Add DataModel:GetService(name)

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased Changes
 * Added `Instance:Clone()` for copying instances all over the place, as is Roblox tradition. ([#12](https://github.com/rojo-rbx/remodel/issues/12))
+* Added `DataModel:GetService()` for finding services and creating them if they don't exist, like Roblox does.
 * Improved error messages in preparation for [#7](https://github.com/rojo-rbx/remodel/issues/7) to be fixed upstream.
 
 ## 0.5.0 (2019-09-21)

README.md

@@ -59,10 +59,11 @@ Remodel supports some parts of Roblox's API in order to make code familiar to ex
 * `<Instance>.ClassName` (read only)
 * `<Instance>.Parent` (read + write)
 * `<Instance>:Destroy()` (0.5.0+)
-* `<Instance>:Clone()`, (**unreleased**)
+* `<Instance>:Clone()` (**unreleased**)
 * `<Instance>:GetChildren()`
 * `<Instance>:FindFirstChild(name)`
 	* The second argument (recursive) is not supported by Remodel.
+* `<DataModel>:GetService(name)` (**unreleased**)
 
 ## Remodel API
 Remodel has its own API that goes beyond what can be done inside Roblox.

src/remodel_api/instance.rs

@@ -3,7 +3,7 @@ use std::{
     sync::{Arc, Mutex},
 };
 
-use rbx_dom_weak::{RbxId, RbxTree};
+use rbx_dom_weak::{RbxId, RbxInstanceProperties, RbxTree};
 use rlua::{Context, FromLua, MetaMethod, ToLua, UserData, UserDataMethods};
 
 #[derive(Clone)]
@@ -109,6 +109,62 @@ impl LuaInstance {
         Ok(children)
     }
 
+    fn get_service(&self, service_name: &str) -> rlua::Result<LuaInstance> {
+        let mut tree = self.tree.lock().unwrap();
+
+        let instance = tree.get_instance(self.id).ok_or_else(|| {
+            rlua::Error::external("Cannot call GetService() on a destroyed instance")
+        })?;
+
+        // It might be cleaner to avoid defining GetService() on all instances,
+        // but we don't have a good mechanism in Remodel to do that right now.
+        if instance.class_name != "DataModel" {
+            return Err(rlua::Error::external(
+                "Cannot call GetService() on an instance that is not a DataModel",
+            ));
+        }
+
+        match rbx_reflection::get_class_descriptor(service_name) {
+            // We should only find services, even if there's a child of
+            // DataModel with a matching ClassName.
+            Some(descriptor) if descriptor.is_service() => {
+                let existing = instance
+                    .get_children_ids()
+                    .iter()
+                    .copied()
+                    .map(|id| tree.get_instance(id).unwrap())
+                    .find(|instance| instance.class_name == service_name);
+
+                match existing {
+                    Some(existing) => Ok(LuaInstance {
+                        tree: Arc::clone(&self.tree),
+                        id: existing.get_id(),
+                    }),
+                    None => {
+                        // If we didn't find an existing service instance,
+                        // construct a new one.
+
+                        let properties = RbxInstanceProperties {
+                            name: service_name.to_owned(),
+                            class_name: service_name.to_owned(),
+                            properties: Default::default(),
+                        };
+
+                        let id = tree.insert_instance(properties, self.id);
+                        Ok(LuaInstance {
+                            tree: Arc::clone(&self.tree),
+                            id,
+                        })
+                    }
+                }
+            }
+            _ => Err(rlua::Error::external(format!(
+                "'{}' is not a valid service.",
+                service_name
+            ))),
+        }
+    }
+
     fn get_class_name<'lua>(
         &self,
         context: rlua::Context<'lua>,
@@ -269,6 +325,10 @@ impl UserData for LuaInstance {
             this.get_children()
         });
 
+        methods.add_method("GetService", |_context, this, name: String| {
+            this.get_service(&name)
+        });
+
         methods.add_meta_method(MetaMethod::ToString, |context, this, _arg: ()| {
             this.meta_to_string(context)
         });

test-scripts/get-service-existing.lua

@@ -0,0 +1,7 @@
+local game = Instance.new("DataModel")
+
+local workspace = Instance.new("Workspace")
+workspace.Parent = game
+
+local found = game:GetService("Workspace")
+assert(found == workspace)

test-scripts/get-service-invalid-service.lua

@@ -0,0 +1,8 @@
+local game = Instance.new("DataModel")
+
+local ok, err = pcall(function()
+	return game:GetService("GitService") -- this service will never exist
+end)
+
+assert(not ok)
+assert(tostring(err):find("GitService") ~= nil)

test-scripts/get-service-new.lua

@@ -0,0 +1,5 @@
+local game = Instance.new("DataModel")
+
+local workspace = game:GetService("Workspace")
+assert(workspace.Parent == game)
+assert(workspace.ClassName == "Workspace")

test-scripts/get-service-not-datamodel.lua

@@ -0,0 +1,8 @@
+local folder = Instance.new("Folder")
+
+local ok, err = pcall(function()
+	return folder:GetService("Workspace")
+end)
+
+assert(not ok)
+assert(tostring(err):find("DataModel") ~= nil)