Re: [PATCH 0/6] Extensions of core.ignorecase=true support

While I tend to agree with case-insensitive searches, I would tend to
question the use of a non-case-preserving / last-use methodology
reminiscent of the days of DOS. I was never terribly fond of DOS nor
of Windows for Workgroups, and this change smacks of that. That said,
as an algorithm it is one legitimate option, I just would not tend to
use it.

Have you thought of other approaches that are case-preserving /
case-insensitive (modern Windows implementations and Mac OS X) or of
case-sensitive (UNIX)? What about giving the user the choice?

Looking back at how flexible and simple folks here on this list made
the EOL support (the best I have seen to date) what if you followed a
similar approach and provided the flexibility to the users by giving
the options to control the behavior themselves, then fall back to
reasonable defaults if left unspecified?

I would imagine having two properties would be somewhat more useful:

core.casepreserving=true|false
core.caseinsensitive=true|false

For Unix-centric environments the defaults would be true & false,
respectively. For mixed Windows/Unix environments users would
configure it as true & true. A combination of false & true,
respectively, would be appropriate for DOS users, but this may be
another option for mixed environments. A combination of false & false
would be impossible by definition.

What this would mean is that searches in the purely Unix world would
store and match sensitively; but in such an environment there may be
issues should any Windows users attempt to work with the repository if
two files having a similar names existed. For Windows users the last
read operation would overwrite the first (not a good thing).

For mixed configurations there are two options, the Windows/Mac
option, and the DOS option.

The nice thing about case-insensitivity is that when requesting a file
by name any capitalization can be used. The bad thing, well come to
think of it, there is none that I can think of, but for those more
religious than I about Unix they may cite otherwise.

-Bob

On Mon, Aug 16, 2010 at 3:38 PM, Johannes Sixt [off-list ref] wrote:

The following patch series extends the core.ignorecase=true support to
handle case insensitive comparisons for the .gitignore file, git status,
and git ls-files.  git add and git fast-import will fold the case of the
file being added, matching that of an already added directory entry.  Case
folding is also applied to git fast-import for renames, copies, and deletes.

The most notable benefit, IMO, is that the case of directories in the
worktree does not matter if, and only if, the directory exists already in
the index with some different case variant.  This helps applications on
Windows that change the case even of directories in unpredictable ways.
Joshua mentioned Perforce as the primary example.

Concerning the implementation, Joshua explained when he initially submitted
the series to the msysgit mailing list:

 git status and add both use an update made to name-hash.c where
 directories, specifically names with a trailing slash, can be looked up
 in a case insensitive manner. After trying a myriad of solutions, this
 seemed to be the cleanest. Does anyone see a problem with embedding the
 directory names in the same hash as the file names? I couldn't find one,
 especially since I append a slash to each directory name.

 The git add path case folding functionality is a somewhat radical
 departure from what Git does now. It is described in detail in patch 5.
 Does anyone have any concerns?

I support the idea of this patch, and I can confirm that it works: I've
used this series in production both with core.ignorecase set to true and
to false, and in the former case, with directories and files with case
different from the index.

Joshua Jensen (6):
 Add string comparison functions that respect the ignore_case
   variable.
 Case insensitivity support for .gitignore via core.ignorecase
 Add case insensitivity support for directories when using git status
 Add case insensitivity support when using git ls-files
 Support case folding for git add when core.ignorecase=true
 Support case folding in git fast-import when core.ignorecase=true

 dir.c         |  105 ++++++++++++++++++++++++++++++++++++++++++++++----------
 dir.h         |    4 ++
 fast-import.c |    7 ++--
 name-hash.c   |   72 ++++++++++++++++++++++++++++++++++++++-
 read-cache.c  |   23 ++++++++++++
 5 files changed, 188 insertions(+), 23 deletions(-)

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