Merge pull request #212 from EFNext/copilot/fix-null-coalesce-issue

Preserve nullable typing for ignored null-conditional access in coalesce expressions

Author: PhenX

src/EntityFrameworkCore.Projectables.Generator/SyntaxRewriters/ExpressionSyntaxRewriter.NullConditionalRewrite.cs

@@ -26,7 +26,29 @@ internal partial class ExpressionSyntaxRewriter
         else if (_nullConditionalRewriteSupport is NullConditionalRewriteSupport.Ignore)
         {
             // Ignore the conditional access and simply visit the WhenNotNull expression
-            return Visit(node.WhenNotNull);
+            var rewrittenExpression = (ExpressionSyntax?)Visit(node.WhenNotNull);
+            if (rewrittenExpression is null)
+            {
+                return null;
+            }
+
+            var typeInfo = _semanticModel.GetTypeInfo(node);
+            var whenNotNullType = _semanticModel.GetTypeInfo(node.WhenNotNull).Type;
+            if (IsCoalesceLeftOperand(node) &&
+                typeInfo.ConvertedType is INamedTypeSymbol { IsValueType: true, OriginalDefinition.SpecialType: SpecialType.System_Nullable_T } nullableType &&
+                whenNotNullType is { IsValueType: true } rewrittenType &&
+                (
+                    SymbolEqualityComparer.Default.Equals(nullableType.TypeArguments[0], rewrittenType) ||
+                    SymbolEqualityComparer.Default.Equals(nullableType, rewrittenType)
+                ))
+            {
+                return SyntaxFactory.CastExpression(
+                    SyntaxFactory.ParseTypeName(nullableType.ToDisplayString(SymbolDisplayFormat.FullyQualifiedFormat)),
+                    SyntaxFactory.ParenthesizedExpression(rewrittenExpression)
+                );
+            }
+
+            return rewrittenExpression;
         }
 
         else if (_nullConditionalRewriteSupport is NullConditionalRewriteSupport.Rewrite)
@@ -105,4 +127,19 @@ private static bool IsNullableValueType(ITypeSymbol? type)
         return type is { IsValueType: true } &&
                type.OriginalDefinition.SpecialType == SpecialType.System_Nullable_T;
     }
+
+    private static bool IsCoalesceLeftOperand(ConditionalAccessExpressionSyntax node)
+    {
+        ExpressionSyntax current = node;
+        var parent = node.Parent;
+
+        while (parent is ParenthesizedExpressionSyntax parenthesizedExpression)
+        {
+            current = parenthesizedExpression;
+            parent = parenthesizedExpression.Parent;
+        }
+
+        return parent is BinaryExpressionSyntax { RawKind: (int)SyntaxKind.CoalesceExpression } coalesceExpression &&
+               coalesceExpression.Left == current;
+    }
 }

tests/EntityFrameworkCore.Projectables.Generator.Tests/NullableTests.NullConditionalNullCoalesceTypeConversion_WithIgnoreSupport.verified.txt

@@ -0,0 +1,15 @@
+// <auto-generated/>
+#nullable disable
+using EntityFrameworkCore.Projectables;
+
+namespace EntityFrameworkCore.Projectables.Generated
+{
+    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+    static class _Product_GetCost
+    {
+        static global::System.Linq.Expressions.Expression<global::System.Func<global::Product, decimal>> Expression()
+        {
+            return (global::Product @this) => (decimal? )(@this.Price.Amount) ?? 0m;
+        }
+    }
+}

tests/EntityFrameworkCore.Projectables.Generator.Tests/NullableTests.cs

@@ -488,6 +488,34 @@ class Foo {
         return Verifier.Verify(result.GeneratedTrees[0].ToString());
     }
 
+    [Fact]
+    public Task NullConditionalNullCoalesceTypeConversion_WithIgnoreSupport()
+    {
+        var compilation = CreateCompilation(@"
+using EntityFrameworkCore.Projectables;
+
+public class Price {
+    public decimal Amount { get; set; }
+}
+
+public class Product {
+    public Price? Price { get; set; }
+
+    [Projectable(AllowBlockBody = true, NullConditionalRewriteSupport = NullConditionalRewriteSupport.Ignore)]
+    public decimal GetCost() {
+        return Price?.Amount ?? 0m;
+    }
+}
+");
+
+        var result = RunGenerator(compilation);
+
+        Assert.Empty(result.Diagnostics);
+        Assert.Single(result.GeneratedTrees);
+
+        return Verifier.Verify(result.GeneratedTrees[0].ToString());
+    }
+
     [Fact]
     public Task NullableValueType_MemberAccess_WithRewriteSupport_IsBeingRewritten()
     {