From 8a1e54d58a3a3dc0d2001cb9368d3b0f9efc12f6 Mon Sep 17 00:00:00 2001
From: greatroar <61184462+greatroar@users.noreply.github.com>
Date: Tue, 23 Nov 2021 19:55:58 +0100
Subject: [PATCH] lib/fs: Optimize Canonicalize
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

When pathSep is a constant, the compiler precomputes pathSep+pathSep and
".."+pathSep instead of emitting function calls to compute "//" and
"../". Benchmark results in lib/osutil:

name                old time/op    new time/op    delta
TraversesSymlink-8    8.86µs ± 3%    8.53µs ± 4%  -3.79%  (p=0.000 n=18+20)

name                old alloc/op   new alloc/op   delta
TraversesSymlink-8    1.06kB ± 0%    1.06kB ± 0%    ~     (all equal)

name                old allocs/op  new allocs/op  delta
TraversesSymlink-8      15.0 ± 0%      15.0 ± 0%    ~     (all equal)
---
 lib/fs/filesystem.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/fs/filesystem.go b/lib/fs/filesystem.go
index 7ab08600f..c19860dd4 100644
--- a/lib/fs/filesystem.go
+++ b/lib/fs/filesystem.go
@@ -253,7 +253,7 @@ func IsInternal(file string) bool {
 // - /foo/bar -> foo/bar
 // - / -> "."
 func Canonicalize(file string) (string, error) {
-	pathSep := string(PathSeparator)
+	const pathSep = string(PathSeparator)
 
 	if strings.HasPrefix(file, pathSep+pathSep) {
 		// The relative path may pretend to be an absolute path within