semdiff: drop metadata directive on the floor

Summary:
the .metadata directive allows us to persist
arbitrary information into the repo. This is used for things
like storing the compiler version (and possibly other things)

Reviewed By: nbenton

Differential Revision: D6982353

fbshipit-source-id: f8c580ca512202043608f40400597ac93c2095fa

hphp/hack/src/hhbc/hhas_lexer.mll

@@ -93,6 +93,7 @@ rule read =
   | ".require"          {REQUIREDIRECTIVE}
   | ".srcloc"           {SRCLOCDIRECTIVE}
   | assertconstraint    {ASSERTCONSTRAINT (Lexing.lexeme lexbuf)}
+  | ".metadata"         {METADATADIRECTIVE}
   | id                  {ID (Lexing.lexeme lexbuf)}
   | triplequoted as lxm {TRIPLEQUOTEDSTRING (String.sub lxm 3 (String.length lxm - 6))}
   | escapequote         {read_php_escaped_string (Buffer.create 17) lexbuf}

hphp/hack/src/hhbc/hhas_parser.mly

@@ -29,6 +29,7 @@ open Hhas_parser_actions
 %token TRYFAULTDIRECTIVE PROPERTYDIRECTIVE FILEPATHDIRECTIVE
 %token ISMEMOIZEWRAPPERDIRECTIVE STATICDIRECTIVE REQUIREDIRECTIVE
 %token SRCLOCDIRECTIVE
+%token METADATADIRECTIVE
 %token LANGLE
 %token RANGLE
 %token COLONCOLON
@@ -290,6 +291,13 @@ srcloc:
  | SRCLOCDIRECTIVE INT COLON INT COMMA INT COLON INT SEMI
    { (($2, $4), ($6, $8)) }
 ;
+
+metadata:
+ | METADATADIRECTIVE ID EQUALS ID SEMI nl { (* do nothing *) }
+ | METADATADIRECTIVE ID EQUALS STRING SEMI nl { (* do nothing *) }
+ | METADATADIRECTIVE ID EQUALS TRIPLEQUOTEDSTRING SEMI nl { (* do nothing *) }
+;
+
 staticdirective:
  | STATICDIRECTIVE VNAME EQUALS ID
    { ($2, $4) }
@@ -561,6 +569,7 @@ decllist:
     | FILEPATHDIRECTIVE STRING SEMI nl decllist {$5}
     | STRICTDIRECTIVE INT SEMI nl decllist { StrictTypes_decl ($2 = 1L) :: $5}
     | HHFILE INT SEMI nl decllist { HHFile_decl ($2 = 1L) :: $5 }
+    | metadata decllist { $2 }
 ;
 includesdecl:
     | INCLUDESDIRECTIVE {

hphp/hack/test/semdiff/ignore_metadata_directive.1.hhas

@@ -0,0 +1,14 @@
+# starts here
+
+.filepath "/data/users/gregorynisbet/fbsource/fbcode/hphp/hack/test/semdiff/ignore_metadata_directive.1.hhas";
+
+.metadata a = b;
+
+.hh_file 1;
+
+.main {
+  Int 1
+  RetC
+}
+
+# /data/users/gregorynisbet/fbsource/fbcode/hphp/hack/test/semdiff/ignore_metadata_directive.1.hhas

hphp/hack/test/semdiff/ignore_metadata_directive.2.hhas

@@ -0,0 +1,12 @@
+# starts here
+
+.filepath "/data/users/gregorynisbet/fbsource/fbcode/hphp/hack/test/semdiff/ignore_metadata_directive.2.hhas";
+
+.hh_file 1;
+
+.main {
+  Int 1
+  RetC
+}
+
+# /data/users/gregorynisbet/fbsource/fbcode/hphp/hack/test/semdiff/ignore_metadata_directive.2.hhas