Merge pull request #21926 from nkcsgexi/dot-self-optional-base

SyntaxNodes: DotSelfExpr should have optional base expression.

Author: nkcsgexi

test/Syntax/Outputs/round_trip_parse_gen.swift.withkinds

@@ -532,7 +532,7 @@ struct S <TypeInheritanceClause>: <InheritedType><SimpleTypeIdentifier>Q</Simple
   @_implements(<ImplementsAttributeArguments><SimpleTypeIdentifier>P</SimpleTypeIdentifier>, x</ImplementsAttributeArguments>)</Attribute>
   var <PatternBinding><IdentifierPattern>y</IdentifierPattern><TypeAnnotation>: <SimpleTypeIdentifier>String</SimpleTypeIdentifier></TypeAnnotation></PatternBinding></VariableDecl></MemberDeclListItem><MemberDeclListItem><FunctionDecl><Attribute>
   @_implements(<ImplementsAttributeArguments><SimpleTypeIdentifier>P</SimpleTypeIdentifier>, g<DeclNameArguments>()</DeclNameArguments></ImplementsAttributeArguments>)</Attribute>
-  func h<FunctionSignature><ParameterClause>() </ParameterClause></FunctionSignature><CodeBlock>{}</CodeBlock></FunctionDecl></MemberDeclListItem><MemberDeclListItem><VariableDecl><Attribute>
+  func h<FunctionSignature><ParameterClause>() </ParameterClause></FunctionSignature><CodeBlock>{ <SequenceExpr><DiscardAssignmentExpr>_ </DiscardAssignmentExpr><AssignmentExpr>= </AssignmentExpr><KeyPathExpr>\<DotSelfExpr>.self </DotSelfExpr></KeyPathExpr></SequenceExpr>}</CodeBlock></FunctionDecl></MemberDeclListItem><MemberDeclListItem><VariableDecl><Attribute>
 
   @available(<AvailabilityArgument>*, </AvailabilityArgument><AvailabilityArgument><AvailabilityLabeledArgument>deprecated: <VersionTuple>1.2</VersionTuple></AvailabilityLabeledArgument>, </AvailabilityArgument><AvailabilityArgument><AvailabilityLabeledArgument>message: "ABC"</AvailabilityLabeledArgument></AvailabilityArgument>)</Attribute><DeclModifier>
   fileprivate(set) </DeclModifier>var <PatternBinding><IdentifierPattern>x</IdentifierPattern><TypeAnnotation>: <SimpleTypeIdentifier>String</SimpleTypeIdentifier></TypeAnnotation></PatternBinding></VariableDecl></MemberDeclListItem>

test/Syntax/round_trip_parse_gen.swift

@@ -532,7 +532,7 @@ struct S : Q, Equatable {
   @_implements(P, x)
   var y: String
   @_implements(P, g())
-  func h() {}
+  func h() { _ = \.self }
 
   @available(*, deprecated: 1.2, message: "ABC")
   fileprivate(set) var x: String

utils/gyb_syntax_support/ExprNodes.py

@@ -309,10 +309,10 @@
                    is_optional=True),
          ]),
 
-    # dot-self-expr -> expr '.' 'self'
+    # dot-self-expr -> expr? '.' 'self'
     Node('DotSelfExpr', kind='Expr',
          children=[
-             Child('Expression', kind='Expr'),
+             Child('Expression', kind='Expr', is_optional=True),
              Child('Dot', kind='Token',
                    token_choices=[
                        'PeriodToken', 'PrefixPeriodToken'