Various improvements to syntax highlighting. (#917)

* Various improvements to syntax highlighting.

Look behind regexp patterns are not recommended in syntax files,
especially with the new NFA engine. So we should try to avoid them.
Highlighting of methods, fields, methods, structs and interfaces should
be much faster now.

Consolidated two options g:go_highlight_structs and
g:go_highlight_interfaces into one g:go_highlight_types.

* added goVarArgs match

explicitly match variadic args, so they are not detected as goField
instead.

README.md

@@ -181,8 +181,7 @@ To change it:
 let g:go_highlight_functions = 1
 let g:go_highlight_methods = 1
 let g:go_highlight_fields = 1
-let g:go_highlight_structs = 1
-let g:go_highlight_interfaces = 1
+let g:go_highlight_types = 1
 let g:go_highlight_operators = 1
 let g:go_highlight_build_constraints = 1
 ```

doc/vim-go.txt

@@ -1118,23 +1118,17 @@ Highlights method names. By default it's disabled. >
 
 	let g:go_highlight_methods = 0
 <
-                                                  *'g:go_highlight_structs'*
+                                                  *'g:go_highlight_types'*
 
-Highlights struct names. By default it's disabled. >
+Highlights struct and interface names. By default it's disabled. >
 
-  let g:go_highlight_structs = 0
+  let g:go_highlight_types = 0
 <
                                                   *'g:go_highlight_fields'*
 
 Highlights field names. By default it's disabled. >
 
   let g:go_highlight_fields = 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

@@ -71,12 +71,8 @@ if !exists("g:go_highlight_fields")
   let g:go_highlight_fields = 0
 endif
 
-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
+if !exists("g:go_highlight_types")
+  let g:go_highlight_types = 0
 endif
 
 if !exists("g:go_highlight_build_constraints")
@@ -98,12 +94,10 @@ endif
 syn case match
 
 syn keyword     goDirective         package import
-syn keyword     goDeclaration       var const type
-syn keyword     goDeclType          struct interface
+syn keyword     goDeclaration       var const
 
 hi def link     goDirective         Statement
 hi def link     goDeclaration       Keyword
-hi def link     goDeclType          Keyword
 
 " Keywords within functions
 syn keyword     goStatement         defer go goto return break continue fallthrough
@@ -129,10 +123,6 @@ hi def link     goUnsignedInts      Type
 hi def link     goFloats            Type
 hi def link     goComplexes         Type
 
-" Treat func specially: it's a declaration at the start of a line, but a type
-" elsewhere. Order matters here.
-syn match       goDeclaration       /\<func\>/
-
 
 " Predefined functions and values
 syn match       goBuiltins          /\<\v(append|cap|close|complex|copy|delete|imag|len)\ze\(/
@@ -301,38 +291,42 @@ hi def link     goOperator          Operator
 
 " Functions;
 if g:go_highlight_functions != 0
-  syn match goFunction              /\(func\s\+\)\@<=\w\+\((\)\@=/
-  syn match goFunction              /\()\s\+\)\@<=\w\+\((\)\@=/
+  syn match goDeclaration       /\<func\>/ nextgroup=goReceiver,goFunction skipwhite skipnl
+  syn match goReceiver /([^),]\+)/ contained nextgroup=goFunction contains=goReceiverType skipwhite skipnl
+  syn match goReceiverType /\(\s\|*\)\w\+)/hs=s+1,he=e-1 contained
+  syn match goFunction /\w\+/ contained
+else
+  syn match       goDeclaration       /\<func\>/
 endif
+hi def link     goReceiverType      Type
 hi def link     goFunction          Function
 
 " Methods;
 if g:go_highlight_methods != 0
-  syn match goMethod                /\(\.\)\@<=\w\+\((\)\@=/
+  syn match goMethod                /\.\w\+(/hs=s+1,he=e-1
 endif
 hi def link     goMethod            Type
 
 " Fields;
 if g:go_highlight_fields != 0
-  syn match goField                 /\(\.\)\@<=\a\+\([\ \n\r\:\)]\)\@=/
+  syn match goVarArgs               /\.\.\.\w\+\>/
+  syn match goField                 /\.\a\+\([\ \n\r\:\)\[]\)\@=/hs=s+1
 endif
-hi def link    goField              Type
-
-" Structs;
-if g:go_highlight_structs != 0
-  syn match goStruct                /\(.\)\@<=\w\+\({\)\@=/
-  syn match goStructDef             /\(type\s\+\)\@<=\w\+\(\s\+struct\s\+{\)\@=/
-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\+\(\s\+interface\s\+{\)\@=/
+hi def link    goField              Identifier
+
+" Structs & Interfaces;
+if g:go_highlight_types != 0
+  syn match goTypeConstructor      /\<\w\+{/he=e-1
+  syn match goTypeDecl             /\<type\>/ nextgroup=goTypeName skipwhite skipnl
+  syn match goTypeName             /\w\+/ contained nextgroup=goDeclType skipwhite skipnl
+  syn match goDeclType             /\<interface\|struct\>/ contained skipwhite skipnl
+else
+  syn keyword goDeclType           struct interface
 endif
-hi def link     goInterface         Function
-hi def link     goInterfaceDef      Function
+hi def link     goTypeConstructor   Type
+hi def link     goTypeName          Type
+hi def link     goTypeDecl          Keyword
+hi def link     goDeclType          Keyword
 
 " Build Constraints
 if g:go_highlight_build_constraints != 0