Preserve C# explicit-interface symbol identities

README.md

@@ -93,6 +93,15 @@ cdidx license --json
 cdidx validate
 ```
 
+For C# explicit-interface implementations, symbol output and outlines keep the
+short display name (`Run`, `Value`, `Changed`, or `Item`). Qualified exact-name
+queries use the interface spelling, such as `IFoo.Run<T>`, `IFoo.Value`,
+`IFoo.Changed`, and `IFoo.Item` (`IFoo.this` is accepted as an indexer alias).
+Generic parameter spelling is normalized to arity, so `IFoo.Run<TValue>` has the
+same exact identity as `IFoo.Run<T>`. An unqualified exact query such as `Run`
+remains a discovery alias and may return explicit implementations alongside
+same-named public members; use the qualified spelling to select one identity.
+
 `doctor --env-inventory=full` accepts exact `--env-domain`,
 `--env-category`, and `--env-sensitivity` filters that compose with AND.
 Its JSON form accepts `--max-json-bytes` as a whole-document UTF-8 byte cap;
@@ -527,6 +536,14 @@ cdidx license --json
 cdidx validate
 ```
 
+C# の明示的 interface 実装では、symbol 出力と outline は短い表示名
+（`Run`、`Value`、`Changed`、`Item`）を維持します。修飾した exact-name query には
+`IFoo.Run<T>`、`IFoo.Value`、`IFoo.Changed`、`IFoo.Item` のような interface 表記を使い、
+indexer では `IFoo.this` も alias として受け付けます。generic parameter の表記は arity に
+正規化されるため、`IFoo.Run<TValue>` と `IFoo.Run<T>` は同じ完全一致 identity です。
+`Run` のような非修飾の完全一致 query は discovery alias のままで、同名の public member と
+明示的実装をともに返す場合があります。1つの identity を選ぶには修飾表記を使ってください。
+
 `doctor --env-inventory=full` は、AND で合成される完全一致の
 `--env-domain`、`--env-category`、`--env-sensitivity` filter を受け付けます。
 JSON 形式では `--max-json-bytes` を文書全体の UTF-8 byte cap として利用できるため、

TESTING_GUIDE.md

@@ -81,6 +81,7 @@ Use `docs/test-doc-maintenance-plan.md` before moving oversized suites or adding
   Extractor coverage is split by language or feature area with partial test classes, while shared helpers remain on the root `SymbolExtractorTests` / `ReferenceExtractorTests` parts.
   YAML sequence-hierarchy fixtures must keep sequence items path-only, count empty/scalar/alias items in stable indexes, preserve anchor and block-scalar boundaries, assert logical qualified paths separately from nearest emitted symbol parents, and prove a normal full scan refreshes unchanged YAML rows stamped with the prior extractor contract.
   C# declaration-boundary regressions should pair a direct extractor fixture with a real-index `symbols --exact-name` query. Keep invocation and parameter continuations beside valid multi-line methods, constructors, delegates, and local functions so both false-positive rejection and declaration ranges remain observable.
+  C# explicit-interface identity coverage pairs extractor assertions for methods, properties, events, and indexers with persisted exact qualified/unqualified queries, fold rewrite validation, inspect/outline checks, and LSP definition/reference scoping. Include multiple and inherited interfaces, generic arity, a same-named public member, and a qualified return type that must not be mistaken for an explicit-interface qualifier.
   C# callable-containment fixtures should cover block-bodied test methods, local and nested local functions, named lambdas, expression-bodied members, and nested types together, asserting both symbol parents and call-reference containers.
   Repository-metadata coverage lives in `SymbolExtractorRepositoryMetadataTests.cs` and `ReferenceExtractorRepositoryMetadataTests.cs`; keep TOML, JSON Lines, ignore/attributes, EditorConfig, `.rules`, and application-manifest capability assertions coordinated with conservative local-path and malformed-record controls.
   Capability-regression fixtures that require an unsupported language use the explicit `text` placeholder or an ambiguity bucket; do not use a recognized repository-metadata format as the unsupported control.
@@ -1010,6 +1011,7 @@ dotnet test --filter "FullyQualifiedName~GitHelperTests"
   extractor のカバレッジは言語または機能領域ごとの partial test class に分割し、共有 helper は root 側の `SymbolExtractorTests` / `ReferenceExtractorTests` に残します。
   YAML sequence hierarchy の fixture では、sequence item を path 専用のまま保ち、empty / scalar / alias item を安定した index に数え、anchor と block scalar の境界を維持し、論理 qualified path と最寄りの出力済み symbol parent を分けて検証し、旧 extractor contract が stamp された未変更 YAML row を通常の full scan が更新することも確認してください。
   C# の declaration boundary に関する regression では、extractor を直接呼ぶ fixture と、実 index に対する `symbols --exact-name` query を組み合わせてください。呼び出し・parameter の continuation と、正当な複数行 method、constructor、delegate、local function を同居させ、false positive の拒否と宣言 range の両方を観測可能にします。
+  C# の明示的 interface identity coverage では、method、property、event、indexer の extractor assertion と、永続化後の修飾 / 非修飾の完全一致 query、fold rewrite 検証、inspect / outline、LSP の definition / reference scope を組み合わせます。複数および継承 interface、generic arity、同名 public member に加え、明示的 interface qualifier と誤認してはならない修飾 return type を含めてください。
   C# の callable containment fixture では、block body の test method、local / nested local function、named lambda、expression-bodied member、nested type を同居させ、symbol の親と call reference の container の両方を検証してください。
   repository metadata の coverage は `SymbolExtractorRepositoryMetadataTests.cs` と `ReferenceExtractorRepositoryMetadataTests.cs` に置きます。TOML、JSON Lines、ignore / attributes、EditorConfig、`.rules`、application manifest の capability assertion を、保守的な local-path 抽出と malformed-record control に同期させてください。
   未対応言語を必要とする capability regression fixture には明示的な `text` placeholder または ambiguity bucket を使い、認識済み repository metadata 形式を未対応 control に使わないでください。

changelog.d/unreleased/4866.fixed.md

@@ -0,0 +1,20 @@
+---
+category: fixed
+issues:
+  - 4866
+affected:
+  - src/CodeIndex/Database
+  - src/CodeIndex/Indexer
+  - tests/CodeIndex.Tests
+  - README.md
+  - DEVELOPER_GUIDE.md
+  - TESTING_GUIDE.md
+---
+
+## English
+
+- **C# explicit-interface members now retain distinct symbol identities (#4866)** — Exact qualified queries preserve the interface qualifier and generic arity for methods, properties, events, and indexers without merging them with same-named public members, including indexer aliases when no language filter is supplied. Short display names remain available through a separately indexed Unicode-folded discovery alias across CLI, inspect, outline, and LSP navigation. `backfill-fold` upgrades the previous C# naming contract without reparsing when persisted signatures are available; legacy databases without that reconstruction evidence remain unready and request a C# refresh instead of receiving a false v3 readiness stamp.
+
+## 日本語
+
+- **C# の明示的 interface member が個別の symbol identity を保持するようになりました (#4866)** — method、property、event、indexer の完全一致 query で interface qualifier と generic arity を保持し、言語 filter 未指定時の indexer alias を含めて同名の public member と統合しません。CLI、inspect、outline、LSP navigation では、短い表示名を別途 index 化した Unicode-folded discovery alias として引き続き利用できます。`backfill-fold` は永続 signature が残る場合に source の再解析なしで以前の C# naming contract を更新し、復元根拠がない legacy DB には誤った v3 readiness stamp を付けず C# refresh を案内します。

src/CodeIndex/Cli/DiffCommandRunner.cs

@@ -222,6 +222,7 @@ private static DiffJsonResult CompareDatabasesCore(
             "sub_kind",
             "name",
             "name_folded",
+            "display_name_folded",
             "line",
             "start_line",
             "start_column",
@@ -1301,6 +1302,9 @@ private static string BuildSymbolRowsSql(SqliteConnection connection)
         var metadataTargetSourceExpr = ColumnExists(connection, "symbols", "metadata_target_source")
             ? "symbols.metadata_target_source"
             : "NULL";
+        var displayNameFoldedExpr = ColumnExists(connection, "symbols", "display_name_folded")
+            ? "symbols.display_name_folded"
+            : "NULL";
 
         return $$"""
             SELECT
@@ -1309,6 +1313,7 @@ private static string BuildSymbolRowsSql(SqliteConnection connection)
                 symbols.sub_kind,
                 symbols.name,
                 symbols.name_folded,
+                {{displayNameFoldedExpr}},
                 symbols.line,
                 symbols.start_line,
                 symbols.start_column,
@@ -1332,6 +1337,7 @@ ORDER BY
                 symbols.sub_kind,
                 symbols.name,
                 symbols.name_folded,
+                {{displayNameFoldedExpr}},
                 symbols.line,
                 symbols.start_line,
                 symbols.start_column,

src/CodeIndex/Cli/IndexCommandRunner.Maintenance.cs

@@ -570,6 +570,16 @@ internal static int RunBackfillFold(
             if (!options.DryRun)
                 db.InitializeSchema();
             var writer = new DbWriter(db);
+            if (writer.TryGetNewerCSharpSymbolNameContractVersion(out var newerCSharpContract))
+            {
+                return WriteCommandError(
+                    options.Json,
+                    jsonOptions,
+                    $"C# symbol-name contract version {newerCSharpContract} is newer than supported version {DbContext.CSharpSymbolNameContractVersion}",
+                    CommandExitCodes.DatabaseError,
+                    "Use the same or a newer CodeIndex version that wrote this database; this version will not rewrite or downgrade its C# identities.",
+                    CommandErrorCodes.DbError);
+            }
 
             var userVersionBefore = db.GetUserVersion();
             var foldReadyBefore = (userVersionBefore & DbContext.FoldReadyFlag) != 0;
@@ -579,11 +589,29 @@ internal static int RunBackfillFold(
             var storedFoldFingerprint = db.GetMetaString("fold_key_fingerprint");
             var foldMetadataCurrentBefore = storedFoldVersion == currentFoldVersion
                 && storedFoldFingerprint == currentFoldFingerprint;
+            var csharpSymbolNameContractUpgradeRequired =
+                writer.HasAnyFilesWithLanguage("csharp")
+                && !string.Equals(
+                db.GetMetaString(DbContext.CSharpSymbolNameContractVersionMetaKey),
+                DbContext.CSharpSymbolNameContractVersion.ToString(
+                    System.Globalization.CultureInfo.InvariantCulture),
+                StringComparison.Ordinal);
+            if (csharpSymbolNameContractUpgradeRequired
+                && !writer.CanReconstructCSharpExplicitInterfaceIdentitiesFromPersistedRows())
+            {
+                return WriteCommandError(
+                    options.Json,
+                    jsonOptions,
+                    "C# explicit-interface identities cannot be reconstructed because legacy symbol signatures are missing",
+                    CommandExitCodes.DatabaseError,
+                    "Refresh the C# files with `cdidx index <projectPath>` (or rebuild the index) before retrying `cdidx backfill-fold`.",
+                    CommandErrorCodes.DbError);
+            }
             foldReadyBefore = foldReadyBefore && foldMetadataCurrentBefore;
             // Missing or mismatched fold metadata means persisted keys may have been generated
             // by a different fold algorithm/runtime, so refresh every row from source names.
             // fold metadata 未記録 / 不一致時は全行再計算して version/runtime skew を解消する。
-            var rewriteAll = !foldMetadataCurrentBefore;
+            var rewriteAll = writer.ResolveFoldBackfillRewriteAll(!foldMetadataCurrentBefore);
 
             var symbols = 0;
             var symbolReferences = 0;
@@ -617,6 +645,7 @@ internal static int RunBackfillFold(
                         "Retry `cdidx backfill-fold`. If the DB still does not verify, rebuild it with `cdidx index <projectPath> --rebuild`.",
                         CommandErrorCodes.DbError);
                 }
+                writer.MarkCSharpSymbolNameContractReady();
 
                 transaction.Commit();
                 userVersionAfter = db.GetUserVersion();

src/CodeIndex/Database/DbContext.ConnectionFunctions.cs

@@ -57,6 +57,10 @@ internal static void RegisterConnectionFunctions(SqliteConnection connection)
                 var leafName = SqlNameResolver.GetLeafName(name);
                 return leafName.Length == 0 ? null : NameFold.Fold(leafName) ?? leafName;
             });
+        connection.CreateFunction(
+            "codeindex_name_fold",
+            (string? name) => NameFold.Fold(name),
+            isDeterministic: true);
         connection.CreateFunction(
             "sql_normalize_name",
             (string? name) => string.IsNullOrWhiteSpace(name) ? null : SqlNameResolver.NormalizeQualifiedName(name));

src/CodeIndex/Database/DbContext.ReadMigrations.cs

@@ -255,10 +255,13 @@ PRIMARY KEY(reference_id, symbol_id)
         // not fail on legacy DBs where the column did not exist yet.
         // #86: folded 列を追加してから folded index を作らないと legacy DB でクラッシュする。
         yield return ("EnsureColumn symbols.name_folded", () => EnsureColumn("symbols", "name_folded", "TEXT"));
+        yield return ("EnsureColumn symbols.display_name_folded", () => EnsureColumn("symbols", "display_name_folded", "TEXT"));
         yield return ("EnsureColumn symbol_references.symbol_name_folded", () => EnsureColumn("symbol_references", "symbol_name_folded", "TEXT"));
         yield return ("EnsureColumn symbol_references.container_name_folded", () => EnsureColumn("symbol_references", "container_name_folded", "TEXT"));
         yield return ("CREATE INDEX idx_symbols_name_folded",
             () => Execute("CREATE INDEX IF NOT EXISTS idx_symbols_name_folded                ON symbols(name_folded)"));
+        yield return ("CREATE INDEX idx_symbols_display_name_folded",
+            () => Execute("CREATE INDEX IF NOT EXISTS idx_symbols_display_name_folded ON symbols(display_name_folded) WHERE display_name_folded IS NOT NULL"));
         yield return ("CREATE INDEX idx_symbols_file_name_folded",
             () => Execute("CREATE INDEX IF NOT EXISTS idx_symbols_file_name_folded ON symbols(file_id, name_folded)"));
         yield return ("CREATE INDEX idx_symbols_file_name_nocase",

src/CodeIndex/Database/DbContext.SchemaInitialization.cs

@@ -137,7 +137,9 @@ container_kind  TEXT CHECK (container_kind IS NULL OR container_kind IN (" + sym
         visibility      TEXT,
         return_type     TEXT,
         is_metadata_target INTEGER,
-        metadata_target_source TEXT
+        metadata_target_source TEXT,
+        name_folded     TEXT,
+        display_name_folded TEXT
     )");
 
         // Indexed references table / 参照インデックステーブル
@@ -228,6 +230,7 @@ private void MigrateCoreTableColumns()
         // COLLATE NOCASE path (correct for ASCII, misses non-ASCII casing — #86 fix).
         // #86: --exact 用の Unicode 折り畳み列。レガシー行は NULL のまま、再 index で埋まる。
         EnsureColumn("symbols", "name_folded", "TEXT");
+        EnsureColumn("symbols", "display_name_folded", "TEXT");
         EnsureColumn("symbol_references", "symbol_name_folded", "TEXT");
         EnsureColumn("symbol_references", "container_name_folded", "TEXT");
         EnsureColumn("symbol_references", "is_self_reference", "INTEGER NOT NULL DEFAULT 0");
@@ -315,6 +318,11 @@ private void CreateCoreSchemaIndexes()
         // the NOCASE indexes above. Both sets coexist so mixed-state DBs cannot regress.
         // #86: 折り畳み列のインデックス。FoldReadyFlag が立っている DB でだけ使う。
         Execute("CREATE INDEX IF NOT EXISTS idx_symbols_name_folded                ON symbols(name_folded)");
+        // Explicit-interface identities occupy name_folded, while unqualified discovery uses
+        // the separately persisted display-name fold. Both predicates stay indexed.
+        // 明示的 interface identity は name_folded、非修飾 discovery は別途永続化した
+        // display-name fold を使い、両方の predicate を index 対応に保つ。
+        Execute("CREATE INDEX IF NOT EXISTS idx_symbols_display_name_folded ON symbols(display_name_folded) WHERE display_name_folded IS NOT NULL");
         // Reference-source and ranked-candidate resolution repeatedly combines the folded
         // symbol name with file or container scope. Keep those probes bounded for every
         // indexed language, including the NOCASE fallback used by partially migrated DBs.
@@ -432,10 +440,11 @@ container_kind  TEXT CHECK (container_kind IS NULL OR container_kind IN ({symbol
                     return_type     TEXT,
                     is_metadata_target INTEGER,
                     metadata_target_source TEXT,
-                    name_folded     TEXT
+                    name_folded     TEXT,
+                    display_name_folded TEXT
                 )
                 """,
-                "id, file_id, kind, sub_kind, name, line, start_line, start_column, end_line, body_start_line, body_end_line, signature, container_kind, container_name, container_qualified_name, family_key, visibility, return_type, is_metadata_target, metadata_target_source, name_folded");
+                "id, file_id, kind, sub_kind, name, line, start_line, start_column, end_line, body_start_line, body_end_line, signature, container_kind, container_name, container_qualified_name, family_key, visibility, return_type, is_metadata_target, metadata_target_source, name_folded, display_name_folded");
             RebuildReferenceLineTablesWithRequiredFileId();
             RebuildTableWithRequiredFileId(
                 "file_issues",
@@ -726,10 +735,11 @@ container_kind  TEXT CHECK (container_kind IS NULL OR container_kind IN ({symbol
                 return_type     TEXT,
                 is_metadata_target INTEGER,
                 metadata_target_source TEXT,
-                name_folded     TEXT
+                name_folded     TEXT,
+                display_name_folded TEXT
             )
             """;
-        const string symbolsColumns = "id, file_id, kind, sub_kind, name, line, start_line, start_column, end_line, body_start_line, body_end_line, signature, container_kind, container_name, container_qualified_name, family_key, visibility, return_type, is_metadata_target, metadata_target_source, name_folded";
+        const string symbolsColumns = "id, file_id, kind, sub_kind, name, line, start_line, start_column, end_line, body_start_line, body_end_line, signature, container_kind, container_name, container_qualified_name, family_key, visibility, return_type, is_metadata_target, metadata_target_source, name_folded, display_name_folded";
         var symbolReferencesCreateSql =
             $"""
             CREATE TABLE symbol_references (