Fix relpath when path and startpath are in the same drive (JuliaLang#…

…40323)

* Fix relpath when path and startpath are in the same drive

When startpath == ".", assume the startpath is in the same drive.
This subsequently required tweaking the existing logic to then
canonicalize the drive casing in instances where the drive casing
differs.

base/path.jl

@@ -517,12 +517,16 @@ function relpath(path::String, startpath::String = ".")
  curdir = "."
  pardir = ".."
  path == startpath && return curdir
- path_drive, path_without_drive = splitdrive(path)
- startpath_drive, startpath_without_drive = splitdrive(startpath)
- path_arr = split(abspath(path_without_drive), path_separator_re)
- start_arr = split(abspath(startpath_without_drive), path_separator_re)
  if Sys.iswindows()
- lowercase(path_drive) != lowercase(startpath_drive) && return abspath(path)
+ path_drive, path_without_drive = splitdrive(path)
+ startpath_drive, startpath_without_drive = splitdrive(startpath)
+ isempty(startpath_drive) && (startpath_drive = path_drive) # by default assume same as path drive
+ uppercase(path_drive) == uppercase(startpath_drive) || return abspath(path) # if drives differ return first path
+ path_arr = split(abspath(path_drive * path_without_drive), path_separator_re)
+ start_arr = split(abspath(path_drive * startpath_without_drive), path_separator_re)
+ else
+ path_arr = split(abspath(path), path_separator_re)
+ start_arr = split(abspath(startpath), path_separator_re)
  end
  i = 0
  while i < min(length(path_arr), length(start_arr))

test/path.jl

@@ -290,6 +290,10 @@
  # Additional cases
  @test_throws ArgumentError relpath(S("$(sep)home$(sep)user$(sep)dir_withendsep$(sep)"), "")
  @test_throws ArgumentError relpath(S(""), S("$(sep)home$(sep)user$(sep)dir_withendsep$(sep)"))
+
+ # issue 40237
+ path = "..$(sep)a$(sep)b$(sep)c"
+ @test relpath(abspath(path)) == path
  end
  test_relpath()
  end