Ensure reformat-on-submit is handled correctly

src/PrettyPrompt/Panes/CodePane.cs

@@ -163,6 +163,19 @@ internal void Bind(CompletionPane completionPane, OverloadPane overloadPane)
         this.overloadPane = overloadPane;
     }
 
+    /// <summary>
+    /// Re-capture the submit result's text from the current document, so the returned result matches
+    /// what's shown (and saved to history) after auto-formatting, not the pre-format snapshot.
+    /// </summary>
+    internal void RefreshSubmitResultText()
+    {
+        if (Result is not { IsSuccess: true })
+        {
+            return;
+        }
+        Result = new PromptResult(isSuccess: true, Document.GetText().EnvironmentNewlines(), Result.SubmitKeyInfo);
+    }
+
     public async Task OnKeyDown(KeyPress key, CancellationToken cancellationToken)
     {
         if (key.Handled) return;

src/PrettyPrompt/Prompt.cs

@@ -111,7 +111,7 @@ private async Task<PromptResult> ReadLineCoreAsync()
             // grab the code area width every key press, so we rerender appropriately when the console is resized.
             codePane.MeasureConsole();
 
-            await InterpretKeyPress(key, cancellationToken: default).ConfigureAwait(false);
+            var reformatted = await InterpretKeyPress(key, cancellationToken: default).ConfigureAwait(false);
 
             // typing / word-wrapping may have scrolled the console, giving us more room.
             codePane.MeasureConsole();
@@ -140,7 +140,8 @@ private async Task<PromptResult> ReadLineCoreAsync()
                     break;
                 // user submitted the prompt, or a keybinding submitted the prompt
                 case PromptResult or KeyPressCallbackResult:
-                    await RenderSyntaxHighlightedOutput(renderer, codePane, overloadPane, completionPane, key, inputText, result).ConfigureAwait(false);
+                    // a reformat on the submit keystroke must force a repaint (see Renderer.RenderOutput)
+                    await RenderSyntaxHighlightedOutput(renderer, codePane, overloadPane, completionPane, key, inputText, result, forceRedrawOnSubmit: reformatted).ConfigureAwait(false);
                     //wait for potential previous saving
                     await (savePersistentHistoryTask ?? Task.CompletedTask).ConfigureAwait(false);
                     savePersistentHistoryTask = history.SavePersistentHistoryAsync(inputText);
@@ -153,7 +154,7 @@ private async Task<PromptResult> ReadLineCoreAsync()
         Debug.Assert(false, "Should never reach here due to infinite " + nameof(KeyPress.ReadForever));
         return null;
 
-        async Task InterpretKeyPress(KeyPress key, CancellationToken cancellationToken)
+        async Task<bool> InterpretKeyPress(KeyPress key, CancellationToken cancellationToken)
         {
             if (!completionPane.WouldKeyPressCommitCompletionItem(key))
             {
@@ -166,16 +167,19 @@ async Task InterpretKeyPress(KeyPress key, CancellationToken cancellationToken)
             foreach (var panes in keyPressHandlers)
                 await panes.OnKeyUp(key, cancellationToken).ConfigureAwait(false);
 
-            await AutoFormatDocument(key, codePane, cancellationToken).ConfigureAwait(false);
+            var reformatted = await AutoFormatDocument(key, codePane, cancellationToken).ConfigureAwait(false);
 
             //we don't support text selection while completion list is open
             //text selection can put completion list into broken state, where filtering does not work
             //so we want this assert to be true
             Debug.Assert(!completionPane.IsOpen || (codePane.Selection is null));
+
+            return reformatted;
         }
     }
 
-    private async Task AutoFormatDocument(KeyPress key, CodePane codePane, CancellationToken cancellationToken)
+    /// <returns>True if the callback reformatted the document (the buffer was changed), else false.</returns>
+    private async Task<bool> AutoFormatDocument(KeyPress key, CodePane codePane, CancellationToken cancellationToken)
     {
         var text = codePane.Document.GetText();
         var (formattedText, newCaret) = await promptCallbacks.FormatInput(text, codePane.Document.Caret, key, cancellationToken).ConfigureAwait(false);
@@ -187,17 +191,21 @@ private async Task AutoFormatDocument(KeyPress key, CodePane codePane, Cancellat
                 if (formattedText[i] == '\r') ++removedChars;
             }
             codePane.Document.SetContents(codePane, formattedText.Replace("\r\n", "\n"), newCaret - removedChars);
+            // if this keystroke also submitted, the result text was snapshotted pre-format; re-capture it
+            codePane.RefreshSubmitResultText();
+            return true;
         }
         else
         {
             Debug.Assert(codePane.Document.Caret == newCaret);
+            return false;
         }
     }
 
-    private async Task RenderSyntaxHighlightedOutput(Renderer renderer, CodePane codePane, OverloadPane overloadPane, CompletionPane completionPane, KeyPress key, string inputText, PromptResult? result)
+    private async Task RenderSyntaxHighlightedOutput(Renderer renderer, CodePane codePane, OverloadPane overloadPane, CompletionPane completionPane, KeyPress key, string inputText, PromptResult? result, bool forceRedrawOnSubmit = false)
     {
         var highlights = await highlighter.HighlightAsync(inputText, cancellationToken: default).ConfigureAwait(false);
-        renderer.RenderOutput(result, codePane, overloadPane, completionPane, highlights, key);
+        renderer.RenderOutput(result, codePane, overloadPane, completionPane, highlights, key, forceRedrawOnSubmit);
     }
 
     private async Task<PromptResult?> HandleKeyPressAction(CodePane codePane, KeyPress key, string inputText, CancellationToken cancellationToken)

src/PrettyPrompt/Rendering/Renderer.cs

@@ -56,11 +56,13 @@ public void RenderOutput(
         OverloadPane overloadPane,
         CompletionPane completionPane,
         IReadOnlyCollection<FormatSpan> highlights,
-        KeyPress key)
+        KeyPress key,
+        bool forceRedraw = false)
     {
         if (result is not null)
         {
-            bool redraw = false;
+            // reformat-on-submit leaves the on-screen line stale, so repaint it. https://github.com/waf/CSharpRepl/issues/356
+            bool redraw = forceRedraw;
             if (wasTextSelectedDuringPreviousRender && codePane.Selection is null)
             {
                 redraw = true;

tests/PrettyPrompt.Tests/PromptTests.cs

@@ -111,6 +111,45 @@ public async Task ReadLine_WordWrap()
         );
     }
 
+    /// <summary>
+    /// Regression test for https://github.com/waf/CSharpRepl/issues/356.
+    /// When <see cref="PromptCallbacks.FormatInput"/> reformats the buffer on the very keystroke that
+    /// submits the prompt, the submit render path must force a redraw so the committed line shows the
+    /// formatted text. Otherwise the on-screen line is left showing the stale pre-format text, because
+    /// the reformat happened after the previous render and the submit path skips redrawing by default.
+    /// </summary>
+    [Fact]
+    public async Task ReadLine_FormatInputReformatsOnSubmit_RedrawsFormattedText()
+    {
+        var console = ConsoleStub.NewConsole();
+        console.StubInput($"hello{Enter}");
+
+        var prompt = new Prompt(
+            callbacks: new TestPromptCallbacks
+            {
+                // Only reformat on the submit keystroke (Enter), so the formatted text has never been
+                // rendered before submit - that's the scenario the fix addresses.
+                FormatInputCallback = (text, caret, keyPress) =>
+                    Task.FromResult(
+                        keyPress.ConsoleKeyInfo.Key == Enter
+                            ? (text.ToUpperInvariant(), caret)
+                            : (text, caret))
+            },
+            console: console);
+
+        var result = await prompt.ReadLineAsync();
+
+        Assert.True(result.IsSuccess);
+
+        // The returned result reflects the formatted text (re-captured after AutoFormatDocument), not the
+        // pre-format snapshot taken when the submit key was first handled.
+        Assert.Equal("HELLO", result.Text);
+
+        // ...and the final render repaints it; without the forced redraw the screen would still show the
+        // lowercase "hello" typed before the submit keystroke.
+        Assert.Contains("HELLO", console.GetFinalOutput());
+    }
+
     [Fact]
     public async Task ReadLine_HorizontalNavigationKeys()
     {

tests/PrettyPrompt.Tests/TestPromptCallbacks.cs

@@ -16,6 +16,7 @@ namespace PrettyPrompt.Tests;
 internal delegate Task<IReadOnlyCollection<FormatSpan>> HighlightCallbackAsync(string text);
 internal delegate Task<KeyPress> TransformKeyPressAsyncCallbackAsync(string text, int caret, KeyPress keyPress);
 internal delegate Task<(IReadOnlyList<OverloadItem>, int ArgumentIndex)> GetOverloadsCallbackAsync(string text, int caret);
+internal delegate Task<(string Text, int Caret)> FormatInputCallbackAsync(string text, int caret, KeyPress keyPress);
 
 internal class TestPromptCallbacks : PromptCallbacks
 {
@@ -29,6 +30,7 @@ internal class TestPromptCallbacks : PromptCallbacks
     public HighlightCallbackAsync? HighlightCallback { get; set; }
     public TransformKeyPressAsyncCallbackAsync? TransformKeyPressCallback { get; set; }
     public GetOverloadsCallbackAsync? GetOverloadsCallback { get; set; }
+    public FormatInputCallbackAsync? FormatInputCallback { get; set; }
 
     public TestPromptCallbacks(params (KeyPressPattern Pattern, KeyPressCallbackAsync Callback)[]? keyPressCallbacks)
     {
@@ -100,4 +102,12 @@ GetOverloadsCallback is null ?
             base.GetOverloadsAsync(text, caret, cancellationToken) :
             GetOverloadsCallback(text, caret);
     }
+
+    protected override Task<(string Text, int Caret)> FormatInput(string text, int caret, KeyPress keyPress, CancellationToken cancellationToken)
+    {
+        return
+            FormatInputCallback is null ?
+            base.FormatInput(text, caret, keyPress, cancellationToken) :
+            FormatInputCallback(text, caret, keyPress);
+    }
 }