Reject reversed ignore character ranges

changelog.d/unreleased/1624.fixed.md

@@ -0,0 +1,16 @@
+---
+category: fixed
+issues:
+  - 1624
+affected:
+  - src/CodeIndex/Indexer/Scanning/FileIndexer.cs
+  - tests/CodeIndex.Tests/FileIndexerTests.cs
+---
+
+## English
+
+- **Reversed ignore character ranges are now rejected (#1624)** — `.gitignore` and `.cdidxignore` patterns such as `[z-a]` are skipped with a warning instead of compiling into a matcher that silently matches nothing.
+
+## 日本語
+
+- **ignore ルールの逆順文字範囲を拒否するようにしました (#1624)** — `.gitignore` と `.cdidxignore` の `[z-a]` のような pattern は、何にも一致しない matcher として静かに受理されず、警告付きで skipped されます。

src/CodeIndex/Indexer/Scanning/FileIndexer.cs

@@ -845,6 +845,9 @@ private static void AppendCharacterClassLiteral(StringBuilder builder, char ch,
 
         private static bool TryAppendCharacterClassRange(StringBuilder builder, char start, char end, bool ignoreCase)
         {
+            if (start > end)
+                throw new ArgumentException("reversed character class range");
+
             builder.Append(EscapeCharacterClassLiteral(start));
             builder.Append('-');
             builder.Append(EscapeCharacterClassLiteral(end));

tests/CodeIndex.Tests/FileIndexerTests.cs

@@ -2266,6 +2266,7 @@ public void ScanFilesDetailed_SkipsMalformedIgnoreRulesWithoutAborting()
             Assert.Equal(7, scanResult.Errors.Count);
             Assert.All(scanResult.Errors, error => Assert.Contains(".gitignore:", error.Path, StringComparison.Ordinal));
             Assert.All(scanResult.Errors, error => Assert.Contains("Invalid ignore rule skipped", error.Message, StringComparison.Ordinal));
+            Assert.Contains(scanResult.Errors, error => error.Message == "Invalid ignore rule skipped: reversed character class range");
             Assert.All(scanResult.Errors, error => Assert.Equal(FileIndexer.ScanIssueSeverity.Warning, error.Severity));
         }
         finally