Add folding for documentation comment blocks

Author: dkearns

syntax/dart.vim

@@ -28,6 +28,15 @@ syn keyword dartCommentTodo     contained TODO FIXME XXX TBD
 syn match   dartLineComment     "//.*" contains=dartTodo,@Spell
 syn match   dartCommentSkip     "^[ \t]*\*\($\|[ \t]\+\)"
 syn region  dartComment         start="/\*"  end="\*/" contains=@Spell,dartTodo
+syn match   dartDocComment      "///.*"                contains=dartTodo,@Spell
+
+if !exists("g:dart_no_documentation_fold")
+  syn region dartDocComment  start="/\*\*"                      end="\*/"                        contains=dartTodo,@Spell fold
+  syn region dartCommentFold start="^\s*///.*\n\%(^\s*///\)\@=" end="^\s*///.*\n\%(^\s*///\)\@!" contains=dartDocComment  fold transparent keepend
+else
+  syn region dartDocComment  start="/\*\*"                      end="\*/"                        contains=dartTodo,@Spell
+endif
+
 syn keyword dartReserved        assert async await class const export extends external final hide import implements interface library mixin on show super sync yield
 syn match   dartNumber          "-\=\<\d\+L\=\>\|0[xX][0-9a-fA-F]\+\>"
 
@@ -65,6 +74,7 @@ hi def link dartBoolean         Boolean
 hi def link dartBranch          Conditional
 hi def link dartComment         Comment
 hi def link dartConditional     Conditional
+hi def link dartDocComment      Comment
 hi def link dartDQString        String
 hi def link dartEscape          SpecialChar
 hi def link dartException       Exception