feat(compiler): Support pattern matching "or" patterns (#1173)

* feat(compiler): Support pattern matching "or" patterns

* Add new error states

* or tests

* Snapshots

* Add clarifying comments

* Remove Either implementation

* Remove inaccurate comment

* Note impossible case

* Reference optimization issue

* Add a few destructuring smoke tests

Author: ospencer

compiler/src/middle_end/linearize.re

@@ -3862,6 +3862,32 @@ program: LET LPAREN WASMI64 COMMA EOL WHILE
 ## In state 3, spurious reduction of production nonempty_list(eol) -> EOL
 ## In state 5, spurious reduction of production eols -> nonempty_list(eol)
 ##
+program: LET NUMBER_INT PIPE WHILE
+##
+## Ends in an error in state: 345.
+##
+## pattern -> pattern PIPE . pattern [ WHEN THICKARROW RPAREN RBRACK RBRACE PIPE EQUAL EOL COMMA COLON ]
+## pattern -> pattern PIPE . eols pattern [ WHEN THICKARROW RPAREN RBRACK RBRACE PIPE EQUAL EOL COMMA COLON ]
+##
+## The known suffix of the stack is as follows:
+## pattern PIPE
+##
+program: LET NUMBER_INT PIPE EOL WHILE
+##
+## Ends in an error in state: 404.
+##
+## pattern -> pattern PIPE eols . pattern [ WHEN THICKARROW RPAREN RBRACK RBRACE PIPE EQUAL EOL COMMA COLON ]
+##
+## The known suffix of the stack is as follows:
+## pattern PIPE eols
+##
+## WARNING: This example involves spurious reductions.
+## This implies that, although the LR(1) items shown above provide an
+## accurate view of the past (what has been recognized so far), they
+## may provide an INCOMPLETE view of the future (what was expected next).
+## In state 3, spurious reduction of production nonempty_list(eol) -> EOL
+## In state 5, spurious reduction of production eols -> nonempty_list(eol)
+##
 
 Expected a pattern.
 

compiler/src/middle_end/matchcomp.re

@@ -250,6 +250,7 @@ pattern:
   | type_id { Pat.construct ~loc:(to_loc $loc) $1 [] }
   | lbrack rbrack { Pat.list ~loc:(to_loc $loc) [] }
   | lbrack lseparated_nonempty_list(comma, list_item_pat) comma? rbrack { Pat.list ~loc:(to_loc $loc) $2 }
+  | pattern pipe_op opt_eols pattern { Pat.or_ ~loc:(to_loc $loc) $1 $4 }
 
 list_item_pat:
   | ELLIPSIS pattern { ListSpread ($2, to_loc $loc) }