Diff for "CaseFoldExtension"

Differences between revisions 6 and 15 (spanning 9 versions)

Fold: Case Folding Rescue

This extension is not distributed with Mercurial.

Repository: http://bitbucket.org/bradobro/hgfold/

Tested with: Mercurial 1.6

Status: Not updating. With Mercurial 1.7.5 (and perhaps earlier), Mercurial does saner things on Windows when case-collisions cause an update abort. It is not possible to recover without this extension by hg mv-ing one of the offending files. My employer is seeing fewer case folding problems and considering manual fixes to them. If this proves insufficient, this extension may be resurrected.

Definitions

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.)

Basic understandings about filename collisions.

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

(Done) Add options to merge and update that will treat collisions as conflicts that need merging.
Adding options to other commands (add, addrem, commit, clone, and rename) to handle/prevent folds.
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

Mercurial Command Extension

This extension demonstrates a way of extending existing mercurial commands (as opposed to simply adding a new command). There are risks and advantages to this. It tries to do it as safely as possible:

The original command entry if found and retained.
New options are audited so they will not overlap with existing command options (even future ones).
Command help and syntax is augmented.
A wrapper function is called instead of the original command function. Best practice is for that wrapper, if it learns that its extra services are not needed, to execute the original command function with the arguments pertinent to it.

Other Types of Filename Collisions

This extension acknowledges that there are other ways for filenames to collid besides case. By changing the definition of collisionFinder.cannonize(), it can be taught to find other types of filename collisions.

I welcome any suggestions.

-  ⇤ ← Revision 6 as of 2009-04-28 11:56:27 → 
  Size: 4025
  Editor: BradOlson
  Comment: This title is betterr for Moinmoin searching.
+   ← Revision 15 as of 2011-04-02 00:19:54 → ⇥
  Size: 4070
  Editor: GregWard
  Comment: standard link terminology
-Deletions are marked like this.
+Additions are marked like this.
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+## page was renamed from CaseFoldPlugin
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-'''This extension is in proposal stage.'''
+'''This extension is not distributed with Mercurial.'''
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-Download site: Under Discussion
+Repository: http://bitbucket.org/bradobro/hgfold/
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-=== Jargon ===
+Tested with: Mercurial 1.6

Status: Not updating. With Mercurial 1.7.5 (and perhaps earlier), Mercurial does saner things on Windows when case-collisions cause an update abort. It is not possible to recover without this extension by hg mv-ing one of the offending files. My employer is seeing fewer case folding problems and considering manual fixes to them. If this proves insufficient, this extension may be resurrected.

=== Definitions ===
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-It's developed with these core principles (open for community discussion, cf. CaseFolding):
+Basic understandings about filename collisions.
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-. This is an easy thing to get wrong, so it needs community input.
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+Line 32:
-It proposes the following phases (also open to discussion):
+It proposes the following phases:
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-. (Current) Add commands that will:
  A. Optionally, use FixcaseExtension to coerce the case of filenames in the working copy to match that of the manifest. (This is not front burner for me, since my team's app manages filename case and my boss wants me to get on with the next two: )
  A. List the collisions that would happen on a merge.
  A. Offer a way to merge, treating collisions as conflicts or, if that isn't possible, splitting the collisions off into separate files.
 1. Adding options to merge, add, and commit providing the above functionality.
 1. Making a '''versioned''' means of telling merge, add, and commit to make the above functionality default.

The burning issue for phase 1 is I have 2000 potential users, most on Windows systems, some with 20 commits/day, and even in my small beta test group, we have jammed repos (can't be merged) because somebody's code (surely not mine!) every once in awhile will create filename with the wrong case. We need a sane way out.
+. (Done) Add options to ''merge'' and ''update'' that will treat collisions as conflicts that need merging.
 1. Adding options to other commands (''add'', ''addrem'', ''commit'', ''clone'', and ''rename'') to handle/prevent folds.
 1. Add .hgfold to define cannonical forms of filenames and flag that a repository needs to behave as if file names case-insensitive
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+''hg help update'' and ''hg help merge'' have been augmented to describe this extension.
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-hg fold [-r REV] [--list|--split] - merge in a CI-aware manner 
    --list    - no action, just list the files that would collide in the merge
    --split   - give the collisions names that will be unique on a CIFS 
                (default behavior is to treat as conflicts and merge
+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
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-A couple big questions:
+=== Mercurial Command Extension ===
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-. 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?
 1. 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."
+This extension demonstrates a way of extending existing mercurial commands (as opposed to simply adding a new command). There are risks and advantages to this. It tries to do it as safely as possible:

 1. The original command entry if found and retained.
 1. New options are audited so they will not overlap with existing command options (even future ones).
 1. Command help and syntax is augmented.
 1. A wrapper function is called instead of the original command function. Best practice is for that wrapper, if it learns that its extra services are not needed, to execute the original command function with the arguments pertinent to it.

=== Other Types of Filename Collisions ===

This extension acknowledges that there are other ways for filenames to collid besides case. By changing the definition of collisionFinder.cannonize(), it can be taught to find other types of filename collisions.

I welcome any suggestions.
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+Other approaches are outlined at CaseFolding.
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-CategoryExtension
+CategoryExtensionsByOthers