fix

[lofcz]

No description provided.

[Copilot]

🟢 Approval recommended

The generator changes are guarded, well-covered by new tests, and the remaining feedback is limited to minor nullable-warning cleanups in the new test file.

Pull request overview

This PR fixes source-generator collection cloning for issue #50 by switching from CollectionKind-based assumptions to verifying the actual constructor/API surface of the concrete type the generator will instantiate, preventing invalid capacity/copy-ctor/CollectionsMarshal fast paths and falling back to the runtime cloner when codegen can’t be proven correct.

Changes:

• Add regression tests for issue #50 covering Collection<T>, BindingList<T>, derived collection/dictionary types, getter-only collections, stack ordering, and a non-verifiable custom enumerable fallback.
• Introduce CollectionCapabilities and generation guards (CanGenerateCollectionHelper / CanGenerateDictionaryHelper) so helpers are only emitted when construction + population are guaranteed to compile and behave correctly.
• Tighten fast paths in CollectionHelperGenerator to require verified capacity/copy constructors and exact List<T> before using CollectionsMarshal.

File summaries

File	Description
src/FastCloner.Tests/SourceGeneratorIssue50Tests.cs	Adds comprehensive regression coverage for issue #50 scenarios and edge cases.
src/FastCloner.SourceGenerator/TypeAnalyzer.cs	Adds CollectionCapabilities, helper-generation viability checks, and fixes immutable set kind ordering.
src/FastCloner.SourceGenerator/NonPublicAccessorEmitter.cs	Adds null-forgiving operators to suppress nullability warnings in generated accessor code.
src/FastCloner.SourceGenerator/NestedTypeCollector.cs	Gates helper registration on verified collection/dictionary capabilities and propagates capability flags into MemberModel.
src/FastCloner.SourceGenerator/MemberModel.cs	Extends MemberModel to carry verified concrete collection capability flags.
src/FastCloner.SourceGenerator/MemberCollector.cs	Reworks getter-only collection “populatable” detection to be API-based instead of a whitelist.
src/FastCloner.SourceGenerator/MemberCloneGenerator.cs	Adds null-forgiving on Cloner<T>.Clone(...) argument (safe due to null-guard in Clone).
src/FastCloner.SourceGenerator/CollectionHelperGenerator.cs	Requires verified ctor surfaces for capacity/copy ctor fast paths and restricts CollectionsMarshal usage to exact List<T>.

Review details

Suppressed comments (3)

src/FastCloner.Tests/SourceGeneratorIssue50Tests.cs:237

• clone.Items is nullable (DerivedIntDictionary?), but it’s indexed/assigned without ! after only runtime assertions, which will trigger nullable warnings.

        await Assert.That(clone.Items["b"]).IsEqualTo(2);

        clone.Items["c"] = 3;

src/FastCloner.Tests/SourceGeneratorIssue50Tests.cs:274

• clone.Numbers is nullable (DerivedIntHashSet?), but it’s used without ! after only runtime assertions, which will trigger nullable warnings.

        clone.Numbers.Add(4);

src/FastCloner.Tests/SourceGeneratorIssue50Tests.cs:256

• clone.Items is nullable (DerivedObservableCollection?), but it’s indexed without ! after only runtime assertions, which will trigger nullable warnings.

        await Assert.That(clone.Items[0]).IsNotSameReferenceAs(original.Items![0]);
        await Assert.That(clone.Items[0].Name).IsEqualTo("First");

• Files reviewed: 8/8 changed files
• Comments generated: 1
• Review effort level: Lite

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[github-actions]

Deep Clone Benchmarks

• OS: ubuntu-latest
• Generated (UTC): 2026-08-24 19:58:40

Current FastCloner vs DeepCloner

Benchmark	DeepCloner	FastCloner	Delta Time	DC Alloc	FC Alloc	Delta Alloc
SmallObject	100.00 ns	68.76 ns	-31% faster	184 B	48 B	-74% less
FileSpec	487.82 ns	305.07 ns	-37% faster	920 B	416 B	-55% less
StringArray_1000	517.10 ns	513.52 ns	~same	8,160 B	8,024 B	~same
SmallObjectWithCollections	661.90 ns	387.21 ns	-42% faster	1,096 B	576 B	-47% less
DynamicWithDictionary	1,364.77 ns	1,031.48 ns	-24% faster	2,712 B	1,600 B	-41% less
MediumNestedObject	1,747.80 ns	1,112.42 ns	-36% faster	3,416 B	1,616 B	-53% less
DynamicWithNestedObject	1,872.89 ns	1,250.00 ns	-33% faster	3,560 B	1,776 B	-50% less
DynamicWithArray	5,631.93 ns	4,365.43 ns	-22% faster	8,800 B	2,744 B	-69% less
LargeEventDocument_10MB	66,494.96 ns	37,605.24 ns	-43% faster	129,792 B	49,824 B	-62% less
ObjectList_100	166,277.69 ns	109,639.14 ns	-34% faster	318,888 B	149,816 B	-53% less
ObjectDictionary_50	823,703.29 ns	178,222.54 ns	-78% faster	549,665 B	218,768 B	-60% less
LargeLogBatch_10MB	5,653,225.52 ns	3,545,243.32 ns	-37% faster	3,564,655 B	2,649,126 B	-26% less

FastCloner vs latest next baseline

• Baseline generated (UTC): 2026-08-24 19:57:52
• Regression thresholds: time > 5%, alloc > 5%

Status	Benchmark	Delta Time	Delta Alloc
🟢	DynamicWithArray	-7% faster	~same
⚪	DynamicWithDictionary	-3% faster	~same
⚪	DynamicWithNestedObject	~same	~same
🔴	FileSpec	+6% slower	~same
⚪	LargeEventDocument_10MB	-2% faster	~same
🔴	LargeLogBatch_10MB	+7% slower	~same
⚪	MediumNestedObject	-2% faster	~same
⚪	ObjectDictionary_50	+4% slower	~same
⚪	ObjectList_100	+4% slower	~same
🟢	SmallObject	-15% faster	~same
🔴	SmallObjectWithCollections	+6% slower	~same
⚪	StringArray_1000	~same	~same

Regressions

• FileSpec: time +6% slower, alloc ~same
• LargeLogBatch_10MB: time +7% slower, alloc ~same
• SmallObjectWithCollections: time +6% slower, alloc ~same

Improvements

• DynamicWithArray: time -7% faster, alloc ~same
• SmallObject: time -15% faster, alloc ~same

Mixed changes

• none