lib: support additional clipboard types (#7996)

* clipboard: Reduce unnecessary special-casing on stdin

Ideally the parameter would just be removed-users could always
just do "clipcopy < some-file". but removing the parameter would break
backwards compatibility.

In any case, this simplifies the logic considerably.

* clipboard: Avoid unnecessary re-detection each time

Previously, OS detection would happen on each invocation. This makes it
happen once (unless it fails, in which case it will try again on the
next invocation).

This has the additional benefit of localizing the platform-specific
checks and commands, too, versus spreading them out in separate
functions.

* clipboard: Add support for several more clipboards

This implements essentially the same heuristic as neovim, with the additional
(existing) special support for Cygwin.
See: e682d799fa/runtime/autoload/provider/clipboard.vim (L55-L121)
  - pbcopy, pbpaste (macOS)
  - cygwin (Windows running Cygwin)
  - wl-copy, wl-paste (if $WAYLAND_DISPLAY is set)
  - xclip (if $DISPLAY is set)
  - xsel (if $DISPLAY is set)
  - lemonade (for SSH) https://github.com/pocke/lemonade
  - doitclient (for SSH) http://www.chiark.greenend.org.uk/~sgtatham/doit/
  - win32yank (Windows)
  - tmux (if $TMUX is set)

* clipboard: Fix tmux clipcopy after testing

Tmux must have special handling for /dev/stdin since it's managing the
terminal itself. This was tested with tmux-2.9a on macOS.

* clipboard: Fix bad expansion of exit-code test

lib/clipboard.zsh

@@ -3,10 +3,23 @@
 # This file has support for doing system clipboard copy and paste operations
 # from the command line in a generic cross-platform fashion.
 #
-# On OS X and Windows, the main system clipboard or "pasteboard" is used. On other
-# Unix-like OSes, this considers the X Windows CLIPBOARD selection to be the
-# "system clipboard", and the X Windows `xclip` command must be installed.
-
+# This is uses essentially the same heuristic as neovim, with the additional
+# special support for Cygwin.
+# See: https://github.com/neovim/neovim/blob/e682d799fa3cf2e80a02d00c6ea874599d58f0e7/runtime/autoload/provider/clipboard.vim#L55-L121
+#
+# - pbcopy, pbpaste (macOS)
+# - cygwin (Windows running Cygwin)
+# - wl-copy, wl-paste (if $WAYLAND_DISPLAY is set)
+# - xclip (if $DISPLAY is set)
+# - xsel (if $DISPLAY is set)
+# - lemonade (for SSH) https://github.com/pocke/lemonade
+# - doitclient (for SSH) http://www.chiark.greenend.org.uk/~sgtatham/doit/
+# - win32yank (Windows)
+# - tmux (if $TMUX is set)
+#
+# Defines two functions, clipcopy and clippaste, based on the detected platform.
+##
+#
 # clipcopy - Copy data to clipboard
 #
 # Usage:
@@ -15,41 +28,8 @@
 #
 #  clipcopy <file>         - copies a file's contents to clipboard
 #
-function clipcopy() {
-  emulate -L zsh
-  local file=$1
-  if [[ $OSTYPE == darwin* ]]; then
-    if [[ -z $file ]]; then
-      pbcopy
-    else
-      cat $file | pbcopy
-    fi
-  elif [[ $OSTYPE == (cygwin|msys)* ]]; then
-    if [[ -z $file ]]; then
-      cat > /dev/clipboard
-    else
-      cat $file > /dev/clipboard
-    fi
-  else
-    if (( $+commands[xclip] )); then
-      if [[ -z $file ]]; then
-        xclip -in -selection clipboard
-      else
-        xclip -in -selection clipboard $file
-      fi
-    elif (( $+commands[xsel] )); then
-      if [[ -z $file ]]; then
-        xsel --clipboard --input 
-      else
-        cat "$file" | xsel --clipboard --input
-      fi
-    else
-      print "clipcopy: Platform $OSTYPE not supported or xclip/xsel not installed" >&2
-      return 1
-    fi
-  fi
-}
-
+##
+#
 # clippaste - "Paste" data from clipboard to stdout
 #
 # Usage:
@@ -67,20 +47,55 @@ function clipcopy() {
 #
 #   # Paste to a file
 #   clippaste > file.txt
-function clippaste() {
+#
+function detect-clipboard() {
   emulate -L zsh
-  if [[ $OSTYPE == darwin* ]]; then
-    pbpaste
-  elif [[ $OSTYPE == (cygwin|msys)* ]]; then
-    cat /dev/clipboard
+
+  if [[ "${OSTYPE}" == darwin* ]] && (( ${+commands[pbcopy]} )) && (( ${+commands[pbpaste]} )); then
+    function clipcopy() { pbcopy < "${1:-/dev/stdin}"; }
+    function clippaste() { pbpaste; }
+  elif [[ "${OSTYPE}" == (cygwin|msys)* ]]; then
+    function clipcopy() { cat "${1:-/dev/stdin}" > /dev/clipboard; }
+    function clippaste() { cat /dev/clipboard; }
+  elif [ -n "${WAYLAND_DISPLAY:-}" ] && (( ${+commands[wl-copy]} )) && (( ${+commands[wl-paste]} )); then
+    function clipcopy() { wl-copy < "${1:-/dev/stdin}"; }
+    function clippaste() { wl-paste; }
+  elif [ -n "${DISPLAY:-}" ] && (( ${+commands[xclip]} )); then
+    function clipcopy() { xclip -in -selection clipboard < "${1:-/dev/stdin}"; }
+    function clippaste() { xclip -out -selection clipboard; }
+  elif [ -n "${DISPLAY:-}" ] && (( ${+commands[xsel]} )); then
+    function clipcopy() { xsel --clipboard --input < "${1:-/dev/stdin}"; }
+    function clippaste() { xsel --clipboard --output; }
+  elif (( ${+commands[lemonade]} )); then
+    function clipcopy() { lemonade copy < "${1:-/dev/stdin}"; }
+    function clippaste() { lemonade paste; }
+  elif (( ${+commands[doitclient]} )); then
+    function clipcopy() { doitclient wclip < "${1:-/dev/stdin}"; }
+    function clippaste() { doitclient wclip -r; }
+  elif (( ${+commands[win32yank]} )); then
+    function clipcopy() { win32yank -i < "${1:-/dev/stdin}"; }
+    function clippaste() { win32yank -o; }
+  elif [ -n "${TMUX:-}" ] && (( ${+commands[tmux]} )); then
+    function clipcopy() { tmux load-buffer "${1:--}"; }
+    function clippaste() { tmux save-buffer -; }
   else
-    if (( $+commands[xclip] )); then
-      xclip -out -selection clipboard
-    elif (( $+commands[xsel] )); then
-      xsel --clipboard --output
+    function _retry_clipboard_detection_or_fail() {
+      local clipcmd="${1}"; shift
+      if detect-clipboard; then
+        "${clipcmd}" "$@"
       else
-      print "clipcopy: Platform $OSTYPE not supported or xclip/xsel not installed" >&2
+        print "${clipcmd}: Platform $OSTYPE not supported or xclip/xsel not installed" >&2
         return 1
       fi
+    }
+    function clipcopy() { _retry_clipboard_detection_or_fail clipcopy "$@"; }
+    function clippaste() { _retry_clipboard_detection_or_fail clippaste "$@"; }
+    return 1
   fi
 }
+
+# Detect at startup. A non-zero exit here indicates that the dummy clipboards were set,
+# which is not really an error. If the user calls them, they will attempt to redetect
+# (for example, perhaps the user has now installed xclip) and then either print an error
+# or proceed successfully.
+detect-clipboard || true