Commit: patch 9.1.2134: Terminal doesn't handle split UTF-8 sequence after ASCII

[Christian Brabandt]

patch 9.1.2134: Terminal doesn't handle split UTF-8 sequence after ASCII

Commit: https://github.com/vim/vim/commit/b24a1d9291b2d7fe202237a5d531076a095887d6
Author: zeertzjq <zeer...@outlook.com>
Date: Fri Feb 6 09:48:20 2026 +0000

patch 9.1.2134: Terminal doesn't handle split UTF-8 sequence after ASCII

Problem: Terminal doesn't handle split UTF-8 sequence after ASCII.
Solution: Only use one UTF-8 encoding state per vterm state (zeertzjq).

fixes: #16559
closes: #18640

Signed-off-by: zeertzjq <zeer...@outlook.com>
Signed-off-by: Christian Brabandt <c...@256bit.org>

diff --git a/runtime/doc/version9.txt b/runtime/doc/version9.txt
index 5b43fa91b..73083398b 100644
--- a/runtime/doc/version9.txt
+++ b/runtime/doc/version9.txt
@@ -52486,4 +52486,8 @@ Patch 9.1.2133
Problem: Another case of buffer overflow with 'helpfile'.
Solution: Leave room for "tags" in the buffer (zeertzjq).

+Patch 9.1.2134
+Problem: Terminal doesn't handle split UTF-8 sequence after ASCII.
+Solution: Only use one UTF-8 encoding state per vterm state (zeertzjq).
+
vim:tw=78:ts=8:noet:ft=help:norl:fdm=manual:nofoldenable
diff --git a/src/libvterm/src/state.c b/src/libvterm/src/state.c
index ee36ad4c2..aff97b076 100644
--- a/src/libvterm/src/state.c
+++ b/src/libvterm/src/state.c
@@ -297,6 +297,8 @@ static int on_text(const char bytes[], size_t len, void *user)
!(bytes[eaten] & 0x80) ? &state->encoding[state->gl_set] :
state->vt->mode.utf8 ? &state->encoding_utf8 :
&state->encoding[state->gr_set];
+ if (encoding->enc == state->encoding_utf8.enc)
+ encoding = &state->encoding_utf8; // Only use one UTF-8 encoding state.

(*encoding->enc->decode)(encoding->enc, encoding->data,
codepoints, &npoints, state->gsingle_set ? 1 : (int)maxpoints,
diff --git a/src/libvterm/t/14state_encoding.test b/src/libvterm/t/14state_encoding.test
index b1f5d6985..2fd90e438 100644
--- a/src/libvterm/t/14state_encoding.test
+++ b/src/libvterm/t/14state_encoding.test
@@ -103,3 +103,12 @@ PUSH "AB\xc4\x88D"
putglyph 0x0042 1 0,1
putglyph 0x0108 1 0,2
putglyph 0x0044 1 0,3
+
+!Split UTF-8 after US-ASCII
+RESET
+PUSH "AB\xc4"
+ putglyph 0x0041 1 0,0
+ putglyph 0x0042 1 0,1
+PUSH "\x88D"
+ putglyph 0x0108 1 0,2
+ putglyph 0x0044 1 0,3
diff --git a/src/testdir/test_terminal3.vim b/src/testdir/test_terminal3.vim
index ff8f8c206..b637a6652 100644
--- a/src/testdir/test_terminal3.vim
+++ b/src/testdir/test_terminal3.vim
@@ -1124,4 +1124,28 @@ func Test_terminal_backspace_on_windows()
let $PROMPT = save_prompt
endfunc

+func Test_terminal_split_utf8()
+ CheckUnix
+
+ let buf = term_start('cat', {})
+ let chan = buf->term_getjob()->job_getchannel()
+ call ch_sendraw(chan, "1: \xc3")
+ call WaitForAssert({-> assert_equal('1: ', term_getline(buf, 1))})
+ call ch_sendraw(chan, "\xa5\xcc\xb2
")
+ call WaitForAssert({-> assert_equal('1: å̲', term_getline(buf, 1))})
+ call WaitForAssert({-> assert_equal('1: å̲', term_getline(buf, 2))})
+ call ch_sendraw(chan, "2: \xc3\xa5")
+ call WaitForAssert({-> assert_equal('2: å', term_getline(buf, 3))})
+ call ch_sendraw(chan, "\xcc\xb2
")
+ call WaitForAssert({-> assert_equal('2: å̲', term_getline(buf, 3))})
+ call WaitForAssert({-> assert_equal('2: å̲', term_getline(buf, 4))})
+ call ch_sendraw(chan, "3: \xc3\xa5\xcc")
+ call WaitForAssert({-> assert_equal('3: å', term_getline(buf, 5))})
+ call ch_sendraw(chan, "\xb2
")
+ call WaitForAssert({-> assert_equal('3: å̲', term_getline(buf, 5))})
+ call WaitForAssert({-> assert_equal('3: å̲', term_getline(buf, 6))})
+
+ exe buf .. "bwipe!"
+endfunc
+
" vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index fea5c51ed..a9967e2bb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -734,6 +734,8 @@ static char *(features[]) =

static int included_patches[] =
{ /* Add new patch number below this line */
+/**/
+ 2134,
/**/
2133,
/**/