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fix: preserve nullable annotation on generic return type in setup interface#723

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vbreuss merged 1 commit into
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topic/preserve-nullable-annotation-on-generic-return-type
Apr 30, 2026
Merged

fix: preserve nullable annotation on generic return type in setup interface#723
vbreuss merged 1 commit into
mainfrom
topic/preserve-nullable-annotation-on-generic-return-type

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@vbreuss vbreuss commented Apr 30, 2026

A T? return on a generic method whose T carries a non-value-type constraint (class, class?, an interface, or notnull) cannot be expressed in the explicit setup-interface implementation: CS0460 forbids restating the inherited constraint and where T : default (CS8822) conflicts with those constraints. Without a clause the compiler resolves bare T? as Nullable<T> and reports CS0453/CS9334/CS0738/CS0266.

The setup-side return type now drops the trailing ? for these methods. NRT annotations are erased at runtime, so the underlying setup object is unchanged. The user-facing mock body keeps T? because the constraint is visible there.

@vbreuss
fix: preserve nullable annotation on generic return type in setup int…
8eedb33 
…erface

A `T?` return on a generic method whose `T` carries a non-value-type constraint
(`class`, `class?`, an interface, or `notnull`) cannot be expressed in the explicit
setup-interface implementation: CS0460 forbids restating the inherited constraint
and `where T : default` (CS8822) conflicts with those constraints. Without a clause
the compiler resolves bare `T?` as `Nullable<T>` and reports CS0453/CS9334/CS0738/CS0266.

The setup-side return type now drops the trailing `?` for these methods. NRT
annotations are erased at runtime, so the underlying setup object is unchanged.
The user-facing mock body keeps `T?` because the constraint is visible there.
@vbreuss vbreuss self-assigned this Apr 30, 2026
@vbreuss vbreuss added the bug Something isn't working label Apr 30, 2026
@vbreuss vbreuss enabled auto-merge (squash) April 30, 2026 05:12
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sonarqubecloud Bot commented Apr 30, 2026

Quality Gate Passed Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
56.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

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github-actions Bot commented Apr 30, 2026

Test Results

    21 files  ±0      21 suites  ±0   9m 34s ⏱️ - 1m 46s
 3 850 tests ±0   3 849 ✅ ±0  1 💤 ±0  0 ❌ ±0 
25 064 runs  ±0  25 063 ✅ ±0  1 💤 ±0  0 ❌ ±0 

Results for commit 8eedb33. ± Comparison against base commit 16693da.

@vbreuss vbreuss merged commit 74753ac into main Apr 30, 2026
16 checks passed
@vbreuss vbreuss deleted the topic/preserve-nullable-annotation-on-generic-return-type branch April 30, 2026 05:21
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github-actions Bot commented Apr 30, 2026

🚀 Benchmark Results

Details 
BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)

AMD EPYC 7763 2.79GHz, 1 CPU, 4 logical and 2 physical cores

.NET SDK 10.0.203

[Host] : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3


Job=InProcess  Toolchain=InProcessEmitToolchain  IterationCount=15

LaunchCount=1  WarmupCount=10
Method Mean Error StdDev Ratio RatioSD Gen0 Gen1 Allocated Alloc Ratio
Event_Mockolate 338.5 ns 6.26 ns 5.86 ns 1.00 0.02 0.1254 0.0005 2.05 KB 1.00
Event_Moq 15,977.0 ns 49.92 ns 44.25 ns 47.21 0.79 0.7324 - 12.51 KB 6.09
Event_NSubstitute 5,713.4 ns 42.78 ns 40.02 ns 16.88 0.30 0.5493 0.0076 9.05 KB 4.40
Event_FakeItEasy 212,533.4 ns 940.83 ns 834.02 ns 628.05 10.70 0.7324 0.4883 15.39 KB 7.49
Event_Imposter 1,390.5 ns 15.86 ns 14.84 ns 4.11 0.08 0.5379 0.0153 8.8 KB 4.29
Event_TUnitMocks 184.0 ns 1.58 ns 1.48 ns 0.54 0.01 0.0837 0.0002 1.37 KB 0.67
Details 
BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)

AMD EPYC 7763 2.45GHz, 1 CPU, 4 logical and 2 physical cores

.NET SDK 10.0.203

[Host] : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3


Job=InProcess  Toolchain=InProcessEmitToolchain  IterationCount=15

LaunchCount=1  WarmupCount=10
Method N Mean Error StdDev Ratio RatioSD Gen0 Gen1 Allocated Alloc Ratio
Indexer_Mockolate 1 1,054.5 ns 47.21 ns 44.16 ns 1.00 0.06 0.2460 0.0019 4.03 KB 1.00
Indexer_Moq 1 218,590.8 ns 1,221.96 ns 1,083.24 ns 207.63 8.59 0.9766 0.4883 20.57 KB 5.10
Indexer_NSubstitute 1 9,733.9 ns 39.24 ns 36.71 ns 9.25 0.38 0.7782 - 12.84 KB 3.18
Indexer_FakeItEasy 1 12,587.9 ns 62.64 ns 55.53 ns 11.96 0.49 0.8392 - 13.96 KB 3.46
Indexer_Imposter 1 998.0 ns 45.65 ns 42.70 ns 0.95 0.06 0.3147 0.0038 5.16 KB 1.28
Indexer_Mockolate 10 2,629.0 ns 12.46 ns 11.65 ns 1.00 0.01 0.3090 - 5.09 KB 1.00
Indexer_Moq 10 230,324.5 ns 1,042.07 ns 974.76 ns 87.61 0.52 1.7090 1.4648 30.09 KB 5.92
Indexer_NSubstitute 10 23,416.4 ns 68.94 ns 61.11 ns 8.91 0.04 1.5564 0.0305 25.63 KB 5.04
Indexer_FakeItEasy 10 26,932.2 ns 308.52 ns 288.59 ns 10.24 0.12 2.1667 - 35.55 KB 6.99
Indexer_Imposter 10 2,318.2 ns 20.98 ns 19.62 ns 0.88 0.01 0.4845 0.0076 7.97 KB 1.57
Details 
BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)

AMD EPYC 7763 2.45GHz, 1 CPU, 4 logical and 2 physical cores

.NET SDK 10.0.203

[Host] : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3


Job=InProcess  Toolchain=InProcessEmitToolchain  IterationCount=15

LaunchCount=1  WarmupCount=10
Method N Mean Error StdDev Ratio RatioSD Gen0 Gen1 Allocated Alloc Ratio
Method_Mockolate 1 485.8 ns 23.54 ns 20.87 ns 1.00 0.06 0.1416 0.0010 2.32 KB 1.00
Method_Moq 1 180,596.3 ns 868.20 ns 769.64 ns 372.37 15.43 0.4883 - 14.58 KB 6.28
Method_NSubstitute 1 5,716.5 ns 75.07 ns 70.22 ns 11.79 0.51 0.5569 0.0076 9.12 KB 3.93
Method_FakeItEasy 1 5,965.7 ns 62.09 ns 58.08 ns 12.30 0.52 0.4959 - 8.11 KB 3.50
Method_Imposter 1 602.7 ns 25.58 ns 23.93 ns 1.24 0.07 0.2470 0.0029 4.04 KB 1.74
Method_TUnitMocks 1 679.2 ns 14.95 ns 13.25 ns 1.40 0.06 0.1774 0.0010 2.9 KB 1.25
Method_Mockolate 10 758.4 ns 8.70 ns 8.14 ns 1.00 0.01 0.1545 0.0010 2.53 KB 1.00
Method_Moq 10 186,650.2 ns 1,007.00 ns 892.68 ns 246.14 2.78 0.9766 0.7324 18.48 KB 7.30
Method_NSubstitute 10 8,601.0 ns 105.32 ns 98.51 ns 11.34 0.17 0.7324 0.0153 12.07 KB 4.77
Method_FakeItEasy 10 9,585.8 ns 89.75 ns 79.56 ns 12.64 0.17 0.9766 0.0305 16.05 KB 6.34
Method_Imposter 10 1,216.8 ns 31.45 ns 29.41 ns 1.60 0.04 0.3376 0.0057 5.52 KB 2.18
Method_TUnitMocks 10 1,759.1 ns 32.63 ns 30.53 ns 2.32 0.05 0.2747 0.0019 4.49 KB 1.77
Details 
BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)

AMD EPYC 7763 2.45GHz, 1 CPU, 4 logical and 2 physical cores

.NET SDK 10.0.203

[Host] : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3


Job=InProcess  Toolchain=InProcessEmitToolchain  IterationCount=15

LaunchCount=1  WarmupCount=10
Method N Mean Error StdDev Ratio RatioSD Gen0 Gen1 Allocated Alloc Ratio
Property_Mockolate 1 517.3 ns 3.08 ns 2.73 ns 1.00 0.01 0.1574 0.0010 2.58 KB 1.00
Property_Moq 1 11,667.5 ns 81.47 ns 72.22 ns 22.56 0.18 0.6104 - 10.39 KB 4.03
Property_NSubstitute 1 7,394.8 ns 16.49 ns 14.62 ns 14.30 0.08 0.6943 0.0076 11.45 KB 4.44
Property_FakeItEasy 1 8,220.2 ns 16.81 ns 14.90 ns 15.89 0.09 0.6866 - 11.24 KB 4.36
Property_Imposter 1 430.9 ns 1.01 ns 0.84 ns 0.83 0.00 0.1912 0.0019 3.13 KB 1.21
Property_TUnitMocks 1 738.6 ns 1.18 ns 1.10 ns 1.43 0.01 0.1526 0.0010 2.51 KB 0.97
Property_Mockolate 10 1,030.1 ns 3.28 ns 3.07 ns 1.00 0.00 0.1869 - 3.07 KB 1.00
Property_Moq 10 18,267.0 ns 41.67 ns 38.98 ns 17.73 0.06 1.0986 - 18.28 KB 5.95
Property_NSubstitute 10 17,134.8 ns 22.57 ns 20.01 ns 16.63 0.05 1.2817 0.0305 21.08 KB 6.87
Property_FakeItEasy 10 19,496.7 ns 43.41 ns 40.61 ns 18.93 0.07 1.8616 - 30.81 KB 10.03
Property_Imposter 10 1,101.5 ns 1.97 ns 1.65 ns 1.07 0.00 0.2842 0.0019 4.67 KB 1.52
Property_TUnitMocks 10 2,115.1 ns 5.24 ns 4.64 ns 2.05 0.01 0.2823 - 4.66 KB 1.52
Details 
BenchmarkDotNet v0.15.8, Linux Ubuntu 24.04.4 LTS (Noble Numbat)

AMD EPYC 7763 2.79GHz, 1 CPU, 4 logical and 2 physical cores

.NET SDK 10.0.203

[Host] : .NET 10.0.7 (10.0.7, 10.0.726.21808), X64 RyuJIT x86-64-v3


Job=InProcess  Toolchain=InProcessEmitToolchain  IterationCount=15

LaunchCount=1  WarmupCount=10
Method Mean Error StdDev Ratio RatioSD Gen0 Gen1 Allocated Alloc Ratio
Callback_Mockolate 397.4 ns 5.10 ns 4.77 ns 1.00 0.02 0.1197 - 1.96 KB 1.00
Callback_Moq 96,915.8 ns 356.44 ns 315.97 ns 243.92 2.92 0.4883 0.2441 8.88 KB 4.53
Callback_NSubstitute 4,218.9 ns 19.21 ns 17.97 ns 10.62 0.13 0.4730 0.0076 7.74 KB 3.95
Callback_FakeItEasy 4,658.8 ns 11.46 ns 8.95 ns 11.73 0.14 0.4120 0.0153 6.81 KB 3.47
Callback_Imposter 396.8 ns 1.80 ns 1.51 ns 1.00 0.01 0.1454 0.0010 2.38 KB 1.22
Callback_TUnitMocks 587.0 ns 3.00 ns 2.50 ns 1.48 0.02 0.1602 0.0010 2.63 KB 1.34

@github-actions github-actions Bot added the state: released The issue is released label Apr 30, 2026
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