patch 9.1.2006: MS-Windows: ANSI colors not correct in terminal

Problem:  ANSI escape colors are not displayed correctly in
          non-termguicolors in vim (cli) on Windows. The red and blue
          channels seem to be swapped.
Cause:    When converting VTerm ANSI index colors to cterm colors in
          terminal.c, the Windows case equivalent to NR-16 (:help
          cterm-colors) is ignored.
Solution: Created and used a table to convert ANSI indexed colors to
          cterm's NR-16 representation (Windows only). This table
          corresponds to the inverse conversion of cterm_ansi_idx in
          term.c. The values in both tables are exactly the same, but
          the meanings are opposite, so they are separate tables
          (Muraoka Taro).

closes: #18931

Signed-off-by: Muraoka Taro <koron.kaoriya@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: koron

src/term.c

@@ -7642,7 +7642,7 @@ static const char_u ansi_table[16][3] = {
 
 # if defined(MSWIN)
 // Mapping between cterm indices < 16 and their counterpart in the ANSI palette.
-static const char_u cterm_ansi_idx[] = {
+const char_u cterm_ansi_idx[] = {
     0, 4, 2, 6, 1, 5, 3, 7, 8, 12, 10, 14, 9, 13, 11, 15
 };
 # endif

src/termdefs.h

@@ -233,3 +233,8 @@ typedef enum {
     TMODE_RAW,	    // terminal mode for Normal and Insert mode
     TMODE_UNKNOWN   // after executing a shell
 } tmode_T;
+
+#if defined(MSWIN)
+// Mapping between cterm indices < 16 and their counterpart in the ANSI palette.
+extern const char_u cterm_ansi_idx[];
+#endif

src/terminal.c

@@ -3033,7 +3033,20 @@ color2index(VTermColor *color, int fg, int *boldp)
     {
 	// Use the color as-is if possible, give up otherwise.
 	if (color->index < t_colors)
-	    return color->index + 1;
+	{
+	    uint8_t index = color->index;
+#ifdef MSWIN
+	    // Convert ANSI palette to cterm color index.
+	    // cterm_ansi_idx is a table for the reverse conversion from cterm
+	    // color index to ANSI palette. However, the current table can
+	    // be used for this conversion as well.
+	    // Note: If the contents of cterm_ansi_idx change in the future, a
+	    // different table may be needed for this purpose.
+	    if (index < 16)
+		index = cterm_ansi_idx[index];
+#endif
+	    return index + 1;
+	}
 	// 8-color terminals can actually display twice as many colors by
 	// setting the high-intensity/bold bit.
 	else if (t_colors == 8 && fg && color->index < 16)

src/testdir/test_terminal3.vim

@@ -1037,4 +1037,55 @@ func Test_terminal_visual_empty_listchars()
   call StopVimInTerminal(buf)
 endfunc
 
+func Test_terminal_ansi_color_windows_cui()
+  if !has('win32') || has('gui_running')
+    throw 'Skipped: only for the Windows CUI'
+  endif
+  if exists('$APPVEYOR')
+    throw 'Skipped: this test cannot be performed because AppVeyor does not support ANSI escape sequences'
+  endif
+
+  call assert_equal('dark', &background)
+
+  " Outputs 16 ANSI colors as background colors
+  let ansi = ''
+  for i in range(16)
+    let ansi ..= printf("\e[%dm%X", i + (i < 8 ? 40 : 92), i)
+  endfor
+  let ansi ..= "\e[40m\n"
+  call writefile([ansi], 'XANSIcolor', 'D')
+
+  let expected_chars = '0123456789ABCDEF'
+  let expected_colors = [
+        \ '#000000', '#e00000', '#00e000', '#e0e000',
+        \ '#0000e0', '#e000e0', '#00e0e0', '#e0e0e0',
+        \ '#808080', '#ff4040', '#40ff40', '#ffff40',
+        \ '#4040ff', '#ff40ff', '#40ffff', '#ffffff',
+        \ ]
+
+  " Ideally, 16 colors should be checked. However, in the current CI
+  " environment, the 16th color is something other than white, and we don't
+  " know the cause nor solution. After discussion, we decided to check only 15
+  " colors for the time being.
+  " FIXME: Check all 16 colors in the future.
+  let len_to_check = 15
+  let expected_colors = expected_colors[:len_to_check-1]
+
+  " First, make sure vim can display correct ANSI color text in terminal.
+  let buf = term_start("cmd /C type XANSIcolor")
+  call WaitForAssert({-> assert_equal(expected_chars, term_scrape(buf, 1)[:15]->map({_, v -> v['chars']})->join(''))})
+  call assert_equal(expected_colors, term_scrape(buf, 1)[:len_to_check-1]->map({_, v -> v['bg']}))
+  bwipeout!
+
+  " Next, check if vim can do the same thing in the vim terminal in terminal.
+  let lines = [
+        \ 'call term_start("cmd /C type XANSIcolor")'
+        \ ]
+  call writefile(lines, 'XloadANSI', 'D')
+  let cmd = GetVimCommandCleanTerm()
+  let buf = term_start(cmd .. '-S XloadANSI')
+  call WaitForAssert({-> assert_equal(expected_chars, term_scrape(buf, 1)[:15]->map({_, v -> v['chars']})->join(''))})
+  call assert_equal(expected_colors, term_scrape(buf, 1)[:len_to_check-1]->map({_, v -> v['bg']}))
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -734,6 +734,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2006,
 /**/
     2005,
 /**/