Fix scp completions to support bidirectional transfer

Also hardcode standard /bin/ls to avoid issues with `ls` aliases on the
target, and inherit the (improved) list of remotes from `ssh`.

CHANGELOG.md

@@ -81,6 +81,7 @@ This section is for changes merged to the `major` branch that are not also merge
   - `npm`<sup>†</sup>
   - `python`/`python2`/`python3`
   - `service`
+  - `scp`
   - `ssh` (#4344)
   - `sudo` (see above)
   - `yarn`<sup>&#x2217;</sup><sup>†</sup>

share/completions/scp.fish

@@ -22,28 +22,39 @@ function __scp_remote_path_prefix
     and echo $path_prefix[2]
 end
 
+function __fish_no_scp_remote_specified
+    set -l tokens (commandline -t)
+    # can't use `for token in tokens[1..-2]` due to https://github.com/fish-shell/fish-shell/issues/4897
+    set -e tokens[-1]
+    for token in $tokens # ignoring current token
+        if string match -e @ -- $token
+            return 1
+        end
+    end
+    return 0
+end
+
 #
 # scp specific completions
 #
 
 #
-# Hostname
+# Inherit user/host completions from ssh
 #
-complete -c scp -d Hostname -n "commandline --cut-at-cursor --current-token | string match -v '*:*'" -a "
-(__fish_complete_user_at_hosts):"
+complete -c scp -d Remote -n "__fish_no_scp_remote_specified; and not string match -e : (commandline -ct)" -a "(complete -C'ssh ' | string replace -r '\t.*' ':')"
 
 #
 # Local path
 #
-complete -c scp -d "Local Path" -n "commandline -ct | string match ':'"
+complete -c scp -d "Local Path" -n "not string match @ -- (commandline -ct)"
 
 #
 # Remote path
 #
-complete -c scp -d "Remote Path" -f -n "commandline --cut-at-cursor --current-token | string match -r '.+:'" -a "
-(__scp_remote_target):(
-	# Get the list of remote files from the scp target.
-        ssh (__scp2ssh_port_number) -o 'BatchMode yes' (__scp_remote_target) ls\ -dp\ (__scp_remote_path_prefix)\* 2>/dev/null
+# Get the list of remote files from the scp target.
+complete -c scp -d "Remote Path" -f -n "commandline -ct | string match -eq ':'" -a "
+(__scp_remote_target):( \
+        ssh (__scp2ssh_port_number) -o 'BatchMode yes' (__scp_remote_target) /bin/ls\ -dp\ (__scp_remote_path_prefix)\* 2>/dev/null
 )
 "
 complete -c scp -s B -d "Batch mode"

share/completions/ssh.fish

@@ -6,7 +6,7 @@ __fish_complete_ssh ssh
 #
 # ssh specific completions
 #
-complete -x -c ssh -d Hostname -a "(__fish_complete_user_at_hosts)"
+complete -x -c ssh -d "Remote" -a "(__fish_complete_user_at_hosts)"
 
 # Disable as username completion is not very useful.
 # complete -x -c ssh -d User -a "
@@ -51,4 +51,4 @@ function __ssh_history_completions --argument limit
 	history --prefix ssh | sed -n "s/.* \([A-Za-z0-9._:-]\+@[A-Za-z0-9._:-]\+\).*/\1/p" | head -n $limit
 end
 
-complete -k -c ssh -a '(__ssh_history_completions 100)' -f
+complete -k -c ssh -a '(__ssh_history_completions 100)' -f -d "Remote"