Re: [PATCH v8 7/7] convert: add round trip check based on 'core.checkRoundtripEncoding'

> On 25 Feb 2018, at 20:50, Eric Sunshine <sunshine@sunshineco.com> wrote:
> 
> On Sat, Feb 24, 2018 at 11:28 AM,  <lars.schneider@autodesk.com> wrote:
>> 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>
>> ---
>> diff --git a/convert.c b/convert.c
>> @@ -289,6 +289,39 @@ static void trace_encoding(const char *context, const char *path,
>> +static int check_roundtrip(const char* enc_name)
>> +{
>> +       /*
>> +        * check_roundtrip_encoding contains a string of space and/or
>> +        * comma separated encodings (eg. "UTF-16, ASCII, CP1125").
>> +        * Search for the given encoding in that string.
>> +        */
>> +       const char *found = strcasestr(check_roundtrip_encoding, enc_name);
>> +       const char *next = found + strlen(enc_name);
> 
> Is this pointer arithmetic undefined behavior (according to the C
> standard) if NULL is returned by strcasestr()? If so, how comfortable
> are we with this? Perhaps if you add an 'if' into the mix, you can
> avoid it:
> 
>    if (found) {
>        const char *next = found + strlen(enc_name);
>        return ...long complicated expression...;
>    }
>    return false;

>> +
>> +               if (!re_src || src_len != re_src_len ||
>> +                   memcmp(src, re_src, src_len)) {
>> +                       const char* msg = _("encoding '%s' from %s to %s and "
>> +                                           "back is not the same");
>> +                       die(msg, path, enc->name, default_encoding);
> 
> Last two arguments need to be swapped.

>> +               }
>> +
>> +               free(re_src);
>> +       }
>> +
>>        strbuf_attach(buf, dst, dst_len, dst_len + 1);
>>        return 1;
>> }
>> diff --git a/t/t0028-working-tree-encoding.sh b/t/t0028-working-tree-encoding.sh
>> @@ -225,4 +225,45 @@ test_expect_success 'error if encoding garbage is already in Git' '
>> +test_expect_success 'check roundtrip encoding' '
>> +       text="hallo there!\nroundtrip test here!" &&
>> +       printf "$text" | iconv -f UTF-8 -t SHIFT-JIS >roundtrip.shift &&
>> +       printf "$text" | iconv -f UTF-8 -t UTF-16 >roundtrip.utf16 &&
>> +       echo "*.shift text working-tree-encoding=SHIFT-JIS" >>.gitattributes &&
>> +
>> +       # SHIFT-JIS encoded files are round-trip checked by default...
>> +       GIT_TRACE=1 git add .gitattributes roundtrip.shift 2>&1 >/dev/null |
>> +               grep "Checking roundtrip encoding for SHIFT-JIS" &&
> 
> Why redirect to /dev/null? If something does go wrong somewhere, the
> more output available for debugging the problem, the better, so
> throwing it away unnecessarily seems contraindicated.

>> +       git reset &&
>> +
>> +       # ... unless we overwrite the Git config!
>> +       test_config core.checkRoundtripEncoding "garbage" &&
>> +       ! GIT_TRACE=1 git add .gitattributes roundtrip.shift 2>&1 >/dev/null |
>> +               grep "Checking roundtrip encoding for SHIFT-JIS" &&
>> +       test_unconfig core.checkRoundtripEncoding &&
> 
> The "unconfig" won't take place if the test fails. Instead of
> test_config/test_unconfig, you could use '-c' to set the config
> transiently for the git-add operation:
> 
>    ! GIT_TRACE=1 git -c core.checkRoundtripEncoding=garbage add ...

>> +       git reset &&
>> +
>> +       # UTF-16 encoded files should not be round-trip checked by default...
>> +       ! GIT_TRACE=1 git add roundtrip.utf16 2>&1 >/dev/null |
>> +               grep "Checking roundtrip encoding for UTF-16" &&
>> +       git reset &&
>> +
>> +       # ... unless we tell Git to check it!
>> +       test_config_global core.checkRoundtripEncoding "UTF-16, UTF-32" &&
>> +       GIT_TRACE=1 git add roundtrip.utf16 2>&1 >/dev/null |
>> +               grep "Checking roundtrip encoding for UTF-16" &&
>> +       git reset &&
>> +
>> +       # ... unless we tell Git to check it!
>> +       # (here we also check that the casing of the encoding is irrelevant)
>> +       test_config_global core.checkRoundtripEncoding "UTF-32, utf-16" &&
>> +       GIT_TRACE=1 git add roundtrip.utf16 2>&1 >/dev/null |
>> +               grep "Checking roundtrip encoding for UTF-16" &&
>> +       git reset &&
>> +
>> +       # cleanup
>> +       rm roundtrip.shift roundtrip.utf16 &&
>> +       git reset --hard HEAD
>> +'
> 
> Same comment as for patch 5/7: This cleanup won't happen if the test
> fails. Instead, use test_when_finished() earlier in the test:
> 
>    test_expect_success 'check roundtrip encoding' '
>        test_when_finished "rm -f roundtrip.shift roundtrip.utf16; git
> reset --hard HEAD" &&
>        ...