From 3f82d3a9753f29bb2007a24fc5ef434774c22824 Mon Sep 17 00:00:00 2001
From: Kai Moschcau <kai.moschcau@sabre.com>
Date: Tue, 30 Jul 2019 12:32:39 +0200
Subject: [PATCH] Improve multibyte character handling in branch ext

This fixes a bug that causes a mangled statusline. The bug occurs, when
the `displayed_head_limit` variable is set and causes the substring
expression to take a substring, which ends in the middle of a multi-byte
character.

This patch replaces the byte-based methods for measuring the
length of the branch name and creating a substring with methods that are
character-based and multi-byte aware.

It also has the nice side effect of making the length measuring more
accurate, by taking the actual display width of multi-byte characters
and the ambiwidth setting into account.

Since we need to take into account older Vim 7.4 (which might not have
the strcharpart() function), do introduce a compatibility wrapper in
airline#util that checks for the existence of the function before using
it. Older Vims will keep on using the byte-based index. I suppose Vim
7.4 before the strcharpart() function was available (patch 7.4.1730)
shouldn't be in use anymore.

closes #1948
---
 autoload/airline/extensions/branch.vim | 6 ++++--
 autoload/airline/util.vim              | 9 +++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/autoload/airline/extensions/branch.vim b/autoload/airline/extensions/branch.vim
index fc7de3d5..4b8e51ec 100644
--- a/autoload/airline/extensions/branch.vim
+++ b/autoload/airline/extensions/branch.vim
@@ -279,8 +279,10 @@ function! airline#extensions#branch#head()
 
   if exists("g:airline#extensions#branch#displayed_head_limit")
     let w:displayed_head_limit = g:airline#extensions#branch#displayed_head_limit
-    if len(b:airline_head) > w:displayed_head_limit - 1
-      let b:airline_head = b:airline_head[0:(w:displayed_head_limit - 1)].(&encoding ==? 'utf-8' ?  '…' : '.')
+    if strwidth(b:airline_head) > w:displayed_head_limit - 1
+      let b:airline_head =
+            \ airline#util#strcharpart(b:airline_head, 0, w:displayed_head_limit - 1)
+            \ ..(&encoding ==? 'utf-8' ?  '…' : '.')
     endif
   endif
 
diff --git a/autoload/airline/util.vim b/autoload/airline/util.vim
index 973cdfbc..8d67021a 100644
--- a/autoload/airline/util.vim
+++ b/autoload/airline/util.vim
@@ -107,6 +107,15 @@ function! airline#util#strchars(str)
   endif
 endfunction
 
+function! airline#util#strcharpart(...)
+  if exists('*strcharpart')
+    return call('strcharpart',  a:000)
+  else
+    " does not handle multibyte chars :(
+    return a:1[(a:2):(a:3)]
+  endif
+endfunction
+
 function! airline#util#ignore_buf(name)
   let pat = '\c\v'. get(g:, 'airline#ignore_bufadd_pat', '').
         \ get(g:, 'airline#extensions#tabline#ignore_bufadd_pat',