These now parse without parens but print with parens

test/passing/tests/layout_annotation-erased.ml.js-ref

@@ -67,6 +67,13 @@ let g : (_ : value) -> unit = fun _ -> ()
 let f : (_ : immediate) -> (_ : value) = fun _ -> assert false
 let g : (_ : value) -> (_ : immediate) = fun _ -> assert false
 
+type ('a : any, 'b : any, 'c : any) t4
+type 'a t5 = (('a : float64), int, bool) t4
+
+let f : ('a, (_ : value), bool) t4 -> int = fun _ -> 42
+
+type ('a, 'b, 'c) t6 = ('a, 'b, ('c : bits32)) t4
+
 (********************************************)
 (* Test 3: Annotation on types in functions *)
 

test/passing/tests/layout_annotation-erased.ml.ref

@@ -94,6 +94,14 @@ let f : _ -> _ = fun _ -> assert false
 
 let g : _ -> _ = fun _ -> assert false
 
+type ('a, 'b, 'c) t4
+
+type 'a t5 = ('a, int, bool) t4
+
+let f : ('a, _, bool) t4 -> int = fun _ -> 42
+
+type ('a, 'b, 'c) t6 = ('a, 'b, 'c) t4
+
 (********************************************)
 (* Test 3: Annotation on types in functions *)
 

test/passing/tests/layout_annotation.ml

@@ -105,7 +105,6 @@ let f : ('a, _ : value, bool) t4 -> int = fun _ -> 42;;
 
 type ('a, 'b, 'c) t6 = ('a, 'b, 'c : bits32) t4;;
 
-
 (********************************************)
 (* Test 3: Annotation on types in functions *)
 

test/passing/tests/layout_annotation.ml.js-ref

@@ -67,6 +67,13 @@ let g : (_ : value) -> unit = fun _ -> ()
 let f : (_ : immediate) -> (_ : value) = fun _ -> assert false
 let g : (_ : value) -> (_ : immediate) = fun _ -> assert false
 
+type ('a : any, 'b : any, 'c : any) t4
+type 'a t5 = (('a : float64), int, bool) t4
+
+let f : ('a, (_ : value), bool) t4 -> int = fun _ -> 42
+
+type ('a, 'b, 'c) t6 = ('a, 'b, ('c : bits32)) t4
+
 (********************************************)
 (* Test 3: Annotation on types in functions *)
 

test/passing/tests/layout_annotation.ml.ref

@@ -96,6 +96,14 @@ let f : (_ : immediate) -> (_ : value) = fun _ -> assert false
 
 let g : (_ : value) -> (_ : immediate) = fun _ -> assert false
 
+type ('a : any, 'b : any, 'c : any) t4
+
+type 'a t5 = (('a : float64), int, bool) t4
+
+let f : ('a, (_ : value), bool) t4 -> int = fun _ -> 42
+
+type ('a, 'b, 'c) t6 = ('a, 'b, ('c : bits32)) t4
+
 (********************************************)
 (* Test 3: Annotation on types in functions *)
 

vendor/parser-extended/parser.mly

@@ -4193,10 +4193,22 @@ atomic_type:
       { [] }
   | ty = atomic_type
       { [ty] }
-  | LPAREN tys = separated_nontrivial_llist(COMMA, core_type) RPAREN
+  | LPAREN
+    tys = separated_nontrivial_llist(COMMA, one_type_parameter_of_several)
+    RPAREN
       { tys }
 ;
 
+(* Layout annotations on type expressions typically require parens, as in [('a :
+   float64)].  But this is unnecessary when the type expression is used as the
+   parameter of a tconstr with more than one argument, as in [(int, 'b :
+   float64) t]. *)
+%inline one_type_parameter_of_several:
+  | core_type { $1 }
+  | name=mkrhs(tyvar_name_or_underscore) COLON jkind=jkind_annotation
+    { let descr = Ptyp_var (name, jkind) in
+      mktyp ~loc:$sloc descr }
+
 %inline package_core_type: module_type
       { let (lid, cstrs, attrs) = package_type_of_module_type $1 in
         let descr = Ptyp_package (lid, cstrs) in

vendor/parser-standard/parser.mly

@@ -4549,9 +4549,24 @@ atomic_type:
       { [] }
   | ty = atomic_type
       { [ty] }
-  | LPAREN tys = separated_nontrivial_llist(COMMA, core_type) RPAREN
+  | LPAREN
+    tys = separated_nontrivial_llist(COMMA, one_type_parameter_of_several)
+    RPAREN
       { tys }
 
+(* Layout annotations on type expressions typically require parens, as in [('a :
+   float64)].  But this is unnecessary when the type expression is used as the
+   parameter of a tconstr with more than one argument, as in [(int, 'b :
+   float64) t]. *)
+%inline one_type_parameter_of_several:
+  | core_type { $1 }
+  | QUOTE id=ident COLON jkind=jkind_annotation
+    { Jane_syntax.Layouts.type_of ~loc:(make_loc $sloc) @@
+      Ltyp_var { name = Some id; jkind } }
+  | UNDERSCORE COLON jkind=jkind_annotation
+    { Jane_syntax.Layouts.type_of ~loc:(make_loc $sloc) @@
+      Ltyp_var { name = None; jkind } }
+
 %inline package_type: module_type
       { let (lid, cstrs, attrs) = package_type_of_module_type $1 in
         let descr = Ptyp_package (lid, cstrs) in