handle :GoDef from modified buffer

Handle jumping to type definitions from a modified buffer. When the
definition is in the same file, skip trying to open the file that
contains the definition - just set the cursor position. When the
definition is in a different file and the current buffer has unsaved
modifications, use :hide edit instead of :edit.

Fixes #1125

autoload/go/def.vim

@@ -6,6 +6,7 @@ function! go#def#Jump(mode)
   let $GOPATH = go#path#Detect()
 
   let fname = fnamemodify(expand("%"), ':p:gs?\\?/?')
+  let fnameoriginal = fname
   if &modified
     " Write current unsaved buffer to a temp file and use the modified content
     let l:tmpname = tempname()
@@ -44,8 +45,8 @@ function! go#def#Jump(mode)
       let flags = printf(" -tags %s", tags)
     endif
 
-    let fname = shellescape(fname.':#'.go#util#OffsetCursor())
-    let command = printf("%s %s definition %s", bin_path, flags, fname)
+    let target = shellescape(fname.':#'.go#util#OffsetCursor())
+    let command = printf("%s %s definition %s", bin_path, flags, target)
     let out = go#util#System(command)
   else
     call go#util#EchoError('go_def_mode value: '. bin_name .' is not valid. Valid values are: [godef, guru]')
@@ -61,11 +62,17 @@ function! go#def#Jump(mode)
     return
   endif
 
-  call s:jump_to_declaration(out, a:mode)
+  " make sure the jump location doesn't refer to the temp file that was used
+  " when the current buffer is &modified.
+  if &modified && out =~ "^" . fname . ":"
+    let out = substitute(out, fname, fnameoriginal, '')
+  endif
+
+  call s:jump_to_declaration(fnameoriginal, out, a:mode)
   let $GOPATH = old_gopath
 endfunction
 
-function! s:jump_to_declaration(out, mode)
+function! s:jump_to_declaration(from, out, mode)
   " strip line ending
   let out = split(a:out, go#util#LineEnding())[0]
   if go#util#IsWin()
@@ -98,24 +105,35 @@ function! s:jump_to_declaration(out, mode)
   " modes of switchbuf which we need based on the split mode
   let old_switchbuf = &switchbuf
 
-  " jump to existing buffer if, 1. we have enabled it, 2. the buffer is loaded
-  " and 3. there is buffer window number we switch to
-  if get(g:, 'go_def_reuse_buffer', 0) && bufloaded(filename) != 0 && bufwinnr(filename) != -1
-    " jumpt to existing buffer if it exists
-    execute bufwinnr(filename) . 'wincmd w'
-  elseif a:mode == "tab"
-    let &switchbuf = "usetab"
-    if bufloaded(filename) == 0
-      tab split
+  if a:from != filename
+    " jump to existing buffer if, 1. we have enabled it, 2. the buffer is loaded
+    " and 3. there is buffer window number we switch to
+    if get(g:, 'go_def_reuse_buffer', 0) && bufloaded(filename) != 0 && bufwinnr(filename) != -1
+      " jump to existing buffer if it exists
+      execute bufwinnr(filename) . 'wincmd w'
+    else
+      if &modified
+        let cmd = 'hide edit '
+      else
+        let cmd = 'edit '
+      endif
+
+      if a:mode == "tab"
+        let &switchbuf = "usetab"
+        if bufloaded(filename) == 0
+          tab split
+        endif
+      elseif a:mode == "split"
+        split
+      elseif a:mode == "vsplit"
+        vsplit
+      endif
+
+      " open the file and jump to line and column
+      exec cmd . filename
     endif
-  elseif a:mode == "split"
-    split
-  elseif a:mode == "vsplit"
-    vsplit
   endif
 
-  " open the file and jump to line and column
-  exec 'edit '.filename
   call cursor(line, col)
 
   " also align the line to middle of the view