[FIX] qweb/component: fix scoping issue with t-model and t-foreach

Without this fix, the handler set by t-model did not capture properly
the expression that needs to be updated.

closes #474

src/qweb/compilation_context.ts

@@ -47,6 +47,30 @@ export class CompilationContext {
     return id;
   }
 
+  /**
+   * This method generates a "template key", which is basically a unique key
+   * which depends on the currently set keys, and on the iteration numbers (if
+   * we are in a loop).
+   *
+   * Such a key is necessary when we need to associate an id to some element
+   * generated by a template (for example, a component)
+   */
+  generateTemplateKey(): string {
+    const id = this.generateID();
+    let locationExpr = `\`__${this.generateID()}__`;
+    for (let i = 0; i < this.loopNumber - 1; i++) {
+      locationExpr += `\${i${i + 1}}__`;
+    }
+    if (this.lastNodeKey || this.currentKey) {
+      const k = this.lastNodeKey || this.currentKey;
+      this.addLine(`let k${id} = ${locationExpr}\` + ${k};`);
+    } else {
+      locationExpr += this.loopNumber ? `\${i${this.loopNumber}}__\`` : "`";
+      this.addLine(`let k${id} = ${locationExpr};`);
+    }
+    return `k${id}`;
+  }
+
   generateCode(): string[] {
     const shouldTrackScope = this.shouldTrackScope && this.scopeVars.length;
     if (shouldTrackScope) {