[dotnet-linker] Use [DynamicDependency] attributes instead of manual marking when applying the [Preserve] attribute. by rolfbjarne · Pull Request #25001 · dotnet/macios

rolfbjarne · 2026-03-24T17:39:51Z

This makes it easier to move this code out of a custom linker step in the future.

This was simplified a bit because we already had code to do this, but it was only
in effect when using NativeAOT. Generalize it, move it out of the marking phase of
the linker, and run it before marking.

Also move the removal of any [Preserve] attributes to the RemoveAttributes step.

Contributes towards #17693.

Copilot

Pull request overview

This PR refactors how [Preserve] is handled in the dotnet linker pipeline by generating [DynamicDependency] attributes (so preservation intent is expressed in IL rather than via manual marking), aligning with the longer-term goal of reducing/removing custom linker steps (Issue #17693).

Changes:

Replaces the older ApplyPreserveAttribute implementation with a shared implementation (ApplyPreserveAttributeImpl) and introduces a new ApplyPreserveAttributeStep that emits [DynamicDependency] attributes before marking.
Refactors AssemblyModifierStep to support assembly-level modification hooks (ModifyAssembly) and ensures assemblies are only saved when modified.
Wires the new step into the build via MSBuild properties/step registration, and adds a link-context flag to prevent running both the old marking-based logic and the new dynamic-dependency logic.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tools/linker/ApplyPreserveAttribute.cs	Removes the legacy linker-step implementation.
tools/dotnet-linker/dotnet-linker.csproj	Drops compilation/linking of the removed legacy file.
tools/dotnet-linker/Steps/AssemblyModifierStep.cs	Introduces `ModifyAssembly` and seals `TryProcessAssembly` to standardize assembly-save behavior.
tools/dotnet-linker/ApplyPreserveAttributeStep.cs	New step that translates `[Preserve]` into `[DynamicDependency]` attributes pre-mark.
tools/dotnet-linker/ApplyPreserveAttributeBase.cs	Refactors into `ApplyPreserveAttribute` substep + shared `ApplyPreserveAttributeImpl` used by both approaches.
tools/dotnet-linker/AppBundleRewriter.cs	Exposes helpers used by the new step (`GetOrCreateStaticConstructor`, `AddAttributeOnlyOnce`).
tools/common/DerivedLinkContext.cs	Adds a flag to coordinate whether the new step ran.
dotnet/targets/Xamarin.Shared.Sdk.targets	Adds MSBuild property + registers `ApplyPreserveAttributeStep` before `MarkStep`.

tools/dotnet-linker/ApplyPreserveAttributeStep.cs

tools/dotnet-linker/ApplyPreserveAttributeBase.cs

…marking when applying the [Preserve] attribute. This makes it easier to move this code out of a custom linker step in the future. This was simplified a bit because we already had code to do this, but it was only in effect when using NativeAOT. Generalize it, move it out of the marking phase of the linker, and run it before marking. Also move the removal of any [Preserve] attributes to the RemoveAttributes step. Contributes towards #17693.

Copilot

Pull request overview

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

tools/dotnet-linker/ApplyPreserveAttributeBase.cs

vs-mobiletools-engineering-service2 · 2026-04-01T10:23:37Z

✅ [CI Build #d7fde5c] Build passed (Build packages) ✅

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Hash: d7fde5cb5006ae8399dbac4170e47a4d15cd01a4 [PR build]

vs-mobiletools-engineering-service2 · 2026-04-01T10:27:31Z

✅ [PR Build #d7fde5c] Build passed (Detect API changes) ✅

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Hash: d7fde5cb5006ae8399dbac4170e47a4d15cd01a4 [PR build]

vs-mobiletools-engineering-service2 · 2026-04-01T10:39:56Z

✅ API diff for current PR / commit

NET (empty diffs)

iOS: vsdrops gist ( No breaking changes )
tvOS: vsdrops gist ( No breaking changes )
MacCatalyst: vsdrops gist ( No breaking changes )
macOS: vsdrops gist ( No breaking changes )

✅ API diff vs stable

NET (empty diffs)

iOS: vsdrops gist ( No breaking changes )
tvOS: vsdrops gist ( No breaking changes )
MacCatalyst: vsdrops gist ( No breaking changes )
macOS: vsdrops gist ( No breaking changes )

ℹ️ Generator diff

Generator Diff: vsdrops (html) vsdrops (raw diff) gist (raw diff) - Please review changes)

Pipeline on Agent
Hash: d7fde5cb5006ae8399dbac4170e47a4d15cd01a4 [PR build]

vs-mobiletools-engineering-service2 · 2026-04-01T10:50:08Z

✅ [CI Build #d7fde5c] Build passed (Build macOS tests) ✅

Pipeline on Agent
Hash: d7fde5cb5006ae8399dbac4170e47a4d15cd01a4 [PR build]

vs-mobiletools-engineering-service2 · 2026-04-01T12:26:31Z

🔥 [CI Build #d7fde5c] Test results 🔥

Test results

❌ Tests failed on VSTS: test results

4 tests crashed, 1 tests failed, 139 tests passed.

Failures

❌ dotnettests tests (iOS)

🔥 Failed catastrophically on VSTS: test results - dotnettests_ios (no summary found).

Html Report (VSDrops) Download

❌ dotnettests tests (tvOS)

1 tests failed, 0 tests passed.

Failed tests

DotNet tests: Failed (Execution failed with exit code 1)
- Xamarin.Tests.DotNetProjectTest.LinkedWithNativeLibraries(TVOS,"...: Frameworks
  Expected: equivalent to < "/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation", "/System/Library/...

Html Report (VSDrops) Download

❌ monotouch tests (macOS)

🔥 Failed catastrophically on VSTS: test results - monotouch_macos (no summary found).

Html Report (VSDrops) Download

❌ msbuild tests

🔥 Failed catastrophically on VSTS: test results - msbuild (no summary found).

Html Report (VSDrops) Download

❌ sharpie tests

🔥 Failed catastrophically on VSTS: test results - sharpie (no summary found).

Html Report (VSDrops) Download

Successes

✅ cecil: All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests (MacCatalyst): All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests (macOS): All 1 tests passed. Html Report (VSDrops) Download
✅ dotnettests (Multiple platforms): All 1 tests passed. Html Report (VSDrops) Download
✅ framework: All 2 tests passed. Html Report (VSDrops) Download
✅ fsharp: All 4 tests passed. Html Report (VSDrops) Download
✅ generator: All 5 tests passed. Html Report (VSDrops) Download
✅ interdependent-binding-projects: All 4 tests passed. Html Report (VSDrops) Download
✅ introspection: All 6 tests passed. Html Report (VSDrops) Download
✅ linker: All 44 tests passed. Html Report (VSDrops) Download
✅ monotouch (iOS): All 11 tests passed. Html Report (VSDrops) Download
✅ monotouch (MacCatalyst): All 15 tests passed. Html Report (VSDrops) Download
✅ monotouch (tvOS): All 11 tests passed. Html Report (VSDrops) Download
✅ windows: All 3 tests passed. Html Report (VSDrops) Download
✅ xcframework: All 4 tests passed. Html Report (VSDrops) Download
✅ xtro: All 1 tests passed. Html Report (VSDrops) Download

macOS tests

✅ Tests on macOS Monterey (12): All 5 tests passed. Html Report (VSDrops) Download
✅ Tests on macOS Ventura (13): All 5 tests passed. Html Report (VSDrops) Download
✅ Tests on macOS Sonoma (14): All 5 tests passed. Html Report (VSDrops) Download
✅ Tests on macOS Sequoia (15): All 5 tests passed. Html Report (VSDrops) Download
✅ Tests on macOS Tahoe (26): All 5 tests passed. Html Report (VSDrops) Download

Linux Build Verification

✅ Linux build succeeded

Pipeline on Agent
Hash: d7fde5cb5006ae8399dbac4170e47a4d15cd01a4 [PR build]

rolfbjarne requested a review from Copilot March 24, 2026 17:39

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rolfbjarne force-pushed the dev/rolf/use-dynamic-dependency-attributes-applypreserveattribute branch from d09d3b4 to 81457b4 Compare March 24, 2026 18:56

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rolfbjarne force-pushed the dev/rolf/use-dynamic-dependency-attributes-optimizegeneratedcode branch from b6ae4b2 to a2d1483 Compare March 30, 2026 07:25

rolfbjarne force-pushed the dev/rolf/use-dynamic-dependency-attributes-applypreserveattribute branch from 4036efb to 9b7d008 Compare March 30, 2026 07:30

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rolfbjarne force-pushed the dev/rolf/use-dynamic-dependency-attributes-optimizegeneratedcode branch from a2d1483 to 723f6c9 Compare March 31, 2026 07:37

rolfbjarne force-pushed the dev/rolf/use-dynamic-dependency-attributes-applypreserveattribute branch from cade00a to d8b772e Compare March 31, 2026 10:55

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rolfbjarne marked this pull request as ready for review April 1, 2026 10:02

rolfbjarne force-pushed the dev/rolf/use-dynamic-dependency-attributes-applypreserveattribute branch from d8b772e to d7fde5c Compare April 1, 2026 10:02

rolfbjarne requested a review from dalexsoto as a code owner April 1, 2026 10:02

rolfbjarne changed the base branch from dev/rolf/use-dynamic-dependency-attributes-optimizegeneratedcode to main April 1, 2026 10:02

rolfbjarne requested a review from Copilot April 1, 2026 10:02

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vs-mobiletools-engineering-service2 commented Apr 1, 2026

✅ [CI Build #d7fde5c] Build passed (Build packages) ✅

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vs-mobiletools-engineering-service2 commented Apr 1, 2026

✅ [PR Build #d7fde5c] Build passed (Detect API changes) ✅

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vs-mobiletools-engineering-service2 commented Apr 1, 2026

✅ API diff for current PR / commit

✅ API diff vs stable

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vs-mobiletools-engineering-service2 commented Apr 1, 2026

✅ [CI Build #d7fde5c] Build passed (Build macOS tests) ✅

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vs-mobiletools-engineering-service2 commented Apr 1, 2026

🔥 [CI Build #d7fde5c] Test results 🔥

Test results

Failures

❌ dotnettests tests (iOS)

❌ dotnettests tests (tvOS)

Failed tests

❌ monotouch tests (macOS)

❌ msbuild tests

❌ sharpie tests

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macOS tests

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rolfbjarne commented Mar 24, 2026 •

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