Freeze/help user triggered features

When the user presses h or ?, we print a short usage/help text listing
the interactive key bindings.

When the user presses f, we freeze the output text. I personally use
this to copy/paste stuff from the terminal output, that's quite
convenient. There's no visual feedback showing the output text is
paused at the moment. This might be a UX footgun ><

Author: picnoir

lib/NOM/IO.hs

@@ -252,6 +252,10 @@ processTextStream config parser updater maintenance printerMay finalize initialS
   printerMay & maybe keepProcessing \(printer, output_handle) -> do
     linesVar <- newTVarIO 0
     let keepProcessingStdin :: IO ()
+    let toggleHelp :: IO () = atomically $ do
+          print_state <- readTMVar print_state_var
+          writeTMVar print_state_var $ print_state{printHelp = not print_state.printHelp}
+          writeTMVar new_user_input ()
         keepProcessingStdin = forever $ do
           key <- getKey
           case key of
@@ -260,15 +264,21 @@ processTextStream config parser updater maintenance printerMay finalize initialS
                 print_state <- readTMVar print_state_var
                 let print_state_style = if print_state.printName == PrintName then PrintDerivationPath else PrintName
                 writeTMVar print_state_var $ print_state{printName = print_state_style}
-                writeTMVar input_received ()
-            "?" -> do
+                writeTMVar new_user_input ()
+            "?" -> toggleHelp
+            "h" -> toggleHelp
+            "f" -> do
               atomically $ do
-                print_state <- takeTMVar print_state_var
-                putTMVar print_state_var $ print_state{printHelp = True}
-                writeTMVar input_received ()
+                print_state <- readTMVar print_state_var
+                writeTMVar print_state_var $ print_state{freeze = not print_state.freeze}
+                writeTMVar new_user_input ()
             _ -> pure ()
         writeToScreen :: IO ()
-        writeToScreen = writeStateToScreen (not config.silent) linesVar state_var print_state_var output_builder_var refresh_display_var maintenance printer output_handle
+        writeToScreen = do
+          print_state <- atomically $ readTMVar print_state_var
+          case (print_state.freeze, print_state.printHelp) of
+            (True, _) -> pure () -- Freezing the output, do not print anything.
+            _ -> writeStateToScreen (not config.silent) printedLinesVar state_var print_state_var output_builder_var refresh_display_var maintenance printer output_handle
         keepPrinting :: IO ()
         keepPrinting = forever do
           runConcurrently

lib/NOM/Print.hs

@@ -1,4 +1,4 @@
-module NOM.Print (stateToText, showCode, Config (..)) where
+module NOM.Print (stateToText, showCode, helpString, Config (..)) where
 
 import Data.Foldable qualified as Unsafe
 import Data.IntMap.Strict qualified as IntMap
@@ -184,7 +184,7 @@ stateToText config buildState@MkNOMV1State{..} printState = memo printWithSize .
         horizontal
         (vertical <> " ")
         (vertical <> " ")
-        (printBuilds buildState printState hostNums maxHeight now)
+        (if not printState.printHelp then printBuilds buildState printState hostNums maxHeight now else helpString)
     errorDisplay = printErrors nixErrors maxHeight
     traceDisplay = printTraces nixTraces maxHeight
   -- evalMessage = case evaluationState.lastFileName of
@@ -197,6 +197,7 @@ stateToText config buildState@MkNOMV1State{..} printState = memo printWithSize .
   MkDependencySummary{..} = fullSummary
   runningBuilds' = (.host) <$> runningBuilds
   completedBuilds' = (.host) <$> completedBuilds
+
   failedBuilds' = (.host) <$> failedBuilds
   numFailedBuilds = CMap.size failedBuilds
   table time' =
@@ -588,3 +589,12 @@ printDuration diff
 
 timeDiffSeconds :: Int -> Text
 timeDiffSeconds = printDuration . fromIntegral
+
+helpString :: NonEmpty Text
+helpString =
+  fromList
+    [ markup bold " Key Bindings"
+    , "n: toggle derivation name/derivation path print"
+    , "f: toggle screen freeze"
+    , "? or h: toggle help view"
+    ]

lib/NOM/State.hs

@@ -202,6 +202,7 @@ data PrintNameStyle = PrintName | PrintDerivationPath deriving stock (Show, Eq,
 data PrintState = MkPrintState
   { printName :: PrintNameStyle
   , printHelp :: Bool
+  , freeze :: Bool
   }
   deriving stock (Show, Eq, Ord, Generic)
 
@@ -210,6 +211,7 @@ initPrintState =
   MkPrintState
     { printName = PrintName
     , printHelp = False
+    , freeze = False
     }
 
 data NOMV1State = MkNOMV1State