Ignore in-line comments with no diff context

This is unlikely to happen in real life but worth guarding against.

Author: jcansdale

src/GitHub.InlineReviews/Services/PullRequestSessionService.cs

@@ -93,14 +93,13 @@ public IReadOnlyList<IInlineCommentThreadModel> BuildCommentThreads(
                 var chunk = chunks.Last();
                 var diffLines = chunk.Lines.Reverse().Take(5).ToList();
                 var firstLine = diffLines.FirstOrDefault();
-                var diffLineType = firstLine != null ? firstLine.Type : DiffChangeType.None;
-
                 if (firstLine == null)
                 {
-                    log.Warning("Couldn't find diff lines for inline comment. RelativePath={RelativePath}, OriginalCommitSha={Sha}, OriginalPosition={Position}, Chunks={Chunks}, DiffHunk={DiffHunk}",
-                        relativePath, comments.Key.Item1, comments.Key.Item2, chunks.Count(), hunk);
+                    log.Warning("Ignoring in-line comment in {RelativePath} with no diff line context", relativePath);
+                    continue;
                 }
 
+                var diffLineType = firstLine.Type;
                 var thread = new InlineCommentThreadModel(
                     relativePath,
                     comments.Key.Item1,

test/GitHub.InlineReviews.UnitTests/Services/PullRequestSessionServiceTests.cs

@@ -53,6 +53,29 @@ Line 2
                 }
             }
 
+            [Test]
+            public async Task IgnoreCommentsWithNoDiffLineContext()
+            {
+                var baseContents = "Line 1";
+                var headContents = "Line 1";
+
+                var comment = CreateComment(@"@@ -10,7 +10,6 @@ class Program");
+
+                using (var diffService = new FakeDiffService(FilePath, baseContents))
+                {
+                    var diff = await diffService.Diff(FilePath, headContents);
+                    var pullRequest = CreatePullRequest(FilePath, comment);
+                    var target = CreateTarget(diffService);
+
+                    var result = target.BuildCommentThreads(
+                        pullRequest,
+                        FilePath,
+                        diff);
+
+                    Assert.That(result, Is.Empty);
+                }
+            }
+
             [Test]
             public async Task MatchesReviewCommentOnDifferentLine()
             {
@@ -212,7 +235,7 @@ Line 2
 
                     Assert.That(3, Is.EqualTo(threads[0].LineNumber));
                     Assert.That(
-                        new[] 
+                        new[]
                         {
                             Tuple.Create(2, DiffSide.Right),
                             Tuple.Create(3, DiffSide.Right)