misc: Import/Drop commands for Vim

New ftplugin adds Import and Drop commands for Go buffers
in Vim.  These commands ensure that the provided package is
imported (or not imported) in the current Go buffer, using
proper style and ordering, without moving the cursor.

E.g.

    :Import strings
    :ImportAs . strings
    :Drop strings

Two mappings are also introduced to help with the fmt package:

    \f => :Import fmt
    \F => :Drop fmt

R=adg
CC=golang-dev
https://golang.org/cl/4009043

misc/vim/ftplugin/go/import.vim

@@ -0,0 +1,203 @@
+" Copyright 2011 The Go Authors. All rights reserved.
+" Use of this source code is governed by a BSD-style
+" license that can be found in the LICENSE file.
+"
+" import.vim: Vim commands to import/drop Go packages.
+"
+" This filetype plugin adds three new commands for go buffers:
+"
+"   :Import {path}
+"
+"       Import ensures that the provided package {path} is imported
+"       in the current Go buffer, using proper style and ordering.
+"       If {path} is already being imported, an error will be
+"       displayed and the buffer will be untouched.
+" 
+"   :ImportAs {localname} {path}
+"
+"       Same as Import, but uses a custom local name for the package.
+"
+"   :Drop {path}
+"
+"       Remove the import line for the provided package {path}, if
+"       present in the current Go buffer.  If {path} is not being
+"       imported, an error will be displayed and the buffer will be
+"       untouched.
+"
+" In addition to these commands, there are also two shortcuts mapped:
+"
+"   \f  -  Runs :Import fmt
+"   \F  -  Runs :Drop fmt
+"
+" The backslash is the default maplocalleader, so it is possible that
+" your vim is set to use a different character (:help maplocalleader).
+"
+
+if exists("s:loaded") || exists("b:did_ftplugin")
+    finish
+endif
+let s:loaded = 1
+
+command! -buffer -nargs=? Drop call s:SwitchImport(0, '', <f-args>)
+command! -buffer -nargs=1 Import call s:SwitchImport(1, '', <f-args>)
+command! -buffer -nargs=* ImportAs call s:SwitchImport(1, <f-args>)
+map <buffer> <LocalLeader>f :Import fmt<CR>
+map <buffer> <LocalLeader>F :Drop fmt<CR>
+
+function s:SwitchImport(enabled, localname, path)
+    let view = winsaveview()
+    let path = a:path
+
+    " Quotes are not necessary, so remove them if provided.
+    if path[0] == '"'
+        let path = strpart(path, 1)
+    endif
+    if path[len(path)-1] == '"'
+        let path = strpart(path, 0, len(path) - 1)
+    endif
+    if path == ''
+        call s:Error('Import path not provided')
+        return
+    endif
+
+    let qpath = '"' . path . '"'
+    if a:localname != ''
+        let qlocalpath = a:localname . ' ' . qpath
+    else
+        let qlocalpath = qpath
+    endif
+    let indentstr = 0
+    let packageline = -1 " Position of package name statement
+    let appendline = -1  " Position to introduce new import
+    let deleteline = -1  " Position of line with existing import
+    let linesdelta = 0   " Lines added/removed
+
+    " Find proper place to add/remove import.
+    let line = 0
+    while line <= line('$')
+        let linestr = getline(line)
+
+        if linestr =~# '^package\s'
+            let packageline = line
+            let appendline = line
+
+        elseif linestr =~# '^import\s\+('
+            let appendstr = qlocalpath
+            let indentstr = 1
+            let appendline = line
+            while line <= line("$")
+                let line = line + 1
+                let linestr = getline(line)
+                let m = matchlist(getline(line), '^\()\|\(\s\+\)\(\S*\s*\)"\(.\+\)"\)')
+                if empty(m)
+                    continue
+                endif
+                if m[1] == ')'
+                    break
+                endif
+                if a:localname != '' && m[3] != ''
+                    let qlocalpath = printf('%-' . (len(m[3])-1) . 's %s', a:localname, qpath)
+                endif
+                let appendstr = m[2] . qlocalpath
+                let indentstr = 0
+                if m[4] == path
+                    let appendline = -1
+                    let deleteline = line
+                    break
+                elseif m[4] < path
+                    let appendline = line
+                endif
+            endwhile
+            break
+
+        elseif linestr =~# '^import '
+            if appendline == packageline
+                let appendstr = 'import ' . qlocalpath
+                let appendline = line - 1
+            endif
+            let m = matchlist(linestr, '^import\(\s\+\)\(\S*\s*\)"\(.\+\)"')
+            if !empty(m)
+                if m[3] == path
+                    let appendline = -1
+                    let deleteline = line
+                    break
+                endif
+                if m[3] < path
+                    let appendline = line
+                endif
+                if a:localname != '' && m[2] != ''
+                    let qlocalpath = printf("%s %" . len(m[2])-1 . "s", a:localname, qpath)
+                endif
+                let appendstr = 'import' . m[1] . qlocalpath
+            endif
+
+        elseif linestr =~# '^\(var\|const\|type\|func\)\>'
+            break
+
+        endif
+        let line = line + 1
+    endwhile
+
+    " Append or remove the package import, as requested.
+    if a:enabled
+        if deleteline != -1
+            call s:Error(qpath . ' already being imported')
+        elseif appendline == -1
+            call s:Error('No package line found')
+        else
+            if appendline == packageline
+                call append(appendline + 0, '')
+                call append(appendline + 1, 'import (')
+                call append(appendline + 2, ')')
+                let appendline += 2
+                let linesdelta += 3
+                let appendstr = qlocalpath
+                let indentstr = 1
+            endif
+            call append(appendline, appendstr)
+            execute appendline + 1
+            if indentstr
+                execute 'normal >>'
+            endif
+            let linesdelta += 1
+        endif
+    else
+        if deleteline == -1
+            call s:Error(qpath . ' not being imported')
+        else
+            execute deleteline . 'd'
+            let linesdelta -= 1
+
+            if getline(deleteline-1) =~# '^import\s\+(' && getline(deleteline) =~# '^)'
+                " Delete empty import block
+                let deleteline -= 1
+                execute deleteline . "d"
+                execute deleteline . "d"
+                let linesdelta -= 2
+            endif
+
+            if getline(deleteline) == '' && getline(deleteline - 1) == ''
+                " Delete spacing for removed line too.
+                execute deleteline . "d"
+                let linesdelta -= 1
+            endif
+        endif
+    endif
+
+    " Adjust view for any changes.
+    let view.lnum += linesdelta
+    let view.topline += linesdelta
+    if view.topline < 0
+        let view.topline = 0
+    endif
+
+    " Put buffer back where it was.
+    call winrestview(view)
+
+endfunction
+
+function s:Error(s)
+    echohl Error | echo a:s | echohl None
+endfunction
+
+" vim:ts=4:sw=4:et

misc/vim/readme.txt

@@ -21,3 +21,17 @@ commands:
   ln -s $GOROOT/misc/vim/ftdetect/gofiletype.vim $HOME/.vim/ftdetect/
   ln -s $GOROOT/misc/vim/syntax/go.vim $HOME/.vim/syntax
   echo "syntax on" >> $HOME/.vimrc
+
+
+Vim filetype plugins for Go
+===========================
+
+To install one of the available filetype plugins for Go:
+
+  1. Same as 1 above.
+  2. Copy or link one or more plugins from ftplugin/go/*.vim to the
+     Go-specific ftplugin directory underneath your vim runtime directory
+     (normally $HOME/.vim/ftplugin/go/*.vim).
+  3. Add the following line to your .vimrc file (normally $HOME/.vimrc):
+
+     filetype plugin on