[PATCH] mdiff: split on unicode character boundaries when shortening function name

[Denis Laxalde]

Josef 'Jeff' Sipek wrote:
> # HG changeset patch
> # User Josef 'Jeff' Sipek <jeffpc at josefsipek.net>
> # Date 1519251311 18000
> #      Wed Feb 21 17:15:11 2018 -0500
> # Node ID b99df94fdd4813e0ce538a8caa682802da4a6cb2
> # Parent  106872aa15af9919220705ed72c78459774e1575
> mdiff: split on unicode character boundaries when shortening function name
> 
> Splitting the raw bytes may lead to truncating the string in the middle of a
> UTF-8 character which would lead to the generated diff containing an invalid
> byte sequence even though the original data had none.  For example, the
> Unicode codepoint U+308B (る) gets represented as \xe3\x82\x8b in UTF-8.
> Before this change a diff on i18n/ja.po would yield:
> 
> 	@@ -28953,7 +28953,7 @@ msgstr "Mercurial と SSH を併用す<E3><82>
> 
> After this change, the output is cleaner:
> 
> 	@@ -28953,7 +28953,7 @@ msgstr "Mercurial と SSH を併用する場合の注意点:"
> 
> diff --git a/mercurial/mdiff.py b/mercurial/mdiff.py
> --- a/mercurial/mdiff.py
> +++ b/mercurial/mdiff.py
> @@ -348,7 +348,12 @@ def _unidiff(t1, t2, opts=defaultopts):
>              # alphanumeric char.
>              for i in xrange(astart - 1, lastpos - 1, -1):
>                  if l1[i][0:1].isalnum():
> -                    func = ' ' + l1[i].rstrip()[:40]
> +                    func = l1[i].rstrip()
> +                    try:
> +                        func = func.decode("utf-8")[:40].encode("utf-8")
> +                    except:
> +                        func = func[:40]

I'd suggest catching exception types explicitly (UnicodeDecodeError and
UnicodeEncodeError I guess) and avoid "bare" except.

(No idea if the change itself is correct by the way.)

> +                    func = ' ' + func
>                      lastfunc[1] = func
>                      break
>              # by recording this hunk's starting point as the next place to
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