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.

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.

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.

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.

MichalStrehovsky · 2026-04-30T08:41:27Z

+            CustomAttributeValue<TypeDesc> decodedValue,
+            CustomAttributeTypeNameFormatter formatter)
+        {
+            var blobBuilder = new BlobBuilder();


@copilot change the custom attribute encoding logic in this file to use BlobEncoder.CustomAttributeNamedArgumentsEncoder APIs. Use the BlobBuilder that is provided by writeContext.GetSharedBlobBuilder. Follow the existing patterns that the other callers of writeContext.GetSharedBlobBuilder use (the rewriter just returns void, writes to the provided BlobBuilder, do not materialize array).

Done in da3465b. Refactored to use BlobEncoder.CustomAttributeSignature with FixedArgumentsEncoder / CustomAttributeNamedArgumentsEncoder, NamedArgumentTypeEncoder, CustomAttributeElementTypeEncoder, LiteralEncoder, ScalarEncoder, etc. Uses writeContext.GetSharedBlobBuilder() following the established pattern — the rewriter is now void and writes directly to the shared BlobBuilder, no array materialization.

… 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>

MichalStrehovsky · 2026-04-30T11:59:06Z

+            bool needsRewrite = false;
+            CheckArgumentsForRewrite(decodedValue, ref needsRewrite);
+
+            if (!needsRewrite)
+            {
+                blobBuilder.WriteBytes(_module.MetadataReader.GetBlobBytes(customAttribute.Value));
+                return;
+            }


@copilot this optimization is premature, we should rewrite always, this will just make the rewriting logic run rarely and hide bugs

Removed the CheckArgumentsForRewrite/CheckArgumentValueForRewrite optimization in 20a8fef. The blob is now always re-encoded through the EncodeCustomAttributeBlob path.

…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>

MichalStrehovsky · 2026-05-01T11:14:10Z

+            if (argType.IsObject)
+            {
+                type.Object();
+                return;


@copilot The methods in this file have many return statements. Use cascading if/else if/else instead.

Replaced early returns with cascading if/else if/else in EncodeNamedArgumentType, WriteLiteralValue, and WriteScalarValue in 229cd7f2.

MichalStrehovsky · 2026-05-01T11:16:17Z

+            if (type.IsEnum)
+            {
+                encoder.Enum(formatter.FormatName(type, true));
+                return;
+            }
+
+            if (IsSystemType(type))
+            {
+                encoder.SystemType();
+                return;
+            }
+
+            switch (type.UnderlyingType.Category)


@copilot Make the switch over type.Category and handle IsEnum and System.Type in the default case.

Switched to type.Category and moved IsEnum/IsSystemType/IsString handling into the default case in 229cd7f2.

…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>

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

Copilot AI assigned Copilot and MichalStrehovsky Apr 30, 2026

Copilot AI requested review from Copilot and removed request for Copilot April 30, 2026 05:21

Copilot created this pull request from a session on behalf of MichalStrehovsky April 30, 2026 05:21 View session

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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Parse custom attribute value blobs for dependencies and rewrite type name strings in ILTrim#127596

Parse custom attribute value blobs for dependencies and rewrite type name strings in ILTrim#127596
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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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Copilot AI commented Apr 30, 2026 •

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Dependency analysis (`GetStaticDependencies`)

Blob rewriting (`WriteInternal`)