add a Pattern constructor to Extended_ast.t

So it's easier to print patterns, which seems like the main major syntactic category
missing from the type. Granted, no standard source file contains a pattern, but the
same argument applies to core_type.

lib/Extended_ast.ml

@@ -25,6 +25,7 @@ type 'a t =
   | Core_type : core_type t
   | Module_type : module_type t
   | Expression : expression t
+  | Pattern : pattern t
   | Repl_file : repl_file t
   | Documentation : Ocamlformat_odoc_parser.Ast.t t
 
@@ -37,6 +38,7 @@ let of_syntax = function
   | Core_type -> Any Core_type
   | Module_type -> Any Module_type
   | Expression -> Any Expression
+  | Pattern -> Any Pattern
   | Repl_file -> Any Repl_file
   | Documentation -> Any Documentation
 
@@ -50,6 +52,7 @@ let map (type a) (x : a t) (m : Ast_mapper.mapper) : a -> a =
   | Core_type -> m.typ m
   | Module_type -> m.module_type m
   | Expression -> m.expr m
+  | Pattern -> m.pat m
   | Repl_file -> List.map ~f:(m.repl_phrase m)
   | Documentation -> Fn.id
 
@@ -253,6 +256,7 @@ module Parse = struct
     | Core_type -> Parse.core_type ~ocaml_version lexbuf
     | Module_type -> Parse.module_type ~ocaml_version lexbuf
     | Expression -> Parse.expression ~ocaml_version lexbuf
+    | Pattern -> Parse.pattern ~ocaml_version lexbuf
     | Repl_file -> Toplevel_lexer.repl_file ~ocaml_version lexbuf
     | Documentation ->
         let pos = (Location.curr lexbuf).loc_start in
@@ -274,6 +278,7 @@ module Printast = struct
     | Core_type -> core_type
     | Module_type -> module_type
     | Expression -> expression
+    | Pattern -> pattern
     | Repl_file -> repl_file
     | Documentation -> Docstring.dump
 end

lib/Extended_ast.mli

@@ -24,6 +24,7 @@ type 'a t =
   | Core_type : core_type t
   | Module_type : module_type t
   | Expression : expression t
+  | Pattern : pattern t
   | Repl_file : repl_file t
   | Documentation : Ocamlformat_odoc_parser.Ast.t t
 

lib/Fmt_ast.ml

@@ -4817,6 +4817,7 @@ let fmt_file (type a) ~ctx ~fmt_code ~debug (fragment : a Extended_ast.t)
         (fmt_module_type c (sub_mty ~ctx:(Mty mty) mty))
   | Expression, e ->
       fmt_expression c (sub_exp ~ctx:(Str (Ast_helper.Str.eval e)) e)
+  | Pattern, p -> fmt_pattern c (sub_pat ~ctx:(Pld (PPat (p, None))) p)
   | Repl_file, l -> fmt_repl_file c ctx l
   | Documentation, d ->
       (* TODO: [source] and [cmts] should have never been computed when

lib/Std_ast.ml

@@ -21,6 +21,7 @@ type 'a t =
   | Core_type : core_type t
   | Module_type : module_type t
   | Expression : expression t
+  | Pattern : pattern t
   (* not implemented *)
   | Repl_file : unit t
   | Documentation : unit t
@@ -34,6 +35,7 @@ let of_syntax = function
   | Core_type -> Any Core_type
   | Module_type -> Any Module_type
   | Expression -> Any Expression
+  | Pattern -> Any Pattern
   | Repl_file -> Any Repl_file
   | Documentation -> Any Documentation
 
@@ -52,6 +54,7 @@ let map (type a) (x : a t) (m : Ast_mapper.mapper) : a -> a =
   | Core_type -> m.typ m
   | Module_type -> m.module_type m
   | Expression -> m.expr m
+  | Pattern -> m.pat m
   | Repl_file -> Fn.id
   | Documentation -> Fn.id
 
@@ -69,6 +72,7 @@ module Parse = struct
     | Core_type -> Parse.core_type ~ocaml_version lexbuf
     | Module_type -> Parse.module_type ~ocaml_version lexbuf
     | Expression -> Parse.expression ~ocaml_version lexbuf
+    | Pattern -> Parse.pattern ~ocaml_version lexbuf
     | Repl_file -> ()
     | Documentation -> ()
 end
@@ -85,6 +89,7 @@ module Printast = struct
     | Core_type -> core_type 0
     | Module_type -> module_type 0
     | Expression -> expression 0
+    | Pattern -> pattern 0
     | Repl_file -> fun _ _ -> ()
     | Documentation -> fun _ _ -> ()
 end

lib/Std_ast.mli

@@ -24,6 +24,7 @@ type 'a t =
   | Core_type : core_type t
   | Module_type : module_type t
   | Expression : expression t
+  | Pattern : pattern t
   (* not implemented *)
   | Repl_file : unit t
   | Documentation : unit t

lib/Syntax.ml

@@ -16,6 +16,7 @@ type t =
   | Core_type
   | Module_type
   | Expression
+  | Pattern
   | Repl_file
   | Documentation
 

lib/Syntax.mli

@@ -16,6 +16,7 @@ type t =
   | Core_type
   | Module_type
   | Expression
+  | Pattern
   | Repl_file
   | Documentation
 

test/unit/test_translation_unit.ml

@@ -46,6 +46,11 @@ Error: Syntax error
 |}
         ) ]
 
+let test_parse_and_format_pattern =
+  let make_test = test_parse_and_format "pattern" ~fg:Pattern in
+  [ make_test "A 1" ~input:"A 1" ~expected:(Ok "A 1\n")
+  ; make_test "A B C" ~input:"A B C" ~expected:(Ok "A (B C)\n") ]
+
 let test_parse_and_format_module_type =
   let make_test = test_parse_and_format "module_type" ~fg:Module_type in
   [ make_test "sig end" ~input:"sig end" ~expected:(Ok "sig end\n")
@@ -127,5 +132,6 @@ let tests =
     [ test_parse_and_format_core_type
     ; test_parse_and_format_expression
     ; test_parse_and_format_module_type
+    ; test_parse_and_format_pattern
     ; test_parse_and_format_signature
     ; test_parse_and_format_use_file ]