Commit: patch 9.2.0989: libvterm: hang when rendering REP with no preceding char

patch 9.2.0989: libvterm: hang when rendering REP with no preceding char

Commit: https://github.com/vim/vim/commit/785bb3e9b271eb377dbd4157ce281eac7f16a021
Author: Christian Brabandt <[email protected]>
Date:   Thu Aug 20 20:46:08 2026 +0000

    patch 9.2.0989: libvterm: hang when rendering REP with no preceding char
    
    Problem:  When libvterm receives the REP control (CSI b) it repeats the
              preceding graphic character by advancing the cursor by
              "combine_width".  When a graphic char was yet not printed, this
              resulted in an endless loop (Vadím Sukhomlínov).
    Solution: Ignore REP when no graphic character was printed yet, like xterm
              does.
    
    related: #21099
    
    Signed-off-by: Christian Brabandt <[email protected]>
    Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

diff --git a/src/libvterm/src/state.c b/src/libvterm/src/state.c
index 70bce0a23..7a9732b58 100644
--- a/src/libvterm/src/state.c
+++ b/src/libvterm/src/state.c
@@ -1323,6 +1323,13 @@ static int on_csi(const char *leader, const long args[], int argcount, const cha
 
   case 0x62: { // REP - ECMA-48 8.3.103
     const int row_width = THISROWWIDTH(state);
+
+    // ECMA-48 repeats the preceding graphic character; when none was
+    // printed yet "combine_width" is zero and the loop below would never
+    // advance the cursor.  Ignore the control then, like xterm does.
+    if(state->combine_width < 1)
+      break;
+
     count = CSI_ARG_COUNT(args[0]);
     col = state->pos.col + count;
     UBOUND(col, row_width);
diff --git a/src/testdir/test_terminal3.vim b/src/testdir/test_terminal3.vim
index 7d67d6f68..263e9ee34 100644
--- a/src/testdir/test_terminal3.vim
+++ b/src/testdir/test_terminal3.vim
@@ -1396,4 +1396,27 @@ func Test_terminal_negative_col_oob()
   endfor
 endfunc
 
+" This caused a hang
+func Test_terminal_rep_no_preceding_char()
+  CheckUnix
+  CheckExecutable printf
+
+  " REP repeats the preceding graphic character.  When none was printed yet
+  " the repeat width in libvterm is zero, so the cursor never reached the end
+  " column and Vim looped forever while rendering the sequence.
+  let buf = term_start([&shell, &shellcmdflag, 'printf "%s" ' .. shellescape("\<ESC>[9b")],
+        \ #{term_rows: 10, term_cols: 40})
+  call TermWait(buf)
+  " Getting here without a hang is the test.
+  call assert_true(bufexists(buf))
+  exe 'bwipe! ' .. buf
+
+  " REP after a graphic character still repeats it.
+  let buf = term_start([&shell, &shellcmdflag, 'printf "%s" ' .. shellescape("X\<ESC>[4b")],
+        \ #{term_rows: 10, term_cols: 40})
+  call TermWait(buf)
+  call WaitForAssert({-> assert_equal('XXXXX', term_getline(buf, 1))})
+  exe 'bwipe! ' .. buf
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index a8698a9fd..840e5cf8b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -763,6 +763,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    989,
 /**/
     988,
 /**/

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