feat: add FFS0049 — detect unpermitted SuppressMessage attributes by Copilot · Pull Request #422 · funfair-tech/funfair-server-code-analysis

Copilot · 2026-05-10T21:50:14Z

[SuppressMessage] could be used freely on any member as long as it had a Justification, with no enforcement of which warnings are permitted to be suppressed.

Changes

New rule FFS0049 (SuppressMessage is not permitted for '{checkId}'): fires when [SuppressMessage] is used for a (category, checkId) not in an explicit allowlist
Check order: FFS0049 fires first and short-circuits — justification checks (FFS0027/FFS0042) are skipped for unauthorized suppressions since they're moot
AllowedSuppression type: each entry carries Category, CheckIdPrefix, and a WhenAllowed predicate receiving the full SyntaxNodeAnalysisContext, enabling location-aware conditions

Initial allowlist entry

RCS1231 (Roslynator.Analyzers) is permitted only when the suppressed method has a params ReadOnlySpan<T> parameter — the one case where the analyzer fires incorrectly (you can't make a params span ref-readonly):

// ✅ Permitted — params ReadOnlySpan<T> cannot be ref read-only
[SuppressMessage(category: "Roslynator.Analyzers", checkId: "RCS1231: Spans should be ref read-only",
    Justification = "Except when they're in a params parameter")]
private static IReadOnlyList<string> GetFiles(params ReadOnlySpan<string> searchPatterns) { … }

// ❌ FFS0049 — RCS1231 not permitted on a regular method
[SuppressMessage(category: "Roslynator.Analyzers", checkId: "RCS1231", Justification = "Because")]
public static void DoIt(ReadOnlySpan<string> items) { … }

// ❌ FFS0049 — unknown suppression
[SuppressMessage("Example", "ExampleCheckId", Justification = "Because I said so")]
public void DoIt() { … }

Extending the allowlist requires adding a single AllowedSuppression entry to AllowedSuppressions. CheckId prefix matching handles both short form ("RCS1231") and description form ("RCS1231: Spans should be ref read-only"), using case-sensitive ordinal comparison.

credfeto · 2026-05-11T14:30:49Z

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Pull request overview

Adds a new analyzer rule (FFS0049) to restrict [SuppressMessage] usage to an explicit allowlist, making unauthorized suppressions fail fast before justification-related checks run.

Changes:

Introduces FFS0049 (SuppressMessage is not permitted for '{checkId}') and short-circuits further suppression validation when a suppression is not allowlisted.
Adds an allowlist mechanism (AllowedSuppressions) supporting (category, checkIdPrefix) matching plus a context-aware WhenAllowed predicate.
Updates unit tests to expect FFS0049 for non-allowlisted suppressions and to validate the initial allowlisted Roslynator case.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/FunFair.CodeAnalysis/SuppressMessageDiagnosticsAnalyzer.cs	Adds FFS0049, allowlist/predicate evaluation, and early-return behavior before justification checks.
src/FunFair.CodeAnalysis/Helpers/Rules.cs	Adds the new rule ID constant `FFS0049`.
src/FunFair.CodeAnalysis.Tests/SuppressMessageDiagnosticsAnalyzerTests.cs	Updates existing tests for new behavior and adds coverage for allowlisted vs non-allowlisted suppressions.

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+                    p.Modifiers.Any(m => m.IsKind(SyntaxKind.ParamsKeyword)) && IsReadOnlySpanType(p.Type)
+                );
+            }
+        ),
+    ];
+
+    private static bool IsReadOnlySpanType(TypeSyntax? type)
+    {
+        return type switch
+        {
+            GenericNameSyntax generic =>
+                StringComparer.Ordinal.Equals(x: generic.Identifier.Text, y: "ReadOnlySpan"),
+            QualifiedNameSyntax { Right: GenericNameSyntax rightGeneric } =>
+                StringComparer.Ordinal.Equals(x: rightGeneric.Identifier.Text, y: "ReadOnlySpan"),
+            _ => false,
+        };


+                attributeSyntax.ReportDiagnostics(
+                    syntaxNodeAnalysisContext: syntaxNodeAnalysisContext,
+                    rule: RuleNotPermitted,
+                    checkId ?? string.Empty


+            if (named?.Expression is LiteralExpressionSyntax namedLit)
+            {
+                return namedLit.Token.ValueText;
+            }


+            if (positional?.Expression is LiteralExpressionSyntax posLit)
+            {
+                return posLit.Token.ValueText;
+            }


credfeto · 2026-05-11T14:36:22Z

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credfeto · 2026-05-12T09:08:36Z

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Agent-Logs-Url: https://github.com/funfair-tech/funfair-server-code-analysis/sessions/fa2d4473-ba67-4ec5-8d3f-1470d8c494e1 Co-authored-by: credfeto <1020430+credfeto@users.noreply.github.com>

…ing in FFS0049 Agent-Logs-Url: https://github.com/funfair-tech/funfair-server-code-analysis/sessions/fa2d4473-ba67-4ec5-8d3f-1470d8c494e1 Co-authored-by: credfeto <1020430+credfeto@users.noreply.github.com>

… in FFS0049 Prompt: can you whitelist this rule so its allowed anywhere: [SuppressMessage(category: "Nullable.Extended.Analyzer", checkId: "NX0001: Suppression of NullForgiving operator is not required", Justification = "Required here")]

…e SuppressMessage

…hods and classes Prompt: any method with the Benchmark attribute is allowed to suppress [SuppressMessage(category: "codecracker.CSharp", checkId: "CC0091:MarkMembersAsStatic", Justification = "Benchmark")] [SuppressMessage(category: "Microsoft.Performance", checkId: "CA1822:MarkMembersAsStatic", Justification = "Benchmark")] and any class that has methods with Benchmark attribute on them are allowed [SuppressMessage(category: "FunFair.CodeAnalysis", checkId: "FFS0012: Make sealed static or abstract", Justification = "Benchmark")]

credfeto · 2026-05-13T15:14:10Z

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- Added FFS0049, NX0001, CC0091/CA1822/FFS0012 entries to CHANGELOG - Fixed Ordinal comparison entry in CHANGELOG - Updated solution to include .editorconfig and .globalconfig; removed CodeAnalysis.ruleset Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

credfeto · 2026-05-13T15:24:43Z

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- IsReadOnlySpanType now uses semantic model (GetTypeInfo) to verify System.ReadOnlySpan`1 instead of syntax identifier text matching - GetStringAttributeArgument now uses SemanticModel.GetConstantValue so const fields and nameof() expressions are correctly resolved - Fallback checkId in FFS0049 diagnostic changed from empty string to '<unknown>' for clearer error messages Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

credfeto · 2026-05-13T15:29:49Z

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…icsAnalyzer - Extract GetStringAttributeArgument to AttributeArgumentHelpers.GetStringArgument as a reusable helper for any analyzer needing to read attribute argument values - Simplify IsReadOnlySpanType to use ToFullyQualifiedName() from TypeSymbolHelpers instead of two separate MetadataName + namespace checks - Cache SupportedDiagnostics in SupportedDiagnosticsCache static field, consistent with other multi-rule analyzers in the project Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Baseline (net9.0 Release): - NoSuppressionAsync: 560 B - AllowedSuppressionAsync: 560 B - DisallowedSuppressionAsync: 592 B Thresholds set at 1024 B (~1.8x headroom). Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

credfeto · 2026-05-13T16:14:28Z

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Copilot AI assigned Copilot and credfeto May 10, 2026

Copilot started work on behalf of credfeto May 10, 2026 21:50 View session

Copilot AI linked an issue May 10, 2026 that may be closed by this pull request

feat: add analyzer to detect and flag SuppressMessage attributes #420

Closed

Copilot AI changed the title ~~[WIP] Add Roslyn analyzer to detect and flag SuppressMessage attributes~~ feat: add FFS0049 — detect unpermitted SuppressMessage attributes May 10, 2026

Copilot AI requested a review from credfeto May 10, 2026 22:14

Copilot finished work on behalf of credfeto May 10, 2026 22:14

credfeto approved these changes May 11, 2026

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credfeto marked this pull request as ready for review May 11, 2026 14:24

credfeto requested a review from a team as a code owner May 11, 2026 14:24

Copilot AI review requested due to automatic review settings May 11, 2026 14:24

Copilot started reviewing on behalf of credfeto May 11, 2026 14:29 View session

credfeto force-pushed the copilot/add-analyzer-detect-suppressmessage-attributes branch from bcec434 to ce6dc65 Compare May 11, 2026 14:30

Copilot AI reviewed May 11, 2026

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Copilot AI and others added 5 commits May 13, 2026 16:13

feat: add FFS0049 rule to flag unpermitted SuppressMessage attributes

2eafb0e

Agent-Logs-Url: https://github.com/funfair-tech/funfair-server-code-analysis/sessions/fa2d4473-ba67-4ec5-8d3f-1470d8c494e1 Co-authored-by: credfeto <1020430+credfeto@users.noreply.github.com>

fix: use Ordinal (case-sensitive) comparison for checkId prefix match…

eb805e3

…ing in FFS0049 Agent-Logs-Url: https://github.com/funfair-tech/funfair-server-code-analysis/sessions/fa2d4473-ba67-4ec5-8d3f-1470d8c494e1 Co-authored-by: credfeto <1020430+credfeto@users.noreply.github.com>

refactor: convert EnumExtensions to file-scoped class with single-lin…

3283903

…e SuppressMessage

credfeto force-pushed the copilot/add-analyzer-detect-suppressmessage-attributes branch from 3c601be to 9380561 Compare May 13, 2026 15:13

credfeto and others added 2 commits May 13, 2026 16:35

credfeto merged commit 8a3fba8 into main May 13, 2026
24 checks passed

credfeto deleted the copilot/add-analyzer-detect-suppressmessage-attributes branch May 13, 2026 17:58

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feat: add FFS0049 — detect unpermitted SuppressMessage attributes#422

feat: add FFS0049 — detect unpermitted SuppressMessage attributes#422
credfeto merged 9 commits into
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Initial allowlist entry

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Copilot AI commented May 10, 2026 •

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