splitPath() behavior synchronized with splitFile() (#12481)

* splitPath() behavior synchronized with splitFile() having the expected behavior in all languages

splitPath() docstrings update, tests added for both splitPath() and splitFile()

* Path splitting refined and described

changelog.md

@@ -8,6 +8,7 @@
 ### Breaking changes in the standard library
 
 - `base64.encode` no longer supports `lineLen` and `newLine` use `base64.encodeMIME` instead.
+- `os.splitPath()` behavior synchronized with `os.splitFile()` to return "/" as the dir component of "/root_sub_dir" instead of the empty string.
 
 
 ### Breaking changes in the compiler

lib/pure/os.nim

@@ -216,8 +216,12 @@ proc splitPath*(path: string): tuple[head, tail: string] {.
   runnableExamples:
     assert splitPath("usr/local/bin") == ("usr/local", "bin")
     assert splitPath("usr/local/bin/") == ("usr/local/bin", "")
+    assert splitPath("/bin/") == ("/bin", "")
+    when (NimMajor, NimMinor) <= (1, 0):
+        assert splitPath("/bin") == ("", "bin")
+    else:
+        assert splitPath("/bin") == ("/", "bin")
     assert splitPath("bin") == ("", "bin")
-    assert splitPath("/bin") == ("", "bin")
     assert splitPath("") == ("", "")
 
   var sepPos = -1
@@ -226,7 +230,12 @@ proc splitPath*(path: string): tuple[head, tail: string] {.
       sepPos = i
       break
   if sepPos >= 0:
-    result.head = substr(path, 0, sepPos-1)
+    result.head = substr(path, 0,
+      when (NimMajor, NimMinor) <= (1, 0):
+        sepPos-1
+      else:
+        if likely(sepPos >= 1): sepPos-1 else: 0
+    )
     result.tail = substr(path, sepPos+1)
   else:
     result.head = ""
@@ -597,13 +606,17 @@ proc splitFile*(path: string): tuple[dir, name, ext: string] {.
     assert dir == "/usr/local"
     assert name == ""
     assert ext == ""
+    (dir, name, ext) = splitFile("/tmp.txt")
+    assert dir == "/"
+    assert name == "tmp"
+    assert ext == ".txt"
 
   var namePos = 0
   var dotPos = 0
   for i in countdown(len(path) - 1, 0):
     if path[i] in {DirSep, AltSep} or i == 0:
       if path[i] in {DirSep, AltSep}:
-        result.dir = substr(path, 0, max(0, i - 1))
+        result.dir = substr(path, 0, if likely(i >= 1): i - 1 else: 0)
         namePos = i + 1
       if dotPos > i:
         result.name = substr(path, namePos, dotPos - 1)