Improve TypeBuilderInstantiation error messages to guide users to TypeBuilder static methods

[Copilot]

When using PersistedAssemblyBuilder to create generic types, calling MakeGenericType() returns a TypeBuilderInstantiation object. Previously, attempting to access members like constructors, methods, or fields on this instantiated type would throw unhelpful NotSupportedException messages like "Specified method is not supported."

This PR improves the error messages to provide clear guidance on how to properly access members using the static TypeBuilder methods:

Before:

Type instantiatedType = createdType.MakeGenericType(typeof(string));
instantiatedType.GetConstructors(); // NotSupportedException: "Specified method is not supported."

After:

Type instantiatedType = createdType.MakeGenericType(typeof(string));
instantiatedType.GetConstructors(); // NotSupportedException: "This type does not support resolving constructors. Use TypeBuilder.GetConstructor instead."

Changes made:

1. Added error message resources to Strings.resx for methods that have corresponding TypeBuilder static alternatives:

   • NotSupported_TypeBuilderInstantiation_GetConstructor
   • NotSupported_TypeBuilderInstantiation_GetMethod
   • NotSupported_TypeBuilderInstantiation_GetField

2. Updated error messages for methods that have TypeBuilder static alternatives:

   • GetConstructor* methods → Direct users to TypeBuilder.GetConstructor
   • GetMethod* methods → Direct users to TypeBuilder.GetMethod
   • GetField* methods → Direct users to TypeBuilder.GetField

3. Maintained default error messages for methods that don't have TypeBuilder equivalents (Interface, Event, Property, NestedType operations) to avoid providing misleading guidance.

4. Added comprehensive tests to validate the improved error messages and ensure the suggested workarounds continue to function correctly.

The correct workaround is to use the static TypeBuilder methods:

// Instead of: instantiatedType.GetConstructor(Type.EmptyTypes)
ConstructorInfo ctor = TypeBuilder.GetConstructor(instantiatedType, originalConstructor);

// Instead of: instantiatedType.GetMethod("MethodName")  
MethodInfo method = TypeBuilder.GetMethod(instantiatedType, originalMethod);

// Instead of: instantiatedType.GetField("FieldName")
FieldInfo field = TypeBuilder.GetField(instantiatedType, originalField);

This change maintains full backward compatibility while significantly improving the developer experience by providing actionable guidance when encountering this limitation.

Fixes #118506.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[jkotas]

@copilot Please address the feedback above

[Copilot]

@copilot Please address the feedback above

Addressed both feedback items: moved error messages to Strings.resx and reverted methods without TypeBuilder alternatives to use default error messages. Commit c17083d.

[jkotas]

@copilot Please address the feedback above

[Copilot]

@copilot Please address the feedback above

Completed. The error messages have been de-duplicated into a single parameterized resource string using nameof(TypeBuilder.GetConstructor), nameof(TypeBuilder.GetMethod), and nameof(TypeBuilder.GetField) as suggested. Commit d04f6ef.

[Copilot]

Pull Request Overview

This PR improves error messages for TypeBuilderInstantiation objects created when calling MakeGenericType() on a TypeBuilder. Previously, attempting to access constructors, methods, or fields on these instantiated types would throw generic "Specified method is not supported" errors. Now they provide helpful guidance directing users to the appropriate TypeBuilder static methods.

Key changes:

• Enhanced error messages to guide users to TypeBuilder.GetConstructor, TypeBuilder.GetMethod, and TypeBuilder.GetField static methods
• Added comprehensive test coverage to validate the improved error messages
• Maintained backward compatibility while significantly improving developer experience

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
TypeBuilderInstantiationErrorMessageTests.cs	New test file validating improved error messages for TypeBuilderInstantiation member access
TypeBuilderInstantiation.cs	Updated constructor, method, and field access methods to use helpful error messages
Strings.resx	Added new resource string for TypeBuilderInstantiation error messages

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-reflection-emit
See info in area-owners.md if you want to be subscribed.

[jkotas]

/ba-g helix infrastructure failures without logs.