Fix get_base_dir windows top level directory logic

[theraot]

This is a fix for #52048

If we look at the diff for cddff04 we observe that before it was looking for a 3 character string ("://"), and now it is looking for a 2 character string (either ":/" or ":\\").

Edit: Updating the use of substr accordingly fixes windows top level directories (e.g. "C:\\puff") but breaks Godot paths (e.g. "res://puff"). Also, it is worth noting that the code already has an special case for the unix root directory ("/"). Thus, we need to handle:

• Finding "://" (3 characters).
• Finding ":\ (2 characters).
• Finding ":/" (2 characters).
• "/" at the start (1 character).

And we need to be careful with order in which we check because "://" contains ":/".

---

This code demonstrate the change:

func test(s:String):
	print("\"", s, "\" -> \"", s.get_base_dir(), "\"")

func _ready() -> void:
	test("C:")
	test("C:\\")
	test("C:\\puff")
	test("C:\\puff\\")

Before cddff04 (tested in Godot 3.2.3) the output is:

"C:" -> ""
"C:\" -> "C:"
"C:\puff" -> "C:"
"C:\puff\" -> "C:\puff"

After cddff04 (tested in Godot 3.3.3) the output is:

"C:" -> ""
"C:\" -> "C:\"
"C:\puff" -> "C:\p"
"C:\puff\" -> "C:\puff"

With this PR (tested in custom build of Godot 4.0) the output is:

"C:" -> ""
"C:\" -> "C:\"
"C:\puff" -> "C:\"
"C:\puff\" -> "C:\puff"

Bugsquad edit: Fixes #52048.

[theraot]

I think this pull request at the time of writing introduces a new bug: "res://".get_base_dir() return "res:/". I'll address this. Edit: Done.

[theraot]

Added new test cases. They pass on my machine.

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

[theraot]

I opened a pull request for the 3.x branch (I had not noticed the file ustring.cpp was in a different path, which prevent cherrypicking it).

[akien-mga]

I had not noticed the file ustring.cpp was in a different path, which prevent cherrypicking it

FYI, Git can handle file renames fine when cherry-picking, as long as the files are still sensibly similar:

$ git cherry-pick -x ef54d35
Performing inexact rename detection: 100% (3035668/3035668), done.
Auto-merging core/ustring.cpp
[3.x 1755591539] Fix get_base_dir windows top level directory logic
 Author: Theraot <Theraot@gmail.com>
 Date: Mon Aug 23 22:32:13 2021 -0500
 1 file changed, 27 insertions(+), 11 deletions(-)

But now that you made a PR, let's use that.