[et] Simplify path canonicalisation logic (#52275) In order to canonicalise paths, previously we were doing an iterative computation to resolve symlinks to a canonical path, directory by directory. This was because on macOS and other BSDs, readlink doesn't support the `-f` (follow symlinks) option. However, macOS and other BSD-based systems *do* bundle the `realpath` utility, which resolves symlinks. This patch is stacked on top of #52274 and is the second commit (dec38dda38d1ef0bc3a548ef1f750c5855e9d9f4). ## Pre-launch Checklist - [X] I read the [Contributor Guide] and followed the process outlined there for submitting PRs. - [X] I read the [Tree Hygiene] wiki page, which explains my responsibilities. - [X] I read and followed the [Flutter Style Guide] and the [C++, Objective-C, Java style guides]. - [X] I listed at least one issue that this PR fixes in the description above. - [ ] I added new tests to check the change I am making or feature I am adding, or the PR is [test-exempt]. See [testing the engine] for instructions on writing and running engine tests. - [X] I updated/added relevant documentation (doc comments with `///`). - [X] I signed the [CLA]. - [X] All existing and new tests are passing. If you need help, consider asking for advice on the #hackers-new channel on [Discord].  [Contributor Guide]: https://github.com/flutter/flutter/wiki/Tree-hygiene#overview [Tree Hygiene]: https://github.com/flutter/flutter/wiki/Tree-hygiene [test-exempt]: https://github.com/flutter/flutter/wiki/Tree-hygiene#tests [Flutter Style Guide]: https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo [C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style [testing the engine]: https://github.com/flutter/flutter/wiki/Testing-the-engine [CLA]: https://cla.developers.google.com/ [flutter/tests]: https://github.com/flutter/tests [breaking change policy]: https://github.com/flutter/flutter/wiki/Tree-hygiene#handling-breaking-changes [Discord]: https://github.com/flutter/flutter/wiki/Chat

diff --git a/bin/et b/bin/et
index f5389c1..38c6077 100755
--- a/bin/et
+++ b/bin/et

@@ -9,25 +9,19 @@
 # Needed because if it is set, cd may print the path it changed to.
 unset CDPATH
 
-# On Mac OS, readlink -f doesn't work, so follow_links traverses the path one
-# link at a time, and then cds into the link destination and find out where it
-# ends up.
-#
-# The function is enclosed in a subshell to avoid changing the working directory
-# of the caller.
-function follow_links() (
-  cd -P "$(dirname -- "$1")"
-  file="$PWD/$(basename -- "$1")"
-  while [[ -h "$file" ]]; do
-    cd -P "$(dirname -- "$file")"
-    file="$(readlink -- "$file")"
-    cd -P "$(dirname -- "$file")"
-    file="$PWD/$(basename -- "$file")"
-  done
-  echo "$file"
-)
+# Returns the canonical path for its argument, with any symlinks resolved.
+function canonical_path() {
+  if [[ -x "$(which realpath)" ]]; then
+    realpath -q -- "$1"
+  elif [[ -x "$(which readlink)" ]]; then
+    readlink -f -- "$1"
+  else
+    echo "The host platform is not supported by this tool"
+    exit 1
+  fi
+}
 
-SCRIPT_DIR="$(dirname -- "$(follow_links "${BASH_SOURCE[0]}")")"
+SCRIPT_DIR="$(dirname -- "$(canonical_path "${BASH_SOURCE[0]}")")"
 ENGINE_DIR="$(cd "$SCRIPT_DIR/.."; pwd -P)"
 
 case "$(uname -s)" in