[FIX] qweb/component: handle nested t-foreach and components

The way keys were handled in QWeb was mostly ok, but a little naive. It
is fine when we deal with a list of dom nodes, since the reconciliation
algorithm need only to be able to differentiate/reconcile nodes in that
list, but it is an issue with components, which needs to globally be
able to find themselves in their parent's children map.

Because of the way this was handled, there were situations were Owl
internal virtual dom would crash, since components wrongly assumed that
they were already rendered in a different place.

To fix this, we generalize the way keys are generated, by concatenating
all sub keys coming from each iteration loops.

closes #584

src/qweb/qweb.ts

@@ -402,8 +402,8 @@ export class QWeb extends EventBus {
       ctx.shouldDefineResult = false;
       ctx.addLine(`let c${ctx.parentNode} = extra.parentNode;`);
       if (defineKey) {
-        ctx.currentKey = `key${ctx.generateID()}`;
-        ctx.addLine(`let ${ctx.currentKey} = extra.key || '';`);
+        ctx.addLine(`let key0 = extra.key || "";`);
+        ctx.hasKey0 = true;
       }
     }
     this._compileNode(elem, ctx);
@@ -482,9 +482,6 @@ export class QWeb extends EventBus {
       }
       return;
     }
-    if (ctx !== ctx.rootContext) {
-      ctx = ctx.subContext("currentKey", ctx.currentKey);
-    }
 
     const firstLetter = node.tagName[0];
     if (firstLetter === firstLetter.toUpperCase()) {
@@ -759,8 +756,8 @@ export class QWeb extends EventBus {
       }
     }
     let nodeID = ctx.generateID();
-    let nodeKey = ctx.currentKey || nodeID;
-    const parts = [`key:${nodeKey}`];
+    let key = ctx.loopNumber || ctx.hasKey0 ? `\`\${key${ctx.loopNumber}}_${nodeID}\`` : nodeID;
+    const parts = [`key:${key}`];
     if (attrs.length + tattrs.length > 0) {
       parts.push(`attrs:{${attrs.join(",")}}`);
     }
@@ -789,6 +786,9 @@ export class QWeb extends EventBus {
     ctx.addLine(`let vn${nodeID} = h('${node.nodeName}', p${nodeID}, c${nodeID});`);
     if (ctx.parentNode) {
       ctx.addLine(`c${ctx.parentNode}.push(vn${nodeID});`);
+    } else if (ctx.loopNumber || ctx.hasKey0) {
+      ctx.rootContext.shouldDefineResult = true;
+      ctx.addLine(`result = vn${nodeID};`);
     }
 
     return nodeID;