GPR#187: local open for patterns

This commits extends the pattern syntax to support local open in
patterns. Four new constructions mirroring the expression constructions
are added

    * `M.(pattern)`
    * `M.[pattern_list]` ⟺ M.([pattern_list])
    * `M.{labeled_pattern_list}` ⟺ M.({label_pattern_list})
    * `M.[| .. |] ⟺ M.( [| .. |] )

At the typing phase, the construction `M.(pattern)` brings all
identifiers defined within M inside the scope and then proceed with the
typing of `pattern`. All others constructions are desugared to the
`M.(..)` construction during parsing.

Questionable implementation details:
* Currently, the local pattern open use the `type_open` function like
the local expression pattern. However, this implies that values defined
inside `M` are also brought to the scope. A specialized
`type_open_for_pattern` would be more efficient.

1 files changed, 38 insertions, 14 deletions

diff --git a/parsing/parser.mly b/parsing/parser.mly
index 7acb0d644a..2cc6042544 100644
--- a/parsing/parser.mly
+++ b/parsing/parser.mly
@@ -1751,6 +1751,12 @@ pattern:
       { expecting 3 "pattern" }
   | EXCEPTION ext_attributes pattern %prec prec_constr_appl
       { mkpat_attrs (Ppat_exception $3) $2}
+  | mod_longident DOT LPAREN pattern RPAREN
+    { mkpat @@ Ppat_open (mkrhs $1 1, $4)}
+  | mod_longident DOT LPAREN pattern error
+    {unclosed "(" 3 ")" 5  }
+  | mod_longident DOT LPAREN error
+    { expecting 4 "pattern" }
   | pattern attribute
       { Pat.attr $1 $2 }
   | pattern_gen { $1 }
@@ -1806,20 +1812,19 @@ simple_pattern_not_ident:
       { mkpat(Ppat_variant($1, None)) }
   | SHARP type_longident
       { mkpat(Ppat_type (mkrhs $2 2)) }
-  | LBRACE lbl_pattern_list RBRACE
-      { let (fields, closed) = $2 in mkpat(Ppat_record(fields, closed)) }
-  | LBRACE lbl_pattern_list error
-      { unclosed "{" 1 "}" 3 }
-  | LBRACKET pattern_semi_list opt_semi RBRACKET
-      { reloc_pat (mktailpat (rhs_loc 4) (List.rev $2)) }
-  | LBRACKET pattern_semi_list opt_semi error
-      { unclosed "[" 1 "]" 4 }
-  | LBRACKETBAR pattern_semi_list opt_semi BARRBRACKET
-      { mkpat(Ppat_array(List.rev $2)) }
-  | LBRACKETBAR BARRBRACKET
-      { mkpat(Ppat_array []) }
-  | LBRACKETBAR pattern_semi_list opt_semi error
-      { unclosed "[|" 1 "|]" 4 }
+  | simple_delimited_pattern
+      { $1 }
+  | mod_longident DOT simple_delimited_pattern
+      { mkpat @@ Ppat_open(mkrhs $1 1, $3) }
+  | mod_longident DOT LPAREN RPAREN
+      { mkpat @@ Ppat_open( mkrhs $1 1, mkpat @@
+                 Ppat_construct ( mkrhs (Lident "()") 4, None) ) }
+  | mod_longident DOT LPAREN pattern RPAREN
+      { mkpat @@ Ppat_open (mkrhs $1 1, $4)}
+  | mod_longident DOT LPAREN pattern error
+      {unclosed "(" 3 ")" 5  }
+  | mod_longident DOT LPAREN error
+      { expecting 4 "pattern" }
   | LPAREN pattern RPAREN
       { reloc_pat $2 }
   | LPAREN pattern error
@@ -1842,6 +1847,25 @@ simple_pattern_not_ident:
   | extension
       { mkpat(Ppat_extension $1) }
 ;
+simple_delimited_pattern:
+  | LBRACE lbl_pattern_list RBRACE
+    { let (fields, closed) = $2 in mkpat(Ppat_record(fields, closed)) }
+  | LBRACE lbl_pattern_list error
+    { unclosed "{" 1 "}" 3 }
+  | LBRACE lbl_pattern_list error
+    { unclosed "{" 1 "}" 3 }
+  | LBRACKET pattern_semi_list opt_semi RBRACKET
+    { reloc_pat (mktailpat (rhs_loc 4) (List.rev $2)) }
+  | LBRACKET RBRACKET
+    { mkpat @@ Ppat_construct ( mkrhs (Lident "[]") 1, None) }
+  | LBRACKET pattern_semi_list opt_semi error
+    { unclosed "[" 1 "]" 4 }
+  | LBRACKETBAR pattern_semi_list opt_semi BARRBRACKET
+    { mkpat(Ppat_array(List.rev $2)) }
+  | LBRACKETBAR BARRBRACKET
+    { mkpat(Ppat_array []) }
+  | LBRACKETBAR pattern_semi_list opt_semi error
+    { unclosed "[|" 1 "|]" 4 }
 
 pattern_comma_list:
     pattern_comma_list COMMA pattern            { $3 :: $1 }