[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). Allocations here 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<T> (even when there are no ConditionBaseAttribute present)
2. A LINQ GroupBy operator object

After:

Attribute[] attributes = ReflectHelper.Instance.GetCustomAttributesCached(type);

// Fast path: no ConditionBaseAttribute (common case) → zero allocations
bool hasConditionAttr = false;
foreach (Attribute attr in attributes)
{
    if (attr is ConditionBaseAttribute) { hasConditionAttr = true; break; }
}

if (!hasConditionAttr) { ignoreMessage = null; return false; }

// Uncommon path: manual grouping with lazy Dictionary allocation
Dictionary<string, (bool Satisfied, string? FirstIgnoreMessage)> groups = [];
// ...

Direct iteration over the cached Attribute[] — no iterator, no LINQ operator. The Dictionary is allocated only when a ConditionBaseAttribute is present (the uncommon case).

Performance Evidence

Methodology: Object allocation count per IsIgnored call.

Scenario	Before (objects)	After
No ConditionBaseAttribute (common)	1 yield iterator + 1 GroupBy operator	0
[Ignore] / condition attr present	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 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.

Closes #7992
Closes #7993

Generated by Daily Perf Improver · ● 1.8M · ◷

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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 25280157015 -n agent -D /tmp/agent-25280157015

# Create a new branch
git checkout -b perf-assist/eliminate-linq-allocations-isignored-aa25bab8269044b6

# Apply the patch (--3way handles cross-repo patches where files may already exist)
git am --3way /tmp/agent-25280157015/aw-perf-assist-eliminate-linq-allocations-isignored.patch

# Push the branch to origin
git push origin perf-assist/eliminate-linq-allocations-isignored-aa25bab8269044b6

# 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-aa25bab8269044b6 --repo microsoft/testfx

Show patch preview (104 of 104 lines)

From 2caeae545777a1528a63c8afb39e72a0b15cb0ea Mon Sep 17 00:00:00 2001
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Sun, 3 May 2026 13:21:00 +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),
the fast path exits with zero allocations. In the uncommon case (ConditionBaseAttribute
present), a Dictionary is allocated instead of a LINQ Lookup, which is
comparable or better.

Preserves semantics: OR within group, AND across groups, first ignore message
per unsatisfied group.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../Helpers/AttributeHelpers.cs               | 62 ++++++++++++++-----
 1 file changed, 46 insertions(+), 16 deletions(-)

diff --git a/src/Adapter/MSTestAdapter.PlatformServices/Helpers/AttributeHelpers.cs b/src/Adapter/MSTestAdapter.PlatformServices/Helpers/AttributeHelpers.cs
index a2bbcbe..59907e8 100644
--- a/src/Adapter/MSTestAdapter.PlatformServices/Helpers/AttributeHelpers.cs
+++ b/src/Adapter/MSTestAdapter.PlatformServices/Helpers/AttributeHelpers.cs
@@ -9,27 +9,57 @@ 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)
+        // Use GetCustomAttributesCached to avoid allocating a yield iterator and LINQ GroupBy operator.
+        // IsIgnored is called twic
... (truncated)