Parse custom attribute value blobs for dependencies and rewrite type name strings in ILTrim by Copilot · Pull Request #127596 · dotnet/runtime

Copilot · 2026-04-30T05:21:33Z

Description

CustomAttributeNode had two TODOs: it wasn't parsing the custom attribute value blob for dependencies, and it wasn't rewriting type name strings that could become stale after trimming removes type forwarders.

Dependency analysis (`GetStaticDependencies`)

Decodes the custom attribute blob via CustomAttributeTypeProvider and reports dependencies for:

typeof() arguments
Enum types (needed for boxing)
Property setters and fields referenced in named arguments
Non-primitive array element types

Follows the same pattern as CustomAttributeBasedDependencyAlgorithm in ILCompiler. All dependency helper methods accept a DependencyList parameter and use .Add() directly, avoiding yield return and IEnumerable overhead. GetStaticDependencies creates and returns the populated DependencyList. The unnecessary customAttribute.Constructor.IsNil guard has been removed since custom attributes always have a constructor. Dependency blob parsing and named argument handling are inlined directly into GetStaticDependencies rather than delegated to standalone methods. Constructor resolution uses TryGetMethod (backed by GetObject(handle, NotFoundBehavior.ReturnNull)) instead of try/catch.

Blob rewriting (`WriteInternal`)

Always re-encodes the blob using BlobEncoder.CustomAttributeSignature with FixedArgumentsEncoder and CustomAttributeNamedArgumentsEncoder APIs to resolve type name strings to their definitions. Uses writeContext.GetSharedBlobBuilder() following the established pattern of other callers — the rewriter writes directly to the provided BlobBuilder without materializing an intermediate array. The blob is unconditionally re-encoded (no early-out optimization) to ensure the encoding logic is always exercised and bugs are not hidden. The encoding logic is inlined directly into RewriteCustomAttributeBlob rather than delegated to a standalone method. Constructor resolution uses TryGetMethod instead of try/catch.

This handles the case where trimming drops type forwarders — e.g. typeof(object) stored as System.Object, System.Runtime gets re-encoded as System.Object, System.Private.CoreLib via CustomAttributeTypeNameFormatter.

Code style

Methods use cascading if/else if/else instead of early return statements.
EncodeElementType switches on type.Category and handles IsEnum and System.Type in the default case, rather than checking them before the switch.
Exception handling uses catch (Exception ex) when (ex is TypeSystemException or BadImageFormatException) to collapse multiple catch blocks.

Test results

24 previously-expected-failing tests now pass and have been removed from ILTrimExpectedFailures.txt (382 passed, 0 failed).

…ame strings Implement custom attribute blob parsing in CustomAttributeNode: 1. GetStaticDependencies now decodes the custom attribute value blob and reports dependencies for typeof() arguments, enum types, property setters, and fields referenced in the blob. 2. WriteInternal now re-encodes the blob with type name strings resolved to their definitions, handling cases where trimming drops type forwarders (e.g. re-encoding "System.Object, System.Runtime" to "System.Object, System.Private.CoreLib"). Remove 24 tests from ILTrimExpectedFailures.txt that now pass. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/f4173cc7-fd45-4a62-9a1c-1a31c06cc85b Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

… remove unused parameter - Catch TypeSystemException and BadImageFormatException instead of base Exception - Add DependencyNode type alias to reduce verbose fully-qualified type names - Remove unused isFixedArg parameter from WriteArgumentValue - Hoist constructor resolution out of named argument loop - Fix duplicate CustomAttributeTypeNameFormatter allocations Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/f4173cc7-fd45-4a62-9a1c-1a31c06cc85b Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

dotnet-policy-service · 2026-04-30T05:48:50Z

Tagging subscribers to this area: @agocke, @dotnet/illink
See info in area-owners.md if you want to be subscribed.

… BlobBuilder Use BlobEncoder.CustomAttributeSignature with FixedArgumentsEncoder and CustomAttributeNamedArgumentsEncoder instead of manual byte writing. Use writeContext.GetSharedBlobBuilder() following established patterns. Removed byte[] materialization - writes directly to shared BlobBuilder. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/d078b767-9d76-41e5-9168-8f6651786108 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

…bute blobs Remove CheckArgumentsForRewrite/CheckArgumentValueForRewrite that skipped rewriting when no typeof() references were found. Always rewrite to exercise the encoding logic and surface bugs. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/46e2e54d-5313-4538-8274-c5cfe241e547 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

…pe.Category - Replace early returns with cascading if/else if/else in EncodeNamedArgumentType, WriteLiteralValue, and WriteScalarValue. - Switch on type.Category instead of type.UnderlyingType.Category in EncodeElementType, handling IsEnum and System.Type in the default case. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/683a21bb-4e07-4219-81e8-b0a320967bd3 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

MichalStrehovsky · 2026-05-04T00:57:32Z

@@ -61,7 +68,154 @@ public override IEnumerable<DependencyListEntry> GetStaticDependencies(NodeFacto
            if (!customAttribute.Constructor.IsNil)


@copilot this customAttribute.Constructor.IsNil is never true, we can remove that. Custom attributes always depend on the attribute constructor at minimum.

Removed the Constructor.IsNil guard in 48062a1.

MichalStrehovsky · 2026-05-04T00:57:35Z

+            foreach (CustomAttributeTypedArgument<TypeDesc> fixedArg in value.FixedArguments)
+            {
+                foreach (var entry in GetDependenciesFromCustomAttributeArgument(factory, fixedArg.Type, fixedArg.Value))
+                    yield return entry;


@copilot this still has too many yield return iterating values obtained from elsewhere. Rewrite all the methods here to accept a DependencyList parameter and simply .Add the results to the DependencyList. Change IEnumerable<DependencyListEntry> GetStaticDependencies(NodeFactory factory) to simply return the DepednecyList that we populated.

Rewritten in 48062a1. All dependency helper methods now accept a DependencyList parameter and use .Add() directly. GetStaticDependencies creates and returns the DependencyList.

…endencyList with .Add - Remove unnecessary `customAttribute.Constructor.IsNil` guard since custom attributes always have a constructor. - Rewrite GetStaticDependencies to return a DependencyList populated via .Add. - Convert all helper methods (GetDependenciesFromCustomAttributeBlob, GetDependenciesFromCustomAttributeArgument, GetDependenciesFromPropertySetter, GetDependenciesFromField) to accept a DependencyList parameter and .Add directly, eliminating yield return and IEnumerable overhead. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/f59c4055-f47c-4e90-9a3e-b04855a33de1 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

MichalStrehovsky · 2026-05-04T02:35:07Z

+            {
+                decodedValue = customAttribute.DecodeValue(new CustomAttributeTypeProvider(_module));
+            }
+            catch (TypeSystemException)


@copilot collapse this into catch (Exception ex) when (ex is TypeSystemException or BadImageFormatException) and do the same for the catch below.

Done in a102e20. Both catch blocks (in GetStaticDependencies and RewriteCustomAttributeBlob) now use catch (Exception ex) when (ex is TypeSystemException or BadImageFormatException).

MichalStrehovsky · 2026-05-04T02:35:38Z

+                return dependencies;
+            }
+
+            GetDependenciesFromCustomAttributeBlob(dependencies, factory, decodedValue);


@copilot inline the method into here, we don't need a standalone method.

Inlined in a102e20.

MichalStrehovsky · 2026-05-04T02:36:45Z

+                return;
+            }
+
+            EncodeCustomAttributeBlob(customAttribute, decodedValue, blobBuilder);


@copilot inline the method into here, we don't need a standalone method.

Inlined in a102e20.

MichalStrehovsky · 2026-05-04T02:38:49Z

+            MethodDesc constructor;
+            try
+            {
+                constructor = _module.GetMethod(customAttribute.Constructor);


@copilot use GetObject(handle, NotFoundBehavior.ReturnNull) as MethodDesc so that we don't need a try/catch.

Done in a102e20. Using _module.TryGetMethod(customAttribute.Constructor) which calls GetObject(handle, NotFoundBehavior.ReturnNull) as MethodDesc under the hood.

- Collapse separate TypeSystemException/BadImageFormatException catch blocks into single `catch (Exception ex) when (ex is ... or ...)` in both GetStaticDependencies and RewriteCustomAttributeBlob. - Inline GetDependenciesFromCustomAttributeBlob into GetStaticDependencies. - Inline EncodeCustomAttributeBlob into RewriteCustomAttributeBlob. - Use _module.TryGetMethod (GetObject with NotFoundBehavior.ReturnNull) instead of try/catch for constructor resolution. Agent-Logs-Url: https://github.com/dotnet/runtime/sessions/93abc623-385e-4d42-a955-f61dd8eab979 Co-authored-by: MichalStrehovsky <13110571+MichalStrehovsky@users.noreply.github.com>

Copilot AI and others added 2 commits April 30, 2026 04:17

Copilot AI assigned Copilot and MichalStrehovsky Apr 30, 2026

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github-actions Bot added the area-NativeAOT-coreclr label Apr 30, 2026

MichalStrehovsky added area-Tools-ILLink .NET linker development as well as trimming analyzers and removed area-NativeAOT-coreclr labels Apr 30, 2026

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build-analysis Bot mentioned this pull request Apr 30, 2026

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

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This was referenced May 1, 2026

slow macOS - "##[error]The job running on agent Azure Pipelines 9 ran longer than the maximum time of 60 minutes." dotnet/dnceng#1883

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The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

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		@@ -61,7 +68,154 @@ public override IEnumerable<DependencyListEntry> GetStaticDependencies(NodeFacto
		if (!customAttribute.Constructor.IsNil)

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Copilot AI commented Apr 30, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Description

Dependency analysis (GetStaticDependencies)

Blob rewriting (WriteInternal)

Code style

Test results

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dotnet-policy-service Bot commented Apr 30, 2026

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Copilot AI commented Apr 30, 2026 •

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Dependency analysis (`GetStaticDependencies`)

Blob rewriting (`WriteInternal`)