Add better Transition debugging information.

Expose a few nice debugging tools when working with a transition:

```ts
interface Transition {
  /**
    In non-production builds, this function will return the stack that this Transition was
    created within. In production builds, this function will not be present.

    @method debugCreationStack
    @return string
  */
  debugCreationStack?: () => string | undefined;

  /**
    In non-production builds, this function will return the stack that this Transition was
    aborted within (or `undefined` if the Transition has not been aborted yet). In production
    builds, this function will not be present.

    @method debugAbortStack
    @return string
  */
  debugAbortStack?: () => string | undefined;

  /**
    In non-production builds, this property references the Transition that _this_ Transition
    was derived from or `undefined` if this transition did not derive from another. In
    production builds, this property will not be present.

    @Property debugPreviousTransition
    @type {Transition | undefined}
  */
  debugPreviousTransition: Maybe<Transition<T>>;
}
```

---

Note: I've confirmed that Ember's build pipeline properly replaces the
`if (DEBUG) {` bits with `true` and `false` as appropriate:

  ```js
  if (true
      /* DEBUG */
  ) {
    var _error = new Error(`Transition creation stack`);

    this.debugCreationStack = () => _error.stack;

    this.debugPreviousTransition = previousTransition;
  }
```

Author: Robert Jackson

ember-cli-build.js

@@ -37,12 +37,27 @@ function resolveRelativeModulePath(name, child) {
 resolveRelativeModulePath.baseDir = () => __dirname;
 
 function toAMD(tree) {
+  const isProduction = process.env.EMBER_ENV === 'production';
+  const isDebug = !isProduction;
+
   return new Babel(tree, {
     moduleIds: true,
     getModuleId: getRelativeModulePath,
     plugins: [
       ['module-resolver', { resolvePath: resolveRelativeModulePath }],
       ['@babel/plugin-transform-modules-amd', { noInterop: true }],
+      [
+        'babel-plugin-debug-macros',
+        {
+          flags: [
+            {
+              source: '@glimmer/env',
+              flags: { DEBUG: isDebug, CI: !!process.env.CI },
+            },
+          ],
+        },
+        '@glimmer/env inlining',
+      ],
     ],
   });
 }
@@ -95,7 +110,7 @@ module.exports = function () {
   });
   let rrAMD = toAMD(rr);
 
-  let backburner = findLib('backburner.js', 'dist/es6', {
+  let backburner = new Funnel(findLib('backburner.js', 'dist/es6'), {
     files: ['backburner.js'],
     annotation: 'backburner es',
   });

lib/router/transition.ts

@@ -6,6 +6,7 @@ import TransitionAborted, { ITransitionAbortedError } from './transition-aborted
 import { OpaqueIntent } from './transition-intent';
 import TransitionState, { TransitionError } from './transition-state';
 import { log, promiseLabel } from './utils';
+import { DEBUG } from '@glimmer/env';
 
 export type OnFulfilled<T, TResult1> =
   | ((value: T) => TResult1 | PromiseLike<TResult1>)
@@ -65,6 +66,35 @@ export default class Transition<T extends Route> implements Partial<Promise<T>>
   isCausedByAbortingReplaceTransition = false;
   _visibleQueryParams: Dict<unknown> = {};
 
+  /**
+    In non-production builds, this function will return the stack that this Transition was
+    created within. In production builds, this function will not be present.
+
+    @method debugCreationStack
+    @return string
+  */
+  declare debugCreationStack?: () => string | undefined;
+
+  /**
+    In non-production builds, this function will return the stack that this Transition was
+    aborted within (or `undefined` if the Transition has not been aborted yet). In production
+    builds, this function will not be present.
+
+    @method debugAbortStack
+    @return string
+  */
+  declare debugAbortStack?: () => string | undefined;
+
+  /**
+    In non-production builds, this property references the Transition that _this_ Transition
+    was derived from or `undefined` if this transition did not derive from another. In
+    production builds, this property will not be present.
+
+    @property debugPreviousTransition
+    @type {Transition | undefined}
+  */
+  declare debugPreviousTransition: Maybe<Transition<T>>;
+
   constructor(
     router: Router<T>,
     intent: Maybe<OpaqueIntent>,
@@ -86,6 +116,17 @@ export default class Transition<T extends Route> implements Partial<Promise<T>>
     this.pivotHandler = undefined;
     this.sequence = -1;
 
+    if (DEBUG) {
+      let error = new Error(`Transition creation stack`);
+
+      this.debugCreationStack = () => error.stack;
+
+      // not aborted yet, will be replaced when `this.isAborted` is set
+      this.debugAbortStack = () => undefined;
+
+      this.debugPreviousTransition = previousTransition;
+    }
+
     if (error) {
       this.promise = Promise.reject(error);
       this.error = error;
@@ -250,9 +291,17 @@ export default class Transition<T extends Route> implements Partial<Promise<T>>
   rollback() {
     if (!this.isAborted) {
       log(this.router, this.sequence, this.targetName + ': transition was aborted');
+
+      if (DEBUG) {
+        let error = new Error(`Transition aborted stack`);
+
+        this.debugAbortStack = () => error.stack;
+      }
+
       if (this.intent !== undefined && this.intent !== null) {
         this.intent.preTransitionState = this.router.state;
       }
+
       this.isAborted = true;
       this.isActive = false;
       this.router.activeTransition = undefined;

package.json

@@ -31,14 +31,17 @@
     "start": "ember server",
     "test": "ember test"
   },
-  "dependencies": {},
+  "dependencies": {
+    "@glimmer/env": "^0.1.7"
+  },
   "devDependencies": {
     "@babel/plugin-transform-modules-amd": "^7.10.5",
     "@babel/plugin-transform-modules-commonjs": "^7.10.4",
     "@types/node": "^12.7.5",
     "@types/qunit": "^2.9.1",
     "@typescript-eslint/eslint-plugin": "^3.7.0",
     "@typescript-eslint/parser": "^3.7.0",
+    "babel-plugin-debug-macros": "^0.3.3",
     "backburner.js": "^2.6.0",
     "broccoli-babel-transpiler": "^7.6.0",
     "broccoli-concat": "^4.2.4",

yarn.lock

@@ -216,6 +216,11 @@
     exec-sh "^0.3.2"
     minimist "^1.2.0"
 
+"@glimmer/env@^0.1.7":
+  version "0.1.7"
+  resolved "https://registry.yarnpkg.com/@glimmer/env/-/env-0.1.7.tgz#fd2d2b55a9029c6b37a6c935e8c8871ae70dfa07"
+  integrity sha1-/S0rVakCnGs3psk16MiHGucN+gc=
+
 "@iarna/[email protected]":
   version "2.2.5"
   resolved "https://registry.yarnpkg.com/@iarna/toml/-/toml-2.2.5.tgz#b32366c89b43c6f8cefbdefac778b9c828e3ba8c"
@@ -903,6 +908,13 @@ atob@^2.1.2:
   resolved "https://registry.yarnpkg.com/atob/-/atob-2.1.2.tgz#6d9517eb9e030d2436666651e86bd9f6f13533c9"
   integrity sha512-Wm6ukoaOGJi/73p/cl2GvLjTI5JM1k/O14isD73YML8StrH/7/lRFgmg8nICZgD3bZZvjwCGxtMOD3wWNAu8cg==
 
+babel-plugin-debug-macros@^0.3.3:
+  version "0.3.3"
+  resolved "https://registry.yarnpkg.com/babel-plugin-debug-macros/-/babel-plugin-debug-macros-0.3.3.tgz#29c3449d663f61c7385f5b8c72d8015b069a5cb7"
+  integrity sha512-E+NI8TKpxJDBbVkdWkwHrKgJi696mnRL8XYrOPYw82veNHPDORM9WIQifl6TpIo8PNy2tU2skPqbfkmHXrHKQA==
+  dependencies:
+    semver "^5.3.0"
+
 babel-plugin-dynamic-import-node@^2.3.3:
   version "2.3.3"
   resolved "https://registry.yarnpkg.com/babel-plugin-dynamic-import-node/-/babel-plugin-dynamic-import-node-2.3.3.tgz#84fda19c976ec5c6defef57f9427b3def66e17a3"
@@ -6310,7 +6322,7 @@ semver-diff@^3.1.1:
   dependencies:
     semver "^6.3.0"
 
-"semver@2 || 3 || 4 || 5", semver@^5.4.1, semver@^5.5.0:
+"semver@2 || 3 || 4 || 5", semver@^5.3.0, semver@^5.4.1, semver@^5.5.0:
   version "5.7.1"
   resolved "https://registry.yarnpkg.com/semver/-/semver-5.7.1.tgz#a954f931aeba508d307bbf069eff0c01c96116f7"
   integrity sha512-sauaDf/PZdVgrLTNYHRtpXa1iRiKcaebiKQ1BJdpQlWH2lCvexQdX55snPFyK7QzpudqbCI0qXFfOasHdyNDGQ==