Diff for "CaseFoldExtension"

Fold: Case Folding Rescue

This extension is in proposal stage.

Author: BradOlson

Download site: [http://files.movedbylight.com/cgi-bin/hg/hgfold/]

Jargon

FS

Filesystem (file system).

CS

Case-sensitive (case-preserving), a context where "THEGREENTREE" and "thegreentree" refer to two different files.

CI

Case-insensitive (case-folding), a context where "THEGREENTREE" and "thegreentree" refer to the same file or entity.

Collision

Case collision, two names that differ only by case.

Overview

This extension seeks to comprehensively deal with the problem of Mercurial filename case collisions in merges and updates. (It does not address Mercurial's internal storage, which is and needs to be CI no matter the file system, cf. CaseFoldingPlan.)

It's developed with these core principles (open for community discussion, cf. CaseFolding):

1. It takes a person to decide whether a project's filenames are CI or CS. Current FS is not an adequate decider.
2. In a CS project, a collision is just another file; in a CI project, a collision is a conflict.

3. Mercurial users need sane ways to remedy collisions on a CIFS. (It's easy to fix them on a CSFS, but on a CIFS you have to modify parentage, which can get dangerous. See FixingCaseCollisions.)

It proposes the following phases:

1. (Done) Add options to merge and update that will treat collisions as conflicts that need merging.

2. Adding options to other commands (add, addrem, commit, clone, and rename) to handle/prevent folds.

3. Add .hgfold to define cannonical forms of filenames and flag that a repository needs to behave as if file names case-insensitive

Limitations

This extension has not been tested on filenames containing characters outside the basic Roman set.

Configuration

Configure your .hgrc to enable the extension by adding following lines:

[extensions]
fold = /full/path/to/fold.py

Usage

hg help update and hg help merge have been augmented to describe this extension.

hg update --fold [-C] [-d DATE] [[-r] REV]
    -n --dry-run  do not perform actions, just print output
    --fold     treat filename collisions as the same file, merging as needed

hg merge --fold [-f] [[-r] REV]
    -n --dry-run  do not perform actions, just print output
    --fold     treat filename collisions as the same file, merging as needed

Development Discussion

A couple big questions:

1. Is coercing case to manifest ever the right thing? What if your software is trying to rename a file to some cannonical case as a correction to application or user sloppiness?

2. CI merging two heads could result in more than a three-way merge this extension hasn't been used consistently on all copies. For instance, You even on a Windows machine you could end up with two heads that each have files "Apple" and "apple". That's a five-way merge. And finding a common ancestor gets really strange. What if Apple-1, Apple-2, and apple-1 share an ancestor, but apple-2 was added independently. The best thing would be some core declaration upon hg init declaring a repo to be CI for all adds, commits, and merges. But until then, we're effectively telling Mercurial, "You know that thing you didn't think was a conflict? Well, it is. So merge it."

Other Solutions

CategoryExtension