Use nil checks for defaults when applicable

changelog/pending/20230208--sdkgen-go--prevent-defaults-from-overriding-set-values.yaml

@@ -0,0 +1,4 @@
+changes:
+- type: fix
+  scope: sdkgen/go
+  description: Prevent defaults from overriding set values.

pkg/codegen/go/gen.go

@@ -1350,8 +1350,12 @@ func (pkg *pkgContext) genObjectDefaultFunc(w io.Writer, name string,
 			if err != nil {
 				return err
 			}
-			pkg.needsUtils = true
-			fmt.Fprintf(w, "if isZero(tmp.%s) {\n", pkg.fieldName(nil, p))
+			if isNilType(p.Type) {
+				fmt.Fprintf(w, "if tmp.%s == nil {\n", pkg.fieldName(nil, p))
+			} else {
+				pkg.needsUtils = true
+				fmt.Fprintf(w, "if isZero(tmp.%s) {\n", pkg.fieldName(nil, p))
+			}
 			pkg.assignProperty(w, p, "tmp", dv, !p.IsRequired())
 			fmt.Fprintf(w, "}\n")
 		} else if funcName := pkg.provideDefaultsFuncName(p.Type); funcName != "" {
@@ -1708,8 +1712,12 @@ func (pkg *pkgContext) genResource(w io.Writer, r *schema.Resource, generateReso
 			if err != nil {
 				return err
 			}
-			pkg.needsUtils = true
-			fmt.Fprintf(w, "\tif isZero(args.%s) {\n", pkg.fieldName(r, p))
+			if isNilType(p.Type) {
+				fmt.Fprintf(w, "\tif args.%s == nil {\n", pkg.fieldName(r, p))
+			} else {
+				pkg.needsUtils = true
+				fmt.Fprintf(w, "\tif isZero(args.%s) {\n", pkg.fieldName(r, p))
+			}
 			assign(p, dv)
 			fmt.Fprintf(w, "\t}\n")
 		} else if name := pkg.provideDefaultsFuncName(p.Type); name != "" && !pkg.disableObjectDefaults {

pkg/codegen/testing/test/testdata/dashed-import-schema/go/codegen-manifest.json

@@ -10,7 +10,6 @@
     "plant-provider/tree/v1/init.go",
     "plant-provider/tree/v1/nursery.go",
     "plant-provider/tree/v1/pulumiEnums.go",
-    "plant-provider/tree/v1/pulumiUtilities.go",
     "plant-provider/tree/v1/rubberTree.go"
   ]
 }

pkg/codegen/testing/test/testdata/different-enum/go/codegen-manifest.json

@@ -10,7 +10,6 @@
     "plant/tree/v1/init.go",
     "plant/tree/v1/nursery.go",
     "plant/tree/v1/pulumiEnums.go",
-    "plant/tree/v1/pulumiUtilities.go",
     "plant/tree/v1/rubberTree.go"
   ]
 }

pkg/codegen/testing/test/testdata/plain-and-default/dotnet/ModuleResource.cs

@@ -12,6 +12,10 @@ namespace Pulumi.FooBar
     [FooBarResourceType("foobar::ModuleResource")]
     public partial class ModuleResource : global::Pulumi.CustomResource
     {
+        [Output("optional_bool")]
+        public Output<bool?> Optional_bool { get; private set; } = null!;
+
+
         /// <summary>
         /// Create a ModuleResource resource with the given unique name, arguments, and options.
         /// </summary>