[Trimming] Fix startup crash when TypeMapAssemblyTarget attribute survives but target assembly is fully trimmed by Copilot · Pull Request #130589 · dotnet/runtime

Copilot · 2026-07-12T21:51:19Z

In trimmed CoreCLR apps, a TypeMapAssemblyTarget attribute could survive trimming even when its named assembly was fully trimmed (all its TypeMap entries were conditional on trim targets that were never marked). At runtime, TypeMapLazyDictionary unconditionally calls Assembly.Load for every surviving attribute, crashing with FileNotFoundException.

Changes

Fix — ILLink TypeMapHandler.cs

TypeMapAssemblyTarget attributes are now only marked when their target assembly is also marked (has surviving entries or is otherwise kept).
Added _pendingAssemblyTargetsByAssembly: when a group is seen but the target assembly is not yet marked, the attribute is deferred here rather than immediately marked.
TriggerPendingAssemblyTargets() is internal and called only from MarkStep.MarkAssembly whenever an assembly is first marked — ensuring deferred attributes are flushed regardless of assembly visitation order.
A comment notes that this is a slight over-approximation: ideally the attribute would only be kept when the target assembly has a surviving TypeMapAttribute, but the added complexity is not justified for a narrow case.
If the target assembly can't be resolved in the linker input at all, the attribute is silently dropped (Assembly.Load would fail anyway).

Fix — MarkStep.cs

MarkAssembly calls _typeMapHandler.TriggerPendingAssemblyTargets(assembly) to flush any pending TypeMapAssemblyTarget attributes for the assembly being marked, regardless of the order in which TypeMap entries are visited.

Test

New test TypeMapAssemblyTargetRemovedWhenAllEntriesTrimmed with two dependency assemblies: a shared group-type assembly, and a conditional.dll with only conditional TypeMap entries (trim target never marked). Verifies via [RemovedAttributeInAssembly] and [RemovedAssembly] that the TypeMapAssemblyTarget attribute and the conditional assembly are both removed from the linked output.

…no surviving entries Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>

….cs and assemblynative.cpp Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>

AaronRobinsonMSFT · 2026-07-12T23:11:26Z

@copilot No changes should be done to CoreCLR itself. This is entirely a trimming issue. When the trimmer decides to remove a type based on the typemap reference algorithm, it should also remove the typemap attributes that reference it.

Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>

Copilot · 2026-07-12T23:15:16Z

@copilot No changes should be done to CoreCLR itself. This is entirely a trimming issue. When the trimmer decides to remove a type based on the typemap reference algorithm, it should also remove the t...

Reverted all changes to assemblynative.cpp in commit $(git rev-parse --short HEAD). The fix is now purely in the ILLink trimmer (TypeMapHandler.cs): TypeMapAssemblyTarget attributes are only marked when their target assembly has at least one surviving TypeMap/TypeMapAssociation entry, so dangling attributes are removed at trim time rather than relying on any CoreCLR defense.

@copilot No changes should be done to CoreCLR itself. This is entirely a trimming issue. When the trimmer decides to remove a type based on the typemap reference algorithm, it should also remove the t...

Reverted all changes to assemblynative.cpp in commit 516910c2. The fix is now purely in the ILLink trimmer (TypeMapHandler.cs): TypeMapAssemblyTarget attributes are only marked when their target assembly has at least one surviving TypeMap/TypeMapAssociation entry, so dangling attributes are removed at trim time rather than relying on any CoreCLR defense.

dotnet-policy-service · 2026-07-13T00:24:47Z

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Copilot

Pull request overview

This PR updates ILLink’s type map handling to avoid keeping TypeMapAssemblyTargetAttribute<TGroup> metadata that can reference assemblies which end up not being present after trimming, and adds a new regression test case in the linker test suite.

Changes:

Update TypeMapHandler to defer marking TypeMapAssemblyTarget attributes until the referenced target assembly is known to be kept (or drop the attribute if the assembly can’t be resolved in linker input).
Add a new linker test plus two dependency assemblies to cover the “all TypeMap entries trimmed away” scenario.

Show a summary per file

File	Description
src/tools/illink/src/linker/Linker/TypeMapHandler.cs	Adds deferral/flush mechanism for `TypeMapAssemblyTarget` marking, keyed by resolved target assembly.
src/tools/illink/test/Mono.Linker.Tests.Cases/Reflection/TypeMapAssemblyTargetRemovedWhenAllEntriesTrimmed.cs	New test case intended to validate removal of a dangling `TypeMapAssemblyTarget` attribute.
src/tools/illink/test/Mono.Linker.Tests.Cases/Reflection/Dependencies/TypeMapAllConditionalGroupDep.cs	New dependency assembly containing a group marker type for the test.
src/tools/illink/test/Mono.Linker.Tests.Cases/Reflection/Dependencies/TypeMapAllConditionalEntriesDep.cs	New dependency assembly containing only conditional TypeMap entries.

Copilot's findings

Files reviewed: 4/4 changed files
Comments generated: 1

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

+            if (_context.Annotations.IsMarked(targetAssembly))
+            {
+                // Target assembly is already in the output because it has surviving TypeMap entries.
+                MarkTypeMapAttribute(entry, new DependencyInfo(DependencyKind.TypeMapAssemblyTarget, callingMethod));
+            }


… MarkStep Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

Copilot · 2026-07-13T17:08:47Z

@copilot Please update the PR description to reflect the current changes in this PR.

Updated. The current PR description now reflects the actual changes:

Fix — ILLink TypeMapHandler.cs (only change in this PR)

TypeMapAssemblyTarget attributes are now only marked when their target assembly is also marked (has surviving TypeMap/TypeMapAssociation entries or is otherwise kept).
_pendingAssemblyTargetsByAssembly: when a group is seen but the target assembly has no surviving entries yet, the attribute is deferred here rather than immediately marked.
TriggerPendingAssemblyTargets() is now internal and called from two sites to avoid ordering-dependent behavior: (1) from MarkTypeMapAttribute whenever a TypeMap/TypeMapAssociation entry is marked, and (2) from MarkStep.MarkAssembly whenever an assembly is first marked, ensuring deferred attributes are flushed regardless of visitation order.
If the target assembly can't be resolved in the linker input at all, the attribute is silently dropped.

Test

TypeMapAssemblyTargetRemovedWhenAllEntriesTrimmed: two dependency assemblies (a shared group-type assembly and a conditional.dll with only conditional TypeMap entries whose trim target is never marked). Verifies the TypeMapAssemblyTarget attribute is removed from the main assembly after linking.

(No CoreCLR changes — the previous assemblynative.cpp change was reverted.)

…ttribute, update comment Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

Initial plan

c30fd11

Copilot AI assigned Copilot and AaronRobinsonMSFT Jul 12, 2026

Copilot AI requested review from Copilot and removed request for Copilot July 12, 2026 21:51

github-project-automation Bot added this to AppModel Jul 12, 2026

Copilot AI linked an issue Jul 12, 2026 that may be closed by this pull request

[Trimming] Startup crash when TypeMapAssemblyTarget attribute kept but target assembly trimmed #130587

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Copilot started work on behalf of AaronRobinsonMSFT July 12, 2026 21:51 View session

github-actions Bot added the area-AssemblyLoader-coreclr only use for closed issues label Jul 12, 2026

Fix TypeMapAssemblyTarget attribute removal when target assembly has …

dcf1d89

…no surviving entries Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>

Copilot AI requested review from Copilot and removed request for Copilot July 12, 2026 22:23

dotnet-policy-service Bot added the linkable-framework Issues associated with delivering a linker friendly framework label Jul 12, 2026

Address code review: rename param, improve comments in TypeMapHandler…

2c9bb9f

….cs and assemblynative.cpp Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>

Copilot AI requested review from Copilot and removed request for Copilot July 12, 2026 22:27

Copilot AI changed the title ~~[WIP] Fix startup crash caused by TypeMapAssemblyTarget attribute~~ [Trimming] Fix startup crash when TypeMapAssemblyTarget attribute survives but target assembly is fully trimmed Jul 12, 2026

Copilot AI requested a review from AaronRobinsonMSFT July 12, 2026 22:28

Copilot finished work on behalf of AaronRobinsonMSFT July 12, 2026 22:28

Copilot AI temporarily deployed to copilot-pat-pool July 12, 2026 23:09 Inactive

Copilot started work on behalf of AaronRobinsonMSFT July 12, 2026 23:12 View session

Revert CoreCLR assemblynative.cpp changes - fix is trimmer-only

516910c

Co-authored-by: AaronRobinsonMSFT <30635565+AaronRobinsonMSFT@users.noreply.github.com>

Copilot AI requested review from Copilot and removed request for Copilot July 12, 2026 23:15

Copilot finished work on behalf of AaronRobinsonMSFT July 12, 2026 23:15

AaronRobinsonMSFT requested review from MichalStrehovsky and jtschuster July 12, 2026 23:20

jkotas removed the area-AssemblyLoader-coreclr only use for closed issues label Jul 13, 2026

This was referenced Jul 13, 2026

Unable to pull image from mcr.microsoft.com #117164

Open

Wasm.Build.NativeRebuild.Tests.ReferenceNewAssemblyRebuildTest.ReferenceNewAssembly failure: Expected changed file: driver-gen.c #130540

Open

AaronRobinsonMSFT marked this pull request as ready for review July 13, 2026 15:54

AaronRobinsonMSFT requested a review from sbomer as a code owner July 13, 2026 15:54

Copilot AI review requested due to automatic review settings July 13, 2026 15:54

Copilot started reviewing on behalf of AaronRobinsonMSFT July 13, 2026 15:54 View session

Copilot AI reviewed Jul 13, 2026

View reviewed changes

Comment thread ...test/Mono.Linker.Tests.Cases/Reflection/TypeMapAssemblyTargetRemovedWhenAllEntriesTrimmed.cs

jtschuster reviewed Jul 13, 2026

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Comment thread src/tools/illink/src/linker/Linker/TypeMapHandler.cs

Potential fix for pull request finding

1a5f5d0

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings July 13, 2026 16:47

jtschuster temporarily deployed to copilot-pat-pool July 13, 2026 16:47 — with GitHub Actions Inactive

Copilot started reviewing on behalf of jtschuster July 13, 2026 16:47 View session

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Copilot started work on behalf of jtschuster July 13, 2026 16:54 View session

Fix ordering: call TriggerPendingAssemblyTargets from MarkAssembly in…

27cd6c1

… MarkStep Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

Copilot AI requested review from Copilot and removed request for Copilot July 13, 2026 17:08

Copilot finished work on behalf of jtschuster July 13, 2026 17:09

Copilot AI requested a review from jtschuster July 13, 2026 17:09

jtschuster reviewed Jul 13, 2026

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Comment thread src/tools/illink/src/linker/Linker/TypeMapHandler.cs Outdated

Copilot started work on behalf of jtschuster July 13, 2026 18:19 View session

Remove redundant TriggerPendingAssemblyTargets call from MarkTypeMapA…

0d63a40

…ttribute, update comment Co-authored-by: jtschuster <36744439+jtschuster@users.noreply.github.com>

Copilot AI requested review from Copilot and removed request for Copilot July 13, 2026 18:28

Copilot finished work on behalf of jtschuster July 13, 2026 18:29

Copilot AI requested a review from jtschuster July 13, 2026 18:29

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[Trimming] Fix startup crash when TypeMapAssemblyTarget attribute survives but target assembly is fully trimmed#130589

[Trimming] Fix startup crash when TypeMapAssemblyTarget attribute survives but target assembly is fully trimmed#130589
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