Make ConfigurationBinder source generator feature-complete

[layomia]

Follow up work for the configuration binding source generator (#44493, #82179).

Preview 3

• Support objects with parameterless ctors
• Initial collection support (readonly collections were left out)

Preview 4

• Implement proper parsing of primitives in config binder generator #83533
• Add SDK prop (EnableConfigurationBinderGenerator) to serve as gesture to invoke generator (e.g. EnableRequestDelegateGenerator flag) (as part of How should we represent source-generators / analyzers that are off by default? sdk#30872) and include generator in the ASP.NET Targeting Pack

Preview 5

• Finish collection support (i.e readonly collections) - Support remaining collections in config binder generator #86285

Preview 6

• Implement the right constructor invocation logic for classes, structs, record (+ init-only setters / required props) - Add support for types with parameterized ctors to config binder gen #86365
• Support all applicable ConfigurationBinder method overloads in binding generator #83600

Preview 7

• Close on whether binding customization is needed: Extensibility for Configuration Binding Source Generator #83599

RC 1

• Iterate on config binding generator parsing pipeline to benefit from input caching provided by the incremental-generator feature #83534
• Use Roslyn interceptors feature in config binder generator #89322

Stretch / tbd / validation

• Add benchmarks for configuration binding source generator output vs reflection implementation performance#2929
• Enable nullable annotations in generator project

FX DC feedback

There may be bad UX edge cases that need to be investigated, such as :

• The roslyn analyzers report an unused using-import from where the existing extension methods are (might be topically unlikely)
  • write the smallest possible source file that could invoke each hook and make sure that we don't have unused usings after source generator hooks the callsite.
• Concerns around callers using static invocation syntax instead of instance/extension syntax.
  • feature not a bug
  • make sure it triggers linker warning
  • have documentation on that linker warning that leads people to using the generator. 
• The generator might end up toggling itself on and off (by removing the calls to the existing methods)
  • have a discussion and review the triggering logic with folks from the compiler team

[ghost]

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Issue Details

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[WIP] Placeholder for follow up work for the upcoming ConfigurationBinder source generator (#44493).

The task is to make all the ConfigurationBinder tests (which are now shared with the reflection-based implementation) pass. Identified work items include:

• Implement the right constructor invocation logic for each POCO-style target config type

Author:	layomia
Assignees:	layomia
Labels:	area-Extensions-Configuration
Milestone:	8.0.0

[jkotas]

Also, we should have this source generator documented at https://learn.microsoft.com/en-us/dotnet/core/extensions/configuration. Once the documentation is available, please update this link to point to it.

[layomia]

Closing. Tracking remaining 8.0 work in https://github.com/orgs/dotnet/projects/303/views/1.