Add feature detection

Checks whether `zpty` gives a file descriptor, which was not the case in
older versions of zsh.

Based on https://github.com/mafredri/zsh-async/blob/a4b2f81c966a00eeb38876d505d97423cc8addfd/async.zsh#L395-L401

Makefile

@@ -5,6 +5,7 @@ SRC_FILES := \
 	$(SRC_DIR)/setup.zsh \
 	$(SRC_DIR)/config.zsh \
 	$(SRC_DIR)/util.zsh \
+	$(SRC_DIR)/features.zsh \
 	$(SRC_DIR)/deprecated.zsh \
 	$(SRC_DIR)/bind.zsh \
 	$(SRC_DIR)/highlight.zsh \

src/features.zsh

@@ -0,0 +1,19 @@
+
+#--------------------------------------------------------------------#
+# Feature Detection                                                  #
+#--------------------------------------------------------------------#
+
+_zsh_autosuggest_feature_detect() {
+	typeset -g _ZSH_AUTOSUGGEST_ZPTY_RETURNS_FD
+	typeset -h REPLY
+
+	zpty $ZSH_AUTOSUGGEST_PTY_NAME :
+
+	if (( REPLY )); then
+		_ZSH_AUTOSUGGEST_ZPTY_RETURNS_FD=1
+	else
+		_ZSH_AUTOSUGGEST_ZPTY_RETURNS_FD=0
+	fi
+
+	zpty -d $ZSH_AUTOSUGGEST_PTY_NAME
+}

src/start.zsh

@@ -7,6 +7,7 @@
 _zsh_autosuggest_start() {
 	add-zsh-hook -d precmd _zsh_autosuggest_start
 
+	_zsh_autosuggest_feature_detect
 	_zsh_autosuggest_check_deprecated_config
 	_zsh_autosuggest_bind_widgets
 }

zsh-autosuggestions.zsh

@@ -111,6 +111,25 @@ _zsh_autosuggest_escape_command() {
 	echo -E "${1//(#m)[\"\'\\()\[\]|*?~]/\\$MATCH}"
 }
 
+#--------------------------------------------------------------------#
+# Feature Detection                                                  #
+#--------------------------------------------------------------------#
+
+_zsh_autosuggest_feature_detect() {
+	typeset -g _ZSH_AUTOSUGGEST_ZPTY_RETURNS_FD
+	typeset -h REPLY
+
+	zpty $ZSH_AUTOSUGGEST_PTY_NAME :
+
+	if (( REPLY )); then
+		_ZSH_AUTOSUGGEST_ZPTY_RETURNS_FD=1
+	else
+		_ZSH_AUTOSUGGEST_ZPTY_RETURNS_FD=0
+	fi
+
+	zpty -d $ZSH_AUTOSUGGEST_PTY_NAME
+}
+
 #--------------------------------------------------------------------#
 # Handle Deprecated Variables/Widgets                                #
 #--------------------------------------------------------------------#
@@ -570,6 +589,7 @@ add-zsh-hook precmd _zsh_autosuggest_async_recreate_pty
 _zsh_autosuggest_start() {
 	add-zsh-hook -d precmd _zsh_autosuggest_start
 
+	_zsh_autosuggest_feature_detect
 	_zsh_autosuggest_check_deprecated_config
 	_zsh_autosuggest_bind_widgets
 }