hamarb123.Analyzers

A bunch of analysers I find useful - including a defensive copies analyser.

See Shipped Analysers on GitHub for the list of analysers included.

NuGet link:

Table Of Contents

• Configuration
• Defensive Copies Analysers (C# Only)
• Non-Ordinal String APIs Analyser
• Nullable If Analyser (VB.NET Only)

Configuration

You can use the MSBuild property Hamarb123AnalyzersDiagnosticsIncludeList to specify an include-list of analysers to run if that's your preference.

For example:

<Hamarb123AnalyzersDiagnosticsIncludeList>HAM0001;HAM0003</Hamarb123AnalyzersDiagnosticsIncludeList>

Defensive Copies Analysers (C# Only)

A defensive copy is something the C# compiler emits in some scenarios to ensure that readonly memory is not mutated.

For example:

class Class1
{
	//A defensive copy is emitted for field1 since we call a mutating method on readonly memory:
	public static int GetValue() => field1.Increment();
	private static readonly Struct1 field1;
}

struct Struct1
{
	private int i;
	public int Increment() => i++;
}

Analysers are included to catch where these occur:

• HAM0001 (warning) where it's meaningfully different behaviour.
• HAM0003 (info) where it's known to be only unnecessary.

Idea behind the below precise definition:

• I consider a defensive copy to basically be: whenever a copy is made as a result of memory not being mutable, that results in a meaningful behavioural difference (compared to if the memory was mutable).
• For classes, this is never the case, since this is not passed by-reference for them (therefore, whether a copy was made of this before calling is irrelevant).
• When calling members on structs cause a defensive copy to be made, there is a meaningful difference since this is passed by-reference, and therefore a different this is received.
• In practical terms though, members that are known to have readonly implementations on structs only cause an IL size and/or performance difference (hence why these are HAM0003 (info) instead of HAM0001 (warning)).

Precise definition of defensive copy (HAM0001):

• A copy of some readonly memory (LHS) is made, so a potentially mutating member (RHS) (which will be a method in IL) can be called.
  • This requires that wrapping Unsafe.AsRef around LHS would elide the copy (otherwise, it's not a defensive copy, just a copy), ignoring safety and issue of ref structs in generics for a moment.
• If call is on a guaranteed non-valuetype, then it's never a defensive copy (since call to method on defensive copy of class is not observable).
• If member implementation is known to be actually readonly (includes constrained implementations on known struct types that don't override it), then it is instead a HAM0003 defensive copy.
• "Actually readonly member" definition:
  • Based on metadata information only, no source info or special knowledge (other than what is guaranteed by runtime) is allowed.
  • Not marked readonly, or otherwise causes a defensive copy.
  • It must be possible to safely elide the defensive copy with Unsafe.AsRef (ignoring issue of ref structs in generics), when assuming that the memory location it's stored in is truly readonly.

Non-Ordinal String APIs Analyser

Some APIs on string do not use ordinal string comparison - this analyser (HAM0004) warns on those.

For example:

class Class1
{
	public bool M(string str)
	{
		//The following returns true for the empty string in latest .NET versions, even though it doesn't contain a null character - this API does not use ordinal string comparison by default.
		return str.EndsWith("\0");
	}
}

Nullable If Analyser (VB.NET Only)

In VB.NET, Boolean? can be used directly in If, ternary, etc. - this often leads to unexpected behaviour for those familiar with C# - this analyser (HAM0002) warns on those.

For example:

Class Class1
	Public Sub M1(str As String)
		If str?.GetHashCode() <> 0 Then
			'This branch is not taken when str is Nothing, even though `str?.GetHashCode()` looks like it should give `Nothing` which is indeed not `0`
		End If
	End Sub
End Class