Fix case where exported properties value is lost

Fixes exported property modified values lost when creating a placeholder script instance with a failed script compilation

- Object set/get will call PlaceHolderScriptInstance's new fallback set/get methods as a last resort. This way, placeholder script instances can keep the values for storage or until the script is compiled successfuly.
- Script::can_instance() will only return true if a real script instance can be created. Otherwise, in the case of placeholder script instances, it will return false.
- Object::set_script(script) is now in charge of requesting the creation of placeholder script instances. It's no longer Script::instance_create(owner)'s duty.
- PlaceHolderScriptInstance has a new method set_build_failed(bool) to determine whether it should call into its script methods or not.
- Fixed a few problems during reloading of C# scripts.

1 files changed, 12 insertions, 0 deletions

diff --git a/core/script_language.h b/core/script_language.h
index 4e81b9b626..c24f237e36 100644
--- a/core/script_language.h
+++ b/core/script_language.h
@@ -115,6 +115,7 @@ public:
 
 	virtual StringName get_instance_base_type() const = 0; // this may not work in all scripts, will return empty if so
 	virtual ScriptInstance *instance_create(Object *p_this) = 0;
+	virtual PlaceHolderScriptInstance *placeholder_instance_create(Object *p_this) { return NULL; }
 	virtual bool instance_has(const Object *p_this) const = 0;
 
 	virtual bool has_source_code() const = 0;
@@ -176,6 +177,9 @@ public:
 
 	virtual bool is_placeholder() const { return false; }
 
+	virtual void property_set_fallback(const StringName &p_name, const Variant &p_value, bool *r_valid);
+	virtual Variant property_get_fallback(const StringName &p_name, bool *r_valid);
+
 	virtual MultiplayerAPI::RPCMode get_rpc_mode(const StringName &p_method) const = 0;
 	virtual MultiplayerAPI::RPCMode get_rset_mode(const StringName &p_variable) const = 0;
 
@@ -319,6 +323,8 @@ class PlaceHolderScriptInstance : public ScriptInstance {
 	ScriptLanguage *language;
 	Ref<Script> script;
 
+	bool build_failed;
+
 public:
 	virtual bool set(const StringName &p_name, const Variant &p_value);
 	virtual bool get(const StringName &p_name, Variant &r_ret) const;
@@ -344,8 +350,14 @@ public:
 
 	void update(const List<PropertyInfo> &p_properties, const Map<StringName, Variant> &p_values); //likely changed in editor
 
+	void set_build_failed(bool p_build_failed) { build_failed = p_build_failed; }
+	bool get_build_failed() const { return build_failed; }
+
 	virtual bool is_placeholder() const { return true; }
 
+	virtual void property_set_fallback(const StringName &p_name, const Variant &p_value, bool *r_valid);
+	virtual Variant property_get_fallback(const StringName &p_name, bool *r_valid);
+
 	virtual MultiplayerAPI::RPCMode get_rpc_mode(const StringName &p_method) const { return MultiplayerAPI::RPC_MODE_DISABLED; }
 	virtual MultiplayerAPI::RPCMode get_rset_mode(const StringName &p_variable) const { return MultiplayerAPI::RPC_MODE_DISABLED; }