Change custom fuzzy completion API

To make it easier to write more complex fzf options. Although this
does not break backward compatibility, users are encouraged to update
their code accordingly.

  # Before
  _fzf_complete "FZF_ARG1 FZF_ARG2..." "$@" < <(
    # Print candidates
  )

  # After
  _fzf_complete FZF_ARG1 FZF_ARG2... -- "$@" < <(
    # Print candidates
  )

5 files changed, 177 insertions, 17 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1a16fd53..41d949e3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,20 @@ CHANGELOG
 - Bug fixes and improvements
 - Vim plugin: Floating windows support
 - bash: Various improvements in key bindings (CTRL-T, CTRL-R, ALT-C)
+- Fuzzy completion API changed
+  ```sh
+  # Previous: fzf arguments given as a single string argument
+  # - This style is still supported, but it is deprecated
+  _fzf_complete "--multi --reverse --prompt=\"doge> \"" "$@" < <(
+    echo foo
+  )
+
+  # New API: multiple fzf arguments before "--"
+  # - More rebust and easier to write options
+  _fzf_complete --multi --reverse --prompt="doge> " -- "$@" < <(
+    echo foo
+  )
+  ```
 
 0.20.0
 ------
diff --git a/README.md b/README.md
index 669881b2..bfd85800 100644
--- a/README.md
+++ b/README.md
@@ -47,6 +47,7 @@ Table of Contents
       * [Environment variables / Aliases](#environment-variables--aliases)
       * [Settings](#settings)
       * [Supported commands](#supported-commands)
+      * [Custom fuzzy completion](#custom-fuzzy-completion)
    * [Vim plugin](#vim-plugin)
    * [Advanced topics](#advanced-topics)
       * [Performance](#performance)
@@ -414,7 +415,7 @@ _fzf_comprun() {
 
   case "$command" in
     cd)           fzf "$@" --preview 'tree -C {} | head -200' ;;
-    export|unset) fzf "$@" --preview "eval 'echo \$'{}" "$@" ;;
+    export|unset) fzf "$@" --preview "eval 'echo \$'{}" ;;
     ssh)          fzf "$@" --preview 'dig {}' ;;
     *)            fzf "$@" ;;
   esac
@@ -433,6 +434,56 @@ _fzf_setup_completion path ag git kubectl
 _fzf_setup_completion dir tree
 ```
 
+#### Custom fuzzy completion
+
+_**(Custom completion API is experimental and subject to change)**_
+
+For a command named _"COMMAND"_, define `_fzf_complete_COMMAND` function using
+`_fzf_complete` helper.
+
+```sh
+# Custom fuzzy completion for "doge" command
+#   e.g. doge **<TAB>
+_fzf_complete_doge() {
+  _fzf_complete --multi --reverse --prompt="doge> " -- "$@" < <(
+    echo very
+    echo wow
+    echo such
+    echo doge
+  )
+}
+```
+
+- The arguments before `--` are the options to fzf.
+- After `--`, simply pass the original completion arguments unchanged (`"$@"`).
+- Then write a set of commands that generates the completion candidates and
+  feed its output to the function using process substitution (`< <(...)`).
+
+zsh will automatically pick up the function using the naming convention but in
+bash you have to manually associate the function with the command using
+`complete` command.
+
+```sh
+[ -n "$BASH" ] && complete -F _fzf_complete_doge -o default -o bashdefault doge
+```
+
+If you need to post-process the output from fzf, define
+`_fzf_complete_COMMAND_post` as follows.
+
+```sh
+_fzf_complete_foo() {
+  _fzf_complete --multi --reverse --header-lines=3 -- "$@" < <(
+    ls -al
+  )
+}
+
+_fzf_complete_foo_post() {
+  awk '{print $NF}'
+}
+
+[ -n "$BASH" ] && complete -F _fzf_complete_foo -o default -o bashdefault foo
+```
+
 Vim plugin
 ----------
 
diff --git a/shell/completion.bash b/shell/completion.bash
index bd94c51a..b1f7ac97 100644
--- a/shell/completion.bash
+++ b/shell/completion.bash
@@ -190,6 +190,27 @@ __fzf_generic_path_completion() {
 }
 
 _fzf_complete() {
+  # Split arguments around --
+  local args rest str_arg i sep
+  args=("$@")
+  sep=
+  for i in "${!args[@]}"; do
+    if [[ "${args[$i]}" = -- ]]; then
+      sep=$i
+      break
+    fi
+  done
+  if [[ -n "$sep" ]]; then
+    str_arg=
+    rest=("${args[@]:$((sep + 1)):${#args[@]}}")
+    args=("${args[@]:0:$sep}")
+  else
+    str_arg=$1
+    args=()
+    shift
+    rest=("$@")
+  fi
+
   local cur selected trigger cmd post
   post="$(caller 0 | awk '{print $2}')_post"
   type -t "$post" > /dev/null 2>&1 || post=cat
@@ -200,7 +221,7 @@ _fzf_complete() {
   if [[ "$cur" == *"$trigger" ]]; then
     cur=${cur:0:${#cur}-${#trigger}}
 
-    selected=$(FZF_DEFAULT_OPTS="--height ${FZF_TMUX_HEIGHT:-40%} --reverse $FZF_DEFAULT_OPTS $FZF_COMPLETION_OPTS $1" __fzf_comprun "$2" -q "$cur" | $post | tr '\n' ' ')
+    selected=$(FZF_DEFAULT_OPTS="--height ${FZF_TMUX_HEIGHT:-40%} --reverse $FZF_DEFAULT_OPTS $FZF_COMPLETION_OPTS $str_arg" __fzf_comprun "${rest[0]}" "${args[@]}" -q "$cur" | $post | tr '\n' ' ')
     selected=${selected% } # Strip trailing space not to repeat "-o nospace"
     if [ -n "$selected" ]; then
       COMPREPLY=("$selected")
@@ -210,8 +231,7 @@ _fzf_complete() {
     printf '\e[5n'
     return 0
   else
-    shift
-    _fzf_handle_dynamic_completion "$cmd" "$@"
+    _fzf_handle_dynamic_completion "$cmd" "${rest[@]}"
   fi
 }
 
@@ -243,7 +263,7 @@ _fzf_complete_kill() {
 }
 
 _fzf_host_completion() {
-  _fzf_complete '+m' "$@" < <(
+  _fzf_complete +m -- "$@" < <(
     cat <(cat ~/.ssh/config ~/.ssh/config.d/* /etc/ssh/ssh_config 2> /dev/null | command grep -i '^\s*host\(name\)\? ' | awk '{for (i = 2; i <= NF; i++) print $1 " " $i}' | command grep -v '[*?]') \
         <(command grep -oE '^[[a-z0-9.,:-]+' ~/.ssh/known_hosts | tr ',' '\n' | tr -d '[' | awk '{ print $1 " " $1 }') \
         <(command grep -v '^\s*\(#\|$\)' /etc/hosts | command grep -Fv '0.0.0.0') |
@@ -252,13 +272,13 @@ _fzf_host_completion() {
 }
 
 _fzf_var_completion() {
-  _fzf_complete '-m' "$@" < <(
+  _fzf_complete -m -- "$@" < <(
     declare -xp | sed 's/=.*//' | sed 's/.* //'
   )
 }
 
 _fzf_alias_completion() {
-  _fzf_complete '-m' "$@" < <(
+  _fzf_complete -m -- "$@" < <(
     alias | sed 's/=.*//' | sed 's/.* //'
   )
 }
diff --git a/shell/completion.zsh b/shell/completion.zsh
index 95f6d685..e82de4c9 100644
--- a/shell/completion.zsh
+++ b/shell/completion.zsh
@@ -107,16 +107,38 @@ _fzf_feed_fifo() (
 )
 
 _fzf_complete() {
-  local fifo fzf_opts lbuf cmd matches post
+  setopt localoptions ksh_arrays
+  # Split arguments around --
+  local args rest str_arg i sep
+  args=("$@")
+  sep=
+  for i in {0..$#args}; do
+    if [[ "${args[$i]}" = -- ]]; then
+      sep=$i
+      break
+    fi
+  done
+  if [[ -n "$sep" ]]; then
+    str_arg=
+    rest=("${args[@]:$((sep + 1)):${#args[@]}}")
+    args=("${args[@]:0:$sep}")
+  else
+    str_arg=$1
+    args=()
+    shift
+    rest=("$@")
+  fi
+
+  local fifo lbuf cmd matches post
   fifo="${TMPDIR:-/tmp}/fzf-complete-fifo-$$"
-  fzf_opts=$1
-  lbuf=$2
+  lbuf=${rest[0]}
   cmd=$(__fzf_extract_command "$lbuf")
-  post="${funcstack[2]}_post"
+  post="${funcstack[1]}_post"
+  echo "$post"
   type $post > /dev/null 2>&1 || post=cat
 
   _fzf_feed_fifo "$fifo"
-  matches=$(FZF_DEFAULT_OPTS="--height ${FZF_TMUX_HEIGHT:-40%} --reverse $FZF_DEFAULT_OPTS $FZF_COMPLETION_OPTS" __fzf_comprun "$cmd" ${(Q)${(Z+n+)fzf_opts}} -q "${(Q)prefix}" < "$fifo" | $post | tr '\n' ' ')
+  matches=$(FZF_DEFAULT_OPTS="--height ${FZF_TMUX_HEIGHT:-40%} --reverse $FZF_DEFAULT_OPTS $FZF_COMPLETION_OPTS $str_arg" __fzf_comprun "$cmd" "${args[@]}" -q "${(Q)prefix}" < "$fifo" | $post | tr '\n' ' ')
   if [ -n "$matches" ]; then
     LBUFFER="$lbuf$matches"
   fi
@@ -125,14 +147,14 @@ _fzf_complete() {
 }
 
 _fzf_complete_telnet() {
-  _fzf_complete '+m' "$@" < <(
+  _fzf_complete +m -- "$@" < <(
     command grep -v '^\s*\(#\|$\)' /etc/hosts | command grep -Fv '0.0.0.0' |
         awk '{if (length($2) > 0) {print $2}}' | sort -u
   )
 }
 
 _fzf_complete_ssh() {
-  _fzf_complete '+m' "$@" < <(
+  _fzf_complete +m -- "$@" < <(
     setopt localoptions nonomatch
     command cat <(cat ~/.ssh/config ~/.ssh/config.d/* /etc/ssh/ssh_config 2> /dev/null | command grep -i '^\s*host\(name\)\? ' | awk '{for (i = 2; i <= NF; i++) print $1 " " $i}' | command grep -v '[*?]') \
         <(command grep -oE '^[[a-z0-9.,:-]+' ~/.ssh/known_hosts | tr ',' '\n' | tr -d '[' | awk '{ print $1 " " $1 }') \
@@ -142,19 +164,19 @@ _fzf_complete_ssh() {
 }
 
 _fzf_complete_export() {
-  _fzf_complete '-m' "$@" < <(
+  _fzf_complete -m -- "$@" < <(
     declare -xp | sed 's/=.*//' | sed 's/.* //'
   )
 }
 
 _fzf_complete_unset() {
-  _fzf_complete '-m' "$@" < <(
+  _fzf_complete -m -- "$@" < <(
     declare -xp | sed 's/=.*//' | sed 's/.* //'
   )
 }
 
 _fzf_complete_unalias() {
-  _fzf_complete '+m' "$@" < <(
+  _fzf_complete +m -- "$@" < <(
     alias | sed 's/=.*//'
   )
 }
diff --git a/test/test_go.rb b/test/test_go.rb
index fa4a6ef9..9bacb8ba 100755
--- a/test/test_go.rb
+++ b/test/test_go.rb
@@ -2064,6 +2064,21 @@ module CompletionTest
     tmux.send_keys :Enter
     tmux.until { |lines| lines[-1].include? 'test3test4' }
   end
+
+  def test_custom_completion_api
+    %w[f g].each do |command|
+      tmux.prepare
+      tmux.send_keys "#{command} b**", :Tab
+      tmux.until do |lines|
+        lines.item_count == 2 && lines.match_count == 1 &&
+          lines.any_include?("prompt-#{command}") &&
+          lines.any_include?("preview-#{command}-bar")
+      end
+      tmux.send_keys :Enter
+      tmux.until { |lines| lines[-1].include?("#{command} #{command}barbar") }
+      tmux.send_keys 'C-u'
+    end
+  end
 end
 
 class TestBash < TestBase
@@ -2149,3 +2164,41 @@ source "<%= BASE %>/shell/key-bindings.<%= __method__ %>"
 
 PS1= PROMPT_COMMAND= HISTFILE= HISTSIZE=100
 unset <%= UNSETS.join(' ') %>
+
+# Old API
+_fzf_complete_f() {
+  _fzf_complete "--multi --prompt \"prompt-f> \"" "$@" < <(
+    echo foo
+    echo bar
+  )
+}
+
+# New API
+_fzf_complete_g() {
+  _fzf_complete --multi --prompt "prompt-g> " -- "$@" < <(
+    echo foo
+    echo bar
+  )
+}
+
+_fzf_complete_f_post() {
+  awk '{print "f" $0 $0}'
+}
+
+_fzf_complete_g_post() {
+  awk '{print "g" $0 $0}'
+}
+
+[ -n "$BASH" ] && complete -F _fzf_complete_f -o default -o bashdefault f
+[ -n "$BASH" ] && complete -F _fzf_complete_g -o default -o bashdefault g
+
+_fzf_comprun() {
+  local command=$1
+  shift
+
+  case "$command" in
+    f) fzf "$@" --preview 'echo preview-f-{}' ;;
+    g) fzf "$@" --preview 'echo preview-g-{}' ;;
+    *) fzf "$@" ;;
+  esac
+}