Commit: patch 9.2.0891: MS-Windows: filename-modifier ":8:t" causes underflow

patch 9.2.0891: MS-Windows: filename-modifier ":8:t" causes underflow

Commit: https://github.com/vim/vim/commit/a3df0ea61b708534fb0a2277216adaacf79ece43
Author: Hirohito Higashi <[email protected]>
Date:   Sat Aug 1 13:26:21 2026 +0000

    patch 9.2.0891: MS-Windows: filename-modifier ":8:t" causes underflow
    
    Problem:  On MS-Windows using ":8" with ":t", ":e" or ":r" in one
              fnamemodify() gives a wrong result or an out of memory error.
    Solution: Recompute the tail after ":8" replaced the name
              (Hirohito Higashi).
    
    related: #20899
    closes:  #20903
    
    Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
    Signed-off-by: Hirohito Higashi <[email protected]>
    Signed-off-by: Christian Brabandt <[email protected]>

diff --git a/src/filepath.c b/src/filepath.c
index 8bdba335c..e70b9c300 100644
--- a/src/filepath.c
+++ b/src/filepath.c
@@ -586,6 +586,10 @@ repeat:
 	    }
 	    *fnamelen = l;
 	}
+
+	// The name was replaced by the short name, "tail" points into the
+	// previous name.
+	tail = gettail(*fnamep);
     }
 #endif // MSWIN
 
diff --git a/src/testdir/test_shortpathname.vim b/src/testdir/test_shortpathname.vim
index b3d7b82be..a1d9d9816 100644
--- a/src/testdir/test_shortpathname.vim
+++ b/src/testdir/test_shortpathname.vim
@@ -101,4 +101,24 @@ func Test_ColonEight_notexists()
   call assert_equal(non_exists, fnamemodify(non_exists, ':p:8'))
 endfunc
 
+" ":8" replaces the name, the modifiers after it must use the new name.
+func Test_ColonEight_then_tail()
+  let dir = 'c:/Xtest_C8tail'
+  call s:SetupDir(dir)
+
+  let file = dir . '/longfilename.txt'
+
+  call mkdir(dir, 'D')
+  call writefile([], file, 'D')
+
+  let sfile = fnamemodify(file, ':p:8')
+  if sfile ==? fnamemodify(file, ':p')
+    throw 'Skipped: 8.3 short names are not created on this volume'
+  endif
+
+  call assert_equal(fnamemodify(sfile, ':t'), fnamemodify(file, ':p:8:t'))
+  call assert_equal(fnamemodify(sfile, ':e'), fnamemodify(file, ':p:8:e'))
+  call assert_equal(fnamemodify(sfile, ':r'), fnamemodify(file, ':p:8:r'))
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/version.c b/src/version.c
index 09996f74b..c48aca0ff 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    891,
 /**/
     890,
 /**/

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