convert: add round trip check based on 'core.checkRoundtripEncoding'

UTF supports lossless conversion round tripping and conversions between
UTF and other encodings are mostly round trip safe as Unicode aims to be
a superset of all other character encodings. However, certain encodings
(e.g. SHIFT-JIS) are known to have round trip issues [1].

Add 'core.checkRoundtripEncoding', which contains a comma separated
list of encodings, to define for what encodings Git should check the
conversion round trip if they are used in the 'working-tree-encoding'
attribute.

Set SHIFT-JIS as default value for 'core.checkRoundtripEncoding'.

[1] https://support.microsoft.com/en-us/help/170559/prb-conversion-problem-between-shift-jis-and-unicode

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/config.c b/config.c
index 1f003fb..d0ada9f 100644
--- a/config.c
+++ b/config.c
@@ -1172,6 +1172,11 @@ static int git_default_core_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.checkroundtripencoding")) {
+		check_roundtrip_encoding = xstrdup(value);
+		return 0;
+	}
+
 	if (!strcmp(var, "core.notesref")) {
 		notes_ref_name = xstrdup(value);
 		return 0;