Fix issue where partial accept duplicates last word

When z-sy-h is enabled after autosuggestion widgets have already been
bound, partial accepting the last part of a suggestion will result in
that string being duplicated.

I was able to reproduce using the following versions of the two plugins:
- z-sy-h: dde84e1b25f059a298ce3189cddfd0778f998df3
- z-asug: ae315ded4d

and running the following commands interactively one after another:

```
zsh -df
% source path/to/zsh-autosuggestions.zsh
% source path/to/zsh-syntax-highlighting.zsh
% bindkey -e
% bindkey <alt-f>         # shows 'bindkey -e-e'
```

The order of the `source` statements matters and the issue cannot be
reproduced if the two source statements are executed together on one
line.

The problem is very similar to this one:
  https://github.com/zsh-users/zsh-autosuggestions/issues/126#issuecomment-217121315

See GitHub issue #483

README.md

@@ -79,9 +79,11 @@ Widgets that modify the buffer and are not found in any of these arrays will fet
 Set `ZSH_AUTOSUGGEST_BUFFER_MAX_SIZE` to an integer value to disable autosuggestion for large buffers. The default is unset, which means that autosuggestion will be tried for any buffer size. Recommended value is 20.
 This can be useful when pasting large amount of text in the terminal, to avoid triggering autosuggestion for strings that are too long.
 
-### Enable Asynchronous Mode
+### Asynchronous Mode
 
-As of `v0.4.0`, suggestions can be fetched asynchronously. To enable this behavior, set the `ZSH_AUTOSUGGEST_USE_ASYNC` variable (it can be set to anything).
+Suggestions are fetched asynchronously by default in zsh versions 5.0.8 and greater. To disable asynchronous suggestions and fetch them synchronously instead, `unset ZSH_AUTOSUGGEST_USE_ASYNC` after sourcing the plugin.
+
+Alternatively, if you are using a version of zsh older than 5.0.8 and want to enable asynchronous mode, set the `ZSH_AUTOSUGGEST_USE_ASYNC` variable after sourcing the plugin (it can be set to anything). Note that there is [a bug](https://github.com/zsh-users/zsh-autosuggestions/issues/364#issuecomment-481423232) in versions of zsh older than 5.0.8 where <kbd>ctrl</kbd> + <kbd>c</kbd> will fail to reset the prompt immediately after fetching a suggestion asynchronously.
 
 ### Disabling automatic widget re-binding
 
@@ -89,13 +91,13 @@ Set `ZSH_AUTOSUGGEST_MANUAL_REBIND` (it can be set to anything) to disable autom
 
 ### Ignoring history suggestions that match a pattern
 
-Set `ZSH_AUTOSUGGEST_HISTORY_IGNORE` to a glob pattern to prevent offering suggestions for history entries that match the pattern. For example, set it to `"cd *"` to never suggest any `cd` commands from history. Or set to `"?(#c50,)"` to never suggest anything 50 characters or longer.
+Set `ZSH_AUTOSUGGEST_HISTORY_IGNORE` to a [glob pattern](http://zsh.sourceforge.net/Doc/Release/Expansion.html#Glob-Operators) to prevent offering suggestions for history entries that match the pattern. For example, set it to `"cd *"` to never suggest any `cd` commands from history. Or set to `"?(#c50,)"` to never suggest anything 50 characters or longer.
 
 **Note:** This only affects the `history` and `match_prev_cmd` suggestion strategies.
 
 ### Skipping completion suggestions for certain cases
 
-Set `ZSH_AUTOSUGGEST_COMPLETION_IGNORE` to a glob pattern to prevent offering completion suggestions when the buffer matches that pattern. For example, set it to `"git *"` to disable completion suggestions for git subcommands.
+Set `ZSH_AUTOSUGGEST_COMPLETION_IGNORE` to a [glob pattern](http://zsh.sourceforge.net/Doc/Release/Expansion.html#Glob-Operators) to prevent offering completion suggestions when the buffer matches that pattern. For example, set it to `"git *"` to disable completion suggestions for git subcommands.
 
 **Note:** This only affects the `completion` suggestion strategy.
 

spec/options/use_async_spec.rb

@@ -1,7 +0,0 @@
-describe 'suggestion fetching' do
-  it 'is performed synchronously'
-
-  context 'when ZSH_AUTOSUGGEST_USE_ASYNC is set' do
-    it 'is performed asynchronously'
-  end
-end

src/bind.zsh

@@ -69,7 +69,7 @@ _zsh_autosuggest_bind_widgets() {
 	ignore_widgets=(
 		.\*
 		_\*
-		autosuggest-\*
+		${_ZSH_AUTOSUGGEST_BUILTIN_ACTIONS/#/autosuggest-}
 		$ZSH_AUTOSUGGEST_ORIGINAL_WIDGET_PREFIX\*
 		$ZSH_AUTOSUGGEST_IGNORE_WIDGETS
 	)

src/start.zsh

@@ -21,11 +21,13 @@ _zsh_autosuggest_start() {
 # Mark for auto-loading the functions that we use
 autoload -Uz add-zsh-hook is-at-least
 
-# If zle is already running, go ahead and start the autosuggestion widgets.
-# Otherwise, wait until the next precmd.
-if zle; then
-	_zsh_autosuggest_start
-	(( ! ${+ZSH_AUTOSUGGEST_MANUAL_REBIND} )) && add-zsh-hook precmd _zsh_autosuggest_start
-else
-	add-zsh-hook precmd _zsh_autosuggest_start
+# Automatically enable asynchronous mode in newer versions of zsh. Disable for
+# older versions because there is a bug when using async mode where ^C does not
+# work immediately after fetching a suggestion.
+# See https://github.com/zsh-users/zsh-autosuggestions/issues/364
+if is-at-least 5.0.8; then
+	typeset -g ZSH_AUTOSUGGEST_USE_ASYNC=
 fi
+
+# Start the autosuggestion widgets on the next precmd
+add-zsh-hook precmd _zsh_autosuggest_start

src/widgets.zsh

@@ -20,7 +20,7 @@ _zsh_autosuggest_enable() {
 
 # Toggle suggestions (enable/disable)
 _zsh_autosuggest_toggle() {
-	if [[ -n "${_ZSH_AUTOSUGGEST_DISABLED+x}" ]]; then
+	if (( ${+_ZSH_AUTOSUGGEST_DISABLED} )); then
 		_zsh_autosuggest_enable
 	else
 		_zsh_autosuggest_disable
@@ -79,7 +79,7 @@ _zsh_autosuggest_modify() {
 	fi
 
 	# Bail out if suggestions are disabled
-	if [[ -n "${_ZSH_AUTOSUGGEST_DISABLED+x}" ]]; then
+	if (( ${+_ZSH_AUTOSUGGEST_DISABLED} )); then
 		return $?
 	fi
 
@@ -173,11 +173,13 @@ _zsh_autosuggest_execute() {
 _zsh_autosuggest_partial_accept() {
 	local -i retval cursor_loc
 
-	# Save the contents of the buffer so we can restore later if needed
+	# Save the original buffer/postdisplay so we can restore later if needed
 	local original_buffer="$BUFFER"
+	local original_postdisplay="$POSTDISPLAY"
 
 	# Temporarily accept the suggestion.
 	BUFFER="$BUFFER$POSTDISPLAY"
+	unset POSTDISPLAY
 
 	# Original widget moves the cursor
 	_zsh_autosuggest_invoke_original_widget $@
@@ -197,16 +199,30 @@ _zsh_autosuggest_partial_accept() {
 		# Clip the buffer at the cursor
 		BUFFER="${BUFFER[1,$cursor_loc]}"
 	else
-		# Restore the original buffer
+		# Restore the original buffer/postdisplay
 		BUFFER="$original_buffer"
+		POSTDISPLAY="$original_postdisplay"
 	fi
 
 	return $retval
 }
 
 () {
+	typeset -ga _ZSH_AUTOSUGGEST_BUILTIN_ACTIONS
+
+	_ZSH_AUTOSUGGEST_BUILTIN_ACTIONS=(
+		clear
+		fetch
+		suggest
+		accept
+		execute
+		enable
+		disable
+		toggle
+	)
+
 	local action
-	for action in clear modify fetch suggest accept partial_accept execute enable disable toggle; do
+	for action in $_ZSH_AUTOSUGGEST_BUILTIN_ACTIONS modify partial_accept; do
 		eval "_zsh_autosuggest_widget_$action() {
 			local -i retval
 
@@ -223,12 +239,7 @@ _zsh_autosuggest_partial_accept() {
 		}"
 	done
 
-	zle -N autosuggest-fetch _zsh_autosuggest_widget_fetch
-	zle -N autosuggest-suggest _zsh_autosuggest_widget_suggest
-	zle -N autosuggest-accept _zsh_autosuggest_widget_accept
-	zle -N autosuggest-clear _zsh_autosuggest_widget_clear
-	zle -N autosuggest-execute _zsh_autosuggest_widget_execute
-	zle -N autosuggest-enable _zsh_autosuggest_widget_enable
-	zle -N autosuggest-disable _zsh_autosuggest_widget_disable
-	zle -N autosuggest-toggle _zsh_autosuggest_widget_toggle
+	for action in $_ZSH_AUTOSUGGEST_BUILTIN_ACTIONS; do
+		zle -N autosuggest-$action _zsh_autosuggest_widget_$action
+	done
 }

zsh-autosuggestions.zsh

@@ -199,7 +199,7 @@ _zsh_autosuggest_bind_widgets() {
 	ignore_widgets=(
 		.\*
 		_\*
-		autosuggest-\*
+		${_ZSH_AUTOSUGGEST_BUILTIN_ACTIONS/#/autosuggest-}
 		$ZSH_AUTOSUGGEST_ORIGINAL_WIDGET_PREFIX\*
 		$ZSH_AUTOSUGGEST_IGNORE_WIDGETS
 	)
@@ -282,7 +282,7 @@ _zsh_autosuggest_enable() {
 
 # Toggle suggestions (enable/disable)
 _zsh_autosuggest_toggle() {
-	if [[ -n "${_ZSH_AUTOSUGGEST_DISABLED+x}" ]]; then
+	if (( ${+_ZSH_AUTOSUGGEST_DISABLED} )); then
 		_zsh_autosuggest_enable
 	else
 		_zsh_autosuggest_disable
@@ -341,7 +341,7 @@ _zsh_autosuggest_modify() {
 	fi
 
 	# Bail out if suggestions are disabled
-	if [[ -n "${_ZSH_AUTOSUGGEST_DISABLED+x}" ]]; then
+	if (( ${+_ZSH_AUTOSUGGEST_DISABLED} )); then
 		return $?
 	fi
 
@@ -435,11 +435,13 @@ _zsh_autosuggest_execute() {
 _zsh_autosuggest_partial_accept() {
 	local -i retval cursor_loc
 
-	# Save the contents of the buffer so we can restore later if needed
+	# Save the original buffer/postdisplay so we can restore later if needed
 	local original_buffer="$BUFFER"
+	local original_postdisplay="$POSTDISPLAY"
 
 	# Temporarily accept the suggestion.
 	BUFFER="$BUFFER$POSTDISPLAY"
+	unset POSTDISPLAY
 
 	# Original widget moves the cursor
 	_zsh_autosuggest_invoke_original_widget $@
@@ -459,16 +461,30 @@ _zsh_autosuggest_partial_accept() {
 		# Clip the buffer at the cursor
 		BUFFER="${BUFFER[1,$cursor_loc]}"
 	else
-		# Restore the original buffer
+		# Restore the original buffer/postdisplay
 		BUFFER="$original_buffer"
+		POSTDISPLAY="$original_postdisplay"
 	fi
 
 	return $retval
 }
 
 () {
+	typeset -ga _ZSH_AUTOSUGGEST_BUILTIN_ACTIONS
+
+	_ZSH_AUTOSUGGEST_BUILTIN_ACTIONS=(
+		clear
+		fetch
+		suggest
+		accept
+		execute
+		enable
+		disable
+		toggle
+	)
+
 	local action
-	for action in clear modify fetch suggest accept partial_accept execute enable disable toggle; do
+	for action in $_ZSH_AUTOSUGGEST_BUILTIN_ACTIONS modify partial_accept; do
 		eval "_zsh_autosuggest_widget_$action() {
 			local -i retval
 
@@ -485,14 +501,9 @@ _zsh_autosuggest_partial_accept() {
 		}"
 	done
 
-	zle -N autosuggest-fetch _zsh_autosuggest_widget_fetch
-	zle -N autosuggest-suggest _zsh_autosuggest_widget_suggest
-	zle -N autosuggest-accept _zsh_autosuggest_widget_accept
-	zle -N autosuggest-clear _zsh_autosuggest_widget_clear
-	zle -N autosuggest-execute _zsh_autosuggest_widget_execute
-	zle -N autosuggest-enable _zsh_autosuggest_widget_enable
-	zle -N autosuggest-disable _zsh_autosuggest_widget_disable
-	zle -N autosuggest-toggle _zsh_autosuggest_widget_toggle
+	for action in $_ZSH_AUTOSUGGEST_BUILTIN_ACTIONS; do
+		zle -N autosuggest-$action _zsh_autosuggest_widget_$action
+	done
 }
 
 #--------------------------------------------------------------------#
@@ -854,11 +865,13 @@ _zsh_autosuggest_start() {
 # Mark for auto-loading the functions that we use
 autoload -Uz add-zsh-hook is-at-least
 
-# If zle is already running, go ahead and start the autosuggestion widgets.
-# Otherwise, wait until the next precmd.
-if zle; then
-	_zsh_autosuggest_start
-	(( ! ${+ZSH_AUTOSUGGEST_MANUAL_REBIND} )) && add-zsh-hook precmd _zsh_autosuggest_start
-else
-	add-zsh-hook precmd _zsh_autosuggest_start
+# Automatically enable asynchronous mode in newer versions of zsh. Disable for
+# older versions because there is a bug when using async mode where ^C does not
+# work immediately after fetching a suggestion.
+# See https://github.com/zsh-users/zsh-autosuggestions/issues/364
+if is-at-least 5.0.8; then
+	typeset -g ZSH_AUTOSUGGEST_USE_ASYNC=
 fi
+
+# Start the autosuggestion widgets on the next precmd
+add-zsh-hook precmd _zsh_autosuggest_start