Add support for generic constraints (#84)

* - Implement support for interface constraints so they carry over to generated decorator class.

* Update test project from .net 7 to .net 8 so PR CI works.

Author: CodingFlow

DecoratorGenerator.UnitTests/DecoratorGenerator.UnitTests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 

DecoratorGenerator.UnitTests/ITigerConstraints.cs

@@ -0,0 +1,11 @@
+using DecoratorGenerator;
+
+namespace SampleLibrary;
+
+[Decorate]
+public interface ITigerConstraints
+{
+    string Roar();
+
+    string Trait<T>(T trait) where T : class, ICat, new();
+}

DecoratorGenerator.UnitTests/Tests.cs

@@ -62,6 +62,29 @@ public async Task OneInterface_Properties() {
         }.RunAsync();
     }
 
+    [Test]
+    public async Task OneInterface_Constraints() {
+        var source = await ReadCSharpFile<ITigerConstraints>();
+        var generated = await ReadCSharpFile<TigerConstraintsDecorator>();
+
+        await new VerifyCS.Test
+        {
+            TestState = {
+                ReferenceAssemblies = ReferenceAssemblies.Net.Net60,
+                AdditionalReferences =
+                {
+                    implementationAssembly,
+                    Assembly.GetExecutingAssembly()
+                },
+                Sources = { source },
+                GeneratedSources =
+                {
+                    (typeof(Main), "TigerConstraintsDecorator.generated.cs", SourceText.From(generated, Encoding.UTF8, SourceHashAlgorithm.Sha256)),
+                },
+            },
+        }.RunAsync();
+    }
+
     [Test]
     public async Task OneInterface_NestedNamespace() {
         var source = await ReadCSharpFile<INested>();

DecoratorGenerator.UnitTests/TigerConstraintsDecorator.generated.cs

@@ -0,0 +1,22 @@
+// <auto-generated/>
+#nullable restore
+namespace SampleLibrary;
+
+public abstract class TigerConstraintsDecorator : ITigerConstraints
+{
+    private ITigerConstraints tigerConstraints;
+
+    protected TigerConstraintsDecorator(ITigerConstraints tigerConstraints) {
+        this.tigerConstraints = tigerConstraints;
+    }
+
+
+
+    public virtual string Roar() {
+        return tigerConstraints.Roar();
+    }
+
+    public virtual string Trait<T>(T trait) where T : class, SampleLibrary.ICat, new() {
+        return tigerConstraints.Trait<T>(trait);
+    }
+}

DecoratorGenerator/OutputGenerator.cs

@@ -51,7 +51,28 @@ public abstract class {className} : {@interface.Name}
                 var typeParametersStrings = method.TypeParameters.Select(t => t.ToDisplayString());
                 var parametersStrings = method.Parameters.Select(p => $@"{p.Type} {p.Name}");
                 var formattedAccessibility = (method.ReturnType.DeclaredAccessibility != Accessibility.NotApplicable ? method.ReturnType.DeclaredAccessibility : Accessibility.Public).ToString().ToLower();
-                var signature = $@"{formattedAccessibility} virtual {method.ReturnType} {method.Name}{(method.IsGenericMethod ? $@"<{string.Join(", ", typeParametersStrings)}>" : string.Empty)}({string.Join(", ", parametersStrings)})";
+                var formattedGenericTypeParameters = method.IsGenericMethod ? $@"<{string.Join(", ", typeParametersStrings)}>" : string.Empty;
+                var formattedConstraintsStrings = method.TypeParameters.Select(t => {
+                    var constraintsStrings = new List<string>();
+
+                    if (t.HasReferenceTypeConstraint) {
+                        constraintsStrings.Add("class");
+                    }
+                    
+                    if (t.HasNotNullConstraint) {
+                        constraintsStrings.Add("notnull");
+                    }
+                    constraintsStrings = constraintsStrings.Concat(t.ConstraintTypes.ToList().Select(ct => ct.ToDisplayString())).ToList();
+
+                    if (t.HasConstructorConstraint) {
+                        constraintsStrings.Add("new()");
+                    }
+
+                    return constraintsStrings.Any() ? $@"where {t.ToDisplayString()} : {string.Join(", ", constraintsStrings)}" : string.Empty;
+                })
+                    .Where(cs => cs != string.Empty);
+                var formattedConstraints = string.Join(" ", formattedConstraintsStrings);
+                var signature = $@"{formattedAccessibility} virtual {method.ReturnType} {method.Name}{formattedGenericTypeParameters}({string.Join(", ", parametersStrings)}){(formattedConstraints != string.Empty ? $@" {formattedConstraints}" : string.Empty)}";
                 var callParameters = $@"{string.Join(", ", method.Parameters.Select(p => p.Name))}";
 
                 var call = $@"{targetFieldName}.{method.Name}{(method.IsGenericMethod ? $@"<{string.Join(", ", typeParametersStrings)}>" : string.Empty)}({callParameters})";