From a08ea3f6433b842b0e342509e5ddd53907a863b0 Mon Sep 17 00:00:00 2001
From: Andrew Scott <atscott@google.com>
Date: Wed, 9 Mar 2022 11:48:19 -0800
Subject: [PATCH] refactor(router): Make a few adjustments to createUrlTree for
 clarity (#45306)

* `tree` function now accepts the old root rather than the old
  `UrlTree`. The `urlTree` argument was only used to get the `root`.
  This change makes it more clear what that pararmeter is used for and
  what's actually being used
* Move the `oldRoot` (previously `urlTree`) to be the first argument of `tree`.
  This change now mirrors the argument order for `replaceSegment` and
  can be read from left to right more easily "in this root,
  replace this old segment group with this new segment group".
* Extract `newRoot` to a variable. This just makes it more clear what's
  going on at the end rather than combining a bunch of operations into
  one.

These changes are being made so that hopefully a future refactor can be
done which does not rely on the `urlTree` argument at all in the
`createUrlTree` function. These refactorings will make it easier to see
1:1 functionlity in these various places.

PR Close #45306
---
 packages/router/src/create_url_tree.ts | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/packages/router/src/create_url_tree.ts b/packages/router/src/create_url_tree.ts
index d79a06eba79..a074bce1e11 100644
--- a/packages/router/src/create_url_tree.ts
+++ b/packages/router/src/create_url_tree.ts
@@ -15,13 +15,13 @@ export function createUrlTree(
     route: ActivatedRoute, urlTree: UrlTree, commands: any[], queryParams: Params|null,
     fragment: string|null): UrlTree {
   if (commands.length === 0) {
-    return tree(urlTree.root, urlTree.root, urlTree, queryParams, fragment);
+    return tree(urlTree.root, urlTree.root, urlTree.root, queryParams, fragment);
   }
 
   const nav = computeNavigation(commands);
 
   if (nav.toRoot()) {
-    return tree(urlTree.root, new UrlSegmentGroup([], {}), urlTree, queryParams, fragment);
+    return tree(urlTree.root, urlTree.root, new UrlSegmentGroup([], {}), queryParams, fragment);
   }
 
   const startingPosition = findStartingPosition(nav, urlTree, route);
@@ -30,7 +30,7 @@ export function createUrlTree(
       updateSegmentGroupChildren(
           startingPosition.segmentGroup, startingPosition.index, nav.commands) :
       updateSegmentGroup(startingPosition.segmentGroup, startingPosition.index, nav.commands);
-  return tree(startingPosition.segmentGroup, segmentGroup, urlTree, queryParams, fragment);
+  return tree(urlTree.root, startingPosition.segmentGroup, segmentGroup, queryParams, fragment);
 }
 
 function isMatrixParams(command: any): boolean {
@@ -46,7 +46,7 @@ function isCommandWithOutlets(command: any): command is {outlets: {[key: string]
 }
 
 function tree(
-    oldSegmentGroup: UrlSegmentGroup, newSegmentGroup: UrlSegmentGroup, urlTree: UrlTree,
+    oldRoot: UrlSegmentGroup, oldSegmentGroup: UrlSegmentGroup, newSegmentGroup: UrlSegmentGroup,
     queryParams: Params|null, fragment: string|null): UrlTree {
   let qp: any = {};
   if (queryParams) {
@@ -55,11 +55,12 @@ function tree(
     });
   }
 
-  if (urlTree.root === oldSegmentGroup) {
+  if (oldRoot === oldSegmentGroup) {
     return new UrlTree(newSegmentGroup, qp, fragment);
   }
 
-  return new UrlTree(replaceSegment(urlTree.root, oldSegmentGroup, newSegmentGroup), qp, fragment);
+  const newRoot = replaceSegment(oldRoot, oldSegmentGroup, newSegmentGroup);
+  return new UrlTree(newRoot, qp, fragment);
 }
 
 function replaceSegment(