Check against this usage in computed functions

src/utils/isThisGetCallExpression.ts

@@ -0,0 +1,8 @@
+import { Node } from '../interfaces';
+
+export default function isThisGetCallExpression(node: Node): boolean {
+		return node.type === 'CallExpression' &&
+				node.callee.type === 'MemberExpression' &&
+				node.callee.object.type === 'ThisExpression' &&
+				node.callee.property.name === 'get';
+}

src/utils/walkThroughTopFunctionScope.ts

@@ -0,0 +1,21 @@
+import { Node } from '../interfaces';
+import { walk } from 'estree-walker';
+
+export default function walkThroughTopFunctionScope(body: Node, callback: Function) {
+  let lexicalDepth = 0;
+  walk(body, {
+    enter(node: Node) {
+      if (/^Function/.test(node.type)) {
+        lexicalDepth += 1;
+      } else if (lexicalDepth === 0) {
+        callback(node)
+      }
+    },
+
+    leave(node: Node) {
+      if (/^Function/.test(node.type)) {
+        lexicalDepth -= 1;
+      }
+    },
+  });
+}

src/validate/js/propValidators/computed.ts

@@ -2,6 +2,8 @@ import checkForDupes from '../utils/checkForDupes';
 import checkForComputedKeys from '../utils/checkForComputedKeys';
 import { Validator } from '../../';
 import { Node } from '../../../interfaces';
+import walkThroughTopFunctionScope from '../../../utils/walkThroughTopFunctionScope';
+import isThisGetCallExpression from '../../../utils/isThisGetCallExpression';
 
 const isFunctionExpression = new Set([
 	'FunctionExpression',
@@ -27,7 +29,23 @@ export default function computed(validator: Validator, prop: Node) {
 			);
 		}
 
-		const params = computation.value.params;
+		const { body, params } = computation.value;
+
+		walkThroughTopFunctionScope(body, (node: Node) => {
+			if (isThisGetCallExpression(node) && !node.callee.property.computed) {
+				validator.error(
+					`Cannot use this.get(...) — it must be passed into the computed function as an argument`,
+					node.start
+				);
+			}
+
+			if (node.type === 'ThisExpression') {
+				validator.error(
+					`Computed should be pure functions — they do not have access to the component instance and cannot use 'this'. Did you mean to put this in 'methods'?`,
+					node.start
+				);
+			}
+		});
 
 		if (params.length === 0) {
 			validator.error(

src/validate/js/propValidators/helpers.ts

@@ -3,6 +3,8 @@ import checkForComputedKeys from '../utils/checkForComputedKeys';
 import { walk } from 'estree-walker';
 import { Validator } from '../../';
 import { Node } from '../../../interfaces';
+import walkThroughTopFunctionScope from '../../../utils/walkThroughTopFunctionScope';
+import isThisGetCallExpression from '../../../utils/isThisGetCallExpression';
 
 export default function helpers(validator: Validator, prop: Node) {
 	if (prop.value.type !== 'ObjectExpression') {
@@ -18,45 +20,24 @@ export default function helpers(validator: Validator, prop: Node) {
 	prop.value.properties.forEach((prop: Node) => {
 		if (!/FunctionExpression/.test(prop.value.type)) return;
 
-		let lexicalDepth = 0;
 		let usesArguments = false;
 
-		walk(prop.value.body, {
+		walkThroughTopFunctionScope(prop.value.body, (node: Node) => {
-			enter(node: Node) {
+			if (isThisGetCallExpression(node) && !node.callee.property.computed) {
-				if (/^Function/.test(node.type)) {
+				validator.error(
-					lexicalDepth += 1;
+					`Cannot use this.get(...) — it must be passed into the helper function as an argument`,
-				} else if (lexicalDepth === 0) {
+					node.start
-					// handle special case that's caused some people confusion — using `this.get(...)` instead of passing argument
+				);
-					// TODO do the same thing for computed values?
+			}
-					if (
+
-						node.type === 'CallExpression' &&
+			if (node.type === 'ThisExpression') {
-						node.callee.type === 'MemberExpression' &&
+				validator.error(
-						node.callee.object.type === 'ThisExpression' &&
+					`Helpers should be pure functions — they do not have access to the component instance and cannot use 'this'. Did you mean to put this in 'methods'?`,
-						node.callee.property.name === 'get' &&
+					node.start
-						!node.callee.property.computed
+				);
-					) {
+			} else if (node.type === 'Identifier' && node.name === 'arguments') {
-						validator.error(
+				usesArguments = true;
-							`Cannot use this.get(...) — it must be passed into the helper function as an argument`,
+			}
-							node.start
-						);
-					}
-
-					if (node.type === 'ThisExpression') {
-						validator.error(
-							`Helpers should be pure functions — they do not have access to the component instance and cannot use 'this'. Did you mean to put this in 'methods'?`,
-							node.start
-						);
-					} else if (node.type === 'Identifier' && node.name === 'arguments') {
-						usesArguments = true;
-					}
-				}
-			},
-
-			leave(node: Node) {
-				if (/^Function/.test(node.type)) {
-					lexicalDepth -= 1;
-				}
-			},
 		});
 
 		if (prop.value.params.length === 0 && !usesArguments) {

test/validator/samples/computed-purify-check-no-this/errors.json

@@ -0,0 +1,8 @@
+[{
+  "message": "Computed should be pure functions — they do not have access to the component instance and cannot use 'this'. Did you mean to put this in 'methods'?",
+  "pos": 83,
+  "loc": {
+    "line": 7,
+    "column": 4
+  }
+}]

test/validator/samples/computed-purify-check-no-this/input.html

@@ -0,0 +1,11 @@
+<button>{{foo}}</button>
+
+<script>
+	export default {
+		computed: {
+			foo () {
+				this.set({ foo: true });
+			}
+		}
+	}
+</script>

test/validator/samples/computed-purify-check-this-get/errors.json

@@ -0,0 +1,8 @@
+[{
+  "message": "Cannot use this.get(...) — it must be passed into the computed function as an argument",
+  "pos": 73,
+  "loc": {
+    "line": 7,
+    "column": 11
+  }
+}]

test/validator/samples/computed-purify-check-this-get/input.html

@@ -0,0 +1,11 @@
+{{foo}}
+
+<script>
+	export default {
+		computed: {
+			foo () {
+				return this.get( 'bar' );
+			}
+		}
+	}
+</script>

test/validator/samples/helper-purity-check-this-get/input.html

@@ -8,4 +8,4 @@
 			}
 		}
 	}
-</script>
+</script>