Disallow default values on nullably-typed params

Azure · Jan 9, 2023 · cd10b2c · cd10b2c
1 parent 0262e37
commit cd10b2c
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Showing 3 changed files with 23 additions and 0 deletions.
diff --git a/src/Bicep.Core.IntegrationTests/UserDefinedTypeTests.cs b/src/Bicep.Core.IntegrationTests/UserDefinedTypeTests.cs
@@ -428,4 +428,17 @@ public void Warning_should_be_shown_when_setting_unknown_properties_on_unsealed_
             ("BCP037", DiagnosticLevel.Warning, "The property \"prop\" is not allowed on objects of type \"{ }\". No other properties are allowed."),
         });
     }
+
+    [TestMethod]
+    public void Error_should_be_emitted_when_setting_a_default_value_on_a_nullable_parameter()
+    {
+        var result = CompilationHelper.Compile(ServicesWithUserDefinedTypes, @"
+#disable-next-line no-unused-params
+param myParam string? = 'foo'
+");
+
+        result.Should().HaveDiagnostics(new[] {
+            ("BCP317", DiagnosticLevel.Error, "Nullable-typed parameters may not be assigned default values. They have an implicit default of 'null' that cannot be overridden."),
+        });
+    }
 }
diff --git a/src/Bicep.Core/Diagnostics/DiagnosticBuilder.cs b/src/Bicep.Core/Diagnostics/DiagnosticBuilder.cs
@@ -1806,6 +1806,11 @@ public ErrorDiagnostic NestedRuntimePropertyAccessNotSupported(string? resourceS
                 TextSpan,
                 "BCP316",
                 $@"Using nullable types requires enabling EXPERIMENTAL feature ""{nameof(ExperimentalFeaturesEnabled.UserDefinedTypes)}"".");
+
+            public ErrorDiagnostic NullableTypedParamsMayNotHaveDefaultValues() => new(
+                TextSpan,
+                "BCP317",
+                "Nullable-typed parameters may not be assigned default values. They have an implicit default of 'null' that cannot be overridden.");
         }
 
         public static DiagnosticBuilderInternal ForPosition(TextSpan span)

diff --git a/src/Bicep.Core/TypeSystem/TypeAssignmentVisitor.cs b/src/Bicep.Core/TypeSystem/TypeAssignmentVisitor.cs
@@ -377,6 +377,11 @@ public override void VisitParameterDeclarationSyntax(ParameterDeclarationSyntax
                 if (syntax.Modifier != null)
                 {
                     diagnostics.WriteMultiple(this.ValidateIdentifierAccess(syntax.Modifier));
+
+                    if (TypeValidator.AreTypesAssignable(LanguageConstants.Null, declaredType))
+                    {
+                        diagnostics.Write(DiagnosticBuilder.ForPosition(syntax.Modifier).NullableTypedParamsMayNotHaveDefaultValues());
+                    }
                 }
 
                 if (declaredType is ErrorType)