Fix highlighting of and-types

A new region is used to avoid matching the 'and' keyword too often (that
would interfere with let-and and module-rec-and.

Author: Julow

syntax/ocaml.vim

@@ -6,6 +6,7 @@
 "               Issac Trotts      <[email protected]>
 " URL:          https://github.com/ocaml/vim-ocaml
 " Last Change:
+"               2022 Jul 20 - Improved highlighting of type decl (Jules Aguillon)
 "               2019 Nov 05 - Accurate type highlighting (Maëlan)
 "               2018 Nov 08 - Improved highlighting of operators (Maëlan)
 "               2018 Apr 22 - Improved support for PPX (Andrey Popp)
@@ -332,10 +333,6 @@ syn match ocamlTypeVariance contained "[-+!]\ze *\('\|\<_\>\)"
 syn match ocamlTypeVariance contained "[-+] *!\+\ze *\('\|\<_\>\)"
 syn match ocamlTypeVariance contained "! *[-+]\+\ze *\('\|\<_\>\)"
 
-syn cluster ocamlTypeContained add=ocamlTypeEq
-syn match    ocamlTypeEq       contained  "[+:]\?="
-hi link ocamlTypeEq ocamlKeyChar
-
 syn cluster ocamlTypeExpr add=ocamlTypeVar,ocamlTypeConstr,ocamlTypeAnyVar,ocamlTypeBuiltin
 syn match    ocamlTypeVar      contained   "'\(\l\|_\)\(\w\|'\)*\>"
 syn match    ocamlTypeConstr   contained  "\<\(\l\|_\)\(\w\|'\)*\>"
@@ -467,10 +464,15 @@ hi link ocamlTypeSumAnnot ocamlTypeCatchAll
 
 " RHS of a ocamlTypeDef
 syn region ocamlTypeDefImpl
-\ matchgroup=ocamlKeyword start="\(=\|:\|of\)"
+\ matchgroup=ocamlKeyword start="\<of\>"
+\ matchgroup=ocamlKeyChar start=":="
+\ matchgroup=ocamlKeyChar start=":"
+\ matchgroup=ocamlKeyChar start="="
 \ matchgroup=NONE end="\(\<type\>\|\<exception\>\|\<val\>\|\<module\>\|\<class\>\|\<method\>\|\<constraint\>\|\<inherit\>\|\<object\>\|\<struct\>\|\<open\>\|\<include\>\|\<let\>\|\<external\>\|\<in\>\|\<end\>\|)\|]\|}\|;\|;;\)\@="
+\ matchgroup=NONE end="\(\<and\>\)\@="
 \ contained skipwhite skipempty
-\ contains=@ocamlTypeExpr,ocamlTypeEq,ocamlTypePrivate,ocamlTypeDefDots,ocamlTypeRecordDecl,ocamlTypeSumDecl,ocamlTypeDefAnd,ocamlComment,ocamlPpx
+\ contains=@ocamlTypeExpr,ocamlTypePrivate,ocamlTypeDefDots,ocamlTypeRecordDecl,ocamlTypeSumDecl,ocamlComment,ocamlPpx
+\ nextgroup=ocamlTypeDefAnd
 hi link ocamlTypeDefImpl ocamlTypeCatchAll
 
 " Type context opened by “type” (type definition) and “constraint” (type
@@ -482,7 +484,18 @@ syn region ocamlTypeDef
 \ matchgroup=ocamlLCIdentifier end="\<\l\(\w\|'\)*\>"
 \ contains=@ocamlAllErrs,ocamlComment,ocamlTypeVariance,ocamlTypeVar
 \ skipwhite skipempty
-\ nextgroup=ocamlTypeDefImpl
+\ nextgroup=ocamlTypeDefImpl,ocamlTypeDefAnd
+
+" Type context opened by “type” (type definition) and “constraint” (type
+" constraint).
+" Match the opening keyword and the identifier then jump into
+" ocamlTypeDefImpl.
+syn region ocamlTypeDefAnd
+\ matchgroup=ocamlKeyword start="\<and\>"
+\ matchgroup=ocamlLCIdentifier end="\<\l\(\w\|'\)*\>"
+\ contains=@ocamlAllErrs,ocamlComment,ocamlTypeVariance,ocamlTypeVar
+\ skipwhite skipempty
+\ nextgroup=ocamlTypeDefImpl,ocamlTypeDefAnd
 
 " Exception definitions. Like ocamlTypeDef, jump into ocamlTypeDefImpl.
 syn region ocamlExceptionDef
@@ -495,9 +508,6 @@ syn region ocamlExceptionDef
 syn cluster ocamlTypeContained add=ocamlTypePrivate
 syn keyword ocamlTypePrivate contained private
 hi link ocamlTypePrivate ocamlKeyword
-syn cluster ocamlTypeContained add=ocamlTypeDefAnd
-syn keyword ocamlTypeDefAnd contained and
-hi link ocamlTypeDefAnd ocamlKeyword
 syn cluster ocamlTypeContained add=ocamlTypeDefDots
 syn match ocamlTypeDefDots contained "\.\."
 hi link ocamlTypeDefDots ocamlKeyChar
@@ -513,7 +523,7 @@ syn match ocamlKeyword "(\_s*exception\>"lc=1
 " Type context opened by “:” (countless kinds of type annotations) and “:>”
 " (type coercions)
 syn region ocamlTypeAnnot matchgroup=ocamlKeyChar start=":\(>\|\_s*type\>\|[>:=]\@!\)"
-\ matchgroup=NONE end="\(\<type\>\|\<exception\>\|\<val\>\|\<module\>\|\<class\>\|\<method\>\|\<constraint\>\|\<inherit\>\|\<object\>\|\<struct\>\|\<open\>\|\<include\>\|\<let\>\|\<external\>\|\<in\>\|\<end\>\|)\|]\|}\|;\|;;\)\@="
+\ matchgroup=NONE end="\(\<type\>\|\<exception\>\|\<val\>\|\<module\>\|\<class\>\|\<method\>\|\<constraint\>\|\<inherit\>\|\<object\>\|\<struct\>\|\<open\>\|\<include\>\|\<let\>\|\<external\>\|\<in\>\|\<end\>\|\<and\>\|)\|]\|}\|;\|;;\)\@="
 \ matchgroup=NONE end="\(;\|}\)\@="
 \ matchgroup=NONE end="\(=\|:>\)\@="
 \ contains=@ocamlTypeExpr,ocamlComment,ocamlPpx