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Documentation/i18n.txt: clarify character encoding support

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As a "distributed" VCS, git should better define the encodings of its core
textual data structures, in particular those that are part of the network
protocol.

That git is encoding agnostic is only really true for blob objects. E.g.
the 'non-NUL bytes' requirement of tree and commit objects excludes
UTF-16/32, and the special meaning of '/' in the index file as well as
space and linefeed in commit objects eliminates EBCDIC and other non-ASCII
encodings.

Git expects bytes < 0x80 to be pure ASCII, thus CJK encodings that partly
overlap with the ASCII range are problematic as well. E.g. fmt_ident()
removes trailing 0x5C from user names on the assumption that it is ASCII
'\'. However, there are over 200 GBK double byte codes that end in 0x5C.

UTF-8 as default encoding on Linux and respective path translations in the
Mac and Windows versions have established UTF-8 NFC as de-facto standard
for path names.

Update the documentation in i18n.txt to reflect the current status-quo.

Signed-off-by: Karsten Blees <blees@dcon.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Karsten Blees 2015-07-01 21:10:47 +02:00 committed by Junio C Hamano
parent a5fe66802f
commit 3a59e5954e
1 changed files with 23 additions and 10 deletions
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33
Documentation/i18n.txt
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@ -1,18 +1,31 @@
At the core level, Git is character encoding agnostic.
- The pathnames recorded in the index and in the tree objects
are treated as uninterpreted sequences of non-NUL bytes.
What readdir(2) returns are what are recorded and compared
with the data Git keeps track of, which in turn are expected
to be what lstat(2) and creat(2) accepts. There is no such
thing as pathname encoding translation.
Git is to some extent character encoding agnostic.
- The contents of the blob objects are uninterpreted sequences
of bytes. There is no encoding translation at the core
level.
- The commit log messages are uninterpreted sequences of non-NUL
bytes.
- Path names are encoded in UTF-8 normalization form C. This
applies to tree objects, the index file, ref names, as well as
path names in command line arguments, environment variables
and config files (`.git/config` (see linkgit:git-config[1]),
linkgit:gitignore[5], linkgit:gitattributes[5] and
linkgit:gitmodules[5]).
+
Note that Git at the core level treats path names simply as
sequences of non-NUL bytes, there are no path name encoding
conversions (except on Mac and Windows). Therefore, using
non-ASCII path names will mostly work even on platforms and file
systems that use legacy extended ASCII encodings. However,
repositories created on such systems will not work properly on
UTF-8-based systems (e.g. Linux, Mac, Windows) and vice versa.
Additionally, many Git-based tools simply assume path names to
be UTF-8 and will fail to display other encodings correctly.
- Commit log messages are typically encoded in UTF-8, but other
extended ASCII encodings are also supported. This includes
ISO-8859-x, CP125x and many others, but _not_ UTF-16/32,
EBCDIC and CJK multi-byte encodings (GBK, Shift-JIS, Big5,
EUC-x, CP9xx etc.).
Although we encourage that the commit log messages are encoded
in UTF-8, both the core and Git Porcelain are designed not to