map spPayload
+    & mconcat
+    & render
+  where
+    go sp =
+      fromList [Set.singleton (spName sp, spName ref) <> spPayload ref | ref <- spRefs sp]
+        & mconcat
+
+    render :: Set (StoreName s, StoreName s) -> Text
+    render edges =
+      Dot.DotGraph
+        Dot.Strict
+        Dot.Directed
+        Nothing
+        [ Dot.StatementEdge
+            ( Dot.EdgeStatement
+                (Dot.ListTwo (Dot.EdgeNode (mkNodeId from)) (Dot.EdgeNode (mkNodeId to)) [])
+                []
+            )
+          | (from, to) <- toList edges
+        ]
+        & Dot.encode
+
+    mkNodeId :: StoreName s -> Dot.NodeId
+    mkNodeId = fromString . toString . storeNameToShortText
+
+--------------------------------------------------------------------------------
+
 data NixPathInfo = NixPathInfo
   { npiPath :: FilePath,
     npiNarSize :: Int,