Fix VSMEF008 to emit fully-qualified type names in diagnostic messages (#686)

* Initial plan

* Fix VSMEF008 diagnostic to use fully-qualified type names in error message

Co-authored-by: AArnott <3548+AArnott@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: AArnott <3548+AArnott@users.noreply.github.com>

Author: Copilot

src/Microsoft.VisualStudio.Composition.Analyzers/VSMEF008ImportContractTypeMismatchAnalyzer.cs

@@ -183,8 +183,8 @@ private static void AnalyzeMember(
                 context.ReportDiagnostic(Diagnostic.Create(
                     Descriptor,
                     location,
-                    explicitContractType.ToDisplayString(SymbolDisplayFormat.CSharpShortErrorMessageFormat),
-                    expectedType.ToDisplayString(SymbolDisplayFormat.CSharpShortErrorMessageFormat)));
+                    explicitContractType.ToDisplayString(FullyQualifiedTypeNameFormat),
+                    expectedType.ToDisplayString(FullyQualifiedTypeNameFormat)));
             }
         }
     }

test/Microsoft.VisualStudio.Composition.Analyzers.Tests/VSMEF008ImportContractTypeMismatchAnalyzerTests.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using Microsoft.CodeAnalysis.Text;
+using Microsoft.VisualStudio.Composition.Analyzers;
 using VerifyCS = CSharpCodeFixVerifier<Microsoft.VisualStudio.Composition.Analyzers.VSMEF008ImportContractTypeMismatchAnalyzer, Microsoft.CodeAnalysis.Testing.EmptyCodeFixProvider>;
 
 public class VSMEF008ImportContractTypeMismatchAnalyzerTests
@@ -280,4 +281,30 @@ class Foo
             ("vs-mef.ContractNamesAssignability.txt", SourceText.From(allowList)));
         await verifier.RunAsync();
     }
+
+    [Fact]
+    public async Task DiagnosticMessage_UsesFullyQualifiedTypeNames()
+    {
+        string test = """
+            using System.ComponentModel.Composition;
+
+            namespace MyCompany.Services
+            {
+                interface IServiceBroker { }
+                class SVsServiceProvider { }
+
+                class Foo
+                {
+                    [Import(typeof(SVsServiceProvider))]
+                    public IServiceBroker {|#0:Value|} { get; set; }
+                }
+            }
+            """;
+
+        await VerifyCS.VerifyAnalyzerAsync(
+            test,
+            VerifyCS.Diagnostic(VSMEF008ImportContractTypeMismatchAnalyzer.Id)
+                .WithLocation(0)
+                .WithArguments("MyCompany.Services.SVsServiceProvider", "MyCompany.Services.IServiceBroker"));
+    }
 }