Add HandlerTemplate to ScanForTypesAttribute

[Copilot]

ScanForTypesAttribute lacked a way to generate per-type expressions beyond method invocations, forcing users to fall back to Activator when constructors require arguments.

Changes

• New HandlerTemplate property on ScanForTypesAttribute: a string template where T (word-boundary matched) is replaced with the fully-qualified name of each found type
  • For collection-returning methods: template becomes each array element expression
  • For void / first-param-returning methods: template becomes a statement (; appended if absent)
  • Incompatible with Handler — new DI0016 diagnostic enforces this
• MissingCustomHandlerOnGenerateServiceHandler (DI0013) no longer fires when HandlerTemplate is set
• Template placeholder uses \bT\b regex (static compiled) for safe word-boundary replacement

Usage

// Collection return — generate instances with constructor args
[ScanForTypes(AssignableTo = typeof(BaseType), HandlerTemplate = "new T(argument)")]
public partial BaseType[] GetTypeInstances(string argument);

// Void method — generate statements
[ScanForTypes(AssignableTo = typeof(BaseType), HandlerTemplate = "registry.Add(new T(argument))")]
public partial void RegisterInstances(BaseTypeRegistry registry, string argument);

[Dreamescaper]

@copilot
update README.md

[Copilot]

@copilot
update README.md

Done in ea6369c. Added a new "Create instances using constructors with parameters" example section showing both collection-returning and void-method usage, and added HandlerTemplate to the ScanForTypes parameters table.

[Dreamescaper]

@copilot
Make README info less about constructors specifically, and more about any non-standard cases, when Handler is not flexible enough. Constructors would be just one example. Static methods with multiple parameters, typeof manipulations etc.

[Copilot]

@copilot
Make README info less about constructors specifically, and more about any non-standard cases, when Handler is not flexible enough. Constructors would be just one example. Static methods wit...

Updated in 6af0890. The section is now titled "Use a template expression for each matched type" and leads with the general concept before showing three distinct examples: constructor args, a static factory method with multiple parameters, and typeof manipulations — with the void-method variant at the end.