[wasm] Harden ReferenceNewAssemblyRebuildTest against dependency-closure changes

[lewing]

Summary

Wasm.Build.NativeRebuild.Tests.ReferenceNewAssemblyRebuildTest has been failing on the browser-wasm AOT leg (Known Build Error #130540, "Expected changed file: driver-gen.c"). This hardens the test so it no longer depends on the app's incidental dependency closure.

Root cause

The test replaces the app's entry point with one that references a "new" assembly, then asserts that driver-gen.c — the AOT modules table, one mono_aot_register_module line per AOT'd assembly — changes because a new module was added.

It relied on System.Security.Cryptography being absent from WasmBasicTestApp's AOT closure (the swapped entry point used SHA256). That assumption broke when #122093 ("Add Zip Archives password support") added an unconditional System.Security.Cryptography ProjectReference to System.IO.Compression. The app always compiles ZipArchiveInteropTest.cs (uses System.IO.Compression), so crypto is now always in the closure and always AOT'd. The swapped entry point therefore adds no new module, driver-gen.c is byte-identical between build and rebuild, MonoAOTCompiler's CopyIfDifferent skips the write, the timestamp is unchanged, and CompareStat fails.

This is the second time the test rotted this way — #109069 previously switched it from Json to System.Security.Cryptography for the same reason ("Json lib was already referenced before the change in the test").

Fix

Stop guessing which BCL assembly happens to be absent. Instead reference the existing dedicated first-party Library test project (an empty library not referenced by the default app), following the same pattern already used by PInvokeTableGeneratorTests:

• Inject <ProjectReference Include="..\Library\Library.csproj" /> via CopyTestAsset(extraItems: ...).
• Populate Library.cs with a small type via ReplaceFile.
• Point the swapped entry point (NativeRebuildNewAssembly.cs) at that type instead of SHA256.

Library is unused in the first build → trimmed away → absent from the AOT module set. The swapped entry point uses it → rooted → new module in the rebuild → driver-gen.c changes. Because Library is first-party and the test fully controls whether it is referenced, the new-assembly signal is deterministic and immune to future changes in the app's dependency closure.

Fixes #130540.

Related

The underlying dependency regression (crypto rooted into every trimmed app that uses ZipArchive, a browser-wasm size concern) is tracked separately in #130650.

Testing

Not built/run locally — WBT requires a browser-wasm runtime baseline + emscripten and executes in a browser via the Helix/xharness harness. Relying on CI (the failing AOT leg exercises exactly this test) to validate.

Note

This PR was authored with the assistance of GitHub Copilot.

[Copilot]

Pull request overview

Hardens the Wasm.Build.NativeRebuild.Tests.ReferenceNewAssemblyRebuildTest to make the “new AOT module added” signal deterministic by referencing a dedicated first-party test library, instead of relying on an incidental BCL dependency being absent/present in the app’s dependency closure.

Changes:

• Injects a ProjectReference to WasmBasicTestApp/Library into the copied test asset and populates Library.cs with a controlled type.
• Updates the “swapped entry point” (NativeRebuildNewAssembly.cs) to reference the new library type instead of System.Security.Cryptography.
• Adds a new entrypoint source file (NativeRebuildReferencedLibrary.cs) used to overwrite the library’s source during the test setup.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
src/mono/wasm/Wasm.Build.Tests/NativeRebuildTests/ReferenceNewAssemblyRebuildTest.cs	Injects a ProjectReference to the test Library project and replaces Library.cs so the rebuild deterministically pulls in a new rooted assembly.
src/mono/wasm/testassets/EntryPoints/NativeRebuildReferencedLibrary.cs	New testasset snippet defining NewlyReferencedType, used as the “new assembly” signal.
src/mono/wasm/testassets/EntryPoints/NativeRebuildNewAssembly.cs	Switches the rebuilt entry point to call into NewlyReferencedType rather than crypto APIs.

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