fix(util): Path.parent now works on windows (#1168)

On Windows, both forward slash `/` and backslash `\\` work as the path
separator. Linux and MacOS can have backslash as a valid filename
character.

Unit tests are also provided for each platform because `Path.parent`
depends on the local variable `sep` which depends on `jit.os`.

Fixes #1168

lua/luasnip/util/path.lua

@@ -193,14 +193,67 @@ function Path.components(path)
 	return vim.split(path, sep, { plain = true, trimempty = true })
 end
 
-function Path.parent(path)
-	local last_component = path:match("%" .. sep .. "[^" .. sep .. "]+$")
-	if not last_component then
-		return nil
+---Get parent of a path, without trailing separator
+---if path is a directory or does not have a parent, returns nil
+---Example:
+---  On platforms that use "\\" backslash as path separator, e.g., Windows:
+---    Path.parent("C:/project_root/file.txt") -- returns "C:/project_root"
+---    Path.parent([[C:\project_root\file.txt]]) -- returns [[C:\project_root]]
+---
+---    -- the followings return `nil`s
+---    Path.parent("C:/")
+---    Path.parent([[C:\]])
+---    Path.parent([[C:\project_root\]])
+---
+---    -- WARN: although it's unlikely that we will reach the driver's root
+---    -- level, Path.parent("C:\file.txt") returns "C:", and please be
+---    -- cautious when passing the parent path to some vim functions because
+---    -- some vim functions on Windows treat "C:" as a file instead:
+---    --   vim.fn.fnamemodify("C:", ":p") -- returns $CWD .. sep .. "C:"
+---    -- To get the desired result, use vim.fn.fnamemodify("C:" .. sep, ":p")
+---
+---  On platforms that use "/" forward slash as path separator, e.g., linux:
+---    Path.parent("/project_root/file.txt") returns "/project_root"
+---    Path.parent("/file.txt") returns ""
+---
+---    -- the followings return `nil`s
+---    Path.parent("/")
+---    Path.parent("/project_root/")
+---
+---    -- backslash in a valid filename character in linux:
+---    Path.parent([[/project_root/\valid\file\name.txt]]) returns "/project_root"
+Path.parent = (function()
+	local os_sep = sep
+
+	-- for test only
+	if __LUASNIP_TEST_SEP_OVERRIDE then
+		os_sep = __LUASNIP_TEST_SEP_OVERRIDE
 	end
 
-	return path:sub(1, #path - #last_component)
-end
+	if os_sep == "/" then
+		---@param path string
+		---@return string | nil
+		return function(path)
+			local last_component = path:match("[/]+[^/]+$")
+			if not last_component then
+				return nil
+			end
+
+			return path:sub(1, #path - #last_component)
+		end
+	else
+		---@param path string
+		---@return string | nil
+		return function(path)
+			local last_component = path:match("[/\\]+[^/\\]+$")
+			if not last_component then
+				return nil
+			end
+
+			return path:sub(1, #path - #last_component)
+		end
+	end
+end)()
 
 -- returns nil if the file does not exist!
 Path.normalize = uv.fs_realpath

tests/unit/utils_spec.lua

@@ -23,3 +23,89 @@ describe("luasnip.util.str:dedent", function()
 	check("2 and 1", "  one\n two", " one\ntwo")
 	check("2 and 2", "  one\n  two", "one\ntwo")
 end)
+
+describe("luasnip.util.Path.parent", function()
+	local function assert_parents(separator, examples)
+		__LUASNIP_TEST_SEP_OVERRIDE = separator
+		local parent = exec_lua('return require("luasnip.util.path").parent')
+		for _, example in ipairs(examples) do
+			assert.are.same(example.expect, parent(example.path))
+		end
+	end
+
+	-- cleanup
+	after_each(function()
+		__LUASNIP_TEST_SEP_OVERRIDE = nil
+	end)
+
+	describe("backslash as the path separator", function()
+		local examples = {
+			{
+				path = [[C:\Users\username\AppData\Local\nvim-data\log]],
+				expect = [[C:\Users\username\AppData\Local\nvim-data]],
+			},
+			{
+				path = [[C:/Users/username/AppData/Local/nvim-data/log]],
+				expect = [[C:/Users/username/AppData/Local/nvim-data]],
+			},
+			{
+				path = [[D:\Projects\project_folder\source_code.py]],
+				expect = [[D:\Projects\project_folder]],
+			},
+			{
+				path = [[D:/Projects/project_folder/source_code.py]],
+				expect = [[D:/Projects/project_folder]],
+			},
+			{ path = [[E:\Music\\\\]], expect = nil },
+			{ path = [[E:/Music////]], expect = nil },
+			{ path = [[E:\\Music\\\\]], expect = nil },
+			{ path = [[E://Music////]], expect = nil },
+			{ path = [[F:\]], expect = nil },
+			{ path = [[F:\\]], expect = nil },
+			{ path = [[F:/]], expect = nil },
+			{ path = [[F://]], expect = nil },
+		}
+
+		assert_parents("\\", examples)
+	end)
+
+	describe("forward slash as the path separator", function()
+		local examples = {
+			{
+				path = [[/home/usuario/documents/archivo.txt]],
+				expect = [[/home/usuario/documents]],
+			},
+			{
+				path = [[/var/www/html////index.html]],
+				expect = [[/var/www/html]],
+			},
+			{
+				path = [[/mnt/backup/backup_file.tar.gz]],
+				expect = [[/mnt/backup]],
+			},
+			{
+				path = [[/mnt/]],
+				expect = nil,
+			},
+			{
+				path = [[/mnt////]],
+				expect = nil,
+			},
+			{
+				path = [[/project/\backslash\is\legal\in\linux\filename.txt]],
+				expect = [[/project]],
+			},
+			{
+				path = [[/\\\\]],
+				expect = "",
+			},
+			{
+				path = [[/\\\\////]],
+				expect = nil,
+			},
+			{ path = [[/]], expect = nil },
+		}
+
+		assert_parents("/", examples)
+	end)
+end)