feat: union-typed setup and verify overloads for C# 15

.gitattributes

@@ -13,3 +13,6 @@
 # while mounting and running tests in Linux
 *.sh    text eol=lf
 build   text eol=lf
+
+# Snapshot files are regenerated by AcceptSnapshotChanges; collapse them in GitHub diffs
+Tests/Mockolate.SourceGenerators.Tests/Snapshot/Expected/** linguist-generated=true

.github/copilot-instructions.md

@@ -8,7 +8,7 @@ Mockolate is a modern, strongly-typed mocking library for .NET, powered by sourc
 - Source generator-based (no runtime proxy generation)
 - Strongly-typed with compile-time safety
 - AOT compatible (NativeAOT and trimming)
-- Supports .NET Standard 2.0, .NET 8, .NET 10, and .NET Framework 4.8
+- Supports .NET Standard 2.0, .NET 8, .NET 10, .NET 11, and .NET Framework 4.8
 
 ## Architecture
 

.github/workflows/build.yml

@@ -24,6 +24,7 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: Run unit tests (windows)
                 if: matrix.os == 'windows-latest'
                 run: ./build.ps1 CodeCoverage
@@ -54,6 +55,7 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: API checks
                 run: ./build.sh ApiChecks
             -   name: Upload artifacts
@@ -65,6 +67,33 @@ jobs:
                         ./Artifacts/*
                         ./TestResults/*.trx
 
+    union-tests:
+        name: "Union tests (net11.0, C# preview)"
+        runs-on: ubuntu-latest
+        env:
+            DOTNET_NOLOGO: true
+        steps:
+            -   uses: actions/checkout@v7
+                with:
+                    fetch-depth: 0
+            -   name: Setup .NET SDKs
+                uses: actions/setup-dotnet@v6
+                with:
+                    dotnet-version: |
+                        8.0.x
+                        10.0.x
+                    global-json-file: global.json
+            -   name: Union tests
+                run: ./build.sh UnionTests
+            -   name: Upload artifacts
+                if: always()
+                uses: actions/upload-artifact@v7
+                with:
+                    name: Union-tests
+                    path: |
+                        ./Artifacts/*
+                        ./TestResults/*.trx
+
     benchmarks:
         name: "Benchmarks (${{ matrix.benchmark }})"
         strategy:
@@ -92,6 +121,7 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: Run benchmarks
                 run: ./build.sh Benchmarks --benchmark-filter "*${{ matrix.benchmark }}*"
             -   name: Upload artifacts
@@ -122,6 +152,7 @@ jobs:
                 with:
                     dotnet-version: |
                         10.0.x
+                    global-json-file: global.json
             -   name: Publish benchmark report
                 run: ./build.sh PublishBenchmarkReport
                 env:
@@ -144,6 +175,7 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: Run mutation tests
                 run: ./build.sh MutationTests MutationTestDashboard
 
@@ -164,12 +196,13 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: Run sonarcloud analysis
                 run: ./build.sh CodeAnalysis
 
     publish-test-results:
         name: "Publish Tests Results"
-        needs: [ api-tests, unit-tests ]
+        needs: [ api-tests, unit-tests, union-tests ]
         runs-on: ubuntu-latest
         permissions:
             checks: write
@@ -201,6 +234,7 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: Pack nuget packages
                 run: ./build.sh Pack
             -   name: Upload packages

.github/workflows/ci-analysis.yml

@@ -22,6 +22,7 @@ jobs:
                 with:
                     dotnet-version: |
                         10.0.x
+                    global-json-file: global.json
             -   name: Create mutation test comment
                 run: ./build.sh MutationTestComment
                 env:
@@ -43,6 +44,7 @@ jobs:
                 with:
                     dotnet-version: |
                         10.0.x
+                    global-json-file: global.json
             -   name: Create benchmark comment
                 run: ./build.sh BenchmarkComment
                 env:

.github/workflows/ci.yml

@@ -23,6 +23,7 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: Run unit tests (windows)
                 if: matrix.os == 'windows-latest'
                 run: ./build.ps1 CodeCoverage
@@ -53,6 +54,7 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: API checks
                 run: ./build.sh ApiChecks
             -   name: Upload artifacts
@@ -79,6 +81,7 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: Run mutation tests
                 run: ./build.sh MutationTests
             -   name: Upload artifacts
@@ -89,6 +92,33 @@ jobs:
                     path: |
                         ./Artifacts/*
 
+    union-tests:
+        name: "Union tests (net11.0, C# preview)"
+        runs-on: ubuntu-latest
+        env:
+            DOTNET_NOLOGO: true
+        steps:
+            -   uses: actions/checkout@v7
+                with:
+                    fetch-depth: 0
+            -   name: Setup .NET SDKs
+                uses: actions/setup-dotnet@v6
+                with:
+                    dotnet-version: |
+                        8.0.x
+                        10.0.x
+                    global-json-file: global.json
+            -   name: Union tests
+                run: ./build.sh UnionTests
+            -   name: Upload artifacts
+                if: always()
+                uses: actions/upload-artifact@v7
+                with:
+                    name: Union-tests
+                    path: |
+                        ./Artifacts/*
+                        ./TestResults/*.trx
+
     benchmarks:
         name: "Benchmarks (${{ matrix.benchmark }})"
         strategy:
@@ -114,6 +144,7 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: Run benchmarks
                 run: ./build.sh Benchmarks --benchmark-filter "*${{ matrix.benchmark }}*"
             -   name: Upload artifacts
@@ -143,12 +174,13 @@ jobs:
                     dotnet-version: |
                         8.0.x
                         10.0.x
+                    global-json-file: global.json
             -   name: Run sonarcloud analysis
                 run: ./build.sh CodeAnalysis
 
     publish-test-results:
         name: "Publish Tests Results"
-        needs: [ api-tests, unit-tests ]
+        needs: [ api-tests, unit-tests, union-tests ]
         runs-on: ubuntu-latest
         permissions:
             checks: write

.nuke/build.schema.json

@@ -44,6 +44,7 @@
         "Pack",
         "PublishBenchmarkReport",
         "Restore",
+        "UnionTests",
         "UnitTests",
         "UpdateReadme"
       ]

Benchmarks/Mockolate.Benchmarks/Mockolate.Benchmarks.csproj

@@ -1,8 +1,12 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
+	<!-- Pin the classic overloads so results stay comparable to the CI baseline once the SDK defaults to C# 15. -->
+	<Import Project="..\..\Source\Mockolate\build\Mockolate.props"/>
+
 	<PropertyGroup>
 		<OutputType>Exe</OutputType>
-		<TargetFramework>net10.0</TargetFramework>
+		<TargetFramework>net11.0</TargetFramework>
+		<MockolateUnionParameters>false</MockolateUnionParameters>
 		<ImplicitUsings>enable</ImplicitUsings>
 		<Nullable>enable</Nullable>
 		<GenerateProgramFile>false</GenerateProgramFile>

CLAUDE.md

@@ -6,7 +6,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 Mockolate is a strongly-typed .NET mocking library powered by **Roslyn source generators**. Unlike reflection-based mocking libraries, it generates mock implementations at compile time, providing full IntelliSense support and AOT compatibility.
 
-**Supported targets**: .NET Standard 2.0, .NET 8, .NET 10, .NET Framework 4.8
+**Supported targets**: .NET Standard 2.0, .NET 8, .NET 10, .NET 11, .NET Framework 4.8
 
 ## Build and Test Commands
 
@@ -33,7 +33,7 @@ dotnet test Tests/Mockolate.Tests/Mockolate.Tests.csproj --filter "FullyQualifie
 ./build.sh Pack               # Create NuGet packages
 ```
 
-**Requires**: .NET 10 SDK (see `global.json`). For source generator changes, run `dotnet clean && dotnet build` to force regeneration.
+**Requires**: .NET 11 SDK (currently a preview, see `global.json`). For source generator changes, run `dotnet clean && dotnet build` to force regeneration.
 
 ## Architecture
 
@@ -53,6 +53,7 @@ An `IIncrementalGenerator` that runs at compile time and generates `Mock.{TypeNa
 - Handles interfaces, abstract classes, and delegates
 - Emits method overrides that delegate to `MockRegistry`
 - Targets .NET Standard 2.0 (Roslyn constraint)
+- Union mode (`Sources.MockClass.Unions.cs`): with C# 15 (or `MockolateUnionParameters=true`) the setup/verify overloads take `ParameterArg<T>?` or `Func<T, bool>` per parameter instead of the classic matcher/value set; below that the output is unchanged
 
 ### Source/Mockolate.Analyzers + Source/Mockolate.Analyzers.CodeFixers
 Roslyn analyzers that validate mock usage at compile time:

Docs/pages/00-index.md

@@ -5,7 +5,7 @@
 [![Nuget](https://img.shields.io/nuget/v/Mockolate)](https://www.nuget.org/packages/Mockolate)
 
 [**Mockolate**](https://github.com/Testably/Mockolate) is a modern, strongly-typed, AOT-compatible mocking library for .NET, powered by source generators.
-It enables fast, compile-time validated mocking with .NET Standard 2.0, .NET 8, .NET 10 and .NET Framework 4.8.
+It enables fast, compile-time validated mocking with .NET Standard 2.0, .NET 8, .NET 10, .NET 11 and .NET Framework 4.8.
 
 - **Source generator-based**: No runtime proxy generation.
 - **Fast**: Direct dispatch with no reflection or dynamic proxies.

Docs/pages/setup/02-methods.md

@@ -1,6 +1,7 @@
 # Methods
 
-Use `sut.Mock.Setup.MethodName(…)` to set up methods. You can specify argument matchers for each parameter.
+Use `sut.Mock.Setup.MethodName(…)` to set up methods. You can specify argument matchers for each parameter; with C# 15
+you can also pass predicates directly (see *Union Parameters* under Parameter Matching).
 
 ## Returns / Throws
 

Docs/pages/setup/03-indexers.md

@@ -132,3 +132,16 @@ does not intercept.
   methods.
 - Use `.SkippingBaseClass(…)` to override the base class behavior for a specific indexer (only for class mocks).
 - When you specify overlapping setups, the most recently defined setup takes precedence.
+
+## Union Parameters (C# 15)
+
+With C# 15, indexer keys accept predicates directly, in setups and verifications alike:
+
+```csharp
+sut.Mock.Setup[type => type.StartsWith("D")].Returns(10);
+
+sut.Mock.Verify[type => type.StartsWith("D")].Got().Once();
+```
+
+Only an indexer that is the sole indexer of its key count on the type takes union-typed keys; indexers sharing a key
+count keep the classic matcher/value overloads. See *Union Parameters* under Parameter Matching for the details.

Docs/pages/setup/04-parameter-matching.md

@@ -242,6 +242,44 @@ The following cases are rejected at compile time with diagnostic `Mockolate0003`
 - `out` / `ref` / `ref readonly` parameters of a ref-struct type.
 - Methods that return a custom ref struct. (`Span<T>` / `ReadOnlySpan<T>` returns are supported.)
 
+## Union Parameters (C# 15)
+
+When the consuming project compiles with C# 15, Mockolate generates the setup and verify overloads with union-typed
+parameters: every value-capable parameter becomes a `ParameterArg<T>?` that accepts an `It` matcher or a direct value,
+and a `Func<T, bool>` overload accepts a predicate. The number of overloads stays the same as before, but predicates no
+longer need `It.Satisfies`:
+
+```csharp
+sut.Mock.Setup.Dispense(type => type.StartsWith("D"), It.IsAny<int>()).Returns(true);
+
+sut.Mock.Verify.Dispense("Dark", amount => amount > 10).Once();
+```
+
+Union mode is enabled automatically once the compiler ships C# 15 and the project's effective language version is
+C# 15 or later. On a preview compiler, opt in with `<MockolateUnionParameters>true</MockolateUnionParameters>` in the
+project file; `false` keeps the classic overloads on any compiler.
+
+Behaviour of the union-typed parameters:
+
+- `null` and `default` stand for the parameter's declared default value, or for `default(T)` when it has none, exactly
+  as with the classic value overloads.
+- A parameter whose type is a delegate offers the raw delegate instead of a predicate, so a lambda is still matched as
+  a value.
+- For an `object` parameter, a lambda literal is a predicate, while a delegate stored in a variable is a value.
+- Within a union-typed member, `ref`, `out` and `ref readonly` parameters as well as `Span<T>` and `ReadOnlySpan<T>`
+  parameters keep their matcher slot (no predicate for that parameter); `in` parameters behave like by-value ones.
+- Overloaded method names (including a generic sibling; a same-named member in another scope — public, protected or
+  static — does not count), generic methods, `params` methods, members with custom ref-struct parameters, and indexers
+  that share their key count with another same-scope indexer keep the classic matcher/value overloads. Use
+  `It.Satisfies` for predicates there.
+
+The generated `ParameterArg<T>` type relies on `UnionAttribute`, `OverloadResolutionPriorityAttribute` and
+`CallerArgumentExpressionAttribute`. Mockolate declares whichever of them the compilation lacks (neither the referenced
+frameworks nor the project itself provide it). Another generator such as PolySharp can provide them without Mockolate
+noticing; set `<MockolateUnionAttributePolyfills>false</MockolateUnionAttributePolyfills>` to declare that
+`OverloadResolutionPriorityAttribute` and `CallerArgumentExpressionAttribute` come from elsewhere (`UnionAttribute`
+keeps following the compilation), or list the attribute names the project provides.
+
 ## Parameter Predicates
 
 When the method name is unique (no overloads), you can use argument matchers from the `Match` class for more flexible parameters matching:

Pipeline/Build.UnitTest.cs

@@ -51,4 +51,36 @@ partial class Build
 					), completeOnFailure: true
 			);
 		});
+
+	Project[] UnionTestProjects =>
+	[
+		Solution.Tests.Mockolate_Tests,
+		Solution.Tests.Mockolate_Internal_Tests,
+		Solution.Tests.Mockolate_SourceGenerators_Tests,
+		Solution.Tests.Mockolate_ExampleTests,
+	];
+
+	/// <summary>
+	///     Runs the test projects on net11.0 only, where <c>Tests/Directory.Build.props</c> enables the C# preview
+	///     language version and the union-typed setup surface (<c>MockolateUnionParameters</c>).
+	/// </summary>
+	Target UnionTests => _ => _
+		.Unlisted()
+		.DependsOn(Compile)
+		.Executes(() =>
+		{
+			DotNetTest(s => s
+					.SetConfiguration(Configuration)
+					.SetProcessEnvironmentVariable("DOTNET_CLI_UI_LANGUAGE", "en-US")
+					.EnableNoBuild()
+					.SetFramework("net11.0")
+					.SetResultsDirectory(TestResultsDirectory)
+					.CombineWith(
+						UnionTestProjects,
+						(settings, project) => settings
+							.SetProjectFile(project)
+							.AddLoggers($"trx;LogFileName={project.Name}_net11.0_unions.trx")
+					), completeOnFailure: true
+			);
+		});
 }

README.md

@@ -9,7 +9,7 @@
 [![Mutation testing badge](https://img.shields.io/endpoint?style=flat&url=https%3A%2F%2Fbadge-api.stryker-mutator.io%2Fgithub.com%2FTestably%2FMockolate%2Fmain)](https://dashboard.stryker-mutator.io/reports/github.com/Testably/Mockolate/main)
 
 **Mockolate** is a modern, strongly-typed, AOT-compatible mocking library for .NET, powered by source generators.
-It enables fast, compile-time validated mocking with .NET Standard 2.0, .NET 8, .NET 10 and .NET Framework 4.8.
+It enables fast, compile-time validated mocking with .NET Standard 2.0, .NET 8, .NET 10, .NET 11 and .NET Framework 4.8.
 
 - **Source generator-based**: No runtime proxy generation.
 - **Fast**: Direct dispatch with no reflection or dynamic proxies.

Source/Directory.Build.props

@@ -16,7 +16,7 @@
 	</PropertyGroup>
 
 	<PropertyGroup>
-		<TargetFrameworks>netstandard2.0;net8.0;net10.0</TargetFrameworks>
+		<TargetFrameworks>netstandard2.0;net8.0;net10.0;net11.0</TargetFrameworks>
 	</PropertyGroup>
 
 	<PropertyGroup>