mingw: reencode environment variables on the fly (UTF-16 <-> UTF-8)

On Windows, the authoritative environment is encoded in UTF-16. In Git
for Windows, we convert that to UTF-8 (because UTF-16 is *such* a
foreign idea to Git that its source code is unprepared for it).

Previously, out of performance concerns, we converted the entire
environment to UTF-8 in one fell swoop at the beginning, and upon
putenv() and run_command() converted it back.

Having a private copy of the environment comes with its own perils: when
a library used by Git's source code tries to modify the environment, it
does not really work (in Git for Windows' case, libcurl, see
https://github.com/git-for-windows/git/compare/bcad1e6d58^...bcad1e6d58^2
for a glimpse of the issues).

Hence, it makes our environment handling substantially more robust if we
switch to on-the-fly-conversion in `getenv()`/`putenv()` calls. Based
on an initial version in the MSVC context by Jeff Hostetler, this patch
makes it so.

Surprisingly, this has a *positive* effect on speed: at the time when
the current code was written, we tested the performance, and there were
*so many* `getenv()` calls that it seemed better to convert everything
in one go. In the meantime, though, Git has obviously been cleaned up a
bit with regards to `getenv()` calls so that the Git processes spawned
by the test suite use an average of only 40 `getenv()`/`putenv()` calls
over the process lifetime.

Speaking of the entire test suite: the total time spent in the
re-encoding in the current code takes about 32.4 seconds (out of 113
minutes runtime), whereas the code introduced in this patch takes only
about 8.2 seconds in total. Not much, but it proves that we need not be
concerned about the performance impact introduced by this patch.

Helped-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2 files changed
tree: 25b756a05aae6baac1561488b42c438e824bbc5d
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  310. README.md
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  344. sha1-array.c
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  349. sha1-name.c
  350. sha1dc_git.c
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README.md

Git - fast, scalable, distributed revision control system

Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.

Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.

Please read the file INSTALL for installation instructions.

Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.

See Documentation/gittutorial.txt to get started, then see Documentation/giteveryday.txt for a useful minimum set of commands, and Documentation/git-.txt for documentation of each command. If git has been correctly installed, then the tutorial can also be read with man gittutorial or git help tutorial, and the documentation of each command with man git-<commandname> or git help <commandname>.

CVS users may also want to read Documentation/gitcvs-migration.txt (man gitcvs-migration or git help cvs-migration if git is installed).

The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission). To subscribe to the list, send an email with just “subscribe git” in the body to majordomo@vger.kernel.org. The mailing list archives are available at https://public-inbox.org/git/, http://marc.info/?l=git and other archival sites.

Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.

The maintainer frequently sends the “What's cooking” reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.

The name “git” was given by Linus Torvalds when he wrote the very first version. He described the tool as “the stupid content tracker” and the name as (depending on your mood):

  • random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of “get” may or may not be relevant.
  • stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
  • “global information tracker”: you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
  • “goddamn idiotic truckload of sh*t”: when it breaks