WIP: Fix CLI display corruption when input exceeds terminal width

packages/darklang/cli/core.dark

@@ -533,24 +533,64 @@ let runInteractiveLoop (state: AppState) : Int64 =
       let inputStartColumn =
         Prompt.Display.calculateInputStartColumn locationStr
 
+      // Calculate total line length to detect if it exceeds terminal width
+      let hint = Registry.getCompletionHint state state.prompt.text
+      let totalLineLength =
+        inputStartColumn + (Stdlib.String.length state.prompt.text) + (Stdlib.String.length hint)
+      let terminalWidth = Terminal.getWidth ()
+      let lineExceedsWidth = totalLineLength > terminalWidth
+
       if state.needsFullRedraw then
-        // Redraw entire prompt line (used after commands that change state)
+        // Full redraw (used after commands that change state)
+        let promptText = View.formatPromptWithInput state
+        Stdlib.print promptText
+      else if lineExceedsWidth then
+        // Long line update: overwrite content without clearing first to reduce flicker
+        Stdlib.print "\u001b[?25l" // Hide cursor during redraw
+
+        // Calculate which row the cursor was on based on previous text length
+        let previousTotalLength = inputStartColumn + state.prompt.previousTextLength
+        let previousLineWrapped = previousTotalLength > terminalWidth
+
+        if previousLineWrapped then
+          // Cursor was on a wrapped line, move up to prompt start
+          let wrappedLines = Stdlib.Int64.divide (previousTotalLength - 1L) terminalWidth
+          if wrappedLines > 0L then
+            Stdlib.print (Colors.moveCursorUp wrappedLines)
+
+        // Go to start of line and overwrite with new content
+        Stdlib.print Colors.carriageReturn
         let promptText = View.formatPromptWithInput state
         Stdlib.print promptText
+        // Clear to end of line in case new text is shorter than old
+        Stdlib.print Colors.clearLine
+        Stdlib.print "\u001b[?25h" // Show cursor again
       else
-        // Update only the input portion (used during typing)
+        // Short line incremental update (used during typing when line fits)
         Stdlib.print "\u001b[?25l" // Hide cursor during redraw
         Stdlib.print (Colors.moveCursorToColumn inputStartColumn)
         Stdlib.print Colors.clearLine
         Stdlib.print state.prompt.text
-        let hint = Registry.getCompletionHint state state.prompt.text
         if Stdlib.Bool.not (Stdlib.String.isEmpty hint) then
           Stdlib.print (Colors.hint hint)
         Stdlib.print "\u001b[?25h" // Show cursor again
 
       // Position cursor at correct location within user input
       let cursorColumn = inputStartColumn + state.prompt.cursorPosition
-      Stdlib.print (Colors.moveCursorToColumn cursorColumn)
+      if lineExceedsWidth then
+        // For wrapped lines, calculate which row and column the cursor should be on
+        let absoluteCursorPos = inputStartColumn + state.prompt.cursorPosition
+        let cursorRow = Stdlib.Int64.divide (absoluteCursorPos - 1L) terminalWidth
+        let cursorCol = ((absoluteCursorPos - 1L) % terminalWidth) + 1L
+        // After reprinting, cursor is at end of text - calculate where it should go
+        let textEndRow = Stdlib.Int64.divide (totalLineLength - 1L) terminalWidth
+        // Move up from text end to cursor row if needed
+        let rowDiff = textEndRow - cursorRow
+        if rowDiff > 0L then
+          Stdlib.print (Colors.moveCursorUp rowDiff)
+        Stdlib.print (Colors.moveCursorToColumn cursorCol)
+      else
+        Stdlib.print (Colors.moveCursorToColumn cursorColumn)
     | InteractiveNav navState ->
       // Always display in interactive nav mode - it manages its own screen clearing
       Packages.NavInteractive.display navState

packages/darklang/cli/prompt.dark

@@ -6,39 +6,46 @@ type State =
     cursorPosition: Int64
     commandHistory: List<String>
     historyIndex: Int64
-    savedPrompt: String }
+    savedPrompt: String
+    /// Tracks text length from last display update, used to calculate cursor row for long lines
+    previousTextLength: Int64 }
 
 let initState () : State =
   State
     { text = ""
       cursorPosition = 0L
       commandHistory = []
       historyIndex = -1L
-      savedPrompt = "" }
+      savedPrompt = ""
+      previousTextLength = 0L }
 
 
 module Editing =
   /// Insert text at cursor position
   let insertAtCursor (state: State) (char: String) : State =
+    let prevLen = Stdlib.String.length state.text
     let beforeCursor = Stdlib.String.slice state.text 0L state.cursorPosition
     let afterCursor = Stdlib.String.dropFirst state.text state.cursorPosition
     let newText = beforeCursor ++ char ++ afterCursor
     { state with
         text = newText
         cursorPosition = state.cursorPosition + (Stdlib.String.length char)
         historyIndex = -1L
-        savedPrompt = "" }
+        savedPrompt = ""
+        previousTextLength = prevLen }
 
   /// Delete character before cursor (backspace)
   let deleteBeforeCursor (state: State) : State =
     if state.cursorPosition > 0L then
+      let prevLen = Stdlib.String.length state.text
       let beforeCursor = Stdlib.String.slice state.text 0L (state.cursorPosition - 1L)
       let afterCursor = Stdlib.String.dropFirst state.text state.cursorPosition
       let newText = beforeCursor ++ afterCursor
       { state with
           text = newText
           cursorPosition = state.cursorPosition - 1L
-          historyIndex = -1L }
+          historyIndex = -1L
+          previousTextLength = prevLen }
     else
       state
 
@@ -47,10 +54,11 @@ module Editing =
     let textLength = Stdlib.String.length state.text
 
     if state.cursorPosition < textLength then
+      let prevLen = textLength
       let beforeCursor = Stdlib.String.slice state.text 0L state.cursorPosition
       let afterCursor = Stdlib.String.dropFirst state.text (state.cursorPosition + 1L)
       let newText = beforeCursor ++ afterCursor
-      { state with text = newText; historyIndex = -1L }
+      { state with text = newText; historyIndex = -1L; previousTextLength = prevLen }
     else
       state
 
@@ -76,15 +84,18 @@ module Editing =
 
   /// Clear the prompt text
   let clear (state: State) : State =
+    let prevLen = Stdlib.String.length state.text
     { state with
         text = ""
         cursorPosition = 0L
-        historyIndex = -1L }
+        historyIndex = -1L
+        previousTextLength = prevLen }
 
   /// Set the prompt text and move cursor to end
   let setText (state: State) (text: String) : State =
+    let prevLen = Stdlib.String.length state.text
     let textLength = Stdlib.String.length text
-    { state with text = text; cursorPosition = textLength }
+    { state with text = text; cursorPosition = textLength; previousTextLength = prevLen }
 
 
 module History =
@@ -102,6 +113,7 @@ module History =
   /// Navigate to previous command in history
   let navigatePrevious (state: State) : State =
     if Stdlib.Bool.not (Stdlib.List.isEmpty state.commandHistory) then
+      let prevLen = Stdlib.String.length state.text
       let historyLength = Stdlib.List.length state.commandHistory
       let newIndex =
         if state.historyIndex == -1L then
@@ -123,7 +135,8 @@ module History =
             text = command
             cursorPosition = commandLength
             historyIndex = newIndex
-            savedPrompt = newSavedPrompt }
+            savedPrompt = newSavedPrompt
+            previousTextLength = prevLen }
       | None ->
         state
     else
@@ -132,6 +145,7 @@ module History =
   /// Navigate to next command in history
   let navigateNext (state: State) : State =
     if Stdlib.Bool.not (Stdlib.List.isEmpty state.commandHistory) && state.historyIndex >= 0L then
+      let prevLen = Stdlib.String.length state.text
       let newIndex =
         if state.historyIndex > 0L then
           state.historyIndex - 1L
@@ -142,15 +156,17 @@ module History =
         { state with
             text = state.savedPrompt
             cursorPosition = restoredPromptLength
-            historyIndex = newIndex }
+            historyIndex = newIndex
+            previousTextLength = prevLen }
       else
         match Stdlib.List.getAt state.commandHistory newIndex with
         | Some command ->
           let commandLength = Stdlib.String.length command
           { state with
               text = command
               cursorPosition = commandLength
-              historyIndex = newIndex }
+              historyIndex = newIndex
+              previousTextLength = prevLen }
         | None ->
           state
     else

packages/darklang/cli/utils/colors.dark

@@ -11,6 +11,7 @@ let underline = "\u001b[4m"
 let clearLine = "\u001b[K"
 let carriageReturn = "\r"
 let moveCursorToColumn (col: Int64) : String = $"\u001b[{Stdlib.Int64.toString col}G"
+let moveCursorUp (n: Int64) : String = $"\u001b[{Stdlib.Int64.toString n}A"
 let saveCursor = "\u001b[s"
 let restoreCursor = "\u001b[u"
 /// Move cursor to absolute position (row, col). Used to jump to the status bar without disrupting where the user is typing.