Allocations: Unroll AdditionalFile extension method

[martin-strecker-sonarsource]

Fixes #7440

Tested with Akka.Net in a dotnet build context in a SQ EE SonaryWay run.

This change safes

• 5GB of string allocations caused by calls to Path.GetFileName
• 3GB of delegate allocations for the FirstOrDefault lambda argument
• 1,1 GB for the capture class for the filename parameter.

The total memory allocations are down to 32,5 GB from 41,7GB = 9,2 GB savings (22%)

The number of issues reported stayed the same (3514 warnings).

Before

After

[martin-strecker-sonarsource]

There is a test case for this: The additional file ends with SonarLint.xml but is named FooBarSonarLint.xml.

sonar-dotnet/analyzers/tests/SonarAnalyzer.UnitTest/Common/AnalyzerConfigurationTest.cs

Lines 148 to 155 in be9ca30

	public void HotspotConfiguration_GivenDifferentFileName_WillNotFinishInitialization()
	{
	var sut = new HotspotConfiguration(ruleLoaderMock.Object);
	Initialize(sut, "FooBarSonarLint.xml", "fake SonarLintXml content");
	ruleLoaderMock.Verify(r => r.GetEnabledRules(It.IsAny<string>()), Times.Never);
	}

[martin-strecker-sonarsource]

We should not take any assumptions about the path separator because AdditionalFiles is just a csc.exe command line parameter that was calculated by MSBuild.

[martin-strecker-sonarsource]

Here is what Path.GetFileName does. The span is ToStringed by the method we call
https://github.com/dotnet/runtime/blob/2c4b4c0831d1d9f505ff5d3055c38bb41646021b/src/libraries/System.Private.CoreLib/src/System/IO/Path.cs#L236-L248

        public static ReadOnlySpan<char> GetFileName(ReadOnlySpan<char> path)
        {
            int root = GetPathRoot(path).Length;

            // We don't want to cut off "C:\file.txt:stream" (i.e. should be "file.txt:stream")
            // but we *do* want "C:Foo" => "Foo". This necessitates checking for the root.

            int i = PathInternal.DirectorySeparatorChar == PathInternal.AltDirectorySeparatorChar ?
                path.LastIndexOf(PathInternal.DirectorySeparatorChar) :
                path.LastIndexOfAny(PathInternal.DirectorySeparatorChar, PathInternal.AltDirectorySeparatorChar);

            return path.Slice(i < root ? root : i + 1);
        }

[cristian-ambrosini-sonarsource]

LGTM

[pavel-mikula-sonarsource]

LGTM conceptually. I've left some readability comments

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

100.0% Coverage
0.0% Duplication

[sharwell]

💡 We would typically document this in Roslyn with the following attribute on the method:

[PerformanceSensitive(
    "https://github.com/SonarSource/sonar-dotnet/issues/7440",
    AllowCaptures = false,
    AllowGenericEnumeration = false)]

[sharwell]

It should be possible to use this attribute if you install the Microsoft.CodeAnalysis.PerformanceSensitiveAnalyzers package

[sharwell]

Currently we don't have analyzer enforcement for the constraints of the attribute, but we hope to provide it in the future

[martin-strecker-sonarsource]

Thank you @sharwell for the hint.
I added #7690 to our backlog. We will discuss this internally.