Adding in go_highlight_interfaces option, to provide the same highlig…

README.md

@@ -167,6 +167,7 @@ To change it:
 let g:go_highlight_functions = 1
 let g:go_highlight_methods = 1
 let g:go_highlight_structs = 1
+let g:go_highlight_interfaces = 1
 let g:go_highlight_operators = 1
 let g:go_highlight_build_constraints = 1
 ```

doc/vim-go.txt

@@ -832,6 +832,12 @@ Highlights method names. By default it's disabled. >
 Highlights struct names. By default it's disabled. >
 
 	let g:go_highlight_structs = 0
+<
+                                               *'g:go_highlight_interfaces'*
+
+Highlights interface names. By default it's disabled. >
+
+  let g:go_highlight_interfaces = 0
 <
                                         *'g:go_highlight_build_constraints'*
 

syntax/go.vim

@@ -69,6 +69,10 @@ if !exists("g:go_highlight_structs")
   let g:go_highlight_structs = 0
 endif
 
+if !exists("g:go_highlight_interfaces")
+  let g:go_highlight_interfaces = 0
+endif
+
 if !exists("g:go_highlight_build_constraints")
   let g:go_highlight_build_constraints = 0
 endif
@@ -291,6 +295,14 @@ endif
 hi def link     goStruct            Function
 hi def link     goStructDef         Function
 
+" Interfaces;
+if g:go_highlight_interfaces != 0
+  syn match goInterface             /\(.\)\@<=\w\+\({\)\@=/
+  syn match goInterfaceDef          /\(type\s\+\)\@<=\w\+\(\s\+interface\s\+{\)\@=/
+endif
+hi def link     goInterface         Function
+hi def link     goInterfaceDef      Function
+
 " Build Constraints
 if g:go_highlight_build_constraints != 0
     syn match   goBuildKeyword      display contained "+build"