[Parse] Re-allow prefix operators containing /

Author: hamishknight

include/swift/AST/DiagnosticsParse.def

@@ -94,9 +94,6 @@ ERROR(forbidden_extended_escaping_string,none,
 ERROR(regex_literal_parsing_error,none,
       "%0", (StringRef))
 
-ERROR(prefix_slash_not_allowed,none,
-      "prefix operator may not contain '/'", ())
-
 //------------------------------------------------------------------------------
 // MARK: Lexer diagnostics
 //------------------------------------------------------------------------------

lib/Parse/ParseDecl.cpp

@@ -8528,13 +8528,6 @@ Parser::parseDeclOperator(ParseDeclOptions Flags, DeclAttributes &Attributes) {
                                    Tok.getRawText().front() == '!'))
       diagnose(Tok, diag::postfix_operator_name_cannot_start_with_unwrap);
 
-  // Prefix operators may not contain the `/` character when `/.../` regex
-  // literals are enabled.
-  if (Context.LangOpts.EnableBareSlashRegexLiterals) {
-    if (Attributes.hasAttribute<PrefixAttr>() && Tok.getText().contains("/"))
-      diagnose(Tok, diag::prefix_slash_not_allowed);
-  }
-
   // A common error is to try to define an operator with something in the
   // unicode plane considered to be an operator, or to try to define an
   // operator like "not".  Analyze and diagnose this specifically.

test/StringProcessing/Frontend/enable-flag.swift

@@ -4,7 +4,7 @@
 
 // REQUIRES: swift_in_compiler
 
-prefix operator / // expected-error {{prefix operator may not contain '/'}}
+prefix operator /
 
 _ = /x/
 _ = #/x/#

test/StringProcessing/Parse/forward-slash-regex.swift

@@ -2,9 +2,9 @@
 // REQUIRES: swift_in_compiler
 // REQUIRES: concurrency
 
-prefix operator /  // expected-error {{prefix operator may not contain '/'}}
-prefix operator ^/ // expected-error {{prefix operator may not contain '/'}}
-prefix operator /^/ // expected-error {{prefix operator may not contain '/'}}
+prefix operator /
+prefix operator ^/
+prefix operator /^/
 
 prefix operator !!
 prefix func !! <T>(_ x: T) -> T { x }