Implement LuceneDev1007, 1008, 6000 Analyzers & CodeFix with Unit Tests

Adds diagnostics for dictionary indexer usage ported from Java:

- LuceneDev1007 (Design/Warning): generic IDictionary<,> / IReadOnlyDictionary<,>
  indexer read with a value-type value — may throw KeyNotFoundException.
- LuceneDev1008 (Design/Warning): same, but reference-type value; fix should also
  null-check the result.
- LuceneDev6000 (Usage/Info): non-generic IDictionary indexer read, which returns
  null for missing keys and should be reviewed.

Includes a code fix for LuceneDev1007/1008 that rewrites the common
`return dict[key];` pattern into
`return dict.TryGetValue(key, out var value) ? value : default;`.

Closes #1168.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: paulirwin

src/Lucene.Net.CodeAnalysis.Dev.CodeFixes/LuceneDev1xxx/LuceneDev1007_1008_DictionaryIndexerCodeFixProvider.cs

@@ -0,0 +1,145 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+using System.Collections.Immutable;
+using System.Composition;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Lucene.Net.CodeAnalysis.Dev.Utility;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Formatting;
+
+namespace Lucene.Net.CodeAnalysis.Dev.CodeFixes.LuceneDev1xxx
+{
+    [ExportCodeFixProvider(LanguageNames.CSharp, Name = nameof(LuceneDev1007_1008_DictionaryIndexerCodeFixProvider)), Shared]
+    public sealed class LuceneDev1007_1008_DictionaryIndexerCodeFixProvider : CodeFixProvider
+    {
+        private const string TitleReturn = "Use TryGetValue and return default on missing key";
+
+        public override ImmutableArray<string> FixableDiagnosticIds =>
+            ImmutableArray.Create(
+                Descriptors.LuceneDev1007_GenericDictionaryIndexerValueType.Id,
+                Descriptors.LuceneDev1008_GenericDictionaryIndexerReferenceType.Id);
+
+        public override FixAllProvider GetFixAllProvider() => WellKnownFixAllProviders.BatchFixer;
+
+        public override async Task RegisterCodeFixesAsync(CodeFixContext context)
+        {
+            var root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            if (root == null) return;
+
+            foreach (var diagnostic in context.Diagnostics)
+            {
+                var elementAccess = root.FindToken(diagnostic.Location.SourceSpan.Start)
+                                        .Parent?
+                                        .AncestorsAndSelf()
+                                        .OfType<ElementAccessExpressionSyntax>()
+                                        .FirstOrDefault(e => e.Span.Contains(diagnostic.Location.SourceSpan));
+                if (elementAccess == null)
+                    continue;
+
+                // Only handle the "return dict[key];" pattern automatically.
+                if (elementAccess.Parent is not ReturnStatementSyntax returnStmt
+                    || returnStmt.Expression != elementAccess)
+                {
+                    continue;
+                }
+
+                context.RegisterCodeFix(
+                    CodeAction.Create(
+                        title: TitleReturn,
+                        createChangedDocument: c => ConvertReturnAsync(context.Document, returnStmt, elementAccess, c),
+                        equivalenceKey: TitleReturn),
+                    diagnostic);
+            }
+        }
+
+        private static async Task<Document> ConvertReturnAsync(
+            Document document,
+            ReturnStatementSyntax returnStmt,
+            ElementAccessExpressionSyntax elementAccess,
+            CancellationToken cancellationToken)
+        {
+            var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            if (root == null) return document;
+
+            var receiver = elementAccess.Expression;
+            var keyArg = elementAccess.ArgumentList.Arguments.FirstOrDefault();
+            if (keyArg == null) return document;
+
+            var outName = PickLocalName(returnStmt);
+
+            // receiver.TryGetValue(key, out var <outName>)
+            var tryGetValueInvocation = SyntaxFactory.InvocationExpression(
+                SyntaxFactory.MemberAccessExpression(
+                    SyntaxKind.SimpleMemberAccessExpression,
+                    receiver.WithoutTrivia(),
+                    SyntaxFactory.IdentifierName("TryGetValue")),
+                SyntaxFactory.ArgumentList(SyntaxFactory.SeparatedList(new[]
+                {
+                    keyArg.WithoutTrivia(),
+                    SyntaxFactory.Argument(
+                        SyntaxFactory.DeclarationExpression(
+                            SyntaxFactory.IdentifierName(
+                                SyntaxFactory.Identifier("var")),
+                            SyntaxFactory.SingleVariableDesignation(SyntaxFactory.Identifier(outName))))
+                        .WithRefOrOutKeyword(SyntaxFactory.Token(SyntaxKind.OutKeyword))
+                })));
+
+            // tryGetValueInvocation ? <outName> : default
+            var ternary = SyntaxFactory.ConditionalExpression(
+                tryGetValueInvocation,
+                SyntaxFactory.IdentifierName(outName),
+                SyntaxFactory.LiteralExpression(SyntaxKind.DefaultLiteralExpression,
+                    SyntaxFactory.Token(SyntaxKind.DefaultKeyword)));
+
+            var newReturn = returnStmt.WithExpression(ternary).WithAdditionalAnnotations(Formatter.Annotation);
+
+            var newRoot = root.ReplaceNode(returnStmt, newReturn);
+            return document.WithSyntaxRoot(newRoot);
+        }
+
+        private static string PickLocalName(SyntaxNode context)
+        {
+            // Avoid collisions with identifiers in the enclosing member.
+            var member = context.AncestorsAndSelf().OfType<MemberDeclarationSyntax>().FirstOrDefault();
+            var names = member == null
+                ? ImmutableHashSet<string>.Empty
+                : member.DescendantTokens()
+                        .Where(t => t.IsKind(SyntaxKind.IdentifierToken))
+                        .Select(t => t.ValueText)
+                        .ToImmutableHashSet();
+
+            if (!names.Contains("value"))
+                return "value";
+            for (int i = 1; i < 100; i++)
+            {
+                var candidate = "value" + i;
+                if (!names.Contains(candidate))
+                    return candidate;
+            }
+            return "value";
+        }
+    }
+}

src/Lucene.Net.CodeAnalysis.Dev.Sample/LuceneDev1xxx/LuceneDev1007_1008_DictionaryIndexerSample.cs

@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+using System.Collections.Generic;
+
+namespace Lucene.Net.CodeAnalysis.Dev.Sample.LuceneDev1xxx;
+
+public class LuceneDev1007_1008_DictionaryIndexerSample
+{
+    public int GetIntValue(IDictionary<string, int> dict, string key)
+    {
+        // LuceneDev1007 (value-type value): indexer may throw KeyNotFoundException.
+        return dict[key];
+    }
+
+    public string GetStringValue(IDictionary<string, string> dict, string key)
+    {
+        // LuceneDev1008 (reference-type value): indexer may throw KeyNotFoundException.
+        return dict[key];
+    }
+
+    public void ReadOnlyUsage(IReadOnlyDictionary<string, string> dict, string key)
+    {
+        // LuceneDev1008: also applies to IReadOnlyDictionary<TKey, TValue>.
+        var value = dict[key];
+    }
+
+    public void ConcreteDictionaryUsage(Dictionary<string, string> dict, string key)
+    {
+        // LuceneDev1008: Dictionary<TKey, TValue> implements IDictionary<TKey, TValue>.
+        var value = dict[key];
+    }
+
+    public void AssignmentIsFine(Dictionary<string, int> dict, string key)
+    {
+        // No diagnostic: indexer setter does not throw.
+        dict[key] = 42;
+    }
+}

src/Lucene.Net.CodeAnalysis.Dev.Sample/LuceneDev6xxx/LuceneDev6000_NonGenericDictionaryIndexerSample.cs

@@ -0,0 +1,37 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+using System.Collections;
+
+namespace Lucene.Net.CodeAnalysis.Dev.Sample.LuceneDev6xxx;
+
+public class LuceneDev6000_NonGenericDictionaryIndexerSample
+{
+    public object? GetValue(IDictionary dict, object key)
+    {
+        // LuceneDev6000 (Info): non-generic IDictionary indexer may return null for missing keys.
+        return dict[key];
+    }
+
+    public object? GetValueFromHashtable(Hashtable table, object key)
+    {
+        // LuceneDev6000: Hashtable implements non-generic IDictionary.
+        return table[key];
+    }
+}

src/Lucene.Net.CodeAnalysis.Dev/LuceneDev1xxx/LuceneDev1007_1008_DictionaryIndexerAnalyzer.cs

@@ -0,0 +1,99 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+using System.Collections.Immutable;
+using Lucene.Net.CodeAnalysis.Dev.Utility;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace Lucene.Net.CodeAnalysis.Dev.LuceneDev1xxx
+{
+    [DiagnosticAnalyzer(LanguageNames.CSharp)]
+    public sealed class LuceneDev1007_1008_DictionaryIndexerAnalyzer : DiagnosticAnalyzer
+    {
+        public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics =>
+            ImmutableArray.Create(
+                Descriptors.LuceneDev1007_GenericDictionaryIndexerValueType,
+                Descriptors.LuceneDev1008_GenericDictionaryIndexerReferenceType);
+
+        public override void Initialize(AnalysisContext context)
+        {
+            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.Analyze);
+            context.EnableConcurrentExecution();
+            context.RegisterSyntaxNodeAction(AnalyzeElementAccess, SyntaxKind.ElementAccessExpression);
+        }
+
+        private static void AnalyzeElementAccess(SyntaxNodeAnalysisContext ctx)
+        {
+            var elementAccess = (ElementAccessExpressionSyntax)ctx.Node;
+
+            // Skip assignment targets (setter usage does not throw).
+            if (IsAssignmentTarget(elementAccess))
+                return;
+
+            var symbolInfo = ctx.SemanticModel.GetSymbolInfo(elementAccess, ctx.CancellationToken);
+            var property = symbolInfo.Symbol as IPropertySymbol;
+            if (property == null || !property.IsIndexer)
+                return;
+
+            var containing = property.ContainingType;
+            if (containing == null)
+                return;
+
+            if (!DictionaryTypeHelper.IsGenericDictionaryIndexer(property, containing, out var valueType))
+                return;
+
+            var receiverText = elementAccess.Expression.ToString();
+            var keyText = elementAccess.ArgumentList.ToString();
+            var display = receiverText + keyText;
+
+            var descriptor = IsValueTypeForDiagnostic(valueType!)
+                ? Descriptors.LuceneDev1007_GenericDictionaryIndexerValueType
+                : Descriptors.LuceneDev1008_GenericDictionaryIndexerReferenceType;
+
+            ctx.ReportDiagnostic(Diagnostic.Create(descriptor, elementAccess.GetLocation(), display));
+        }
+
+        private static bool IsAssignmentTarget(ElementAccessExpressionSyntax elementAccess)
+        {
+            // dict[key] = value  -> skip
+            if (elementAccess.Parent is AssignmentExpressionSyntax assignment
+                && assignment.Left == elementAccess
+                && assignment.IsKind(SyntaxKind.SimpleAssignmentExpression))
+            {
+                return true;
+            }
+            return false;
+        }
+
+        private static bool IsValueTypeForDiagnostic(ITypeSymbol valueType)
+        {
+            // Unconstrained type parameters: treat as reference-like (safer — null check may apply).
+            if (valueType is ITypeParameterSymbol tp)
+            {
+                if (tp.HasValueTypeConstraint)
+                    return true;
+                return false;
+            }
+            return valueType.IsValueType;
+        }
+    }
+}