[FIX] qweb: fix issue variables set in body of t-call

The body of a t-call directive may be used to define private variables
to the sub template call.

However, the code that handles t-call worked like this:

- compile sub template if necessary
- then compile body of t-call to extract variables

This means that the variables defined in the t-call body were not yet
processed and available in the context.  Because of that, when the call
to t-esc is done, there is not internal qweb var, and the code simply
outputs a scope['varname'], which is in our case a VDOMArray, so it is
displayed as [object object]

What this fix does is changing the way t-esc works: if we are in the
context of a sub template, then it assumes that any outside variable may
or may not be a VDomArray, so it needs to check and eventually convert
it to a string, if necessary.

closes #719

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

@@ -1502,6 +1502,7 @@ exports[`t-call (template calling recursive template, part 2 2`] = `
     let vn3 = h('p', p3, c3);
     c2.push(vn3);
     let _4 = scope['node'].val;
+    _4 = _4 instanceof utils.VDomArray ? utils.vDomToString(_4) : _4;
     if (_4 != null) {
         c3.push({text: _4});
     }
@@ -1581,6 +1582,7 @@ exports[`t-call (template calling recursive template, part 3 2`] = `
     let vn3 = h('p', p3, c3);
     c2.push(vn3);
     let _4 = scope['node'].val;
+    _4 = _4 instanceof utils.VDomArray ? utils.vDomToString(_4) : _4;
     if (_4 != null) {
         c3.push({text: _4});
     }
@@ -1662,6 +1664,7 @@ exports[`t-call (template calling recursive template, part 4: with t-set recursi
     let vn3 = h('p', p3, c3);
     c2.push(vn3);
     let _4 = scope['node'].val;
+    _4 = _4 instanceof utils.VDomArray ? utils.vDomToString(_4) : _4;
     if (_4 != null) {
         c3.push({text: _4});
     }
@@ -1752,6 +1755,33 @@ exports[`t-call (template calling t-call with t-if 1`] = `
 }"
 `;
 
+exports[`t-call (template calling t-call with t-set inside and body text content 1`] = `
+"function anonymous(context, extra
+) {
+    // Template name: \\"main\\"
+    let utils = this.constructor.utils;
+    let scope = Object.create(context);
+    let h = this.h;
+    let c1 = [], p1 = {key:1};
+    let vn1 = h('div', p1, c1);
+    let _origScope4 = scope;
+    scope = Object.create(scope);
+    scope.__access_mode__ = 'ro';
+    {
+        {
+            let c__0 = [];
+            let c5 = new utils.VDomArray();
+            c5.push({text: \`yip yip\`});
+            scope.val = c5
+            scope[utils.zero] = c__0;
+        }
+        this.constructor.subTemplates['1'].call(this, scope, Object.assign({}, extra, {parentNode: c1, parent: utils.getComponent(context), key: '__6__'}));
+    }
+    scope = _origScope4;
+    return vn1;
+}"
+`;
+
 exports[`t-call (template calling t-call with t-set inside and outside 1`] = `
 "function anonymous(context, extra
 ) {

tests/qweb/qweb.test.ts

@@ -1072,6 +1072,21 @@ describe("t-call (template calling", () => {
     expect(renderToString(qweb1, "main")).toBe("<div><span>ok</span></div>");
     expect(renderToString(qweb2, "main")).toBe("<div><span>ok</span></div>");
   });
+
+  test("t-call with t-set inside and body text content", () => {
+    qweb.addTemplate("sub", `<p><t t-esc="val"/></p>`);
+    qweb.addTemplate(
+      "main",
+      `
+      <div>
+        <t t-call="sub">
+          <t t-set="val">yip yip</t>
+        </t>
+      </div>`
+    );
+    const expected = "<div><p>yip yip</p></div>";
+    expect(renderToString(qweb, "main")).toBe(expected);
+  });
 });
 
 describe("foreach", () => {