Allow folding any comment (#1428)

doc/vim-go.txt

@@ -1623,8 +1623,9 @@ You can enable specific fold regions by setting an array. Possible values are:
 - "import"           `import` block.
 - "varconst"         `var` and `const` blocks.
 - "package_comment"  The package comment.
+- "comment"          Any comment that is not the package comment.
 
-By default they're all enabled:
+By default all except "comment" are enabled:
 >
   let g:go_fold_enable = ['block', 'import', 'varconst', 'package_comment']
 <

syntax/go.vim

@@ -97,6 +97,8 @@ let s:fold_block = 1
 let s:fold_import = 1
 let s:fold_varconst = 1
 let s:fold_package_comment = 1
+let s:fold_comment = 0
+
 if exists("g:go_fold_enable")
   if index(g:go_fold_enable, 'block') == -1
     let s:fold_block = 0
@@ -107,6 +109,9 @@ if exists("g:go_fold_enable")
   if index(g:go_fold_enable, 'varconst') == -1
     let s:fold_varconst = 0
   endif
+  if index(g:go_fold_enable, 'comment') == -1
+    let s:fold_comment = 0
+  endif
   if index(g:go_fold_enable, 'package_comment') == -1
     let s:fold_package_comment = 0
   endif
@@ -163,8 +168,14 @@ hi def link     goPredefinedIdentifiers    goBoolean
 " Comments; their contents
 syn keyword     goTodo              contained TODO FIXME XXX BUG
 syn cluster     goCommentGroup      contains=goTodo
-syn region      goComment           start="/\*" end="\*/" contains=@goCommentGroup,@Spell
+
 syn region      goComment           start="//" end="$" contains=goGenerate,@goCommentGroup,@Spell
+if s:fold_comment
+  syn region    goComment           start="/\*" end="\*/" contains=@goCommentGroup,@Spell fold
+  syn match     goComment           "\v(^\s*//.*\n)+" contains=goGenerate,@goCommentGroup,@Spell fold
+else
+  syn region    goComment           start="/\*" end="\*/" contains=@goCommentGroup,@Spell
+endif
 
 hi def link     goComment           Comment
 hi def link     goTodo              Todo