LAMA0320: Aspects can't be applied to source-generated code

Cause

Source generators add code to your project during compilation. Metalama doesn't support aspects on declarations of this generated code. In particular, at design time, Metalama itself runs as a source generator, and it can't see the output of other source generators.

An analyzer included in the Metalama.Framework package reports LAMA0320 when it finds an aspect attribute on a declaration (a type, method, property, field, event, or parameter) whose syntax tree was produced by a source generator. The most common case is a custom attribute written in a Razor (.razor) or Razor Pages (.cshtml) file, because the Razor compiler turns these files into C# with a source generator. In this case, <Addendum> adds a suggestion to move the code to a code-behind file. In other cases, <Addendum> is empty. <AspectType> is the name of the aspect and <Target> is the target declaration.

This diagnostic requires a source generator and is reported by a Roslyn analyzer, which doesn't run in the snapshot tests of this documentation, so the article has no example.

Resolution

• For Razor components and pages, move the member that needs the aspect from the @code block to a code-behind file, for instance a partial class in a MyComponent.razor.cs file, and add the aspect attribute there.
• For other source generators, add the aspect to a declaration in your own source code. When the generated type is partial, declare the member in a partial part of the type in your source code, or add the aspect with a fabric to declarations in your source code.
• If the generator is your own, generate code that doesn't contain aspect attributes.

See also

• Creating aspects