[FIX] component: make arrow-function capture backwards compatible

When fixing the absence of capture for arrow functions passed as props,
we unintentionally introduced a breaking change: bare function calls in
the arrow functions used to be called  with the rendering context as
their this value and this was no longer the case.

This commit fixes that by intentionally not capturing the value of
functions that are called withing the arrow function.

src/qweb/compilation_context.ts

@@ -162,7 +162,7 @@ export class CompilationContext {
     const tokens = compileExprToArray(expr, this.variables);
     const done = new Set();
     return tokens
-      .map((tok) => {
+      .map((tok, i) => {
         // "this" in captured expressions should be the current component
         if (tok.value === "this") {
           if (!done.has("this")) {
@@ -174,7 +174,14 @@ export class CompilationContext {
         // Variables that should be looked up in the scope. isLocal is for arrow
         // function arguments that should stay untouched (eg "ev => ev" should
         // not become "const ev_1 = scope['ev']; ev_1 => ev_1")
-        if (tok.varName && !tok.isLocal) {
+        if (
+          tok.varName &&
+          !tok.isLocal &&
+          // HACK: for backwards compatibility, we don't capture bare methods
+          // this allows them to be called with the rendering context/scope
+          // as their this value.
+          (!tokens[i + 1] || tokens[i + 1].type !== "LEFT_PAREN")
+        ) {
           if (!done.has(tok.varName)) {
             done.add(tok.varName);
             this.addLine(`const ${tok.varName}_${argId} = ${tok.value};`);

tests/component/__snapshots__/component.test.ts.snap

@@ -1798,6 +1798,61 @@ exports[`props evaluation  arrow function prop captures loop variables 2`] = `
 }"
 `;
 
+exports[`props evaluation  bare function calls in arrow function has rendering context as 'this' 1`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"Parent\\"
+    let utils = this.constructor.utils;
+    let QWeb = this.constructor;
+    let parent = context;
+    let scope = Object.create(context);
+    let h = this.h;
+    let c1 = [], p1 = {key:1};
+    let vn1 = h('div', p1, c1);
+    scope.ctxVal = 2;
+    // Component 'Child'
+    let w3 = '__4__' in parent.__owl__.cmap ? parent.__owl__.children[parent.__owl__.cmap['__4__']] : false;
+    let props3 = {callback:value=>scope['setValue'](value),value:scope['state'].val};
+    if (w3 && w3.__owl__.currentFiber && !w3.__owl__.vnode) {
+        w3.destroy();
+        w3 = false;
+    }
+    if (w3) {
+        w3.__updateProps(props3, extra.fiber, undefined);
+        let pvnode = w3.__owl__.pvnode;
+        c1.push(pvnode);
+    } else {
+        let componentKey3 = \`Child\`;
+        let W3 = scope['Child'] || context.constructor.components[componentKey3] || QWeb.components[componentKey3];
+        if (!W3) {throw new Error('Cannot find the definition of component \\"' + componentKey3 + '\\"')}
+        w3 = new W3(parent, props3);
+        parent.__owl__.cmap['__4__'] = w3.__owl__.id;
+        let fiber = w3.__prepare(extra.fiber, undefined, () => { const vnode = fiber.vnode; pvnode.sel = vnode.sel; });
+        let pvnode = h('dummy', {key: '__4__', hook: {remove() {},destroy(vn) {w3.destroy();}}});
+        c1.push(pvnode);
+        w3.__owl__.pvnode = pvnode;
+    }
+    w3.__owl__.parentLastFiberId = extra.fiber.id;
+    return vn1;
+}"
+`;
+
+exports[`props evaluation  bare function calls in arrow function has rendering context as 'this' 2`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"Child\\"
+    let scope = Object.create(context);
+    let h = this.h;
+    let c5 = [], p5 = {key:5};
+    let vn5 = h('span', p5, c5);
+    let _6 = scope['props'].value;
+    if (_6 != null) {
+        c5.push({text: _6});
+    }
+    return vn5;
+}"
+`;
+
 exports[`props evaluation  t-set with a body expression can be used as textual prop 1`] = `
 "function anonymous(context, extra
 ) {

tests/component/component.test.ts

@@ -1920,6 +1920,49 @@ describe("props evaluation ", () => {
     expect(env.qweb.templates.Child.fn.toString()).toMatchSnapshot();
   });
 
+  test("bare function calls in arrow function has rendering context as 'this'", async () => {
+    expect.assertions(7);
+    let child, parent;
+    class Child extends Component {
+      setup() {
+        child = this;
+      }
+    }
+    env.qweb.addTemplate("Child", `<span><t t-esc="props.value"/></span>`);
+
+    class Parent extends Component {
+      static components = { Child };
+      state = useState({ val: 42 });
+      setup() {
+        parent = this;
+      }
+      setValue(value) {
+        // 'this' is the rendering context, NOT the instance
+        expect(this).not.toBe(parent);
+        // the state in the rendering context should be the same as the instance's
+        expect(this.state).toBe(parent.state);
+        expect((this as any).ctxVal).toBe(2);
+        this.state.val = value;
+      }
+    }
+    env.qweb.addTemplate(
+      "Parent",
+      `<div>
+        <t t-set="ctxVal" t-value="2"/>
+        <Child callback="value => setValue(value)" value="state.val"/>
+      </div>`
+    );
+
+    const widget = new Parent();
+    await widget.mount(fixture);
+    expect(fixture.innerHTML).toBe("<div><span>42</span></div>");
+    child.props.callback(123);
+    await nextTick();
+    expect(fixture.innerHTML).toBe("<div><span>123</span></div>");
+    expect(env.qweb.templates.Parent.fn.toString()).toMatchSnapshot();
+    expect(env.qweb.templates.Child.fn.toString()).toMatchSnapshot();
+  });
+
   test("arrow function prop captures context component instance as 'this' inside slot", async () => {
     expect.assertions(7);
     let child, parent;

tests/qweb/__snapshots__/qweb.test.ts.snap

@@ -3111,8 +3111,7 @@ exports[`t-on t-on with inline statement, part 3 1`] = `
     let c1 = [], p1 = {key:1,on:{}};
     let vn1 = h('button', p1, c1);
     const state_2 = scope['state'];
-    const someFunction_2 = scope['someFunction'];
-    p1.on['click'] = function (e) {if (context.__owl__.status === 5){return}const res = (() => { return state_2.n=someFunction_2(3) })(); if (typeof res === 'function') { res(e) }};
+    p1.on['click'] = function (e) {if (context.__owl__.status === 5){return}const res = (() => { return state_2.n=scope['someFunction'](3) })(); if (typeof res === 'function') { res(e) }};
     c1.push({text: \`Toggle\`});
     return vn1;
 }"