[vim] Popup window support for both Vim and Neovim

e.g.
  let g:fzf_layout = { 'window': { 'width': 0.9, 'height': 0.6 } }

Based on the code from https://github.com/junegunn/fzf.vim/issues/821#issuecomment-581273191
by @lacygoill.

3 files changed, 111 insertions, 61 deletions

diff --git a/README-VIM.md b/README-VIM.md
index 554d748a..103b8e52 100644
--- a/README-VIM.md
+++ b/README-VIM.md
@@ -184,6 +184,7 @@ The following table summarizes the available options.
 | `dir`                      | string        | Working directory                                                     |
 | `up`/`down`/`left`/`right` | number/string | (Layout) Window position and size (e.g. `20`, `50%`)                  |
 | `window` (Vim 8 / Neovim)  | string        | (Layout) Command to open fzf window (e.g. `vertical aboveleft 30new`) |
+| `window` (Vim 8 / Neovim)  | dict          | (Layout) Popup window settings (e.g. `{'width': 0.9, 'height': 0.6}`) |
 
 `options` entry can be either a string or a list. For simple cases, string
 should suffice, but prefer to use list type to avoid escaping issues.
@@ -193,6 +194,16 @@ call fzf#run({'options': '--reverse --prompt "C:\\Program Files\\"'})
 call fzf#run({'options': ['--reverse', '--prompt', 'C:\Program Files\']})
 ```
 
+When `window` entry is a dictionary, fzf will start in a popup window. The
+following options are allowed:
+
+- Required:
+    - `width` [float]
+    - `height` [float]
+- Optional:
+    - `highlight` [string default `'Comment'`]: Highlight group for border
+    - `rounded` [boolean default `v:true`]: Use rounded border
+
 `fzf#wrap`
 ----------
 
@@ -276,44 +287,17 @@ The latest versions of Vim and Neovim include builtin terminal emulator
 - On Terminal Vim with a non-default layout
     - `call fzf#run({'left': '30%'})` or `let g:fzf_layout = {'left': '30%'}`
 
-#### Starting fzf in Neovim floating window
+#### Starting fzf in a popup window
 
 ```vim
-" Using floating windows of Neovim to start fzf
-if has('nvim')
-  function! FloatingFZF(width, height, border_highlight)
-    function! s:create_float(hl, opts)
-      let buf = nvim_create_buf(v:false, v:true)
-      let opts = extend({'relative': 'editor', 'style': 'minimal'}, a:opts)
-      let win = nvim_open_win(buf, v:true, opts)
-      call setwinvar(win, '&winhighlight', 'NormalFloat:'.a:hl)
-      call setwinvar(win, '&colorcolumn', '')
-      return buf
-    endfunction
-
-    " Size and position
-    let width = float2nr(&columns * a:width)
-    let height = float2nr(&lines * a:height)
-    let row = float2nr((&lines - height) / 2)
-    let col = float2nr((&columns - width) / 2)
-
-    " Border
-    let top = '╭' . repeat('─', width - 2) . '╮'
-    let mid = '│' . repeat(' ', width - 2) . '│'
-    let bot = '╰' . repeat('─', width - 2) . '╯'
-    let border = [top] + repeat([mid], height - 2) + [bot]
-
-    " Draw frame
-    let s:frame = s:create_float(a:border_highlight, {'row': row, 'col': col, 'width': width, 'height': height})
-    call nvim_buf_set_lines(s:frame, 0, -1, v:true, border)
-
-    " Draw viewport
-    call s:create_float('Normal', {'row': row + 1, 'col': col + 2, 'width': width - 4, 'height': height - 2})
-    autocmd BufWipeout <buffer> execute 'bwipeout' s:frame
-  endfunction
-
-  let g:fzf_layout = { 'window': 'call FloatingFZF(0.9, 0.6, "Comment")' }
-endif
+" Required:
+" - width [float]
+" - height [float]
+"
+" Optional:
+" - highlight [string default 'Comment']: Highlight group for border
+" - rounded [boolean default v:true]: Use rounded border
+let g:fzf_layout = { 'window': { 'width': 0.9, 'height': 0.6 } }
 ```
 
 #### Hide statusline
diff --git a/doc/fzf.txt b/doc/fzf.txt
index d0744c73..51f0d43f 100644
--- a/doc/fzf.txt
+++ b/doc/fzf.txt
@@ -1,4 +1,4 @@
-fzf.txt	fzf	Last change: November 23 2019
+fzf.txt	fzf	Last change: February 3 2020
 FZF - TABLE OF CONTENTS                                            *fzf* *fzf-toc*
 ==============================================================================
 
@@ -11,7 +11,7 @@ FZF - TABLE OF CONTENTS                                            *fzf* *fzf-to
     fzf#wrap
     Tips
       fzf inside terminal buffer
-        Starting fzf in Neovim floating window
+        Starting fzf in a popup window
         Hide statusline
     License
 
@@ -204,6 +204,7 @@ The following table summarizes the available options.
   `dir`                       | string        | Working directory
   `up` / `down` / `left` / `right`  | number/string | (Layout) Window position and size (e.g.  `20` ,  `50%` )
   `window`  (Vim 8 / Neovim)  | string        | (Layout) Command to open fzf window (e.g.  `vertical aboveleft 30new` )
+  `window`  (Vim 8 / Neovim)  | dict          | (Layout) Popup window settings (e.g.  `{'width': 0.9, 'height': 0.6}` )
  ---------------------------+---------------+----------------------------------------------------------------------
 
 `options` entry can be either a string or a list. For simple cases, string
@@ -212,6 +213,16 @@ should suffice, but prefer to use list type to avoid escaping issues.
     call fzf#run({'options': '--reverse --prompt "C:\\Program Files\\"'})
     call fzf#run({'options': ['--reverse', '--prompt', 'C:\Program Files\']})
 <
+When `window` entry is a dictionary, fzf will start in a popup window. The
+following options are allowed:
+
+ - Required:
+   - `width` [float]
+   - `height` [float]
+ - Optional:
+   - `highlight` [string default `'Comment'`]: Highlight group for border
+   - `rounded` [boolean default `v:true`]: Use rounded border
+
 
 FZF#WRAP
 ==============================================================================
@@ -291,29 +302,17 @@ The latest versions of Vim and Neovim include builtin terminal emulator
    - `call fzf#run({'left': '30%'})` or `let g:fzf_layout = {'left': '30%'}`
 
 
-Starting fzf in Neovim floating window~
-                                    *fzf-starting-fzf-in-neovim-floating-window*
+Starting fzf in a popup window~
+                                            *fzf-starting-fzf-in-a-popup-window*
 >
-    " Using floating windows of Neovim to start fzf
-    if has('nvim')
-      let $FZF_DEFAULT_OPTS .= ' --border --margin=0,2'
-
-      function! FloatingFZF()
-        let width = float2nr(&columns * 0.9)
-        let height = float2nr(&lines * 0.6)
-        let opts = { 'relative': 'editor',
-                   \ 'row': (&lines - height) / 2,
-                   \ 'col': (&columns - width) / 2,
-                   \ 'width': width,
-                   \ 'height': height }
-
-        let win = nvim_open_win(nvim_create_buf(v:false, v:true), v:true, opts)
-        call setwinvar(win, '&winhighlight', 'NormalFloat:Normal')
-      endfunction
-
-      let g:fzf_layout = { 'window': 'call FloatingFZF()' }
-    endif
-
+    " Required:
+    " - width [float]
+    " - height [float]
+    "
+    " Optional:
+    " - highlight [string default 'Comment']: Highlight group for border
+    " - rounded [boolean default v:true]: Use rounded border
+    let g:fzf_layout = { 'window': { 'width': 0.9, 'height': 0.6 } }
 <
 
 Hide statusline~
diff --git a/plugin/fzf.vim b/plugin/fzf.vim
index 21b7d66b..a646432b 100644
--- a/plugin/fzf.vim
+++ b/plugin/fzf.vim
@@ -650,7 +650,11 @@ function! s:split(dict)
   let ppos = s:getpos()
   try
     if s:present(a:dict, 'window')
-      execute 'keepalt' a:dict.window
+      if type(a:dict.window) == type({})
+        call s:popup(a:dict.window)
+      else
+        execute 'keepalt' a:dict.window
+      endif
     elseif !s:splittable(a:dict)
       execute (tabpagenr()-1).'tabnew'
     else
@@ -798,6 +802,69 @@ function! s:callback(dict, lines) abort
   endif
 endfunction
 
+if has('nvim')
+  function s:create_popup(hl, opts) abort
+    let buf = nvim_create_buf(v:false, v:true)
+    let opts = extend({'relative': 'editor', 'style': 'minimal'}, a:opts)
+    let border = has_key(opts, 'border') ? remove(opts, 'border') : []
+    let win = nvim_open_win(buf, v:true, opts)
+    call setwinvar(win, '&winhighlight', 'NormalFloat:'..a:hl)
+    call setwinvar(win, '&colorcolumn', '')
+    if !empty(border)
+      call nvim_buf_set_lines(buf, 0, -1, v:true, border)
+    endif
+    return buf
+  endfunction
+else
+  function! s:create_popup(hl, opts) abort
+    let is_frame = has_key(a:opts, 'border')
+    let buf = is_frame ? '' : term_start(&shell, #{hidden: 1})
+    let id = popup_create(buf, #{
+      \ line: a:opts.row,
+      \ col: a:opts.col,
+      \ minwidth: a:opts.width,
+      \ minheight: a:opts.height,
+      \ zindex: 50 - is_frame,
+    \ })
+
+    if is_frame
+      call setwinvar(id, '&wincolor', a:hl)
+      call setbufline(winbufnr(id), 1, a:opts.border)
+      execute 'autocmd BufWipeout * ++once call popup_close('..id..')'
+    else
+      execute 'autocmd BufWipeout * ++once bwipeout! '..buf
+    endif
+    return winbufnr(id)
+  endfunction
+endif
+
+function! s:popup(opts) abort
+  " Size and position
+  let width = float2nr(&columns * a:opts.width)
+  let height = float2nr(&lines * a:opts.height)
+  let row = float2nr((&lines - height) / 2)
+  let col = float2nr((&columns - width) / 2)
+
+  " Border
+  let edges = get(a:opts, 'rounded', 1) ? ['╭', '╮', '╰', '╯'] : ['┌', '┐', '└', '┘']
+  let bar = repeat('─', width - 2)
+  let top = edges[0] .. bar .. edges[1]
+  let mid = '│' .. repeat(' ', width - 2) .. '│'
+  let bot = edges[2] .. bar .. edges[3]
+  let border = [top] + repeat([mid], height - 2) + [bot]
+
+  let highlight = get(a:opts, 'highlight', 'Comment')
+  let frame = s:create_popup(highlight, {
+    \ 'row': row, 'col': col, 'width': width, 'height': height, 'border': border
+  \ })
+  call s:create_popup('Normal', {
+    \ 'row': row + 1, 'col': col + 2, 'width': width - 4, 'height': height - 2
+  \ })
+  if has('nvim')
+    execute 'autocmd BufWipeout <buffer> bwipeout '..frame
+  endif
+endfunction
+
 let s:default_action = {
   \ 'ctrl-t': 'tab split',
   \ 'ctrl-x': 'split',