Fix #1017: C# null-coalesce ?? operator + add tests for ?.

dotnet-websharper · Aug 29, 2018 · d26a70c · d26a70c
1 parent e514045
commit d26a70c
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Showing 2 changed files with 53 additions and 3 deletions.
diff --git a/src/compiler/WebSharper.Compiler/Translator.fs b/src/compiler/WebSharper.Compiler/Translator.fs
@@ -1439,9 +1439,10 @@ type DotNetToJavaScript private (comp: Compilation, ?inProgress) =
             base.TransformBinary(a, b, c)
 
     override this.TransformCoalesce(a, b, c) =
-        let trA = this.TransformExpression a
-        let trC = innerScope <| fun () -> this.TransformExpression c
-        Coalesce(trA, b, trC)
+        let aId = Id.New()
+        this.TransformLet(aId, a,
+            Conditional(Binary(Var aId, BinaryOperator.``===``, !~Null), c, Var aId)
+        )
 
     override this.TransformWhile(a, b) =
         let trA = this.TransformExpression a

diff --git a/tests/WebSharper.CSharp.Tests/Syntax.cs b/tests/WebSharper.CSharp.Tests/Syntax.cs
@@ -487,6 +487,55 @@ public void Default()
             Equal(default(string), null);
         }
 
+        private class NullTest
+        {
+            int x;
+
+            public NullTest(int x)
+            {
+                this.x = x;
+            }
+
+            public int? X() => this.x;
+
+            public int? Increment() {
+                this.x++;
+                return this.x;
+            }
+        }
+
+        [Test]
+        public void NullConditionalAccess()
+        {
+            NullTest x = null;
+            Equal(x?.X(), null, "object null case");
+            x = new NullTest(42);
+            Equal(x?.X(), 42, "object non null case");
+            Equal(x?.Increment(), 43, "check side effect 1");
+            Equal(x?.Increment(), 44, "check side effect 2");
+
+            int? y = null;
+            Equal(y?.ToString(), null, "Nullable null case");
+            y = 23;
+            Equal(y?.ToString(), "23", "Nullable non-null case");
+        }
+
+        [Test]
+        public void NullCoalesce()
+        {
+            NullTest x = null;
+            Equal((x ?? new NullTest(42)).X(), 42, "object null case");
+            x = new NullTest(53);
+            Equal((x ?? new NullTest(42)).X(), 53, "object non-null case");
+            Equal(x.Increment() ?? 12, 54, "check side effect 1");
+            Equal(x.Increment() ?? 35, 55, "check side effect 2");
+
+            int? y = null;
+            Equal(y ?? 67, 67, "Nullable null case");
+            y = 23;
+            Equal(y ?? 67, 23, "Nullable non-null case");
+        }
+
         public int this[int i] => i * i;
 
         public string this[string x] { get { return x + "!"; } }