MacOS/Linux: autocomplete window doesn't render at bottom of terminal on first prompt

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Release 6.0.2
+
+- Fix broken completion list rendering when the prompt starts near the bottom of the window on macOS/Linux ([waf/CSharpRepl#395](https://github.com/waf/CSharpRepl/issues/395)).
+
 # Release 6.0.1
 
 - Improve macOS and Linux key handling ([#297](https://github.com/waf/PrettyPrompt/pull/297)).

src/PrettyPrompt/Panes/CodePane.cs

@@ -454,12 +454,30 @@ void AppendFiltered(StringBuilder sb, string line)
         }
     }
 
+    /// <summary>
+    /// Corrects TopCoordinate after RenderPrompt writes blank lines to reserve completion-pane room.
+    /// - near the window bottom, those lines scroll the buffer up, so the prompt moves up by however many didn't fit below the cursor.
+    /// - Windows self-corrects via MeasureConsole each keystroke; Linux/macOS can't, so we adjust here from what we wrote (no cursor read).
+    /// - without it, CodeAreaHeight collapses to ~1 and the completion pane can't draw until the next submission. https://github.com/waf/CSharpRepl/issues/395
+    /// </summary>
+    internal void AdjustTopCoordinateForReservedLines(int reservedLines)
+    {
+        var rowsBelowCursor = console.WindowHeight - 1 - TopCoordinate;
+        var scrolledRows = Math.Max(0, reservedLines - rowsBelowCursor);
+        if (scrolledRows > 0)
+        {
+            TopCoordinate = Math.Max(0, TopCoordinate - scrolledRows);
+            CodeAreaHeight = Math.Max(0, console.WindowHeight - TopCoordinate);
+        }
+    }
+
     internal void MeasureConsole()
     {
+        // Re-derive TopCoordinate from the live cursor only on Windows (CursorTop is a cheap local API there); see PR #231 for why it's needed.
+        // - kept Windows-only on purpose: on Linux/macOS CursorTop blocks on an ESC[6n round-trip per read (a network round-trip over SSH), and this runs twice per keystroke.
+        // - dotnet/runtime#88343 (input corruption from that read) is now fixed, but the round-trip cost remains, so we still avoid it off-Windows.
         if(OperatingSystem.IsWindows())
         {
-            // ideally we'd update this in Linux too, but https://github.com/dotnet/runtime/issues/88343 prevents it.
-            // see https://github.com/waf/PrettyPrompt/pull/231 for why we need this line at all.
             TopCoordinate = Math.Max(0, console.CursorTop - console.WindowTop - Cursor.Row);
         }
         this.CodeAreaWidth = Math.Max(0, console.BufferWidth - configuration.Prompt.Length);

src/PrettyPrompt/PrettyPrompt.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <Version>6.0.1</Version>
+    <Version>6.0.2</Version>
 
     <PackageId>PrettyPrompt</PackageId>
     <PackageTags>repl readline console cli</PackageTags>

src/PrettyPrompt/Rendering/Renderer.cs

@@ -44,6 +44,10 @@ public void RenderPrompt(CodePane codePane)
         var newLinesCount = codePane.EmptySpaceAtBottomOfWindowHeight;
         console.Write(new string('\n', newLinesCount) + GetMoveCursorUp(newLinesCount) + GetMoveCursorToColumn(1) + Reset);
         console.Write(configuration.Prompt);
+
+        // those newlines may have scrolled the buffer up (prompt started near the window bottom); let the code pane
+        // correct TopCoordinate, since on non-Windows it can't re-derive it from the OS cursor.
+        codePane.AdjustTopCoordinateForReservedLines(newLinesCount);
     }
 
     public void RenderOutput(

tests/PrettyPrompt.Tests/RendererTests.cs

@@ -95,6 +95,28 @@ public async Task RenderOutput_ConsoleHeightTooSmallAndCursorOnFirstLine_ShowsIn
         Assert.Equal(expectedRender, output);
     }
 
+    [Fact]
+    public void RenderPrompt_StartedAtBottomOfWindow_ReservesRoomForCompletionPane()
+    {
+        // prompt starts on the very bottom row of the window
+        const int Height = 30;
+        var console = ConsoleStub.NewConsole(width: 100, height: Height);
+        console.CursorTop.Returns(Height - 1);
+        console.WindowTop.Returns(0);
+        var configuration = new PromptConfiguration();
+        var renderer = new Renderer(console, configuration);
+        var codePane = new CodePane(console, configuration, new PromptCallbacks(), Substitute.For<IClipboard>());
+
+        var reserved = codePane.EmptySpaceAtBottomOfWindowHeight;
+
+        renderer.RenderPrompt(codePane);
+
+        // RenderPrompt writes `reserved` blank lines to make room for the completion pane; since the prompt
+        // started at the bottom that scrolls the buffer up, moving the prompt up by `reserved` rows.
+        Assert.Equal(Height - 1 - reserved, codePane.TopCoordinate);
+        Assert.Equal(reserved + 1, codePane.CodeAreaHeight);
+    }
+
     private (CodePane codePane, CompletionPane completionPane, OverloadPane overloadPane) BuildUIPanes(string typedInput)
     {
         var callbacks = Substitute.For<IPromptCallbacks>();