feat!: provide variables used in feel expressions

Related to camunda/camunda-modeler#5639

BREAKING CHANGE: getVariables now also returns variables without scope. I.e.: scope is now optional in ProcessVariables

Author: Buckwich

README.md

@@ -2,7 +2,10 @@
 
 [![CI](https://github.com/bpmn-io/variable-resolver/actions/workflows/CI.yml/badge.svg)](https://github.com/bpmn-io/variable-resolver/actions/workflows/CI.yml)
 
-A bpmn-js extension to add and manage additional variable extractors in bpmn diagrams.
+An extension for [bpmn-js](https://github.com/bpmn-io/bpmn-js) that makes the data model of the diagram available to other components.
+
+> [!NOTE]
+> As of version `v3` this library exposes both written and consumed variables, you can filter them via options.
 
 ## Usage
 
@@ -30,19 +33,56 @@ const modeler = new BpmnModeler({
 
 ### Retrieving variables
 
-To retrieve the variables from a diagram, use one of the following methods of the `variableResolver` service:
+Retrieve the variables from a diagram using the `variableResolver` service:
 
 ```javascript
-const elementRegistry = modeler.get('elementRegistry');
 const variableResolver = modeler.get('variableResolver');
+const elementRegistry = modeler.get('elementRegistry');
 
+// retrieve variables relevant to an element
 const task = elementRegistry.get('Task_1');
-const process = elementRegistry.get('Process_1');
 
-await variableResolver.getVariablesForElement(task); // returns variables in the scope of the element
-await variableResolver.getProcessVariables(process); // returns all variables for the process, not filtering by scope
+// default: variables relevant to <task> in its visible scopes
+await variableResolver.getVariablesForElement(task);
+
+// variables read by <task> only
+await variableResolver.getVariablesForElement(task, {
+  read: true,
+  written: false
+});
+
+// all variables written by <task>
+await variableResolver.getVariablesForElement(task, { written: true, read: false });
+
+// local variables only (scope === queried element)
+await variableResolver.getVariablesForElement(task, {
+  local: true,
+  external: false
+});
+
+// non-local variables only (scope !== queried element)
+await variableResolver.getVariablesForElement(task, {
+  local: false,
+  external: true
+});
+
+// retrieve all variables defined in a process
+const processElement = elementRegistry.get('Process_1');
+
+// returns all variables for the process (unfiltered), for local processing
+await variableResolver.getProcessVariables(processElement);
 ```
 
+`getVariablesForElement(element, options)` supports five filter switches:
+
+| Option | Default | Description |
+| --- | --- | --- |
+| `read` | `true` | Include variables consumed by the queried element |
+| `written` | `true` | Include variables written/created by the queried element |
+| `local` | `true` | Include variables local to the queried element scope |
+| `external` | `true` | Include variables outside the queried element scope |
+| `outputMappings` | `true` | Count output-mapping reads as reads |
+
 ### Adding a variable extractor
 
 To add your own variables, extend the `variableProvider` class in your extension. It only needs to implement the `getVariables` method, which takes an element as an argument and returns an array of variables you want to add to the scope of the element. The function can be asynchronous.
@@ -76,11 +116,9 @@ export const MyExtension = {
 
 ### Advanced use-cases
 
-By default, `getVariablesForElement` and `getProcessVariables` will attempt to merge variables with the same name and scope into
-one. Entry structure and types are then mixed.
+By default, `getVariablesForElement` and `getProcessVariables` merge variables with the same name and scope into one - entry structure and types are mixed in the merged representation.
 
-In some cases, you might want access to the raw data, e.g. to run lint rules to detect potential schema mismatches between providers.
-For this, you can use
+In some cases, you might want access to the raw data, e.g. to run lint rules to detect potential schema mismatches between providers. For this, you can use `getRawVariables`:
 
 ```javascript
 const variableResolver = modeler.get('variableResolver');