Make constructor selection in CallSiteFactory deterministic and allocation-lighter

[Copilot]

CallSiteFactory.CreateConstructorCallSite previously depended on an unstable Array.Sort for multi-constructor selection, which made same-arity/same-parameter-set resolution implementation-defined. This change replaces sort-based selection with deterministic reflection-order tracking while preserving existing behavior outside that tie case.

• What changed

  • Replaced sort-and-walk with a single-pass constructor scan in reflection (declaration) order.
  • Precomputes each constructor’s ParameterInfo[] exactly once and reuses it.
  • Tracks the best resolvable constructor by arity; larger resolvable constructors replace smaller ones.
  • Skips CreateArgumentCallSites for constructors smaller than the current best.
  • Preserves existing ambiguity and activation exception shapes/messages.
  • Preserves constructors.Length == 0 and constructors.Length == 1 short-circuit paths unchanged.

• Behavioral delta (intended and scoped)

  • Only changed case: when two resolvable constructors have the same arity and identical parameter type sets, selection is now deterministic (first in declaration order) instead of depending on unstable sort ordering.
  • All other selection outcomes remain unchanged.

• Tests added

  • Same-arity, identical parameter-type set, different parameter order → verifies declaration-order constructor is selected.
  • Same-arity, disjoint parameter types, both resolvable → verifies existing ambiguous-constructor InvalidOperationException.
  • Short resolvable declared before longer resolvable → verifies longer constructor wins.
  • Short resolvable declared before longer non-resolvable → verifies short constructor wins.

// Before: unstable ordering + repeated GetParameters allocations
// Array.Sort(constructors, (a, b) => b.GetParameters().Length.CompareTo(a.GetParameters().Length));

// After: deterministic single-pass with cached parameters
ParameterInfo[][] parametersByConstructor = new ParameterInfo[constructors.Length][];
for (int i = 0; i < constructors.Length; i++)
{
    parametersByConstructor[i] = constructors[i].GetParameters();
}

// Walk in reflection order, keep best resolvable by arity, handle ties via existing ambiguity rule.

• DI suite status
  • DI.Tests and DI.External.Tests pass locally with this change.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-extensions-dependencyinjection
See info in area-owners.md if you want to be subscribed.