Respond to vscode breaking change in 1.79.2 that triggers completion inside words

src/OmniSharp.Roslyn.CSharp/Services/Completion/CompletionListBuilder_Sync.cs

@@ -220,6 +220,15 @@ private static void GetCompletionInfo(
                     }
 
                     changeSpan = updatedChange.Span;
+                    // When inserting at the beginning or middle of a word, we want to only replace characters
+                    // up until the caret position, but not after.  For example when typing at the beginning of a word
+                    // we only want to insert the completion before the rest of the word.
+                    // However, Roslyn returns the entire word as the span to replace, so we have to adjust it.
+                    if (position < changeSpan.End)
+                    {
+                        changeSpan = new(changeSpan.Start, length: position - changeSpan.Start);
+                    }
+
                     (insertText, insertTextFormat) = getPossiblySnippetizedInsertText(updatedChange, adjustedNewPosition);
 
                     // If we're expecting there to be unimported types, put in an explicit sort text to put things already in scope first.

tests/OmniSharp.Roslyn.CSharp.Tests/CompletionFacts.cs

@@ -2250,6 +2250,24 @@ public C()
             }
         }
 
+        [Theory]
+        [InlineData("dummy.cs")]
+        [InlineData("dummy.csx")]
+        public async Task ReplacesUpUntilCursorInMiddleOfWord(string filename)
+        {
+            const string input =
+                @"pub$$class}";
+
+            var completions = await FindCompletionsAsync(filename, input, SharedOmniSharpTestHost);
+            Assert.All(completions.Items, (completion) =>
+            {
+                Assert.Equal(0, completion.TextEdit.StartColumn);
+                Assert.Equal(0, completion.TextEdit.StartLine);
+                Assert.Equal(3, completion.TextEdit.EndColumn);
+                Assert.Equal(0, completion.TextEdit.EndLine);
+            });
+        }
+
         private CompletionService GetCompletionService(OmniSharpTestHost host)
             => host.GetRequestHandler<CompletionService>(EndpointName);