fix: correctly handle mapping to read-only target arrays (#1562)

src/Riok.Mapperly/Descriptors/Mappings/NoOpMapping.cs

@@ -4,9 +4,11 @@
 
 namespace Riok.Mapperly.Descriptors.Mappings;
 
-public class NoOpMapping(ITypeSymbol sourceType, ITypeSymbol targetType) : MethodMapping(sourceType, targetType), IExistingTargetMapping
+public class NoOpMapping(ITypeSymbol sourceType, ITypeSymbol targetType) : IExistingTargetMapping
 {
-    public override IEnumerable<StatementSyntax> BuildBody(TypeMappingBuildContext ctx) => [];
+    public ITypeSymbol SourceType => sourceType;
+    public ITypeSymbol TargetType => targetType;
+    public bool IsSynthetic => true;
 
     public IEnumerable<StatementSyntax> Build(TypeMappingBuildContext ctx, ExpressionSyntax target) => [];
 }

test/Riok.Mapperly.Tests/Mapping/EnumerableExistingTargetTest.cs

@@ -128,4 +128,16 @@ public void MapToExistingInitOnlyCollection()
                 """
             );
     }
+
+    [Fact]
+    public Task MapArrayToReadOnlyArrayShouldDiagnostic()
+    {
+        var source = TestSourceBuilder.Mapping(
+            "A",
+            "B",
+            "class A { public int[] Values { get; set; } public int IntValue { get; } }",
+            "class B { public int[] Values { get; } public int IntValue { set; } }"
+        );
+        return TestHelper.VerifyGenerator(source);
+    }
 }

test/Riok.Mapperly.Tests/_snapshots/EnumerableExistingTargetTest.MapArrayToReadOnlyArrayShouldDiagnostic#Mapper.g.verified.cs

@@ -0,0 +1,13 @@
+//HintName: Mapper.g.cs
+// <auto-generated />
+#nullable enable
+public partial class Mapper
+{
+    [global::System.CodeDom.Compiler.GeneratedCode("Riok.Mapperly", "0.0.1.0")]
+    private partial global::B Map(global::A source)
+    {
+        var target = new global::B();
+        target.IntValue = source.IntValue;
+        return target;
+    }
+}

test/Riok.Mapperly.Tests/_snapshots/EnumerableExistingTargetTest.MapArrayToReadOnlyArrayShouldDiagnostic.verified.txt

@@ -0,0 +1,14 @@
+{
+  Diagnostics: [
+    {
+      Id: RMG083,
+      Title: Cannot map to read only type,
+      Severity: Info,
+      WarningLevel: 1,
+      Location: : (11,4)-(11,36),
+      MessageFormat: Cannot map to read-only type {0},
+      Message: Cannot map to read-only type int[],
+      Category: Mapper
+    }
+  ]
+}