Description
Description
When encountering an abstract type in an object graph the configuration generator tries to create it and throws.
This is inconsistent with the runtime binder, which will use an existing instance.
I wonder if we should warn on this or not. Definitely if the abstract type is the root and we're generating Get calls that's a problem. Anywhere else it could be supported if the member is already initialized - since we won't need to create one in the binder.
Reproduction Steps
Run attached repro project:
bindAbstract.zip
Also shown here: https://gist.github.com/ericstj/121fe52f9a1b5115b246c08605c685c0
To see expected behavior remove EnableConfigurationBindingGenerator. You'll see the output
options.Abstract.GetHashCode() before bind: 55915408
options.Abstract.GetHashCode() after bind: 55915408
John Doe
Note that the runtime binder didn't rely on seeing the derived type and creating a new one -- this is apparent by seeing that the object is the same before and after then bind.
Expected behavior
Repro runs successfully and sets the members on the existing instance of the derived type. Not creating a new instance nor throwing.
Actual behavior
Warning emitted by the source generator:
C:\scratch\bindAbstract\Program.cs(11,1): warning SYSLIB1100: Cannot create instance of type 'MyAbstractClass' because
it is missing a public instance constructor. (https://learn.microsoft.com/dotnet/fundamentals/syslib-diagnostics/syslib
1100.md)
And exception thrown at runtime:
Unhandled exception. System.InvalidOperationException: Cannot create instance of type '<global namespace>.MyAbstractClass' because it is missing a public instance constructor.
at Microsoft.Extensions.Configuration.Binder.SourceGeneration.<BindingExtensions_g>FC276FD7C89D1ED0B2B3E96BAC8F157FABB86A642EAABC54639B357A857C01D08__BindingExtensions.BindCore(IConfiguration configuration, MyOptions& instance, Boolean defaultValueIfNotFound, BinderOptions binderOptions) in C:\scratch\bindAbstract\Microsoft.Extensions.Configuration.Binder.SourceGeneration\Microsoft.Extensions.Configuration.Binder.SourceGeneration.ConfigurationBindingGenerator\BindingExtensions.g.cs:line 144
at Microsoft.Extensions.Configuration.Binder.SourceGeneration.<BindingExtensions_g>FC276FD7C89D1ED0B2B3E96BAC8F157FABB86A642EAABC54639B357A857C01D08__BindingExtensions.Bind_MyOptions(IConfiguration configuration, Object instance) in C:\scratch\bindAbstract\Microsoft.Extensions.Configuration.Binder.SourceGeneration\Microsoft.Extensions.Configuration.Binder.SourceGeneration.ConfigurationBindingGenerator\BindingExtensions.g.cs:line 48
at Program.<Main>$(String[] args) in C:\scratch\bindAbstract\Program.cs:line 11
Regression?
No response
Known Workarounds
Disable generator.
Configuration
No response
Other information
No response