Make WrapperElementsGenerator cacheable using collect-and-execute pattern

[Copilot]

The WrapperElementsGenerator was returning IncrementalValuesProvider<ISymbol>, which isn't cacheable, causing the pipeline to trigger on every build of the bunit.web project.

Changes

Introduced cacheable record types

• ElementInterfacesData: Holds immutable array of element type info
• ElementTypeInfo: Stores Name, FullyQualifiedName, and MetadataName as strings

Implemented collect-and-execute pattern

• Collect phase: Select extracts minimal type information into records during compilation
• Execute phase: Combine merges cached data with CompilationProvider to retrieve full symbols only when needed
• Symbols are reconstructed via GetTypeByMetadataName() using cached metadata names

Added defensive checks

• Interface name processing now validates length before stripping 'I' prefix

Before

var angleSharpAssemblyReference = context
    .CompilationProvider
    .Select((compilation, cancellationToken) => {
        // Returns ISymbol directly - not cacheable
        return compilation.GetAssemblyOrModuleSymbol(meta);
    });

context.RegisterSourceOutput(angleSharpAssemblyReference, GenerateWrapperTypes);

After

var elementInterfaces = context
    .CompilationProvider
    .Select((compilation, cancellationToken) => {
        // Returns cacheable record with strings only
        return new ElementInterfacesData(
            types.Select(t => new ElementTypeInfo(
                t.Name,
                t.ToDisplayString(GeneratorConfig.SymbolFormat),
                GetMetadataName(t)
            )).ToImmutableArray());
    });

var withCompilation = elementInterfaces.Combine(context.CompilationProvider);
context.RegisterSourceOutput(withCompilation, GenerateWrapperTypes);

The generator now caches only hashable data, enabling incremental compilation to skip regeneration when AngleSharp assembly hasn't changed.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>WrapperElementsGenerator cachable</issue_title>
<issue_description>In its current shape the WrapperElementsGenerator does return IncrementalValuesProvider<ISymbol>.
As this isn't cacheable the pipeline get's triggered with every new build of the bunit.web project.

To tackle this we need a collect and execute phase where in the collect phase we retrieve all elements and store them into our own record type so hashing across runs is stable.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes WrapperElementsGenerator cachable #1397

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.