[FIX] qweb/component: refactoring of scoping/variables/slots

This commit is a significant refactoring of the internal of QWeb. It
simplifies the way variables/scoping and slots interact together.  The
main idea is that we use a simple scope object instead of a
context/var/scope object.

This commit also implement the actual correct QWeb semantic for the
t-call directive with a sub body.  Before, we simply extracted the
variables from the body and injected them at the top of the sub
template.  We now simply compile the body before the sub template.

This is a joint work with Lucas (lpe).

closes #541
closes #544
closes #545

closes #557
closes #556

src/qweb/qweb.ts

@@ -87,6 +87,7 @@ interface Utils {
 }
 
 const UTILS: Utils = {
+  zero: Symbol('zero'),
   toObj(expr) {
     if (typeof expr === "string") {
       expr = expr.trim();
@@ -171,7 +172,7 @@ export class QWeb extends EventBus {
   // recursiveTemplates contains sub templates called with t-call, but which
   // ends up in recursive situations.  This is very similar to the slot situation,
   // as in we need to propagate the scope.
-  recursiveFns = {};
+  subTemplates = {};
 
   isUpdating: boolean = false;
   translateFn?: QWebConfig["translateFn"];
@@ -360,23 +361,12 @@ export class QWeb extends EventBus {
       ctx.shouldDefineResult = false;
     }
     if (parentContext) {
-      ctx.templates = Object.create(parentContext.templates);
       ctx.variables = Object.create(parentContext.variables);
       ctx.parentNode = parentContext.parentNode || ctx.generateID();
       ctx.allowMultipleRoots = true;
       ctx.hasParentWidget = true;
       ctx.shouldDefineResult = false;
       ctx.addLine(`let c${ctx.parentNode} = extra.parentNode;`);
-
-      for (let v in parentContext.variables) {
-        let variable = <any>parentContext.variables[v];
-        if (variable.id) {
-          ctx.addLine(`let ${variable.id} = extra.vars.${variable.id};`);
-        }
-      }
-    }
-    if (parentContext) {
-      ctx.addLine("Object.assign(context, extra.fiber.scope);");
     }
     this._compileNode(elem, ctx);
 
@@ -673,7 +663,7 @@ export class QWeb extends EventBus {
       if (name.startsWith("t-att-")) {
         let attName = name.slice(6);
         const v = ctx.getValue(value);
-        let formattedValue = typeof v === "string" ? ctx.formatExpression(v) : v.id;
+        let formattedValue = typeof v === "string" ? ctx.formatExpression(v) : `scope.${v.id}`;
 
         if (attName === "class") {
           ctx.rootContext.shouldDefineUtils = true;