From 402d784b8fc0a7914955eb168ea288338e2025ff Mon Sep 17 00:00:00 2001
From: Aman Gupta <aman@tmm1.net>
Date: Fri, 4 Sep 2020 16:07:12 -0700
Subject: path/filepath: make Rel handle Windows UNC share

Fixes #41230

Change-Id: Iea15e4ae6d56328333fd22de5d78dfcad78ef1bc
Reviewed-on: https://go-review.googlesource.com/c/go/+/253197
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
Trust: Alex Brainman <alex.brainman@gmail.com>
Trust: Emmanuel Odeke <emmanuel@orijtech.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
---
 src/path/filepath/path.go | 4 ++++
 1 file changed, 4 insertions(+)

(limited to 'src/path/filepath/path.go')

diff --git a/src/path/filepath/path.go b/src/path/filepath/path.go
index 2e7b439355..28b30b1ae7 100644
--- a/src/path/filepath/path.go
+++ b/src/path/filepath/path.go
@@ -275,7 +275,11 @@ func Rel(basepath, targpath string) (string, error) {
 	targ = targ[len(targVol):]
 	if base == "." {
 		base = ""
+	} else if base == "" && volumeNameLen(baseVol) > 2 /* isUNC */ {
+		// Treat any targetpath matching `\\host\share` basepath as absolute path.
+		base = string(Separator)
 	}
+
 	// Can't use IsAbs - `\a` and `a` are both relative in Windows.
 	baseSlashed := len(base) > 0 && base[0] == Separator
 	targSlashed := len(targ) > 0 && targ[0] == Separator
-- 
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