[jkoritzinsky]

I wanted to see if we could enable discovering type maps from the assembly that defines the group type to enable more cohesive usage for scenarios without app-wide analysis (like npgsql). Seems relatively clean, so I'm putting it up for review.

Approach

• Add the group's defining assembly as a second root alongside the existing entry root, following group-specific assembly targets with shared deduplication.
• Discover NativeAOT maps lazily from reachable external/proxy requests and discover ILLink groups as they are used. Preserve conditional trimming and independent activation of the two map kinds.
• Keep entry-assembly selection and existing error behavior. The ReadyToRun representation is unchanged; CoreCLR uses the existing per-assembly cached-data or metadata paths.

Regression coverage includes transitive targets, cycles and overlapping roots, entry overrides, generic and array groups, unused groups, empty maps, conditional retention, and genuine duplicate keys. Newly discovered entries can expose duplicate keys that were previously ignored; existing duplicate-key rejection remains intentional.

Validation

Windows x64 validation passed:

• ./build.cmd clr+libs+host -rc checked -lc release - clean baseline passed.
• ./build.cmd clr.runtime+clr.tools -rc checked -lc release - changed VM, NativeAOT compiler, and Crossgen2 build passed.
• ./src/tests/build.cmd generatelayoutonly x64 checked - passed.
• ./src/tests/build.cmd test Interop\TypeMap\TypeMapDefiningAssemblyApp.csproj test Interop\TypeMap\TypeMapEntryAssemblyApp.csproj test Interop\TypeMap\TypeMapApp.csproj x64 checked skipnative - passed; all three generated wrappers passed with DOTNET_ReadyToRun=0.
• The same test build with crossgen2 - passed; all three wrappers passed with RunCrossGen2=1 and the repository SDK selected for R2RDump.
• The same test build with nativeaot - passed; all three native executables exited 100. Four existing IL3000 warnings concern Assembly.Location in R2R-only checks.
• ./dotnet.cmd test src\tools\illink\test\Mono.Linker.Tests\Mono.Linker.Tests.csproj -c Debug --filter FullyQualifiedName~Mono.Linker.Tests.TestCases.Reflection.ReflectionTests - 55 passed.
• ./dotnet.cmd test src\coreclr\tools\aot\ILCompiler.Trimming.Tests\ILCompiler.Trimming.Tests.csproj -c Checked --filter DisplayName~TypeMap -p:RuntimeConfiguration=Checked -p:LibrariesConfiguration=Release - 4 passed.

The defining-assembly regression failed before the fix in CoreCLR, NativeAOT, and ILLink. Linux and other architectures were not run.

Discovery cost

Release BenchmarkDotNet measurements on a Windows x64 VM, using identical map contents in both hosts:

Map creation	Baseline	Changed	Managed allocation
External, same assembly	3.525 us	3.536 us	424 B, unchanged
Proxy, same assembly	4.272 us	4.366 us	1216 B, unchanged
External, additional CoreLib root	3.533 us	7.923 us	424 B, unchanged
Proxy, additional CoreLib root	4.362 us	8.802 us	1216 B, unchanged

Same-assembly discovery is deduplicated. Scanning CoreLib as an additional root adds about 4.4 us per creation in this measurement; this measures map creation, not dictionary lookup. Results are from a single Windows x64 VM, not cross-platform performance evidence.

Resolves #136575

Note

This pull request description and implementation were generated with GitHub Copilot.

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