Add 'out'/'inout' keywords for variance.

Under the `variance` flag, `out` and `inout` will be treated as keywords.

Change-Id: I73ba6871a9f0d410a7b3818833a1f50a5f75fba6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/117203
Commit-Queue: Kallen Tu <[email protected]>
Reviewed-by: Leaf Petersen <[email protected]>

Author: kallentu

pkg/front_end/lib/src/fasta/scanner/abstract_scanner.dart

@@ -73,6 +73,10 @@ abstract class AbstractScanner implements Scanner {
   /// and https://github.com/dart-lang/language/issues/60
   bool _enableTripleShift = false;
 
+  /// Experimental flag for enabling variance.
+  /// See https://github.com/dart-lang/language/issues/524
+  bool _enableVariance = false;
+
   /**
    * The string offset for the next token that will be created.
    *
@@ -139,6 +143,7 @@ abstract class AbstractScanner implements Scanner {
       _enableExtensionMethods = config.enableExtensionMethods;
       _enableNonNullable = config.enableNonNullable;
       _enableTripleShift = config.enableTripleShift;
+      _enableVariance = config.enableVariance;
     }
   }
 
@@ -1483,6 +1488,10 @@ abstract class AbstractScanner implements Scanner {
         (state.keyword == Keyword.LATE || state.keyword == Keyword.REQUIRED)) {
       return tokenizeIdentifier(next, start, allowDollar);
     }
+    if (!_enableVariance &&
+        (state.keyword == Keyword.OUT || state.keyword == Keyword.INOUT)) {
+      return tokenizeIdentifier(next, start, allowDollar);
+    }
     if (($A <= next && next <= $Z) ||
         ($0 <= next && next <= $9) ||
         identical(next, $_) ||
@@ -1907,13 +1916,19 @@ class ScannerConfiguration {
   /// and https://github.com/dart-lang/language/issues/60
   final bool enableTripleShift;
 
+  /// Experimental flag for enabling variance.
+  /// See https://github.com/dart-lang/language/issues/524
+  final bool enableVariance;
+
   const ScannerConfiguration({
     bool enableExtensionMethods,
     bool enableNonNullable,
     bool enableTripleShift,
+    bool enableVariance,
   })  : this.enableExtensionMethods = enableExtensionMethods ?? false,
         this.enableNonNullable = enableNonNullable ?? false,
-        this.enableTripleShift = enableTripleShift ?? false;
+        this.enableTripleShift = enableTripleShift ?? false,
+        this.enableVariance = enableVariance ?? false;
 }
 
 bool _isIdentifierChar(int next, bool allowDollar) {

pkg/front_end/lib/src/scanner/token.dart

@@ -209,6 +209,8 @@ class Keyword extends TokenType {
 
   static const Keyword IN = const Keyword("in", "IN");
 
+  static const Keyword INOUT = const Keyword("inout", "INOUT", isPseudo: true);
+
   static const Keyword INTERFACE =
       const Keyword("interface", "INTERFACE", isBuiltIn: true);
 
@@ -237,6 +239,8 @@ class Keyword extends TokenType {
   static const Keyword OPERATOR =
       const Keyword("operator", "OPERATOR", isBuiltIn: true);
 
+  static const Keyword OUT = const Keyword("out", "OUT", isPseudo: true);
+
   static const Keyword PART =
       const Keyword("part", "PART", isBuiltIn: true, isTopLevelKeyword: true);
 
@@ -321,6 +325,7 @@ class Keyword extends TokenType {
     IMPLEMENTS,
     IMPORT,
     IN,
+    INOUT,
     INTERFACE,
     IS,
     LATE,
@@ -332,6 +337,7 @@ class Keyword extends TokenType {
     OF,
     ON,
     OPERATOR,
+    OUT,
     PART,
     PATCH,
     REQUIRED,

pkg/front_end/test/scanner_test.dart

@@ -544,6 +544,16 @@ abstract class ScannerTestBase {
     _assertKeywordToken("in");
   }
 
+  void test_keyword_inout() {
+    _assertKeywordToken("inout",
+        configuration: ScannerConfiguration(enableVariance: true));
+  }
+
+  void test_keyword_inout_old() {
+    _assertNotKeywordToken("inout",
+        configuration: ScannerConfiguration(enableVariance: false));
+  }
+
   void test_keyword_is() {
     _assertKeywordToken("is");
   }
@@ -590,6 +600,16 @@ abstract class ScannerTestBase {
     _assertKeywordToken("operator");
   }
 
+  void test_keyword_out() {
+    _assertKeywordToken("out",
+        configuration: ScannerConfiguration(enableVariance: true));
+  }
+
+  void test_keyword_out_old() {
+    _assertNotKeywordToken("out",
+        configuration: ScannerConfiguration(enableVariance: false));
+  }
+
   void test_keyword_part() {
     _assertKeywordToken("part");
   }

pkg/front_end/test/spell_checking_list_common.txt

@@ -1354,6 +1354,7 @@ inlined
 inlining
 inner
 innermost
+inout
 input
 inputs
 insert

pkg/front_end/test/token_test.dart

@@ -171,9 +171,11 @@ class Foo {
       Keyword.AWAIT,
       Keyword.FUNCTION,
       Keyword.HIDE,
+      Keyword.INOUT,
       Keyword.NATIVE,
       Keyword.OF,
       Keyword.ON,
+      Keyword.OUT,
       Keyword.PATCH,
       Keyword.SHOW,
       Keyword.SOURCE,