fix: fix nullable arrays (#621)

src/Riok.Mapperly/Descriptors/MappingBuilders/EnumerableMappingBuilder.cs

@@ -54,7 +54,14 @@ or CollectionType.IEnumerable
             // a single Array.Clone / cast mapping call should be sufficient and fast,
             // use a for loop mapping otherwise.
             if (!elementMapping.IsSynthetic)
-                return new ArrayForMapping(ctx.Source, ctx.Target, elementMapping, elementMapping.TargetType);
+            {
+                // upgrade nullability of element type
+                var targetValue =
+                    ctx.CollectionInfos.Target.CollectionType == CollectionType.Array
+                        ? ctx.Types.GetArrayType(elementMapping.TargetType)
+                        : ((INamedTypeSymbol)ctx.Target).ConstructedFrom.Construct(elementMapping.TargetType);
+                return new ArrayForMapping(ctx.Source, targetValue, elementMapping, elementMapping.TargetType);
+            }
 
             return ctx.MapperConfiguration.UseDeepCloning
                 ? new ArrayCloneMapping(ctx.Source, ctx.Target)

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

@@ -466,6 +466,19 @@ public void EnumerableToCustomCollectionWithObjectFactory()
             );
     }
 
+    [Fact]
+    public Task ArrayToReadOnlyCollectionShouldUpgradeNullability()
+    {
+        var source = TestSourceBuilder.Mapping(
+            "A",
+            "B",
+            "class A { public int[] Value { get; set;} }",
+            "class B { public IReadOnlyCollection<string> Value { get; set; } }"
+        );
+
+        return TestHelper.VerifyGenerator(source, TestHelperOptions.DisabledNullable);
+    }
+
     [Fact]
     public Task ShouldUpgradeNullabilityInDisabledNullableContextInSelectClause()
     {

test/Riok.Mapperly.Tests/_snapshots/EnumerableTest.ArrayToReadOnlyCollectionShouldUpgradeNullability#Mapper.g.verified.cs

@@ -0,0 +1,29 @@
+//HintName: Mapper.g.cs
+// <auto-generated />
+#nullable enable
+public partial class Mapper
+{
+    private partial global::B? Map(global::A? source)
+    {
+        if (source == null)
+            return default;
+        var target = new global::B();
+        if (source.Value != null)
+        {
+            target.Value = MapToIReadOnlyCollection(source.Value);
+        }
+
+        return target;
+    }
+
+    private global::System.Collections.Generic.IReadOnlyCollection<string?> MapToIReadOnlyCollection(int[] source)
+    {
+        var target = new string?[source.Length];
+        for (var i = 0; i < source.Length; i++)
+        {
+            target[i] = source[i].ToString();
+        }
+
+        return target;
+    }
+}

test/Riok.Mapperly.Tests/_snapshots/EnumerableTest.ShouldUpgradeNullabilityInDisabledNullableContextInSelectClause#Mapper.g.verified.cs

@@ -25,7 +25,7 @@ public partial class Mapper
         return target;
     }
 
-    private global::D[] MapToDArray(global::C[] source)
+    private global::D?[] MapToDArray(global::C[] source)
     {
         var target = new global::D?[source.Length];
         for (var i = 0; i < source.Length; i++)
@@ -35,4 +35,4 @@ public partial class Mapper
 
         return target;
     }
-}
+}