vim-patch:9.2.0547: "%v" in 'errorformat' is affected by 'tabstop' (#40040)

Problem:  The "%v" item in 'errorformat' interprets the reported
          screen column using the buffer's 'tabstop', so the cursor
          jumps to the wrong column when 'tabstop' is not 8
          (vimpostor).
Solution: When resolving a "%v" column, always count a <tab> as 8
          screen columns, independent of 'tabstop', matching the
          column numbers reported by compilers; keep the multi-byte
          handling.  Also use "%v" in the gcc compiler file and
          update the documentation (Hirohito Higashi).

fixes:  vim/vim#20321
closes: vim/vim#20359

https://github.com/vim/vim/commit/44dcad20f2781ce5c1bd9a851212377859cc5bea

Co-authored-by: Hirohito Higashi <h.east.727@gmail.com>
Co-authored-by: vimpostor <21310755+vimpostor@users.noreply.github.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

runtime/compiler/gcc.vim

@@ -7,6 +7,7 @@
 "			added line suggested by Anton Lindqvist 2016 Mar 31
 "			2024 Apr 03 by The Vim Project (removed :CompilerSet definition)
 "			2025 Dec 17 by The Vim Project (correctly parse: 'make: *** [Makefile:2: all] Error 1')
+"			2026 May 28 by The Vim Project (Use %v to parse column number)
 
 if exists("current_compiler")
   finish
@@ -24,9 +25,9 @@ CompilerSet errorformat=
       \\"%f\"%*\\D%l:\ %m,
       \%-G%f:%l:\ %trror:\ (Each\ undeclared\ identifier\ is\ reported\ only\ once,
       \%-G%f:%l:\ %trror:\ for\ each\ function\ it\ appears\ in.),
-      \%f:%l:%c:\ %trror:\ %m,
-      \%f:%l:%c:\ %tarning:\ %m,
-      \%f:%l:%c:\ %m,
+      \%f:%l:%v:\ %trror:\ %m,
+      \%f:%l:%v:\ %tarning:\ %m,
+      \%f:%l:%v:\ %m,
       \%f:%l:\ %trror:\ %m,
       \%f:%l:\ %tarning:\ %m,
       \%f:%l:\ %m,

runtime/doc/quickfix.txt

@@ -1815,9 +1815,9 @@ Basic items
 	%c		column number (finds a number representing character
 			column of the error, byte index, a <tab> is 1
 			character column)
-	%v		virtual column number (finds a number representing
-			screen column of the error (1 <tab> == 8 screen
-			columns))
+	%v		virtual column number (finds a number representing the
+			screen column of the error, where a <tab> is always 8
+			screen columns regardless of 'tabstop')
 	%k		end column number (finds a number representing
 			the character column of the error, byte index, or a
 			number representing screen end column of the error if

src/nvim/quickfix.c

@@ -3041,6 +3041,30 @@ static int qf_jump_edit_buffer(qf_info_T *qi, qfline_T *qf_ptr, int forceit, int
   return retval;
 }
 
+/// Return the byte index in the current line for screen column "vcol"
+/// (zero-based).  A <tab> is always counted as 8 screen columns, matching the
+/// column numbers compilers report for the "%v" item in 'errorformat',
+/// regardless of the buffer's 'tabstop'.
+static int qf_screen_col_to_idx(colnr_T vcol)
+{
+  const char *line = get_cursor_line_ptr();
+  const char *p = line;
+  colnr_T col = 0;
+
+  while (*p != NUL && col < vcol) {
+    if (*p == TAB) {
+      col += 8 - (col % 8);
+    } else {
+      col += ptr2cells(p);
+    }
+    if (col > vcol) {
+      break;
+    }
+    MB_PTR_ADV(p);
+  }
+  return (int)(p - line);
+}
+
 /// Go to the error line in the current file using either line/column number or
 /// a search pattern.
 static void qf_jump_goto_line(linenr_T qf_lnum, int qf_col, char qf_viscol, char *qf_pattern)
@@ -3055,7 +3079,7 @@ static void qf_jump_goto_line(linenr_T qf_lnum, int qf_col, char qf_viscol, char
     if (qf_col > 0) {
       curwin->w_cursor.coladd = 0;
       if (qf_viscol == true) {
-        coladvance(curwin, qf_col - 1);
+        curwin->w_cursor.col = qf_screen_col_to_idx(qf_col - 1);
       } else {
         curwin->w_cursor.col = qf_col - 1;
       }

test/old/testdir/test_quickfix.vim

@@ -4948,7 +4948,7 @@ endfunc
 " Test for parsing entries using visual screen column
 func Test_viscol()
   enew
-  call writefile(["Col1\tCol2\tCol3"], 'Xfile1')
+  call writefile(["Col1\tCol2\tCol3"], 'Xfile1', 'D')
   edit Xfile1
 
   " Use byte offset for column number
@@ -5013,7 +5013,34 @@ func Test_viscol()
 
   enew | only
   set efm&
-  call delete('Xfile1')
+endfunc
+
+" Test that '%v' is not affected by 'tabstop': a <tab> is always counted as
+" 8 screen columns, matching the column numbers reported by compilers.
+func Test_viscol_tabstop()
+  enew
+  call writefile(["\tABCDEFGH"], 'Xfile1', 'D')
+  edit Xfile1
+  set efm=%f:%l:%v:%m
+
+  " gcc reports column 9 for 'A' (the <tab> expands to 8 columns).  The jump
+  " must land on 'A' (byte 2) for any 'tabstop' value.
+  for ts in [8, 4, 2, 13]
+    exe 'setlocal tabstop=' .. ts
+    cexpr "Xfile1:1:9:XX"
+    call assert_equal(2, col('.'), 'tabstop=' .. ts)
+  endfor
+
+  " A multi-byte character after the tab: 'ä' is 2 bytes but 1 screen cell,
+  " so screen column 10 is the next character 'b' (byte 4).
+  call writefile(["\täbc"], 'Xfile1')
+  edit! Xfile1
+  setlocal tabstop=4
+  cexpr "Xfile1:1:10:XX"
+  call assert_equal(4, col('.'))
+
+  enew | only
+  set efm&
 endfunc
 
 " Test for the quickfix window buffer