feat(editor): Introduce proxy completions to expressions (#5075)

* ⚡ Introduce proxy completions to expressions

* 🧪 Add tests

* ⚡ Replace snippet with alphabetic char completions

* ⚡ Tighten `DateTime` check

* 🧹 Clean up `n8nLang`

* 🔥 Remove duplicate

* 👕 Remove non-null assertion

* ⚡ Confirm that `overlay` is needed

* 🔥 Remove comment

* 🔥 Remove more unneeded code

* 🔥 Remove unneded Pinia setup

* ⚡ Simplify syntax

packages/workflow/src/Expression.ts

@@ -255,7 +255,7 @@ export class Expression {
 		const returnValue = this.renderExpression(parameterValue, data);
 		if (typeof returnValue === 'function') {
 			if (returnValue.name === '$') throw new Error('invalid syntax');
-			throw new Error(`${returnValue.name} is a function. Please add ()`);
+			throw new Error('This is a function. Please add ()');
 		} else if (typeof returnValue === 'string') {
 			return returnValue;
 		} else if (returnValue !== null && typeof returnValue === 'object') {

packages/workflow/src/WorkflowDataProxy.ts

@@ -130,7 +130,7 @@ export class WorkflowDataProxy {
 			return {}; // incoming connection has pinned data, so stub context object
 		}
 
-		if (!that.runExecutionData?.executionData) {
+		if (!that.runExecutionData?.executionData && !that.runExecutionData?.resultData) {
 			throw new ExpressionError(
 				"The workflow hasn't been executed yet, so you can't reference any context data",
 				{
@@ -931,6 +931,18 @@ export class WorkflowDataProxy {
 				return new Proxy(
 					{},
 					{
+						ownKeys(target) {
+							return [
+								'pairedItem',
+								'itemMatching',
+								'item',
+								'first',
+								'last',
+								'all',
+								'context',
+								'params',
+							];
+						},
 						get(target, property, receiver) {
 							if (['pairedItem', 'itemMatching', 'item'].includes(property as string)) {
 								const pairedItemMethod = (itemIndex?: number) => {