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libpath-concepts — OS path models

Unix and Windows file-system path form models under libpath rule sets. Terminology here is provisional.

Table of Contents

Rule sets

A rule set (provisional term) selects which OS path semantics apply to analysis:

Rule set Typical use
unix POSIX-style paths: / separator, single rooted form
windows Drive letters, UNC, \ and / separators, richer relativity lattice

libpath ports may compile for a host OS or analyse paths under an explicit, selectable rule set (including cross-host). Concepts does not define a third hybrid syntax.

Unix model

Under the unix rule set:

  • The path-name separator is / (forward slash).
  • A path is slash-rooted (and, on Unix, absolute) when it begins with /.
  • There is no separate volume concept; the “root” is the leading slash when present.
  • Relative paths do not begin with / (except via ~ home expansion when that feature is enabled — see classification.md).
  • . and .. are directory parts with conventional meaning in higher-level util; the parse model records them lexically.

Examples (provisional illustrations):

Input Classification (typical) Notes
abc/def Relative No leading slash
/abc/def SlashRooted Absolute on Unix
/ SlashRooted Root only; empty entry name
abc/ Relative Trailing separator ⇒ empty entry name

Windows model

Under the windows rule set:

  • Both \ and / may act as path-name separators (libpath treats them equivalently for parsing).
  • Absolute and rooted are distinct (see classification.md):
    • Drive-letter-rooted (C:\, C:/) and UNC-rooted (\\server\share\) are absolute;
    • Slash-rooted (\foo, /foo) is rooted but not absolute;
    • Drive-letter-relative (C:foo) has a volume (C:) but no established root.
  • Volume (provisional) is the drive letter or UNC server/share prefix; it may exist without a complete root.
  • Root (provisional) is the complete root span when established (e.g. C:\, \\server\share\).
  • UNC paths have complete and incomplete forms (\\server vs \\server\share\).
  • Device paths, long-path prefixes (\\?\), and similar extended forms are recognised in mature ports; Phase 1 documents the core lattice — extended forms are scheduled in port TODOs and future fixture expansion.

Examples (provisional illustrations):

Input Classification (typical) Absolute? Rooted?
abc Relative No No
\abc SlashRooted No Yes
C:abc DriveLetterRelative No No
C:\abc DriveLetterRooted Yes Yes
\\srv\share\file UncRooted Yes Yes

Cross-host analysis

A Windows path string may be parsed under windows rules on a Unix host (and vice versa). This supports tools that must reason about foreign path forms without implying that the path is valid on the current host filesystem.

Reference behaviour for absolute vs rooted on Windows is documented in libpath (C/C++): libpath_ParseResult_IsPathAbsolute vs libpath_ParseResult_IsPathRooted.

Separators and normalisation notes

  • Lexical form is what the input string contains after parse-time normalisation flags; concepts does not equate lexical form with OS canonical or resolved paths.
  • Trailing separators affect entry name (always empty when a trailing separator is present) — see parts.md.
  • Repeated slash runs may be invalid or collapsible depending on rule set and parse flags.

What is out of scope

  • URL/URI and other non–file-system schemes;
  • Registry paths, file:// URLs, and ADS/stream notation as first-class concepts;
  • Filesystem operations (stat, realpath, directory iteration).