vim-patch:9.0.2009: cmdline-completion for comma-separated options wrong (#25569)

Problem:  cmdline-completion for comma-separated options wrong
Solution: Fix command-line expansions for options with filenames with
          commas

Fix command-line expansions for options with filenames with commas

Cmdline expansion for option values that take a comma-separated list
of file names is currently not handling file names with commas as the
commas are not escaped. For such options, the commas in file names need
to be escaped (to differentiate from a comma that delimit the list
items). The escaped comma is unescaped in `copy_option_part()` during
option parsing.

Fix as follows:
- Cmdline completion for option values with comma-separated file/folder
  names will not start a new match when seeing `\\,` and will instead
  consider it as one value.
- File/folder regex matching will strip the `\\` when seeing `\\,` to
  make sure it can match the correct files/folders.
- The expanded value will escape `,` with `\\,`, similar to how spaces
  are escaped to make sure the option value is correct on the cmdline.

This fix also takes into account the fact that Win32 Vim handles file
name escaping differently. Typing '\,' for a file name results in it
being handled literally but in other platforms '\,' is interpreted as a
simple ',' and commas need to be escaped using '\\,' instead.

Also, make sure this new logic only applies to comma-separated options
like 'path'. Non-list options like 'set makeprg=<Tab>' and regular ex
commands like `:edit <Tab>` do not require escaping and will continue to
work.

Also fix up documentation to be clearer. The original docs are slightly
misleading in how it discusses triple slashes for 'tags'.

closes: vim/vim#13303
related: vim/vim#13301

https://github.com/vim/vim/commit/54844857fd6933fa4f6678e47610c4b9c9f7a091

Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

4 files changed, 38 insertions, 13 deletions

diff --git a/src/nvim/cmdexpand.c b/src/nvim/cmdexpand.c
index c2469b6574..38be6573c8 100644
--- a/src/nvim/cmdexpand.c
+++ b/src/nvim/cmdexpand.c
@@ -156,8 +156,9 @@ static void wildescape(expand_T *xp, const char *str, int numfiles, char **files
     // and wildmatch characters, except '~'.
     for (int i = 0; i < numfiles; i++) {
       // for ":set path=" we need to escape spaces twice
-      if (xp->xp_backslash == XP_BS_THREE) {
-        p = vim_strsave_escaped(files[i], " ");
+      if (xp->xp_backslash & XP_BS_THREE) {
+        char *pat = (xp->xp_backslash & XP_BS_COMMA) ? " ," : " ";
+        p = vim_strsave_escaped(files[i], pat);
         xfree(files[i]);
         files[i] = p;
 #if defined(BACKSLASH_IN_FILENAME)
@@ -165,6 +166,14 @@ static void wildescape(expand_T *xp, const char *str, int numfiles, char **files
         xfree(files[i]);
         files[i] = p;
 #endif
+      } else if (xp->xp_backslash & XP_BS_COMMA) {
+        if (vim_strchr(files[i], ',') != NULL) {
+          p = vim_strsave_escaped(files[i], ",");
+          if (p != NULL) {
+            xfree(files[i]);
+            files[i] = p;
+          }
+        }
       }
 #ifdef BACKSLASH_IN_FILENAME
       p = vim_strsave_fnameescape(files[i], vse_what);
@@ -2440,15 +2449,23 @@ static int expand_files_and_dirs(expand_T *xp, char *pat, char ***matches, int *
     pat = xstrdup(pat);
     for (int i = 0; pat[i]; i++) {
       if (pat[i] == '\\') {
-        if (xp->xp_backslash == XP_BS_THREE
+        if (xp->xp_backslash & XP_BS_THREE
             && pat[i + 1] == '\\'
             && pat[i + 2] == '\\'
             && pat[i + 3] == ' ') {
           STRMOVE(pat + i, pat + i + 3);
-        }
-        if (xp->xp_backslash == XP_BS_ONE
-            && pat[i + 1] == ' ') {
+        } else if (xp->xp_backslash & XP_BS_ONE
+                   && pat[i + 1] == ' ') {
           STRMOVE(pat + i, pat + i + 1);
+        } else if ((xp->xp_backslash & XP_BS_COMMA)
+                   && pat[i + 1] == '\\'
+                   && pat[i + 2] == ',') {
+          STRMOVE(pat + i, pat + i + 2);
+#ifdef BACKSLASH_IN_FILENAME
+        } else if ((xp->xp_backslash & XP_BS_COMMA)
+                   && pat[i + 1] == ',') {
+          STRMOVE(pat + i, pat + i + 1);
+#endif
         }
       }
     }
diff --git a/src/nvim/cmdexpand_defs.h b/src/nvim/cmdexpand_defs.h
index a302a32852..7c422aca18 100644
--- a/src/nvim/cmdexpand_defs.h
+++ b/src/nvim/cmdexpand_defs.h
@@ -40,9 +40,10 @@ typedef struct expand {
 
 /// values for xp_backslash
 enum {
-  XP_BS_NONE  = 0,  ///< nothing special for backslashes
-  XP_BS_ONE   = 1,  ///< uses one backslash before a space
-  XP_BS_THREE = 2,  ///< uses three backslashes before a space
+  XP_BS_NONE  = 0,    ///< nothing special for backslashes
+  XP_BS_ONE   = 0x1,  ///< uses one backslash before a space
+  XP_BS_THREE = 0x2,  ///< uses three backslashes before a space
+  XP_BS_COMMA = 0x4,  ///< commas need to be escaped with a backslash
 };
 
 /// values for xp_context when doing command line completion
diff --git a/src/nvim/option.c b/src/nvim/option.c
index c0353e52be..0700d0e87e 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -5496,6 +5496,9 @@ void set_context_in_set_cmd(expand_T *xp, char *arg, int opt_flags)
         xp->xp_backslash = XP_BS_ONE;
       }
     }
+    if (flags & P_COMMA) {
+      xp->xp_backslash |= XP_BS_COMMA;
+    }
   }
 
   // For an option that is a list of file names, or comma/colon-separated
@@ -5511,8 +5514,12 @@ void set_context_in_set_cmd(expand_T *xp, char *arg, int opt_flags)
         while (s > xp->xp_pattern && *(s - 1) == '\\') {
           s--;
         }
-        if ((*p == ' ' && (xp->xp_backslash == XP_BS_THREE && (p - s) < 3))
-            || (*p == ',' && (flags & P_COMMA) && ((p - s) % 1) == 0)
+        if ((*p == ' ' && ((xp->xp_backslash & XP_BS_THREE) && (p - s) < 3))
+#if defined(BACKSLASH_IN_FILENAME)
+            || (*p == ',' && (flags & P_COMMA) && (p - s) < 1)
+#else
+            || (*p == ',' && (flags & P_COMMA) && (p - s) < 2)
+#endif
             || (*p == ':' && (flags & P_COLON))) {
           xp->xp_pattern = p + 1;
           break;
diff --git a/src/nvim/options.lua b/src/nvim/options.lua
index 68d88ea0aa..d5f41c5a89 100644
--- a/src/nvim/options.lua
+++ b/src/nvim/options.lua
@@ -8679,8 +8679,8 @@ return {
       deny_duplicates = true,
       desc = [=[
         Filenames for the tag command, separated by spaces or commas.  To
-        include a space or comma in a file name, precede it with a backslash
-        (see |option-backslash| about including spaces and backslashes).
+        include a space or comma in a file name, precede it with backslashes
+        (see |option-backslash| about including spaces/commas and backslashes).
         When a file name starts with "./", the '.' is replaced with the path
         of the current file.  But only when the 'd' flag is not included in
         'cpoptions'.  Environment variables are expanded |:set_env|.  Also see