Ignore extern methods in naming style

src/Analyzers/CSharp/Analyzers/NamingStyle/CSharpNamingStyleDiagnosticAnalyzer.cs

@@ -47,6 +47,14 @@ protected override bool ShouldIgnore(ISymbol symbol)
                 return true;
             }
 
+            if (symbol.IsExtern)
+            {
+                // Extern symbols are mainly P/Invoke and runtime invoke, probably requiring their name
+                // to match external definition exactly.
+                // Simply ignoring them.
+                return true;
+            }
+
             return false;
         }
     }

src/Analyzers/CSharp/Tests/NamingStyles/NamingStylesTests.cs

@@ -1382,5 +1382,17 @@ class C : I
     int [|global::I.X|] => 0;
 }", new TestParameters(options: s_options.PropertyNamesArePascalCase));
         }
+
+        [Fact]
+        [WorkItem(51727, "https://github.com/dotnet/roslyn/issues/51727")]
+        public async Task TestExternAsync()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"
+class C
+{
+    static extern void [|some_p_invoke()|];
+}", new TestParameters(options: s_options.MethodNamesArePascalCase));
+        }
     }
 }

src/Analyzers/VisualBasic/Analyzers/NamingStyle/VisualBasicNamingStyleDiagnosticAnalyzer.vb

@@ -19,6 +19,13 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Diagnostics.Analyzers
                 SyntaxKind.TypeParameter)
 
         Protected Overrides Function ShouldIgnore(symbol As ISymbol) As Boolean
+            If symbol.IsExtern Then
+                ' Extern symbols are mainly P/Invoke And runtime invoke, probably requiring their name
+                ' to match external definition exactly.
+                ' Simply ignoring them.
+                Return True
+            End If
+
             Return False
         End Function
     End Class

src/Analyzers/VisualBasic/Tests/NamingStyles/NamingStylesTests.vb

@@ -497,5 +497,14 @@ End Class",
                 options:=s_options.TypeParameterNamesStartWithT)
         End Function
 
+        <Fact, Trait(Traits.Feature, Traits.Features.NamingStyle)>
+        <WorkItem(51727, "https://github.com/dotnet/roslyn/issues/51727")>
+        Public Async Function TestExternMethod() As Task
+            Await TestMissingInRegularAndScriptAsync(
+"Public Class C
+    Declare Sub [|some_p_invoke|] Lib ""some""()
+End Class",
+                New TestParameters(options:=s_options.MethodNamesArePascalCase))
+        End Function
     End Class
 End Namespace