Rerequest completion items when text is deleted/retyped

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Release 6.0.5 (UNRELEASED)
+
+- Fix the completion list offering items for a word that is no longer typed. The completion callback is now asked again whenever the typed word stops being an extension of the one it was asked about.
+
 # Release 6.0.4
 
 - Support "complex" completion items that rewrite a larger region of the document than the typed word (and reposition the caret) ([304](https://github.com/waf/PrettyPrompt/pull/304)).

src/PrettyPrompt/Panes/CompletionPane.cs

@@ -37,6 +37,13 @@ internal class CompletionPane : IKeyPressHandler
     /// </summary>
     private IReadOnlyList<CompletionItem> allCompletions = Array.Empty<CompletionItem>();
 
+    /// <summary>
+    /// The text of the span <see cref="allCompletions"/> was requested for. Callbacks are free to
+    /// return only the items matching that text, so the list stays usable exactly as long as the
+    /// user keeps extending it.
+    /// </summary>
+    private string allCompletionsFilterText = string.Empty;
+
     /// <summary>
     /// An "ordered view" over <see cref="allCompletions"/> that shows the list filtered by what the user has typed.
     /// </summary>
@@ -71,6 +78,7 @@ private async Task Open(CancellationToken cancellationToken)
         bool wasOpen = IsOpen;
         this.IsOpen = true;
         this.allCompletions = Array.Empty<CompletionItem>();
+        this.allCompletionsFilterText = string.Empty;
         if (!wasOpen)
         {
             await promptCallbacks.CompletionWindowOpenedAsync(codePane.Document.GetText(), codePane.Document.Caret, cancellationToken).ConfigureAwait(false);
@@ -224,17 +232,20 @@ await promptCallbacks.ShouldOpenCompletionWindowAsync(codePane.Document.GetText(
                 }
             }
 
-            if (allCompletions.Count == 0)
+            // We ask the callback once and then only re-rank what it gave us, which is correct for
+            // as long as the user is refining the text we asked about. Deleting back past that text
+            // and typing something else leaves us ranking items for a word that is no longer there
+            // (ask on "G", delete it, type "H", and the G-items get sorted against "H"), so ask again.
+            if (allCompletions.Count == 0 ||
+                !documentText.AsSpan(spanToReplace).StartsWith(allCompletionsFilterText, StringComparison.Ordinal))
             {
                 var completions = await promptCallbacks.GetCompletionItemsAsync(documentText, documentCaret, spanToReplace, cancellationToken).ConfigureAwait(false);
                 if (completions.Any())
                 {
                     allCompletions = completions;
-                    if (completions.Any())
-                    {
-                        int height = Math.Min(codePane.CodeAreaHeight - VerticalPaddingHeight - overloadPane.GetCurrentHeight(), configuration.MaxCompletionItemsCount);
-                        await FilteredView.UpdateItems(completions, documentText, documentCaret, spanToReplace, height, cancellationToken).ConfigureAwait(false);
-                    }
+                    allCompletionsFilterText = documentText.AsSpan(spanToReplace).ToString();
+                    int height = Math.Min(codePane.CodeAreaHeight - VerticalPaddingHeight - overloadPane.GetCurrentHeight(), configuration.MaxCompletionItemsCount);
+                    await FilteredView.UpdateItems(completions, documentText, documentCaret, spanToReplace, height, cancellationToken).ConfigureAwait(false);
                 }
                 else
                 {

tests/PrettyPrompt.Tests/CompletionTests.cs

@@ -800,6 +800,42 @@ public async Task ReadLine_RenderingBug()
         Assert.Contains("bbb │ a vivid description of bbb", output[4]); //after press of 'b' (here was the bug)
     }
 
+    /// <summary>
+    /// A callback that returns only the items matching the typed word -- what a real completion
+    /// provider does, and what <see cref="CompletionTestData"/> deliberately does not do.
+    /// </summary>
+    [Fact]
+    public async Task ReadLine_FilteringCallback_IsAskedAgainAfterTheTypedWordIsDeleted()
+    {
+        var console = ConsoleStub.NewConsole();
+        var prompt = new Prompt(
+            callbacks: new TestPromptCallbacks
+            {
+                CompletionCallback = (text, caret, spanToBeReplaced) =>
+                {
+                    var typedWord = text.AsSpan(spanToBeReplaced).ToString();
+                    return Task.FromResult<IReadOnlyList<CompletionItem>>(
+                        new[] { "green", "grey", "hazel" }
+                            .Where(c => c.StartsWith(typedWord, StringComparison.OrdinalIgnoreCase))
+                            .Select(c => new CompletionItem(c))
+                            .ToArray());
+                }
+            },
+            console: console);
+
+        console.StubInput(
+            $"gr", // the list is fetched for "gr", so it holds green and grey
+            $"{Backspace}{Backspace}", // and is stale from here on: neither is a completion of ""
+            $"h",
+            $"{Enter}", // commits the selected item
+            $"{Enter}");
+
+        var result = await prompt.ReadLineAsync();
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal("hazel", result.Text);
+    }
+
     public static Prompt ConfigurePrompt(IConsole console, PromptConfiguration? configuration = null, string[]? completions = null) =>
         new(
             callbacks: new TestPromptCallbacks