Extend Go completions and revamp zsh comp (#1070) (#1070)

Replace the current Zsh completion with a Zsh completion solution based
on Go completions. This allows to support custom completions (based
on Go completions), but also to standardize the behavior of completion
across all shells.

Also, add support to Go completions for the bash completion annotations:
  BashCompFilenameExt (including Command.MarkFlagFilename() family)
                       - still supported by zsh
  BashCompSubdirsInDir - now supported by zsh
  BashCompOneRequiredFlag (including Command.MarkFlagRequired() family)
                       - now supported by zsh and fish

Finally, remove the suggestin of the = form of flag completion.
The = form is supported, but it will not be suggested to avoid having
duplicated suggestions.

Author: marckhouzam

README.md

@@ -28,8 +28,7 @@ name a few. [This list](./projects_using_cobra.md) contains a more extensive lis
   * [PreRun and PostRun Hooks](#prerun-and-postrun-hooks)
   * [Suggestions when "unknown command" happens](#suggestions-when-unknown-command-happens)
   * [Generating documentation for your command](#generating-documentation-for-your-command)
-  * [Generating bash completions](#generating-bash-completions)
-  * [Generating zsh completions](#generating-zsh-completions)
+  * [Generating shell completions](#generating-shell-completions)
 - [Contributing](#contributing)
 - [License](#license)
 
@@ -50,7 +49,7 @@ Cobra provides:
 * Intelligent suggestions (`app srver`... did you mean `app server`?)
 * Automatic help generation for commands and flags
 * Automatic help flag recognition of `-h`, `--help`, etc.
-* Automatically generated bash autocomplete for your application
+* Automatically generated shell autocomplete for your application (bash, zsh, fish, powershell)
 * Automatically generated man pages for your application
 * Command aliases so you can change things without breaking them
 * The flexibility to define your own help, usage, etc.
@@ -720,14 +719,9 @@ Run 'kubectl help' for usage.
 
 Cobra can generate documentation based on subcommands, flags, etc. Read more about it in the [docs generation documentation](doc/README.md).
 
-## Generating bash completions
+## Generating shell completions
 
-Cobra can generate a bash-completion file. If you add more information to your command, these completions can be amazingly powerful and flexible.  Read more about it in [Bash Completions](bash_completions.md).
-
-## Generating zsh completions
-
-Cobra can generate zsh-completion file. Read more about it in
-[Zsh Completions](zsh_completions.md).
+Cobra can generate a shell-completion file for the following shells: Bash, Zsh, Fish, Powershell. If you add more information to your commands, these completions can be amazingly powerful and flexible.  Read more about it in [Shell Completions](shell_completions.md).
 
 # Contributing
 

bash_completions.go

@@ -62,6 +62,12 @@ __%[1]s_handle_go_custom_completion()
 {
     __%[1]s_debug "${FUNCNAME[0]}: cur is ${cur}, words[*] is ${words[*]}, #words[@] is ${#words[@]}"
 
+    local shellCompDirectiveError=%[3]d
+    local shellCompDirectiveNoSpace=%[4]d
+    local shellCompDirectiveNoFileComp=%[5]d
+    local shellCompDirectiveFilterFileExt=%[6]d
+    local shellCompDirectiveFilterDirs=%[7]d
+
     local out requestComp lastParam lastChar comp directive args
 
     # Prepare the command to request completions for the program.
@@ -95,24 +101,50 @@ __%[1]s_handle_go_custom_completion()
     __%[1]s_debug "${FUNCNAME[0]}: the completion directive is: ${directive}"
     __%[1]s_debug "${FUNCNAME[0]}: the completions are: ${out[*]}"
 
-    if [ $((directive & %[3]d)) -ne 0 ]; then
+    if [ $((directive & shellCompDirectiveError)) -ne 0 ]; then
         # Error code.  No completion.
         __%[1]s_debug "${FUNCNAME[0]}: received error from custom completion go code"
         return
     else
-        if [ $((directive & %[4]d)) -ne 0 ]; then
+        if [ $((directive & shellCompDirectiveNoSpace)) -ne 0 ]; then
             if [[ $(type -t compopt) = "builtin" ]]; then
                 __%[1]s_debug "${FUNCNAME[0]}: activating no space"
                 compopt -o nospace
             fi
         fi
-        if [ $((directive & %[5]d)) -ne 0 ]; then
+        if [ $((directive & shellCompDirectiveNoFileComp)) -ne 0 ]; then
             if [[ $(type -t compopt) = "builtin" ]]; then
                 __%[1]s_debug "${FUNCNAME[0]}: activating no file completion"
                 compopt +o default
             fi
         fi
+    fi
 
+    if [ $((directive & shellCompDirectiveFilterFileExt)) -ne 0 ]; then
+        # File extension filtering
+        local fullFilter filter filteringCmd
+        # Do not use quotes around the $out variable or else newline
+        # characters will be kept.
+        for filter in ${out[*]}; do
+            fullFilter+="$filter|"
+        done
+
+        filteringCmd="_filedir $fullFilter"
+        __%[1]s_debug "File filtering command: $filteringCmd"
+        $filteringCmd
+    elif [ $((directive & shellCompDirectiveFilterDirs)) -ne 0 ]; then
+        # File completion for directories only
+        local subDir
+        # Use printf to strip any trailing newline
+        subdir=$(printf "%%s" "${out[0]}")
+        if [ -n "$subdir" ]; then
+            __%[1]s_debug "Listing directories in $subdir"
+            __%[1]s_handle_subdirs_in_dir_flag "$subdir"
+        else
+            __%[1]s_debug "Listing directories in ."
+            _filedir -d
+        fi
+    else
         while IFS='' read -r comp; do
             COMPREPLY+=("$comp")
         done < <(compgen -W "${out[*]}" -- "$cur")
@@ -343,7 +375,9 @@ __%[1]s_handle_word()
     __%[1]s_handle_word
 }
 
-`, name, ShellCompNoDescRequestCmd, ShellCompDirectiveError, ShellCompDirectiveNoSpace, ShellCompDirectiveNoFileComp))
+`, name, ShellCompNoDescRequestCmd,
+		ShellCompDirectiveError, ShellCompDirectiveNoSpace, ShellCompDirectiveNoFileComp,
+		ShellCompDirectiveFilterFileExt, ShellCompDirectiveFilterDirs))
 }
 
 func writePostscript(buf *bytes.Buffer, name string) {