Add MA0193 Round mode analyzer and code fixes

README.md

@@ -211,6 +211,7 @@ If you are already using other analyzers, you can check [which rules are duplica
 |[MA0190](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0190.md)|Design|Use partial property instead of partial method for GeneratedRegex|ℹ️|✔️|✔️|
 |[MA0191](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0191.md)|Design|Do not use the null-forgiving operator|⚠️|❌|❌|
 |[MA0192](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0192.md)|Usage|Use HasFlag instead of bitwise checks|ℹ️|❌|✔️|
+|[MA0193](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0193.md)|Usage|Use an overload with a MidpointRounding argument|ℹ️|✔️|✔️|
 
 <!-- rules -->
 

docs/README.md

@@ -191,6 +191,7 @@
 |[MA0190](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0190.md)|Design|Use partial property instead of partial method for GeneratedRegex|<span title='Info'>ℹ️</span>|✔️|✔️|
 |[MA0191](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0191.md)|Design|Do not use the null-forgiving operator|<span title='Warning'>⚠️</span>|❌|❌|
 |[MA0192](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0192.md)|Usage|Use HasFlag instead of bitwise checks|<span title='Info'>ℹ️</span>|❌|✔️|
+|[MA0193](https://github.com/meziantou/Meziantou.Analyzer/blob/main/docs/Rules/MA0193.md)|Usage|Use an overload with a MidpointRounding argument|<span title='Info'>ℹ️</span>|✔️|✔️|
 
 |Id|Suppressed rule|Justification|
 |--|---------------|-------------|
@@ -779,6 +780,9 @@ dotnet_diagnostic.MA0191.severity = none
 
 # MA0192: Use HasFlag instead of bitwise checks
 dotnet_diagnostic.MA0192.severity = none
+
+# MA0193: Use an overload with a MidpointRounding argument
+dotnet_diagnostic.MA0193.severity = suggestion
 ```
 
 # .editorconfig - all rules disabled
@@ -1353,4 +1357,7 @@ dotnet_diagnostic.MA0191.severity = none
 
 # MA0192: Use HasFlag instead of bitwise checks
 dotnet_diagnostic.MA0192.severity = none
+
+# MA0193: Use an overload with a MidpointRounding argument
+dotnet_diagnostic.MA0193.severity = none
 ```

docs/Rules/MA0193.md

@@ -0,0 +1,42 @@
+# MA0193 - Use an overload with a MidpointRounding argument
+<!-- sources -->
+Sources: [UseAnOverloadThatHasMidpointRoundingAnalyzer.cs](https://github.com/meziantou/Meziantou.Analyzer/blob/main/src/Meziantou.Analyzer/Rules/UseAnOverloadThatHasMidpointRoundingAnalyzer.cs), [UseAnOverloadThatHasMidpointRoundingFixer.cs](https://github.com/meziantou/Meziantou.Analyzer/blob/main/src/Meziantou.Analyzer.CodeFixers/Rules/UseAnOverloadThatHasMidpointRoundingFixer.cs)
+<!-- sources -->
+
+`Round` overloads without a `MidpointRounding` argument use the default midpoint behavior (`ToEven`), which can be surprising. Prefer an overload that specifies the rounding mode explicitly.
+
+This rule reports calls to:
+
+- `Math.Round(...)`
+- `MathF.Round(...)`
+- `decimal.Round(...)`
+- `IFloatingPoint<TSelf>.Round(...)` and implementations of those members
+
+## Non-compliant code
+
+````csharp
+class Sample
+{
+    void M(decimal value)
+    {
+        _ = Math.Round(2.5);
+        _ = MathF.Round(2.5f);
+        _ = decimal.Round(value, 2);
+    }
+}
+````
+
+## Compliant code
+
+````csharp
+class Sample
+{
+    void M(decimal value)
+    {
+        _ = Math.Round(2.5, MidpointRounding.AwayFromZero);
+        _ = MathF.Round(2.5f, MidpointRounding.AwayFromZero);
+        _ = decimal.Round(value, 2, MidpointRounding.AwayFromZero);
+    }
+}
+````
+

src/Meziantou.Analyzer.CodeFixers/Rules/UseAnOverloadThatHasMidpointRoundingFixer.cs

@@ -0,0 +1,118 @@
+using System.Collections.Immutable;
+using System.Composition;
+using System.Linq;
+using Meziantou.Analyzer.Internals;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CodeActions;
+using Microsoft.CodeAnalysis.CodeFixes;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Editing;
+using Microsoft.CodeAnalysis.Operations;
+
+namespace Meziantou.Analyzer.Rules;
+
+[ExportCodeFixProvider(LanguageNames.CSharp), Shared]
+public sealed class UseAnOverloadThatHasMidpointRoundingFixer : CodeFixProvider
+{
+    public override ImmutableArray<string> FixableDiagnosticIds => ImmutableArray.Create(RuleIdentifiers.UseAnOverloadThatHasMidpointRounding);
+
+    public override FixAllProvider GetFixAllProvider() => WellKnownFixAllProviders.BatchFixer;
+
+    public override async Task RegisterCodeFixesAsync(CodeFixContext context)
+    {
+        var root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+        var nodeToFix = root?.FindNode(context.Span, getInnermostNodeForTie: true);
+        if (nodeToFix is null)
+            return;
+
+        var invocationExpression = nodeToFix as InvocationExpressionSyntax ?? nodeToFix.FirstAncestorOrSelf<InvocationExpressionSyntax>();
+        if (invocationExpression is null)
+            return;
+
+        var semanticModel = await context.Document.GetSemanticModelAsync(context.CancellationToken).ConfigureAwait(false);
+        if (semanticModel is null)
+            return;
+
+        if (semanticModel.GetOperation(invocationExpression, context.CancellationToken) is not IInvocationOperation invocationOperation)
+            return;
+
+        var midpointRoundingSymbol = semanticModel.Compilation.GetBestTypeByMetadataName("System.MidpointRounding");
+        if (midpointRoundingSymbol is null)
+            return;
+
+        if (!TryGetMidpointRoundingParameterInfo(semanticModel.Compilation, invocationOperation, midpointRoundingSymbol, out var parameterInfo))
+            return;
+
+        foreach (var midpointRoundingMember in midpointRoundingSymbol.GetMembers().OfType<IFieldSymbol>())
+        {
+            if (midpointRoundingMember is { IsImplicitlyDeclared: true, Name: "value__" })
+                continue;
+
+            if (!midpointRoundingMember.HasConstantValue)
+                continue;
+
+            var midpointRoundingMemberName = midpointRoundingMember.Name;
+            var title = "Add MidpointRounding." + midpointRoundingMemberName;
+            var codeAction = CodeAction.Create(
+                title,
+                ct => AddMidpointRounding(context.Document, invocationExpression, parameterInfo, midpointRoundingSymbol, midpointRoundingMemberName, ct),
+                equivalenceKey: title);
+
+            context.RegisterCodeFix(codeAction, context.Diagnostics);
+        }
+    }
+
+    private static bool TryGetMidpointRoundingParameterInfo(Compilation compilation, IInvocationOperation invocationOperation, INamedTypeSymbol midpointRoundingSymbol, out AdditionalParameterInfo parameterInfo)
+    {
+        var overloadFinder = new OverloadFinder(compilation);
+        var overload = overloadFinder.FindOverloadWithAdditionalParameterOfType(invocationOperation, new OverloadOptions(IncludeObsoleteMembers: false, AllowOptionalParameters: true), [midpointRoundingSymbol]);
+        if (overload is null)
+        {
+            parameterInfo = default;
+            return false;
+        }
+
+        for (var i = 0; i < overload.Parameters.Length; i++)
+        {
+            if (overload.Parameters[i].Type.IsEqualTo(midpointRoundingSymbol))
+            {
+                parameterInfo = new AdditionalParameterInfo(i, overload.Parameters[i].Name);
+                return true;
+            }
+        }
+
+        parameterInfo = default;
+        return false;
+    }
+
+    private static async Task<Document> AddMidpointRounding(Document document, InvocationExpressionSyntax invocationExpression, AdditionalParameterInfo parameterInfo, INamedTypeSymbol midpointRoundingSymbol, string midpointRoundingMember, CancellationToken cancellationToken)
+    {
+        var editor = await DocumentEditor.CreateAsync(document, cancellationToken).ConfigureAwait(false);
+        var generator = editor.Generator;
+
+        var midpointRoundingExpression = generator.MemberAccessExpression(
+            generator.TypeExpression(midpointRoundingSymbol, addImport: true),
+            midpointRoundingMember);
+
+        var newArgument = (ArgumentSyntax)generator.Argument(midpointRoundingExpression);
+
+        InvocationExpressionSyntax newInvocation;
+        if (parameterInfo.ParameterIndex > invocationExpression.ArgumentList.Arguments.Count)
+        {
+            var namedArgument = (ArgumentSyntax)generator.Argument(parameterInfo.ParameterName, RefKind.None, midpointRoundingExpression);
+            var newArguments = invocationExpression.ArgumentList.Arguments.Add(namedArgument);
+            newInvocation = invocationExpression.WithArgumentList(SyntaxFactory.ArgumentList(newArguments));
+        }
+        else
+        {
+            var newArguments = invocationExpression.ArgumentList.Arguments.Insert(parameterInfo.ParameterIndex, newArgument);
+            newInvocation = invocationExpression.WithArgumentList(SyntaxFactory.ArgumentList(newArguments));
+        }
+
+        editor.ReplaceNode(invocationExpression, newInvocation);
+        return editor.GetChangedDocument();
+    }
+
+    private readonly record struct AdditionalParameterInfo(int ParameterIndex, string? ParameterName);
+}

src/Meziantou.Analyzer.Pack/configuration/default.editorconfig

@@ -571,3 +571,6 @@ dotnet_diagnostic.MA0191.severity = none
 
 # MA0192: Use HasFlag instead of bitwise checks
 dotnet_diagnostic.MA0192.severity = none
+
+# MA0193: Use an overload with a MidpointRounding argument
+dotnet_diagnostic.MA0193.severity = suggestion

src/Meziantou.Analyzer.Pack/configuration/none.editorconfig

@@ -571,3 +571,6 @@ dotnet_diagnostic.MA0191.severity = none
 
 # MA0192: Use HasFlag instead of bitwise checks
 dotnet_diagnostic.MA0192.severity = none
+
+# MA0193: Use an overload with a MidpointRounding argument
+dotnet_diagnostic.MA0193.severity = none

src/Meziantou.Analyzer/RuleIdentifiers.cs

@@ -192,6 +192,7 @@ internal static class RuleIdentifiers
     public const string UsePartialPropertyInsteadOfPartialMethodForGeneratedRegex = "MA0190";
     public const string DoNotUseNullForgiveness = "MA0191";
     public const string UseHasFlagMethod = "MA0192";
+    public const string UseAnOverloadThatHasMidpointRounding = "MA0193";
 
     public static string GetHelpUri(string identifier)
     {

src/Meziantou.Analyzer/Rules/UseAnOverloadThatHasMidpointRoundingAnalyzer.cs

@@ -0,0 +1,121 @@
+using System.Collections.Immutable;
+using System.Linq;
+using Meziantou.Analyzer.Internals;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Operations;
+
+namespace Meziantou.Analyzer.Rules;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public sealed class UseAnOverloadThatHasMidpointRoundingAnalyzer : DiagnosticAnalyzer
+{
+    private static readonly DiagnosticDescriptor Rule = new(
+        RuleIdentifiers.UseAnOverloadThatHasMidpointRounding,
+        title: "Use an overload with a MidpointRounding argument",
+        messageFormat: "Use an overload with a MidpointRounding argument",
+        RuleCategories.Usage,
+        DiagnosticSeverity.Info,
+        isEnabledByDefault: true,
+        description: "",
+        helpLinkUri: RuleIdentifiers.GetHelpUri(RuleIdentifiers.UseAnOverloadThatHasMidpointRounding));
+
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics => ImmutableArray.Create(Rule);
+
+    public override void Initialize(AnalysisContext context)
+    {
+        context.EnableConcurrentExecution();
+        context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+
+        context.RegisterCompilationStartAction(context =>
+        {
+            var midpointRoundingSymbol = context.Compilation.GetBestTypeByMetadataName("System.MidpointRounding");
+            if (midpointRoundingSymbol is null)
+                return;
+
+            var ifloatingPointSymbol = context.Compilation.GetBestTypeByMetadataName("System.Numerics.IFloatingPoint`1");
+            var mathSymbol = context.Compilation.GetBestTypeByMetadataName("System.Math");
+            var mathFSymbol = context.Compilation.GetBestTypeByMetadataName("System.MathF");
+            if (ifloatingPointSymbol is null && mathSymbol is null && mathFSymbol is null)
+                return;
+
+            context.RegisterOperationAction(context => AnalyzeInvocation(context, midpointRoundingSymbol, ifloatingPointSymbol, mathSymbol, mathFSymbol), OperationKind.Invocation);
+        });
+    }
+
+    private static void AnalyzeInvocation(
+        OperationAnalysisContext context,
+        INamedTypeSymbol midpointRoundingSymbol,
+        INamedTypeSymbol? ifloatingPointSymbol,
+        INamedTypeSymbol? mathSymbol,
+        INamedTypeSymbol? mathFSymbol)
+    {
+        var operation = (IInvocationOperation)context.Operation;
+        var method = operation.TargetMethod;
+        if (!IsRoundMethodWithoutMidpointRounding(method, midpointRoundingSymbol))
+            return;
+
+        if (method.ContainingType.IsEqualTo(mathSymbol) || method.ContainingType.IsEqualTo(mathFSymbol))
+        {
+            context.ReportDiagnostic(Rule, operation);
+            return;
+        }
+
+        if (method.ContainingType.SpecialType is SpecialType.System_Decimal)
+        {
+            context.ReportDiagnostic(Rule, operation);
+            return;
+        }
+
+        if (IsIFloatingPointRoundMethod(method, midpointRoundingSymbol, ifloatingPointSymbol) ||
+            IsIFloatingPointRoundImplementation(method, midpointRoundingSymbol, ifloatingPointSymbol))
+        {
+            context.ReportDiagnostic(Rule, operation);
+        }
+    }
+
+    private static bool IsRoundMethodWithoutMidpointRounding(IMethodSymbol method, INamedTypeSymbol midpointRoundingSymbol)
+    {
+        return method.Name is "Round" &&
+               !method.Parameters.Any(parameter => parameter.Type.IsEqualTo(midpointRoundingSymbol));
+    }
+
+    private static bool IsIFloatingPointRoundMethod(IMethodSymbol method, INamedTypeSymbol midpointRoundingSymbol, INamedTypeSymbol? ifloatingPointSymbol)
+    {
+        if (ifloatingPointSymbol is null)
+            return false;
+
+        return IsRoundMethodWithoutMidpointRounding(method, midpointRoundingSymbol) &&
+               method.ContainingType.OriginalDefinition.IsEqualTo(ifloatingPointSymbol);
+    }
+
+    private static bool IsIFloatingPointRoundImplementation(IMethodSymbol method, INamedTypeSymbol midpointRoundingSymbol, INamedTypeSymbol? ifloatingPointSymbol)
+    {
+        if (ifloatingPointSymbol is null || method.ContainingType is null)
+            return false;
+
+        foreach (var explicitImplementation in method.ExplicitInterfaceImplementations)
+        {
+            if (IsIFloatingPointRoundMethod(explicitImplementation, midpointRoundingSymbol, ifloatingPointSymbol))
+                return true;
+        }
+
+        foreach (var interfaceType in method.ContainingType.AllInterfaces)
+        {
+            if (!interfaceType.OriginalDefinition.IsEqualTo(ifloatingPointSymbol))
+                continue;
+
+            foreach (var interfaceMethod in interfaceType.GetMembers(method.Name).OfType<IMethodSymbol>())
+            {
+                if (!IsIFloatingPointRoundMethod(interfaceMethod, midpointRoundingSymbol, ifloatingPointSymbol))
+                    continue;
+
+                var implementation = method.ContainingType.FindImplementationForInterfaceMember(interfaceMethod);
+                if (implementation is IMethodSymbol implementationMethod && implementationMethod.OriginalDefinition.IsEqualTo(method.OriginalDefinition))
+                    return true;
+            }
+        }
+
+        return false;
+    }
+}