From fbf28d1ce77818ec61db490a80190d6722731274 Mon Sep 17 00:00:00 2001
From: Andrey Makarov <ph.makarov@gmail.com>
Date: Sun, 23 Feb 2020 22:22:46 +0300
Subject: [PATCH] fix 3 minor bugs in joinPath (see #13455) (#13462) [backport]

(cherry picked from commit 3dad130034e3212159dda5d61988ca2b18959b24)
---
 lib/pure/os.nim       | 3 ++-
 lib/pure/pathnorm.nim | 3 ++-
 tests/stdlib/tos.nim  | 4 ++++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/lib/pure/os.nim b/lib/pure/os.nim
index d91a135c31..a204f26c43 100644
--- a/lib/pure/os.nim
+++ b/lib/pure/os.nim
@@ -130,6 +130,7 @@ proc joinPath*(head, tail: string): string {.
     when defined(posix):
       assert joinPath("usr", "lib") == "usr/lib"
       assert joinPath("usr", "") == "usr/"
+      assert joinPath("", "") == ""
       assert joinPath("", "lib") == "lib"
       assert joinPath("", "/lib") == "/lib"
       assert joinPath("usr/", "/lib") == "usr/lib"
@@ -138,7 +139,7 @@ proc joinPath*(head, tail: string): string {.
   result = newStringOfCap(head.len + tail.len)
   var state = 0
   addNormalizePath(head, result, state, DirSep)
-  if tail.len == 0:
+  if result.len != 0 and result[^1] notin {DirSep, AltSep} and tail.len == 0:
     result.add DirSep
   else:
     addNormalizePath(tail, result, state, DirSep)
diff --git a/lib/pure/pathnorm.nim b/lib/pure/pathnorm.nim
index 407ec156ce..3659e85e62 100644
--- a/lib/pure/pathnorm.nim
+++ b/lib/pure/pathnorm.nim
@@ -69,7 +69,8 @@ proc addNormalizePath*(x: string; result: var string; state: var int;
   while hasNext(it, x):
     let b = next(it, x)
     if (state shr 1 == 0) and isSlash(x, b):
-      result.add dirSep
+      if result.len == 0 or result[^1] notin {DirSep, AltSep}:
+        result.add dirSep
       state = state or 1
     elif isDotDot(x, b):
       if (state shr 1) >= 1:
diff --git a/tests/stdlib/tos.nim b/tests/stdlib/tos.nim
index ab0cce8de1..6902f3851f 100644
--- a/tests/stdlib/tos.nim
+++ b/tests/stdlib/tos.nim
@@ -338,6 +338,10 @@ block ospaths:
   doAssert joinPath("", "lib") == "lib"
   doAssert joinPath("", "/lib") == unixToNativePath"/lib"
   doAssert joinPath("usr/", "/lib") == unixToNativePath"usr/lib"
+  doAssert joinPath("", "") == unixToNativePath""
+  doAssert joinPath("/" / "") == unixToNativePath"/"
+  doAssert joinPath("/", "/a/b/c") == unixToNativePath"/a/b/c"
+  doAssert joinPath("foo/","") == unixToNativePath"foo/"
 
 block getTempDir:
   block TMPDIR: