Fix escaping string literals in various cases

Summary:
This fixes two bugs:

Interpolated heredocs need to be escaped using heredoc escaping rules, not doublequotedstring rules, but interpolated heredocs are parsed as a SyntaxList, so there's no way to tell the location without looking at the token kind in the lowerer.

Second, \X42 = \x42 in PHP, so both need to escape to the letter A. This adds the "X" case.

Reviewed By: vladima

Differential Revision: D6951735

fbshipit-source-id: fbae7c3006fdc0b832f444625d972a46ed9880f6

hphp/hack/src/parser/full_fidelity_ast.ml

@@ -1050,13 +1050,17 @@ and pExpr ?location:(location=TopLevel) : expr parser = fun node env ->
          (pExpr binary_right_operand env)

    | Token t ->
      (match location with
      | MemberSelect when Token.kind t = TK.Variable -> Lvar (pos_name node env)
      | InDoubleQuotedString -> String (pos, unesc_dbl (text node))
      | InBacktickedString -> String (pos, Php_escaping.unescape_backtick (text node))
      | MemberSelect
      | InGlobalVar
      | TopLevel -> Id (pos_name node env)
      (match location, Token.kind t with
      | MemberSelect, TK.Variable -> Lvar (pos_name node env)
      | InDoubleQuotedString, TK.HeredocStringLiteral
      | InDoubleQuotedString, TK.HeredocStringLiteralHead
      | InDoubleQuotedString, TK.HeredocStringLiteralTail ->
          String (pos, Php_escaping.unescape_heredoc (text node))
      | InDoubleQuotedString, _ -> String (pos, unesc_dbl (text node))
      | InBacktickedString, _ -> String (pos, Php_escaping.unescape_backtick (text node))
      | MemberSelect, _
      | InGlobalVar, _
      | TopLevel, _ -> Id (pos_name node env)
      )

    | YieldExpression { yield_operand; _ } when text yield_operand = "break" ->

hphp/hack/src/utils/php_escaping.ml

@@ -125,7 +125,7 @@ let unescape_literal literal_kind s =
        idx := !idx + unicode_count;
        if next () <> '}' then
          raise (Invalid_string "Invalid UTF-8 escape sequence")
      | 'x' ->
      | 'x' | 'X' ->
        let hex_count = count_f is_hex ~max:2 0 in
        if hex_count = 0 then
          Buffer.add_string buf "\\x"

hphp/test/hhcodegen_failing_tests_php_spec

@@ -1,6 +1,4 @@
spec/tests/constants/core_predefined_constants2.php
spec/tests/lexical_structure/tokens/heredoc_string_literals.php
spec/tests/lexical_structure/tokens/string_literals.php
spec/tests/statements/declare/declare.php
spec/tests/statements/selection/if.php
spec/tests/statements/selection/switch.php
spec/tests/statements/selection/switch.php