Add a language service to map all the IDE diagnostic IDs to an unique...

Add a language service to map all the IDE diagnostic IDs to an unique editorconfig code style option, if any such option exists. This service is used by Configure Severity code action to enable configuring IDE code style diagnostics using syntax: `%option_name% = %option_value%:%severity%`
Remaining IDE diagnostics and all third party diagnostics would be configured using syntax: `dotnet_diagnostc.DiagnosticId.severity = %severity%` by this code action.

I have also added unit tests that ensure that all new IDE diagnostics are explicitly handled in this service to choose the appropriate syntax based on added options.

src/EditorFeatures/Test/Diagnostics/IDEDiagnosticIDConfigurationTests.cs

+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Microsoft.CodeAnalysis.CSharp.Diagnostics;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Editor.UnitTests.Workspaces;
+using Microsoft.CodeAnalysis.Options;
+using Microsoft.CodeAnalysis.Test.Utilities;
+using Microsoft.CodeAnalysis.VisualBasic.Diagnostics;
+using Xunit;
+
+namespace Microsoft.CodeAnalysis.Editor.UnitTests.Diagnostics.ConfigureSeverityLevel
+{
+    [UseExportProvider]
+    public class IDEDiagnosticIDConfigurationTests
+    {
+        private void Verify(string expected, IDiagnosticIdToEditorConfigOptionMappingService service)
+        {
+            using var workspace = new TestWorkspace();
+            var optionSet = workspace.Options;
+
+            var diagnosticIds = new List<string>();
+            foreach (var field in typeof(IDEDiagnosticIds).GetFields())
+            {
+                Assert.Equal(typeof(string), field.FieldType);
+
+                var diagnosticId = field.GetRawConstantValue() as string;
+                Assert.True(!string.IsNullOrEmpty(diagnosticId));
+
+                Assert.StartsWith("IDE", diagnosticId);
+                diagnosticIds.Add(diagnosticId);
+            }
+
+            diagnosticIds.Sort();
+
+            var expectedLines = expected.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries);
+            Assert.True(expectedLines.Length % 2 == 0);
+            var expectedMap = new Dictionary<string, string>();
+            for (int i = 0; i < expectedLines.Length; i += 2)
+            {
+                expectedMap.Add(expectedLines[i], expectedLines[i + 1]);
+            }
+
+            var baseline = new StringBuilder();
+            foreach (var diagnosticId in diagnosticIds)
+            {
+                var editorConfigOption = service.GetMappedEditorConfigOption(diagnosticId);
+                var editorConfigLocation = editorConfigOption?.StorageLocations.OfType<IEditorConfigStorageLocation2>().FirstOrDefault();
+                string editorConfigString;
+                if (editorConfigLocation != null)
+                {
+                    var optionKey = new OptionKey(editorConfigOption, editorConfigOption.IsPerLanguage ? LanguageNames.CSharp : null);
+                    var value = optionSet.GetOption(optionKey);
+                    editorConfigString = editorConfigLocation.GetEditorConfigString(value, optionSet);
+                }
+                else
+                {
+                    editorConfigString = $"dotnet_diagnostic.{diagnosticId}.severity = %value%";
+                }
+
+                // Verify we have an entry for diagnosticId
+                var diagnosticIdString = $"# {diagnosticId}";
+
+                if (expectedLines.Length == 0)
+                {
+                    // Executing test to generate baseline
+                    baseline.AppendLine();
+                    baseline.AppendLine(diagnosticIdString);
+                    baseline.AppendLine(editorConfigString);
+                    continue;
+                }
+
+                if (!expectedMap.TryGetValue(diagnosticIdString, out var expectedValue))
+                {
+                    Assert.False(true, $@"Missing entry:
+
+{diagnosticIdString}
+{editorConfigString}
+");
+                }
+
+                // Verify entries match for diagnosticId
+                if (expectedValue != editorConfigString)
+                {
+                    Assert.False(true, $@"Mismatch for '{diagnosticId}'
+Expected: {expectedValue}
+Actual: {editorConfigString}
+");
+                }
+
+                expectedMap.Remove(diagnosticIdString);
+            }
+
+            if (expectedLines.Length == 0)
+            {
+                Assert.False(true, $"Test Baseline:{baseline}");
+            }
+
+            if (expectedMap.Count > 0)
+            {
+                var extraEntitiesBuilder = new StringBuilder();
+                foreach (var kvp in expectedMap.OrderBy(kvp => kvp.Key))
+                {
+                    extraEntitiesBuilder.AppendLine();
+                    extraEntitiesBuilder.AppendLine(kvp.Key);
+                    extraEntitiesBuilder.AppendLine(kvp.Value);
+                }
+
+                Assert.False(true, $@"Unexpected entries:{extraEntitiesBuilder.ToString()}");
+            }
+        }
+
+        [Fact]
+        public void CSharp_VerifyIDEDiagnosticsAreConfigurable()
+        {
+            var expected = @"
+# IDE0001
+dotnet_diagnostic.IDE0001.severity = %value%
+
+# IDE0002
+dotnet_diagnostic.IDE0002.severity = %value%
+
+# IDE0003
+dotnet_diagnostic.IDE0003.severity = %value%
+
+# IDE0004
+dotnet_diagnostic.IDE0004.severity = %value%
+
+# IDE0005
+dotnet_diagnostic.IDE0005.severity = %value%
+
+# IDE0006
+dotnet_diagnostic.IDE0006.severity = %value%
+
+# IDE0007
+dotnet_diagnostic.IDE0007.severity = %value%
+
+# IDE0008
+dotnet_diagnostic.IDE0008.severity = %value%
+
+# IDE0009
+dotnet_diagnostic.IDE0009.severity = %value%
+
+# IDE0010
+dotnet_diagnostic.IDE0010.severity = %value%
+
+# IDE0011
+csharp_prefer_braces = true:silent
+
+# IDE0016
+csharp_style_throw_expression = true:suggestion
+
+# IDE0017
+dotnet_style_object_initializer = true:suggestion
+
+# IDE0018
+csharp_style_inlined_variable_declaration = true:suggestion
+
+# IDE0019
+csharp_style_pattern_matching_over_as_with_null_check = true:suggestion
+
+# IDE0020
+csharp_style_pattern_matching_over_is_with_cast_check = true:suggestion
+
+# IDE0021
+csharp_style_expression_bodied_constructors = false:silent
+
+# IDE0022
+csharp_style_expression_bodied_methods = false:silent
+
+# IDE0023
+csharp_style_expression_bodied_operators = false:silent
+
+# IDE0024
+csharp_style_expression_bodied_operators = false:silent
+
+# IDE0025
+csharp_style_expression_bodied_properties = true:silent
+
+# IDE0026
+csharp_style_expression_bodied_indexers = true:silent
+
+# IDE0027
+csharp_style_expression_bodied_accessors = true:silent
+
+# IDE0028
+dotnet_style_collection_initializer = true:suggestion
+
+# IDE0029
+dotnet_style_coalesce_expression = true:suggestion
+
+# IDE0030
+dotnet_style_coalesce_expression = true:suggestion
+
+# IDE0031
+dotnet_style_null_propagation = true:suggestion
+
+# IDE0032
+dotnet_style_prefer_auto_properties = true:silent
+
+# IDE0033
+dotnet_style_explicit_tuple_names = true:suggestion
+
+# IDE0034
+csharp_prefer_simple_default_expression = true:suggestion
+
+# IDE0035
+dotnet_diagnostic.IDE0035.severity = %value%
+
+# IDE0036
+dotnet_diagnostic.IDE0036.severity = %value%
+
+# IDE0037
+dotnet_style_prefer_inferred_tuple_names = true:suggestion
+
+# IDE0038
+dotnet_diagnostic.IDE0038.severity = %value%
+
+# IDE0039
+csharp_style_pattern_local_over_anonymous_function = true:suggestion
+
+# IDE0040
+dotnet_style_require_accessibility_modifiers = for_non_interface_members:silent
+
+# IDE0041
+dotnet_style_prefer_is_null_check_over_reference_equality_method = true:suggestion
+
+# IDE0042
+csharp_style_deconstructed_variable_declaration = true:suggestion
+
+# IDE0043
+dotnet_diagnostic.IDE0043.severity = %value%
+
+# IDE0044
+dotnet_style_readonly_field = true:suggestion
+
+# IDE0045
+dotnet_style_prefer_conditional_expression_over_assignment = true:silent
+
+# IDE0046
+dotnet_style_prefer_conditional_expression_over_return = true:silent
+
+# IDE0047
+dotnet_diagnostic.IDE0047.severity = %value%
+
+# IDE0048
+dotnet_diagnostic.IDE0048.severity = %value%
+
+# IDE0049
+dotnet_diagnostic.IDE0049.severity = %value%
+
+# IDE0050
+dotnet_diagnostic.IDE0050.severity = %value%
+
+# IDE0051
+dotnet_diagnostic.IDE0051.severity = %value%
+
+# IDE0052
+dotnet_diagnostic.IDE0052.severity = %value%
+
+# IDE0053
+csharp_style_expression_bodied_lambdas = true:silent
+
+# IDE0054
+dotnet_style_prefer_compound_assignment = true:suggestion
+
+# IDE0055
+dotnet_diagnostic.IDE0055.severity = %value%
+
+# IDE0056
+csharp_style_prefer_index_operator = true:suggestion
+
+# IDE0057
+csharp_style_prefer_range_operator = true:suggestion
+
+# IDE0058
+csharp_style_unused_value_expression_statement_preference = discard_variable:silent
+
+# IDE0059
+csharp_style_unused_value_assignment_preference = discard_variable:suggestion
+
+# IDE0060
+dotnet_code_quality_unused_parameters = all:suggestion
+
+# IDE0061
+csharp_style_expression_bodied_local_functions = false:silent
+
+# IDE0062
+csharp_prefer_static_local_function = true:suggestion
+
+# IDE0063
+csharp_prefer_simple_using_statement = true:suggestion
+
+# IDE0064
+dotnet_diagnostic.IDE0064.severity = %value%
+
+# IDE0065
+csharp_using_directive_placement = outside_namespace:silent
+
+# IDE1001
+dotnet_diagnostic.IDE1001.severity = %value%
+
+# IDE1002
+dotnet_diagnostic.IDE1002.severity = %value%
+
+# IDE1003
+dotnet_diagnostic.IDE1003.severity = %value%
+
+# IDE1004
+dotnet_diagnostic.IDE1004.severity = %value%
+
+# IDE1005
+csharp_style_conditional_delegate_call = true:suggestion
+
+# IDE1006
+dotnet_diagnostic.IDE1006.severity = %value%
+
+# IDE1007
+dotnet_diagnostic.IDE1007.severity = %value%
+
+# IDE1008
+dotnet_diagnostic.IDE1008.severity = %value%
+";
+
+            Verify(expected, new CSharpDiagnosticIdToEditorConfigOptionMappingService());
+        }
+
+        [Fact]
+        public void VisualBasic_VerifyIDEDiagnosticsAreConfigurable()
+        {
+            var expected = @"
+# IDE0001
+dotnet_diagnostic.IDE0001.severity = %value%
+
+# IDE0002
+dotnet_diagnostic.IDE0002.severity = %value%
+
+# IDE0003
+dotnet_diagnostic.IDE0003.severity = %value%
+
+# IDE0004
+dotnet_diagnostic.IDE0004.severity = %value%
+
+# IDE0005
+dotnet_diagnostic.IDE0005.severity = %value%
+
+# IDE0006
+dotnet_diagnostic.IDE0006.severity = %value%
+
+# IDE0007
+dotnet_diagnostic.IDE0007.severity = %value%
+
+# IDE0008
+dotnet_diagnostic.IDE0008.severity = %value%
+
+# IDE0009
+dotnet_diagnostic.IDE0009.severity = %value%
+
+# IDE0010
+dotnet_diagnostic.IDE0010.severity = %value%
+
+# IDE0011
+dotnet_diagnostic.IDE0011.severity = %value%
+
+# IDE0016
+csharp_style_throw_expression = true:suggestion
+
+# IDE0017
+dotnet_style_object_initializer = true:suggestion
+
+# IDE0018
+csharp_style_inlined_variable_declaration = true:suggestion
+
+# IDE0019
+dotnet_diagnostic.IDE0019.severity = %value%
+
+# IDE0020
+dotnet_diagnostic.IDE0020.severity = %value%
+
+# IDE0021
+dotnet_diagnostic.IDE0021.severity = %value%
+
+# IDE0022
+dotnet_diagnostic.IDE0022.severity = %value%
+
+# IDE0023
+dotnet_diagnostic.IDE0023.severity = %value%
+
+# IDE0024
+dotnet_diagnostic.IDE0024.severity = %value%
+
+# IDE0025
+dotnet_diagnostic.IDE0025.severity = %value%
+
+# IDE0026
+dotnet_diagnostic.IDE0026.severity = %value%
+
+# IDE0027
+dotnet_diagnostic.IDE0027.severity = %value%
+
+# IDE0028
+dotnet_style_collection_initializer = true:suggestion
+
+# IDE0029
+dotnet_style_coalesce_expression = true:suggestion
+
+# IDE0030
+dotnet_style_coalesce_expression = true:suggestion
+
+# IDE0031
+dotnet_style_null_propagation = true:suggestion
+
+# IDE0032
+dotnet_style_prefer_auto_properties = true:silent
+
+# IDE0033
+dotnet_style_explicit_tuple_names = true:suggestion
+
+# IDE0034
+dotnet_diagnostic.IDE0034.severity = %value%
+
+# IDE0035
+dotnet_diagnostic.IDE0035.severity = %value%
+
+# IDE0036
+dotnet_diagnostic.IDE0036.severity = %value%
+
+# IDE0037
+dotnet_style_prefer_inferred_tuple_names = true:suggestion
+
+# IDE0038
+dotnet_diagnostic.IDE0038.severity = %value%
+
+# IDE0039
+dotnet_diagnostic.IDE0039.severity = %value%
+
+# IDE0040
+dotnet_style_require_accessibility_modifiers = for_non_interface_members:silent
+
+# IDE0041
+dotnet_style_prefer_is_null_check_over_reference_equality_method = true:suggestion
+
+# IDE0042
+csharp_style_deconstructed_variable_declaration = true:suggestion
+
+# IDE0043
+dotnet_diagnostic.IDE0043.severity = %value%
+
+# IDE0044
+dotnet_style_readonly_field = true:suggestion
+
+# IDE0045
+dotnet_style_prefer_conditional_expression_over_assignment = true:silent
+
+# IDE0046
+dotnet_style_prefer_conditional_expression_over_return = true:silent
+
+# IDE0047
+dotnet_diagnostic.IDE0047.severity = %value%
+
+# IDE0048
+dotnet_diagnostic.IDE0048.severity = %value%
+
+# IDE0049
+dotnet_diagnostic.IDE0049.severity = %value%
+
+# IDE0050
+dotnet_diagnostic.IDE0050.severity = %value%
+
+# IDE0051
+dotnet_diagnostic.IDE0051.severity = %value%
+
+# IDE0052
+dotnet_diagnostic.IDE0052.severity = %value%
+
+# IDE0053
+dotnet_diagnostic.IDE0053.severity = %value%
+
+# IDE0054
+dotnet_style_prefer_compound_assignment = true:suggestion
+
+# IDE0055
+dotnet_diagnostic.IDE0055.severity = %value%
+
+# IDE0056
+dotnet_diagnostic.IDE0056.severity = %value%
+
+# IDE0057
+dotnet_diagnostic.IDE0057.severity = %value%
+
+# IDE0058
+visual_basic_style_unused_value_expression_statement_preference = unused_local_variable:silent
+
+# IDE0059
+visual_basic_style_unused_value_assignment_preference = unused_local_variable:suggestion
+
+# IDE0060
+dotnet_code_quality_unused_parameters = all:suggestion
+
+# IDE0061
+dotnet_diagnostic.IDE0061.severity = %value%
+
+# IDE0062
+dotnet_diagnostic.IDE0062.severity = %value%
+
+# IDE0063
+dotnet_diagnostic.IDE0063.severity = %value%
+
+# IDE0064
+dotnet_diagnostic.IDE0064.severity = %value%
+
+# IDE0065
+dotnet_diagnostic.IDE0065.severity = %value%
+
+# IDE1001
+dotnet_diagnostic.IDE1001.severity = %value%
+
+# IDE1002
+dotnet_diagnostic.IDE1002.severity = %value%
+
+# IDE1003
+dotnet_diagnostic.IDE1003.severity = %value%
+
+# IDE1004
+dotnet_diagnostic.IDE1004.severity = %value%
+
+# IDE1005
+dotnet_diagnostic.IDE1005.severity = %value%
+
+# IDE1006
+dotnet_diagnostic.IDE1006.severity = %value%
+
+# IDE1007
+dotnet_diagnostic.IDE1007.severity = %value%
+
+# IDE1008
+dotnet_diagnostic.IDE1008.severity = %value%
+";
+
+            Verify(expected, new VisualBasicDiagnosticIdToEditorConfigOptionMappingService());
+        }
+    }
+}

src/Features/CSharp/Portable/Diagnostics/Analyzers/CSharpDiagnosticIdToEditorConfigOptionMappingService.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System.Composition;
+using Microsoft.CodeAnalysis.CSharp.CodeStyle;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Host.Mef;
+using Microsoft.CodeAnalysis.Options;
+
+namespace Microsoft.CodeAnalysis.CSharp.Diagnostics
+{
+    [ExportLanguageService(typeof(IDiagnosticIdToEditorConfigOptionMappingService), LanguageNames.CSharp), Shared]
+    internal sealed class CSharpDiagnosticIdToEditorConfigOptionMappingService : AbstractDiagnosticIdToEditorConfigOptionMappingService
+    {
+        protected override (IOption optionOpt, bool handled) TryGetLanguageSpecificOption(string diagnosticId)
+        {
+            IOption option;
+            switch (diagnosticId)
+            {
+                case IDEDiagnosticIds.AddBracesDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferBraces;
+                    break;
+                case IDEDiagnosticIds.InlineAsTypeCheckId:
+                    option = CSharpCodeStyleOptions.PreferPatternMatchingOverAsWithNullCheck;
+                    break;
+                case IDEDiagnosticIds.InlineIsTypeCheckId:
+                    option = CSharpCodeStyleOptions.PreferPatternMatchingOverIsWithCastCheck;
+                    break;
+                case IDEDiagnosticIds.UseExpressionBodyForConstructorsDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferExpressionBodiedConstructors;
+                    break;
+                case IDEDiagnosticIds.UseExpressionBodyForMethodsDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferExpressionBodiedMethods;
+                    break;
+                case IDEDiagnosticIds.UseExpressionBodyForConversionOperatorsDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferExpressionBodiedOperators;
+                    break;
+                case IDEDiagnosticIds.UseExpressionBodyForOperatorsDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferExpressionBodiedOperators;
+                    break;
+                case IDEDiagnosticIds.UseExpressionBodyForPropertiesDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferExpressionBodiedProperties;
+                    break;
+                case IDEDiagnosticIds.UseExpressionBodyForIndexersDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferExpressionBodiedIndexers;
+                    break;
+                case IDEDiagnosticIds.UseExpressionBodyForAccessorsDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferExpressionBodiedAccessors;
+                    break;
+                case IDEDiagnosticIds.UseDefaultLiteralDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferSimpleDefaultExpression;
+                    break;
+                case IDEDiagnosticIds.UseLocalFunctionDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferLocalOverAnonymousFunction;
+                    break;
+                case IDEDiagnosticIds.InvokeDelegateWithConditionalAccessId:
+                    option = CSharpCodeStyleOptions.PreferConditionalDelegateCall;
+                    break;
+                case IDEDiagnosticIds.UseExpressionBodyForLambdaExpressionsDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferExpressionBodiedLambdas;
+                    break;
+                case IDEDiagnosticIds.UseIndexOperatorDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferIndexOperator;
+                    break;
+                case IDEDiagnosticIds.UseRangeOperatorDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferRangeOperator;
+                    break;
+                case IDEDiagnosticIds.ExpressionValueIsUnusedDiagnosticId:
+                    option = CSharpCodeStyleOptions.UnusedValueExpressionStatement;
+                    break;
+                case IDEDiagnosticIds.ValueAssignedIsUnusedDiagnosticId:
+                    option = CSharpCodeStyleOptions.UnusedValueAssignment;
+                    break;
+                case IDEDiagnosticIds.UseExpressionBodyForLocalFunctionsDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferExpressionBodiedLocalFunctions;
+                    break;
+                case IDEDiagnosticIds.MakeLocalFunctionStaticDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferStaticLocalFunction;
+                    break;
+                case IDEDiagnosticIds.UseSimpleUsingStatementDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferSimpleUsingStatement;
+                    break;
+                case IDEDiagnosticIds.MoveMisplacedUsingDirectivesDiagnosticId:
+                    option = CSharpCodeStyleOptions.PreferredUsingDirectivePlacement;
+                    break;
+
+                default:
+                    return (optionOpt: null, handled: false);
+            }
+
+            return (optionOpt: option, handled: true);
+        }
+    }
+}

src/Features/Core/Portable/Diagnostics/Analyzers/AbstractDiagnosticIdToEditorConfigOptionMappingService.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using System.Diagnostics;
+using Microsoft.CodeAnalysis.CodeStyle;
+using Microsoft.CodeAnalysis.Options;
+
+namespace Microsoft.CodeAnalysis.Diagnostics
+{
+    internal abstract class AbstractDiagnosticIdToEditorConfigOptionMappingService : IDiagnosticIdToEditorConfigOptionMappingService
+    {
+        protected abstract (IOption optionOpt, bool handled) TryGetLanguageSpecificOption(string diagnosticId);
+
+        public IOption GetMappedEditorConfigOption(string diagnosticId)
+        {
+            // Service currently only handles IDE Diagnostic IDs, which start with a prefix "IDE".
+            if (!diagnosticId.StartsWith("IDE"))
+            {
+                return default;
+            }
+
+            switch (diagnosticId)
+            {
+                // IDE Diagnostic IDs with no editorconfig option OR no unique editorconfig option to configure
+                // all diagnostics with the given diagnostic ID.
+                case IDEDiagnosticIds.SimplifyNamesDiagnosticId:
+                case IDEDiagnosticIds.SimplifyMemberAccessDiagnosticId:
+                case IDEDiagnosticIds.RemoveQualificationDiagnosticId:
+                case IDEDiagnosticIds.RemoveUnnecessaryCastDiagnosticId:
+                case IDEDiagnosticIds.RemoveUnnecessaryImportsDiagnosticId:
+                case IDEDiagnosticIds.IntellisenseBuildFailedDiagnosticId:
+                case IDEDiagnosticIds.UseImplicitTypeDiagnosticId:
+                case IDEDiagnosticIds.UseExplicitTypeDiagnosticId:
+                case IDEDiagnosticIds.AddQualificationDiagnosticId:
+                case IDEDiagnosticIds.PopulateSwitchDiagnosticId:
+                case IDEDiagnosticIds.RemoveUnreachableCodeDiagnosticId:
+                case IDEDiagnosticIds.OrderModifiersDiagnosticId:
+                case IDEDiagnosticIds.InlineIsTypeWithoutNameCheckDiagnosticsId:
+                case IDEDiagnosticIds.ValidateFormatStringDiagnosticID:
+                case IDEDiagnosticIds.RemoveUnnecessaryParenthesesDiagnosticId:
+                case IDEDiagnosticIds.AddRequiredParenthesesDiagnosticId:
+                case IDEDiagnosticIds.PreferBuiltInOrFrameworkTypeDiagnosticId:
+                case IDEDiagnosticIds.ConvertAnonymousTypeToTupleDiagnosticId:
+                case IDEDiagnosticIds.RemoveUnusedMembersDiagnosticId:
+                case IDEDiagnosticIds.RemoveUnreadMembersDiagnosticId:
+                case IDEDiagnosticIds.FormattingDiagnosticId:
+                case IDEDiagnosticIds.MakeStructFieldsWritable:
+                case IDEDiagnosticIds.AnalyzerChangedId:
+                case IDEDiagnosticIds.AnalyzerDependencyConflictId:
+                case IDEDiagnosticIds.MissingAnalyzerReferenceId:
+                case IDEDiagnosticIds.ErrorReadingRulesetId:
+                case IDEDiagnosticIds.NamingRuleId:
+                case IDEDiagnosticIds.UnboundIdentifierId:
+                case IDEDiagnosticIds.UnboundConstructorId:
+                    return null;
+
+                // IDE Diagnostic IDs with a unique editorconfig option with severity to configure
+                // all diagnostics with the given diagnostic ID.
+                case IDEDiagnosticIds.UseThrowExpressionDiagnosticId:
+                    return CodeStyleOptions.PreferThrowExpression;
+                case IDEDiagnosticIds.UseObjectInitializerDiagnosticId:
+                    return CodeStyleOptions.PreferObjectInitializer;
+                case IDEDiagnosticIds.InlineDeclarationDiagnosticId:
+                    return CodeStyleOptions.PreferInlinedVariableDeclaration;
+                case IDEDiagnosticIds.UseCollectionInitializerDiagnosticId:
+                    return CodeStyleOptions.PreferCollectionInitializer;
+                case IDEDiagnosticIds.UseCoalesceExpressionDiagnosticId:
+                    return CodeStyleOptions.PreferCoalesceExpression;
+                case IDEDiagnosticIds.UseCoalesceExpressionForNullableDiagnosticId:
+                    return CodeStyleOptions.PreferCoalesceExpression;
+                case IDEDiagnosticIds.UseNullPropagationDiagnosticId:
+                    return CodeStyleOptions.PreferNullPropagation;
+                case IDEDiagnosticIds.UseAutoPropertyDiagnosticId:
+                    return CodeStyleOptions.PreferAutoProperties;
+                case IDEDiagnosticIds.UseExplicitTupleNameDiagnosticId:
+                    return CodeStyleOptions.PreferExplicitTupleNames;
+                case IDEDiagnosticIds.UseInferredMemberNameDiagnosticId:
+                    return CodeStyleOptions.PreferInferredTupleNames;
+                case IDEDiagnosticIds.AddAccessibilityModifiersDiagnosticId:
+                    return CodeStyleOptions.RequireAccessibilityModifiers;
+                case IDEDiagnosticIds.UseIsNullCheckDiagnosticId:
+                    return CodeStyleOptions.PreferIsNullCheckOverReferenceEqualityMethod;
+                case IDEDiagnosticIds.UseDeconstructionDiagnosticId:
+                    return CodeStyleOptions.PreferDeconstructedVariableDeclaration;
+                case IDEDiagnosticIds.MakeFieldReadonlyDiagnosticId:
+                    return CodeStyleOptions.PreferReadonly;
+                case IDEDiagnosticIds.UseConditionalExpressionForAssignmentDiagnosticId:
+                    return CodeStyleOptions.PreferConditionalExpressionOverAssignment;
+                case IDEDiagnosticIds.UseConditionalExpressionForReturnDiagnosticId:
+                    return CodeStyleOptions.PreferConditionalExpressionOverReturn;
+                case IDEDiagnosticIds.UseCompoundAssignmentDiagnosticId:
+                    return CodeStyleOptions.PreferCompoundAssignment;
+                case IDEDiagnosticIds.UnusedParameterDiagnosticId:
+                    return CodeStyleOptions.UnusedParameters;
+
+                default:
+                    // Check if there is a unique language specific option for the diagnostic
+                    // i.e. options defined in CSharpCodeStyleOptions and VisualBasicCodeStyleOptions.
+                    var (languageSpecificOptionOpt, handled) = TryGetLanguageSpecificOption(diagnosticId);
+                    if (handled)
+                    {
+                        return languageSpecificOptionOpt;
+                    }
+
+                    Debug.Assert(languageSpecificOptionOpt == null);
+
+                    // Unhandled "IDExxx" diagnostic ID.
+                    throw new System.NotImplementedException($@"'{diagnosticId}' must be handled by {nameof(AbstractDiagnosticIdToEditorConfigOptionMappingService)}.
+Ensure that every IDE diagnosticID is handled by this service as follows:
+  1. If this diagnostic has a unique code style option, such that diagnostic's severity can be configured in .editorconfig with an entry such as 'option_name = option_value:severity', then ensure that this option is returned from this method.
+  2. Otherwise, handle diagnostic ID in this switch statement and return null.");
+            }
+        }
+    }
+}

src/Features/Core/Portable/Diagnostics/Analyzers/IDiagnosticIdToEditorConfigOptionMappingService.cs

+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+using Microsoft.CodeAnalysis.Host;
+using Microsoft.CodeAnalysis.Options;
+
+namespace Microsoft.CodeAnalysis.Diagnostics
+{
+    /// <summary>
+    /// Language service to map <see cref="IDEDiagnosticIds"/> to an unique editorconfig code style option,
+    /// if any such option exists.
+    /// </summary>
+    internal interface IDiagnosticIdToEditorConfigOptionMappingService : ILanguageService
+    {
+        /// <summary>
+        /// Maps each diagnostic ID in <see cref="IDEDiagnosticIds"/> to an <see cref="IOption"/> as follows:
+        ///   1. If the diagnostic has a unique code style option, such that diagnostic's
+        ///      severity can be configured in .editorconfig with an entry such as
+        ///          "%option_name% = %option_value%:%severity%
+        ///      then this option is returned.
+        ///   2. Otherwise, returns null.
+        /// </summary>
+        IOption GetMappedEditorConfigOption(string diagnosticId);
+    }
+}

src/Features/VisualBasic/Portable/Diagnostics/Analyzers/VisualBasicDiagnosticIdToEditorConfigOptionMappingService.vb

+' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
+
+Imports System.Composition
+Imports Microsoft.CodeAnalysis.Diagnostics
+Imports Microsoft.CodeAnalysis.Host.Mef
+Imports Microsoft.CodeAnalysis.Options
+Imports Microsoft.CodeAnalysis.VisualBasic.CodeStyle
+
+Namespace Microsoft.CodeAnalysis.VisualBasic.Diagnostics
+    <ExportLanguageService(GetType(IDiagnosticIdToEditorConfigOptionMappingService), LanguageNames.VisualBasic), [Shared]>
+    Friend NotInheritable Class VisualBasicDiagnosticIdToEditorConfigOptionMappingService
+        Inherits AbstractDiagnosticIdToEditorConfigOptionMappingService
+
+        Protected Overrides Function TryGetLanguageSpecificOption(diagnosticId As String) As (optionOpt As IOption, handled As Boolean)
+            Dim [option] As IOption
+
+            Select Case diagnosticId
+                Case IDEDiagnosticIds.ExpressionValueIsUnusedDiagnosticId
+                    [option] = VisualBasicCodeStyleOptions.UnusedValueExpressionStatement
+                Case IDEDiagnosticIds.ValueAssignedIsUnusedDiagnosticId
+                    [option] = VisualBasicCodeStyleOptions.UnusedValueAssignment
+
+                ' C# specific Diagnostic IDs
+                Case IDEDiagnosticIds.AddBracesDiagnosticId,
+                     IDEDiagnosticIds.InlineAsTypeCheckId,
+                     IDEDiagnosticIds.InlineIsTypeCheckId,
+                     IDEDiagnosticIds.UseExpressionBodyForConstructorsDiagnosticId,
+                     IDEDiagnosticIds.UseExpressionBodyForMethodsDiagnosticId,
+                     IDEDiagnosticIds.UseExpressionBodyForConversionOperatorsDiagnosticId,
+                     IDEDiagnosticIds.UseExpressionBodyForOperatorsDiagnosticId,
+                     IDEDiagnosticIds.UseExpressionBodyForPropertiesDiagnosticId,
+                     IDEDiagnosticIds.UseExpressionBodyForIndexersDiagnosticId,
+                     IDEDiagnosticIds.UseExpressionBodyForAccessorsDiagnosticId,
+                     IDEDiagnosticIds.UseDefaultLiteralDiagnosticId,
+                     IDEDiagnosticIds.UseLocalFunctionDiagnosticId,
+                     IDEDiagnosticIds.InvokeDelegateWithConditionalAccessId,
+                     IDEDiagnosticIds.UseExpressionBodyForLambdaExpressionsDiagnosticId,
+                     IDEDiagnosticIds.UseIndexOperatorDiagnosticId,
+                     IDEDiagnosticIds.UseRangeOperatorDiagnosticId,
+                     IDEDiagnosticIds.UseExpressionBodyForLocalFunctionsDiagnosticId,
+                     IDEDiagnosticIds.MakeLocalFunctionStaticDiagnosticId,
+                     IDEDiagnosticIds.UseSimpleUsingStatementDiagnosticId,
+                     IDEDiagnosticIds.MoveMisplacedUsingDirectivesDiagnosticId
+                    [option] = Nothing
+
+                Case Else
+                    Return (optionOpt:=Nothing, handled:=False)
+            End Select
+
+            Return (optionOpt:=[option], handled:=True)
+        End Function
+    End Class
+End Namespace