fix(mutating): avoid uncompilable mutations in several edge cases

[slang25]

Summary

• Avoid CS0136 by skipping ternary mutation placement when the expression introduces a declaration (e.g. recursive patterns like x is { } v); mutations are forwarded to the enclosing block instead.
• Include auto-generated compilation trees (e.g. GlobalUsings.g.cs) when building semantic models so mutators that consult the semantic model see resolved types.
• Restrict LinqMutator to invocations whose receiver implements IEnumerable<T> (or whose containing type is Enumerable/Queryable/ParallelEnumerable), preventing incorrect rewrites of unrelated methods such as IResponseCookies.Append.
• Skip the ObjectCreationMutator initializer-removal mutation when the target type has any required members (CS9035).

Fixes #3594

Test plan

• Run existing unit test suite
• Verify mutation runs against a project using ASP.NET Core (IResponseCookies.Append) no longer produce CS-failure mutants
• Verify mutation runs against a project using required members no longer produce CS9035 mutants
• Verify mutation runs against a project using recursive patterns no longer produce CS0136 mutants

[Copilot]

Pull request overview

Targeted fixes for four edge cases that caused Stryker to generate uncompilable mutants on modern ASP.NET Core / .NET 10 projects (issue #3594). The changes make several mutators consult the semantic model more carefully and feed it the auto-generated trees it needs (e.g. GlobalUsings.g.cs) so that implicit-using-based types resolve correctly.

Changes:

• Restrict LinqMutator to invocations whose receiver implements IEnumerable<T> or whose containing type is Enumerable/Queryable/ParallelEnumerable, falling back to legacy name-only matching when no semantic model is available.
• Skip the empty-initializer ObjectCreationMutator mutation when the target type (or any base) has required members; promote expression-level mutations to block level when the source expression introduces a declaration (extends ContainsDeclarations to SingleVariableDesignation).
• Include the project's CompilationSyntaxTrees (alongside file trees) when building the semantic models used during mutation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/Stryker.Core/Stryker.Core/Mutators/ObjectCreationMutator.cs	Skip empty-initializer mutation when the type has required members.
src/Stryker.Core/Stryker.Core/Mutators/LinqMutator.cs	Gate LINQ mutations on receiver type / LINQ host type via semantic model.
src/Stryker.Core/Stryker.Core/MutationTest/CsharpMutationProcess.cs	Add auto-generated trees to the semantic models used during mutation.
src/Stryker.Core/Stryker.Core/Mutants/MutationStore.cs	Forward expression mutations to enclosing block when source introduces a declaration.
src/Stryker.Core/Stryker.Core/Helpers/RoslynHelper.cs	Treat SingleVariableDesignation as a declaration for ternary-control checks.

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.

[slang25]

Closing per maintainer feedback to split into focused PRs. Replaced by:

• fix(mutating): include generated trees when building semantic models #3600 — Include generated trees when building semantic models (Semantic models miss auto-generated trees (GlobalUsings.g.cs) during mutation #3599)
• fix(linq-mutator): only mutate calls on IEnumerable<T>-shaped receivers #3601 — LinqMutator: only mutate calls on IEnumerable<T>-shaped receivers (LinqMutator emits non-LINQ mutations on methods named like LINQ operators #3596)
• fix(mutating): avoid CS0136 from recursive/var pattern designations #3602 — Avoid CS0136 from recursive/var pattern designations (Recursive/var pattern designations cause CS0136 in expression-level mutations #3597)
• fix(object-creation-mutator): skip empty initializer for required members #3603 — ObjectCreationMutator: skip empty initializer for required members (ObjectCreationMutator empty-initializer mutation fails CS9035 on types with required members #3598)

Bug #2 from the original write-up (CS9234 interceptor cascade) is largely resolved by #3601 in the common case; I've folded it into the #3601 narrative rather than tracking it separately.