Do not diff __internal property in DiffConfig (#414)

This PR updates the implementation of DiffConfig to remove the
`__internal` property when comparing provider config between old state
and new input. It is observed that the `__internal` property is present
when a default provider is used. This causes a provider replacement
every time a user upgrades pulumi-docker-build, as the `__internal`
property is always stripped from state, so Pulumi will always report a
diff.

Ideally, we should determine if this bug can be fixed in either upstream
pulumi-go-provider or pulumi itself. For now, we will fix this locally
within pulumi-docker-build to unblock our users.

Changes:

- Update DiffConfig implementation to strip `__internal` property from
new inputs.
- Add a nodejs upgrade test to test that this solution works

Fixes: #404

provider/internal/provider.go

@@ -66,7 +66,7 @@ func (c *Config) Configure(ctx context.Context) error {
 
 // NewBuildxProvider returns a new buildx provider.
 func NewBuildxProvider() provider.Provider {
-	return infer.Provider(
+	prov := infer.Provider(
 		infer.Options{
 			Metadata: pschema.Metadata{
 				DisplayName: "docker-build",
@@ -122,6 +122,27 @@ func NewBuildxProvider() provider.Provider {
 			Config: infer.Config[*Config](),
 		},
 	)
+
+	prov.DiffConfig = diffConfigIgnoreInternal(prov.DiffConfig)
+
+	return prov
+}
+
+// TODO(pulumi/pulumi-docker-build#404): Remove this function once the bug is fixed in either
+// upstream pu/pu or pulumi-go-provider.
+
+// diffConfigInternalIgnore is a custom DiffConfig implementation for the buildx provider. This is required to
+// circumvent the bug identified in https://github.com/pulumi/pulumi-docker-build/issues/404.
+// Since `__internal` is currently populated in new inputs, but stripped in old state, we need to
+// ignore this field in the diff. There is no easy way to override DiffConfig to compare inputs only.
+func diffConfigIgnoreInternal(
+	diffConfig func(ctx context.Context, req provider.DiffRequest) (provider.DiffResponse, error),
+) func(ctx context.Context, req provider.DiffRequest) (provider.DiffResponse, error) {
+	return func(ctx context.Context, req provider.DiffRequest) (provider.DiffResponse, error) {
+		delete(req.News, "__internal")
+
+		return diffConfig(ctx, req)
+	}
 }
 
 // Schema returns our package specification.