[Perf Improver] perf: eliminate LINQ allocations in IsIgnored hot path

[Evangelink]

🤖 This PR was created by Perf Improver, an automated AI assistant focused on performance improvements.

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Goal and Rationale

Reduce heap allocations in AttributeExtensions.IsIgnored, which is called twice per test execution — once for the test class (ClassType.IsIgnored) and once for the test method (MethodInfo.IsIgnored). This means the allocations scale linearly with test count.

Approach

Before:

IEnumerable<ConditionBaseAttribute> attributes = ReflectHelper.Instance.GetAttributes<ConditionBaseAttribute>(type);
IEnumerable<IGrouping<string, ConditionBaseAttribute>> groups = attributes.GroupBy(attr => attr.GroupName);
foreach (IGrouping<string, ConditionBaseAttribute>? group in groups)
{
    // ...
}

Every call allocates:

1. A yield iterator state machine from GetAttributes<ConditionBaseAttribute> (even when there are no ConditionBaseAttribute present)
2. A LINQ GroupBy operator object

After:

Attribute[] attributes = ReflectHelper.Instance.GetCustomAttributesCached(type);
Dictionary<string, (bool Satisfied, string? FirstIgnoreMessage)>? groups = null;

foreach (Attribute attr in attributes)
{
    if (attr is not ConditionBaseAttribute condAttr) { continue; }
    // ... manual grouping, groups allocated lazily only if ConditionBaseAttribute found
}

Direct iteration of the cached Attribute[] — no iterator, no LINQ operator. The groups dictionary is allocated only when a ConditionBaseAttribute is present (the uncommon case). For most tests (no [Ignore], no OSCondition, etc.), zero allocations.

Performance Evidence

Methodology: Allocation count per IsIgnored call.

Scenario	Before (objects)	After
No ConditionBaseAttribute (common)	1 yield iterator + 1 GroupBy operator	0
[Ignore] present on class/method	1 yield iterator + LINQ Lookup internals	1 Dictionary
Per test execution (class + method)	~4 iterator/LINQ objects	0 (common case)

For a test suite with 1,000 tests: eliminates ~4,000 short-lived LINQ objects per run in the typical case.

Trade-offs

• Manual grouping logic is slightly more verbose, but follows the established allocation-free pattern used by GetTestPropertiesAsTraits and GetTestCategories in the same codebase.
• The Dictionary allocated in the uncommon case ([Ignore] present) replaces a LINQ Lookup<> — comparable or better allocation profile.
• Semantics are identical: OR within group, AND across groups, first non-null ignore message reported.

Reproducibility

export PATH="$PWD/.dotnet:$PATH"
dotnet restore src/Adapter/MSTestAdapter.PlatformServices/MSTestAdapter.PlatformServices.csproj -p:TargetFramework=net8.0
dotnet build src/Adapter/MSTestAdapter.PlatformServices/MSTestAdapter.PlatformServices.csproj -f net8.0 -warnaserror

Test Status

✅ MSTestAdapter.PlatformServices builds with 0 warnings, 0 errors on net8.0.

Note: MSTestAdapter.PlatformServices.UnitTests has a pre-existing build failure in this environment due to AwesomeAssertions 9.3.0 only shipping netstandard2.1 (no net8.0 folder). This is unrelated to these changes. CI will run the full test suite.

Generated by Daily Perf Improver · ● 4.7M · ◷

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Note

This was originally intended as a pull request, but the git push operation failed.

Workflow Run: View run details and download patch artifact

The patch file is available in the agent artifact in the workflow run linked above.

To create a pull request with the changes:

# Download the artifact from the workflow run
gh run download 25252726962 -n agent -D /tmp/agent-25252726962

# Create a new branch
git checkout -b perf-assist/eliminate-linq-allocations-isignored-99178773751016ab

# Apply the patch (--3way handles cross-repo patches where files may already exist)
git am --3way /tmp/agent-25252726962/aw-perf-assist-eliminate-linq-allocations-isignored.patch

# Push the branch to origin
git push origin perf-assist/eliminate-linq-allocations-isignored-99178773751016ab

# Create the pull request
gh pr create --title '[Perf Improver] perf: eliminate LINQ allocations in IsIgnored hot path' --base main --head perf-assist/eliminate-linq-allocations-isignored-99178773751016ab --repo microsoft/testfx

Show patch preview (108 of 108 lines)

From a459aafc2363c97afdc1b28e1b27eb887f34280c Mon Sep 17 00:00:00 2001
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Sat, 2 May 2026 13:26:23 +0000
Subject: [PATCH] perf: eliminate LINQ allocations in IsIgnored hot path

Replace GetAttributes<ConditionBaseAttribute> (yield iterator) + GroupBy
(LINQ operator) with direct iteration of GetCustomAttributesCached().

IsIgnored() is called twice per test execution - once for the test class,
once for the test method. In the common case (no ConditionBaseAttribute),
this eliminates 2+ heap allocations per call (4+ per test execution) with
no change in semantics.

The grouping logic is preserved:
- OR semantics within a group (same GroupName)
- AND semantics across groups (different GroupNames)
- First non-null ignore message reported for unsatisfied groups

Follows the established allocation-free pattern from GetTestPropertiesAsTraits
and other hot-path methods in ReflectHelper.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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 .../Helpers/AttributeHelpers.cs               | 60 ++++++++++++++-----
 1 file changed, 45 insertions(+), 15 deletions(-)

diff --git a/src/Adapter/MSTestAdapter.PlatformServices/Helpers/AttributeHelpers.cs b/src/Adapter/MSTestAdapter.PlatformServices/Helpers/AttributeHelpers.cs
index a2bbcbe..bc2cf5f 100644
--- a/src/Adapter/MSTestAdapter.PlatformServices/Helpers/AttributeHelpers.cs
+++ b/src/Adapter/MSTestAdapter.PlatformServices/Helpers/AttributeHelpers.cs
@@ -9,28 +9,58 @@ internal static class AttributeExtensions
 {
     public static bool IsIgnored(this ICustomAttributeProvider type, out string? ignoreMessage)
     {
-        IEnumerable<ConditionBaseAttribute> attributes = ReflectHelper.Instance.GetAttributes<ConditionBaseAttribute>(type);
-        IEnumerable<IGrouping<string, ConditionBaseAttribute>> groups = attributes.GroupBy(attr => attr.GroupName);
-        foreach (IGrouping<string, ConditionBaseAttribute>? group in groups)
+   
... (truncated)