Path separator handling

How Mercurial handles path separators

1. Overview

This page is intended to collect information about Mercurial's current path separator behavior and help formulate coherent rules for when paths should be converted.

2. Basics

There are three basic path formats:

• portable (with a forward slash)
• local (slash on Unix, backslash on Windows)

• (what is the third? ??SimonHeimberg)

OS-specific observations:

• Despite usually using backslash, Windows internally will always accept slash instead of backslash ¹

• Backslashes are valid non-separator characters on Unix, which we should be able to store (though the repo may not be usable on Windows)
• On Windows, ui.slash will cause some commands to output slashes

Basic rules:

• paths stored in changelog and manifest should always be in portable format
• paths read from user (command line, config files) may be in either portable or local format
• URLs should always use portable format

APIs:

• convert from native to portable with util.pconvert()
• convert from portable to native with util.localpath()
• util.normpath() converts to portable
• repo.pathto() and dirstate.pathto() converts to local (honors ui.slash)
• util.pathto() converts to local (ignores ui.slash)

3. Audit of current usage

As of Mercurial 2.4, we have the following behavior:

Inferred rules:

• commands for inspecting history should use portable format
• commands for working directory should use local format
• commands that default to the working directory (ie status) should use local format
• diffs should use portable format... for portability

4. Tests

As of 2.4, the Mercurial test suite uses the '(glob)' filter to hide Windows-specific path changes (and ui.slash=on). This has several downsides:

• Unix developers usually fail to mark these paths when writing tests

• doesn't detect accidental regressions (what kind of regressions? ??SimonHeimberg)

• tedious to maintain

Some possible improvements:

• a new filter '(path)' that normalizes local paths but complains about non-local paths

• an automatic filter that accepts "\" for "/" on Windows (when we are not interested where \ is used, proposed here)

• more complete check-code rules to warn Unix devs about non-portable constructs

Questions related to Tests:

• Should we really test with ui.slash=on? Are we not more interested in the normal behavior? (To see where we use local and where portable.)

5. Questions

• Considering how inconsistent Mercurial uses portable vs local slashes:
  • Do Windows users actually rely on Mercurial emitting backslash?
    • One feedback in the forum was that "/" is irritating, but ok, as long as copy and paste works. (Also copying to other programs.)
  • Is there a use case for the setting ui.slash?
    • A user in the forum asked how to print / for \ and was pleased to hear of ui.slash. But he did not tell what for.
• How much time does Mercurial spend normalizing paths and converting slashes over and over?

6. Notes

• Windows accepts / as path sep except
  • the two backslashes at start of a server path (//computer/path/to) in explorer (but mercurial accepts it)