Unused parameter analyzer shouldn't warn for methods that only throw

src/Analyzers/CSharp/Analyzers/RemoveUnusedParametersAndValues/CSharpRemoveUnusedParametersAndValuesDiagnosticAnalyzer.cs

@@ -5,8 +5,10 @@
 using Microsoft.CodeAnalysis.CodeStyle;
 using Microsoft.CodeAnalysis.CSharp.CodeStyle;
 using Microsoft.CodeAnalysis.CSharp.Extensions;
+using Microsoft.CodeAnalysis.CSharp.LanguageService;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.LanguageService;
 using Microsoft.CodeAnalysis.Operations;
 using Microsoft.CodeAnalysis.RemoveUnusedParametersAndValues;
 
@@ -33,6 +35,22 @@ protected override bool MethodHasHandlesClause(IMethodSymbol method)
         protected override bool IsIfConditionalDirective(SyntaxNode node)
             => node is IfDirectiveTriviaSyntax;
 
+        protected override bool ReturnsThrow(SyntaxNode node)
+        {
+            var methodSyntax = (MethodDeclarationSyntax)node;
+            if (methodSyntax.ExpressionBody is not null)
+            {
+                return methodSyntax.ExpressionBody.Expression is ThrowExpressionSyntax;
+            }
+
+            if (methodSyntax.Body is not null && methodSyntax.Body.Statements.Count == 1)
+            {
+                return methodSyntax.Body.Statements[0] is ThrowStatementSyntax;
+            }
+
+            return false;
+        }
+
         protected override CodeStyleOption2<UnusedValuePreference> GetUnusedValueExpressionStatementOption(AnalyzerOptionsProvider provider)
             => ((CSharpAnalyzerOptionsProvider)provider).UnusedValueExpressionStatement;
 

src/Analyzers/CSharp/Tests/RemoveUnusedParametersAndValues/RemoveUnusedParametersTests.cs

@@ -1647,5 +1647,28 @@ public static ICustomMarshaler GetInstance(string [|s|])
 }
 ");
         }
+
+        [Fact, WorkItem(47174, "https://github.com/dotnet/roslyn/issues/65275")]
+        public async Task TestMethodWithUnusedParameterThrowsExpressionBOdy()
+        {
+            await TestDiagnosticMissingAsync(
+@"public class Class
+{
+    public void Method(int [|x|]) => throw new System.Exception();
+}");
+        }
+
+        [Fact, WorkItem(47174, "https://github.com/dotnet/roslyn/issues/65275")]
+        public async Task TestMethodWithUnusedParameterThrowsMethodBody()
+        {
+            await TestDiagnosticMissingAsync(
+@"public class Class
+{
+    public void Method(int [|x|])
+    {
+        throw new System.Exception();
+    }
+}");
+        }
     }
 }

src/Analyzers/Core/Analyzers/RemoveUnusedParametersAndValues/AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer.SymbolStartAnalyzer.BlockAnalyzer.cs

@@ -6,10 +6,12 @@
 using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Linq;
+using System.Threading;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CodeStyle;
 using Microsoft.CodeAnalysis.Diagnostics;
 using Microsoft.CodeAnalysis.FlowAnalysis.SymbolUsageAnalysis;
+using Microsoft.CodeAnalysis.LanguageService;
 using Microsoft.CodeAnalysis.Operations;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Microsoft.CodeAnalysis.Shared.Extensions;

src/Analyzers/Core/Analyzers/RemoveUnusedParametersAndValues/AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer.SymbolStartAnalyzer.cs

@@ -229,8 +229,9 @@ parameter.ContainingSymbol is not IMethodSymbol method ||
 
                 // Ignore parameters of record primary constructors since they map to public properties
                 // TODO: Remove this when implicit operations are synthesised: https://github.com/dotnet/roslyn/issues/47829 
+                var methodSyntax = method.DeclaringSyntaxReferences.FirstOrDefault()?.GetSyntax();
                 if (method.IsConstructor() &&
-                    _compilationAnalyzer.IsRecordDeclaration(method.DeclaringSyntaxReferences.FirstOrDefault()?.GetSyntax()))
+                    _compilationAnalyzer.IsRecordDeclaration(methodSyntax))
                 {
                     return false;
                 }
@@ -270,6 +271,11 @@ parameter.ContainingSymbol is not IMethodSymbol method ||
                     return false;
                 }
 
+                if (_compilationAnalyzer.ReturnsThrow(methodSyntax))
+                {
+                    return false;
+                }
+
                 // Don't report on valid GetInstance method of ICustomMarshaler.
                 // See https://docs.microsoft.com/dotnet/api/system.runtime.interopservices.icustommarshaler#implementing-the-getinstance-method
                 if (method is { MetadataName: "GetInstance", IsStatic: true, Parameters.Length: 1, ContainingType: { } containingType } methodSymbol &&

src/Analyzers/Core/Analyzers/RemoveUnusedParametersAndValues/AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer.cs

@@ -105,6 +105,7 @@ protected AbstractRemoveUnusedParametersAndValuesDiagnosticAnalyzer(
         protected abstract bool SupportsDiscard(SyntaxTree tree);
         protected abstract bool MethodHasHandlesClause(IMethodSymbol method);
         protected abstract bool IsIfConditionalDirective(SyntaxNode node);
+        protected abstract bool ReturnsThrow(SyntaxNode node);
         protected abstract CodeStyleOption2<UnusedValuePreference> GetUnusedValueExpressionStatementOption(AnalyzerOptionsProvider provider);
         protected abstract CodeStyleOption2<UnusedValuePreference> GetUnusedValueAssignmentOption(AnalyzerOptionsProvider provider);
 

src/Analyzers/VisualBasic/Analyzers/RemoveUnusedParametersAndValues/VisualBasicRemoveUnusedParametersAndValuesDiagnosticAnalyzer.vb

@@ -7,6 +7,7 @@ Imports Microsoft.CodeAnalysis.Diagnostics
 Imports Microsoft.CodeAnalysis.Operations
 Imports Microsoft.CodeAnalysis.RemoveUnusedParametersAndValues
 Imports Microsoft.CodeAnalysis.VisualBasic.CodeStyle
+Imports Microsoft.CodeAnalysis.VisualBasic.LanguageService
 Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
 
 Namespace Microsoft.CodeAnalysis.VisualBasic.RemoveUnusedParametersAndValues
@@ -50,6 +51,22 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.RemoveUnusedParametersAndValues
             Return TryCast(expressionStatement.Syntax, CallStatementSyntax) IsNot Nothing
         End Function
 
+        Protected Overrides Function ReturnsThrow(node As SyntaxNode) As Boolean
+            Dim methodStatementSyntax = TryCast(node, MethodStatementSyntax)
+            If methodStatementSyntax IsNot Nothing Then
+                Dim methodSyntax = TryCast(node.Parent, MethodBlockSyntax)
+                If methodSyntax.BlockStatement Is Nothing Then
+                    Return False
+                End If
+
+                If methodSyntax.Statements.Count = 1 Then
+                    Return TryCast(methodSyntax.Statements.First(), ThrowStatementSyntax) IsNot Nothing
+                End If
+            End If
+
+            Return False
+        End Function
+
         Protected Overrides Function IsExpressionOfExpressionBody(expressionStatementOperation As IExpressionStatementOperation) As Boolean
             ' VB does not support expression body
             Return False

src/Analyzers/VisualBasic/Tests/RemoveUnusedParametersAndValues/RemoveUnusedParametersTests.vb

@@ -187,6 +187,18 @@ class C
         if (true)
             throw new NotImplementedException()
     end sub
+end class")
+        End Function
+
+        <Fact, WorkItem(41236, "https://github.com/dotnet/roslyn/issues/41236")>
+        Public Async Function TestMethodBody_OnlyThrowStatement() As Task
+            Await TestDiagnosticMissingAsync(
+"imports system
+
+class C
+    private sub Goo([|i|] as integer)
+        throw new Exception()
+    end sub
 end class")
         End Function
     End Class