commands: add :GoAddTags

This adds a new feature called `:GoAddTags` that add field tags for a
given struct. Checkout the doc for more info.

autoload/go/util.vim

@@ -231,6 +231,50 @@ function! go#util#camelcase(word)
   endif
 endfunction
 
+function! go#util#AddTags(line1, line2, ...)
+  " default is json
+  let l:keys = ["json"]
+  if a:0
+    let l:keys = a:000
+  endif
+
+  let l:line1 = a:line1
+  let l:line2 = a:line2
+
+  " If we're inside a struct and just call this function let us add the tags
+  " to all fields
+  " TODO(arslan): I don't like using patterns. Check if we can move it to
+  " `motion` and do it via AST based position
+  let ln1 = searchpair('struct {', '', '}', 'bcnW')
+  if ln1 == 0
+    echon "vim-go: " | echohl ErrorMsg | echon "cursor is outside the struct" | echohl None
+    return
+  endif
+
+  " searchpair only returns a single position
+  let ln2 = search('}', "cnW")
+
+  " if no range is given we apply for the whole struct
+  if l:line1 == l:line2
+    let l:line1 = ln1 + 1
+    let l:line2 = ln2 - 1
+  endif
+
+  for line in range(l:line1, l:line2)
+    " get the field name (word) that are not part of a commented line
+    let l:matched = matchstr(getline(line), '\(\/\/.*\)\@<!\w\+')
+    if empty(l:matched)
+      continue
+    endif
+
+    let word = go#util#snippetcase(l:matched)
+    let tags = map(copy(l:keys), 'printf("%s:%s", v:val,"\"'. word .'\"")')
+    let updated_line = printf("%s `%s`", getline(line), join(tags, " "))
+
+    " finally, update the line inplace
+    call setline(line, updated_line)
+  endfor
+endfunction
 
 " TODO(arslan): I couldn't parameterize the highlight types. Check if we can
 " simplify the following functions

doc/vim-go.txt

@@ -661,7 +661,21 @@ CTRL-t
       :GoImpl f *Foo io.Writer
       :GoImpl T io.ReadWriteCloser
 <
+                                                              *:GoAddTags*
+:[range]GoAddTags [key] [key1] ...
 
+    Adds field tags for the fields of a struct. If called inside a struct it
+    automatically add field tags with the `json` key and the value
+    automatically generated based on the field name. An error message is given
+    if it's called outside a struct definition.
+
+    If [range] is given, only the selected fields will be changed.
+
+    The default `json` can be changed by providing one or more [key]
+    arguments. An example of adding `xml` and `db` would be:
+>
+      :GoAddTags xml db
+<
                                                               *:GoAutoTypeInfoToggle*
 :GoAutoTypeInfoToggle
 

ftplugin/go/commands.vim

@@ -15,6 +15,8 @@ command! -range=% GoReferrers call go#guru#Referrers(<count>)
 command! -nargs=? GoGuruTags call go#guru#Tags(<f-args>)
 
 
+command! -nargs=* -range GoAddTags call go#util#AddTags(<line1>, <line2>, <f-args>)
+
 command! -range=% GoSameIds call go#guru#SameIds(<count>)
 command! -range=0 GoSameIdsClear call go#guru#ClearSameIds()
 command! -range=% GoSameIdsToggle call go#guru#ToggleSameIds(<count>)