From 9fa38d17a20c8277837dd49301599ed3d8d455f2 Mon Sep 17 00:00:00 2001
From: Lorenzo Cogotti <lcg@doublefourteen.io>
Date: Sat, 23 Sep 2023 16:03:12 +0200
Subject: [PATCH] [strings] Add utility to test whether a path is absolute

---
 strings.lua | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/strings.lua b/strings.lua
index b2e9ea9..d49d286 100644
--- a/strings.lua
+++ b/strings.lua
@@ -155,6 +155,28 @@ function strings.splitpath(path)
     return path:match("(.-)([^\\/]-)(%.?[^%.\\/]*)$")
 end
 
+--- Test whether the path is absolute.
+--
+-- @string path a path to be tested
+-- @string[opt] sep separator pattern, '/' for Unix, '\\' for Windows, if none is provided, path is tested  for both
+-- @treturn boolean true if path is absolute, false otherwise
+function strings.isabspath(path, sep)
+    if sep == nil then
+        -- Conservative test, both Unix-style and Windows-style
+        return strings.isabspath(path, '/') or strings.isabspath(path, '\\')
+    elseif sep == '/' then
+        -- Unix-style
+        return #path >= 1 and path:byte(1) == SLASH
+    elseif sep == '\\' then
+        -- Windows-style
+        return
+            (#path >= 1 and path:byte(1) == BACKSLASH) or
+            (#path >= 3 and path:byte(2) == COLON and path:byte(3) == BACKSLASH)
+    else
+        error(("Unsupported separator pattern: %q"):format(sep))
+    end
+end
+
 --- Test whether a string starts with a prefix.
 --
 -- This is an optimized version of: return s:sub(1, #prefix) == prefix.