[FIX] qweb: properly handle subtemplates in shared templates

With QWeb, we can register globally templates (using the xml tag or
the registerTemplate function). However, these templates, once
compiled, can generate sub template compiled functions. Before this
commit, these sub functions were local to a specific instance.

This means that creating a new QWeb instance and rendering a global
parent template would crash, since it was unable to find the actual sub
function.

This commit fixes the issue: the sub functions are now shared
statically, but with a unique ID, so we do not have issues with sub
functions having a same name in different QWeb instance.

closes #701

src/qweb/base_directives.ts

@@ -234,10 +234,12 @@ QWeb.addDirective({
 
     // Step 2: compile target template in sub templates
     // ------------------------------------------------
-    if (!qweb.subTemplates[subTemplate]) {
-      qweb.subTemplates[subTemplate] = true;
+    let subId = qweb.subTemplates[subTemplate];
+    if (!subId) {
+      subId = QWeb.nextId++;
+      qweb.subTemplates[subTemplate] = subId;
       const subTemplateFn = qweb._compile(subTemplate, nodeTemplate.elem, ctx, true);
-      qweb.subTemplates[subTemplate] = subTemplateFn;
+      QWeb.subTemplates[subId] = subTemplateFn;
     }
 
     // Step 3: compile t-call body if necessary
@@ -275,12 +277,16 @@ QWeb.addDirective({
     const parentNode = ctx.parentNode ? `c${ctx.parentNode}` : "result";
     const extra = `Object.assign({}, extra, {parentNode: ${parentNode}, parent: ${parentComponent}, key: ${key}})`;
     if (ctx.parentNode) {
-      ctx.addLine(`this.subTemplates['${subTemplate}'].call(this, ${callingScope}, ${extra});`);
+      ctx.addLine(
+        `this.constructor.subTemplates['${subId}'].call(this, ${callingScope}, ${extra});`
+      );
     } else {
       // this is a t-call with no parentnode, we need to extract the result
       ctx.rootContext.shouldDefineResult = true;
       ctx.addLine(`result = []`);
-      ctx.addLine(`this.subTemplates['${subTemplate}'].call(this, ${callingScope}, ${extra});`);
+      ctx.addLine(
+        `this.constructor.subTemplates['${subId}'].call(this, ${callingScope}, ${extra});`
+      );
       ctx.addLine(`result = result[0]`);
     }