ShouldBeOneOf lost its params in v5 — variadic call sites fail to compile (CS1503) #1277

Summary

In v5, ShouldBeOneOf lost its params modifier, so the idiomatic actual.ShouldBeOneOf(a, b, c) call no longer compiles (CS1503). This is a source-breaking change for essentially every existing consumer of ShouldBeOneOf, and it isn't mentioned in the 4 → 5 migration guide.

Found while dogfooding 5.0.0-preview.2 against real repositories.

Details

v4.x signature (variadic):

public static void ShouldBeOneOf<T>(this T actual, params T[] expected)

v5 signature (src/Shouldly/ShouldlyExtensionMethods/ShouldBeRangeTestExtensions.cs) — params dropped, presumably to make room for the customMessage overloads:

public static void ShouldBeOneOf<T>(this T? actual, T[] expected, string? customMessage = null, ...)
public static void ShouldBeOneOf<T>(this T? actual, T[] expected, IEqualityComparer<T> comparer, string? customMessage = null, ...)

Because params is gone, any call that passes individual values fails:

result.ShouldBeOneOf(Status.A, Status.B, Status.C);
// error CS1503: Argument 2: cannot convert from 'Status' to 'Status[]'

A call site that already passes a T[] keeps working — only the individual-value form breaks.

Real-world impact

Confirmed source breaks across the repos we upgraded from 4.x:

• dotnet/msbuild — 3 sites (MSBuildClient_Tests.cs:78, BuildManager_Tests.cs:4382/4383)
• JasperFx/Lamar (StructureMap.Testing) — 4 sites
• JasperFx/Wolverine — 2 sites (TransportCompliance.cs:662/714)

ShouldBeOneOf(a, b, c) is the canonical usage, so the practical blast radius is large.

Workaround

Wrap the values in an array:

result.ShouldBeOneOf([Status.A, Status.B, Status.C]); // or new[] { ... } on C# < 12

Suggested fix

Add back a params overload alongside the customMessage overloads (e.g. keep ShouldBeOneOf<T>(this T actual, params T[] expected) and provide the message-carrying variants under a distinct shape), so existing variadic call sites keep compiling. Failing that, this should at least be called out prominently in the 4 → 5 migration guide.