vim-patch:8.2.4387: command line completion doesn't always work properly (#21352)

Problem:    Command line completion doesn't always work properly.
Solution:   Adjust triggering after a "|".  Add more tests. (Yegappan
            Lakshmanan, closes vim/vim#9779)

https://github.com/vim/vim/commit/e3846cf1ebdc4af0b39885153b4703f71a9b919e

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

1 files changed, 13 insertions, 9 deletions

diff --git a/src/nvim/cmdexpand.c b/src/nvim/cmdexpand.c
index 933ad93964..d1a56feef4 100644
--- a/src/nvim/cmdexpand.c
+++ b/src/nvim/cmdexpand.c
@@ -1551,16 +1551,20 @@ static const char *set_context_by_cmdname(const char *cmd, cmdidx_T cmdidx, cons
       // Skip "from" part.
       arg++;
       arg = (const char *)skip_regexp((char *)arg, delim, magic_isset());
-    }
-    // Skip "to" part.
-    while (arg[0] != NUL && (uint8_t)arg[0] != delim) {
-      if (arg[0] == '\\' && arg[1] != NUL) {
+
+      if (arg[0] != NUL && arg[0] == delim) {
+        // Skip "to" part.
         arg++;
+        while (arg[0] != NUL && (uint8_t)arg[0] != delim) {
+          if (arg[0] == '\\' && arg[1] != NUL) {
+            arg++;
+          }
+          arg++;
+        }
+        if (arg[0] != NUL) {  // Skip delimiter.
+          arg++;
+        }
       }
-      arg++;
-    }
-    if (arg[0] != NUL) {  // Skip delimiter.
-      arg++;
     }
     while (arg[0] && strchr("|\"#", arg[0]) == NULL) {
       arg++;
@@ -1591,7 +1595,7 @@ static const char *set_context_by_cmdname(const char *cmd, cmdidx_T cmdidx, cons
         arg = (const char *)skipwhite(arg + 1);
 
         // Check for trailing illegal characters.
-        if (*arg && strchr("|\"\n", *arg) == NULL) {
+        if (*arg == NUL || strchr("|\"\n", *arg) == NULL) {
           xp->xp_context = EXPAND_NOTHING;
         } else {
           return arg;