[FIX] debug tools: do not crash on non json-stringifiable props

closes #595

tests/tooling/debug_script_4.test.ts

@@ -0,0 +1,58 @@
+/**
+ * We can only make one test per file, since the debug tool modify in place
+ * the owl object in a way that is difficult to undo.
+ */
+
+import { debugOwl } from "../../tools/debug";
+import * as owl from "../../src/index";
+
+import { Component, Env } from "../../src/component/component";
+import { xml } from "../../src/tags";
+import { makeTestFixture, makeTestEnv } from "../helpers";
+
+let fixture: HTMLElement = makeTestFixture();
+let env: Env = makeTestEnv();
+Component.env = env;
+
+debugOwl(owl, { logScheduler: true });
+
+test("log a sub component with non stringifiable props", async () => {
+  const steps: string[] = [];
+  const log = console.log;
+  console.log = arg => steps.push(arg);
+
+  class Child extends Component<any,any> {
+      static template = xml`<span><t t-esc="props.obj.val"/></span>`;
+  }
+
+  const circularObject: any = {val: 1};
+  circularObject.circularObject = circularObject;
+
+  class Parent extends Component<any, any> {
+    static template = xml`<div><Child obj="obj"/></div>`;
+    static components = { Child };
+    obj = circularObject;
+
+  }
+
+  const parent = new Parent(null, {});
+  await parent.mount(fixture);
+  parent.unmount();
+
+  expect(steps).toEqual([
+    "[OWL_DEBUG] Parent<id=1> constructor, props={}",
+    "[OWL_DEBUG] Parent<id=1> mount",
+    "[OWL_DEBUG] Parent<id=1> willStart",
+    "[OWL_DEBUG] scheduler: start running tasks queue",
+    "[OWL_DEBUG] Parent<id=1> rendering template",
+    "[OWL_DEBUG] Child<id=2> constructor, props=<JSON error>",
+    "[OWL_DEBUG] Child<id=2> willStart",
+    "[OWL_DEBUG] Child<id=2> rendering template",
+    "[OWL_DEBUG] Child<id=2> mounted",
+    "[OWL_DEBUG] Parent<id=1> mounted",
+    "[OWL_DEBUG] scheduler: stop running tasks queue",
+    "[OWL_DEBUG] Parent<id=1> willUnmount",
+    "[OWL_DEBUG] Child<id=2> willUnmount"
+  ]);
+  console.log = log;
+});