perf(workflow): get_transitions (#18834)

* Load from db only if doc passed is not of type Document. This was
  added earlier to load in case of dicts. ref: #11883
* Move blocks to evaluate only if required
* Add typing hints

(cherry picked from commit a093b7b)

frappe/model/workflow.py

@@ -4,13 +4,18 @@
 from __future__ import unicode_literals
 
 import json
+from typing import TYPE_CHECKING, Union
 
 from six import string_types
 
 import frappe
 from frappe import _
 from frappe.utils import cint
 
+if TYPE_CHECKING:
+	from frappe.model.document import Document
+	from frappe.workflow.doctype.workflow.workflow import Workflow
+
 
 class WorkflowStateError(frappe.ValidationError):
 	pass
@@ -36,20 +41,22 @@ def get_workflow_name(doctype):
 
 
 @frappe.whitelist()
-def get_transitions(doc, workflow=None, raise_exception=False):
+def get_transitions(
+	doc: Union["Document", str, dict], workflow: "Workflow" = None, raise_exception: bool = False
+) -> list[dict]:
 	"""Return list of possible transitions for the given doc"""
-	doc = frappe.get_doc(frappe.parse_json(doc))
+	from frappe.model.document import Document
+
+	if not isinstance(doc, Document):
+		doc = frappe.get_doc(frappe.parse_json(doc))
+		doc.load_from_db()
 
 	if doc.is_new():
 		return []
 
-	doc.load_from_db()
-
-	frappe.has_permission(doc, "read", throw=True)
-	roles = frappe.get_roles()
+	doc.check_permission("read")
 
-	if not workflow:
-		workflow = get_workflow(doc.doctype)
+	workflow = workflow or get_workflow(doc.doctype)
 	current_state = doc.get(workflow.workflow_state_field)
 
 	if not current_state:
@@ -59,11 +66,14 @@ def get_transitions(doc, workflow=None, raise_exception=False):
 			frappe.throw(_("Workflow State not set"), WorkflowStateError)
 
 	transitions = []
+	roles = frappe.get_roles()
+
 	for transition in workflow.transitions:
 		if transition.state == current_state and transition.allowed in roles:
 			if not is_transition_condition_satisfied(transition, doc):
 				continue
 			transitions.append(transition.as_dict())
+
 	return transitions
 
 
@@ -83,7 +93,7 @@ def get_workflow_safe_globals():
 	)
 
 
-def is_transition_condition_satisfied(transition, doc):
+def is_transition_condition_satisfied(transition, doc) -> bool:
 	if not transition.condition:
 		return True
 	else:
@@ -202,7 +212,7 @@ def validate_workflow(doc):
 			)
 
 
-def get_workflow(doctype):
+def get_workflow(doctype) -> "Workflow":
 	return frappe.get_doc("Workflow", get_workflow_name(doctype))