[NFC] Add module selector syntax nodes/children

Changes the syntax tree to represent module selectors:

• A `ModuleSelectorSyntax` node represents a module selector abstractly.
• The following nodes now have an optional `moduleSelector` child:
    • `DeclReferenceExprSyntax`
    • `IdentifierTypeSyntax`
    • `MacroExpansionExprSyntax`
    • `MemberTypeSyntax`
• BasicFormat knows the preferred format for module selectors.

Other components, particularly the parser, were also updated to continue building, though without any changes in behavior. Parser implementation will come in a future commit.

Author: beccadax

CodeGeneration/Sources/SyntaxSupport/CommonNodes.swift

@@ -330,6 +330,25 @@ public let COMMON_NODES: [Node] = [
     ]
   ),
 
+  Node(
+    kind: .moduleSelector,
+    base: .syntax,
+    experimentalFeature: .moduleSelector,
+    nameForDiagnostics: "module selector",
+    children: [
+      Child(
+        name: "moduleName",
+        kind: .token(choices: [.token(.identifier)]),
+        nameForDiagnostics: "module name"
+      ),
+      Child(
+        name: "colonColon",
+        kind: .token(choices: [.token(.colonColon)]),
+        nameForDiagnostics: "'::' operator"
+      ),
+    ]
+  ),
+
   Node(
     kind: .pattern,
     base: .syntax,

CodeGeneration/Sources/SyntaxSupport/DeclNodes.swift

@@ -1554,6 +1554,12 @@ public let DECL_NODES: [Node] = [
         kind: .token(choices: [.token(.pound)]),
         documentation: "The `#` sign."
       ),
+      Child(
+        name: "moduleSelector",
+        kind: .node(kind: .moduleSelector),
+        experimentalFeature: .moduleSelector,
+        isOptional: true
+      ),
       Child(
         name: "macroName",
         kind: .token(choices: [.token(.identifier)])

CodeGeneration/Sources/SyntaxSupport/ExprNodes.swift

@@ -1002,6 +1002,12 @@ public let EXPR_NODES: [Node] = [
     base: .expr,
     nameForDiagnostics: nil,
     children: [
+      Child(
+        name: "moduleSelector",
+        kind: .node(kind: .moduleSelector),
+        experimentalFeature: .moduleSelector,
+        isOptional: true
+      ),
       Child(
         name: "baseName",
         kind: .token(choices: [
@@ -1358,6 +1364,12 @@ public let EXPR_NODES: [Node] = [
         kind: .token(choices: [.token(.pound)]),
         documentation: "The `#` sign."
       ),
+      Child(
+        name: "moduleSelector",
+        kind: .node(kind: .moduleSelector),
+        experimentalFeature: .moduleSelector,
+        isOptional: true
+      ),
       Child(
         name: "macroName",
         kind: .token(choices: [.token(.identifier)])

CodeGeneration/Sources/SyntaxSupport/SyntaxNodeKind.swift

@@ -206,6 +206,7 @@ public enum SyntaxNodeKind: String, CaseIterable, IdentifierConvertible, TypeCon
   case missingPattern
   case missingStmt
   case missingType
+  case moduleSelector
   case multipleTrailingClosureElement
   case multipleTrailingClosureElementList
   case namedOpaqueReturnType

CodeGeneration/Sources/SyntaxSupport/Traits.swift

@@ -92,6 +92,12 @@ public let TRAITS: [Trait] = [
     traitName: "FreestandingMacroExpansion",
     children: [
       Child(name: "pound", kind: .token(choices: [.token(.pound)])),
+      Child(
+        name: "moduleSelector",
+        kind: .node(kind: .moduleSelector),
+        experimentalFeature: .moduleSelector,
+        isOptional: true
+      ),
       Child(name: "macroName", kind: .token(choices: [.token(.identifier)])),
       Child(name: "genericArgumentClause", kind: .node(kind: .genericArgumentClause), isOptional: true),
       Child(name: "leftParen", kind: .token(choices: [.token(.leftParen)]), isOptional: true),

CodeGeneration/Sources/SyntaxSupport/TypeNodes.swift

@@ -365,6 +365,13 @@ public let TYPE_NODES: [Node] = [
         name: "period",
         kind: .token(choices: [.token(.period)])
       ),
+      Child(
+        name: "moduleSelector",
+        kind: .node(kind: .moduleSelector),
+        experimentalFeature: .moduleSelector,
+        nameForDiagnostics: "module selector",
+        isOptional: true
+      ),
       Child(
         name: "name",
         kind: .token(choices: [.token(.identifier), .keyword(.self)]),
@@ -511,6 +518,13 @@ public let TYPE_NODES: [Node] = [
     base: .type,
     nameForDiagnostics: "type",
     children: [
+      Child(
+        name: "moduleSelector",
+        kind: .node(kind: .moduleSelector),
+        experimentalFeature: .moduleSelector,
+        nameForDiagnostics: "module selector",
+        isOptional: true
+      ),
       Child(
         name: "name",
         kind: .token(choices: [

Sources/SwiftBasicFormat/BasicFormat.swift

@@ -308,10 +308,12 @@ open class BasicFormat: SyntaxRewriter {
     case (.atSign, _),
       (.backslash, _),
       (.backtick, _),
+      (.colonColon, .identifier),
       (.dollarIdentifier, .period),  // a.b
       (.endOfFile, _),
       (.exclamationMark, .period),  // myOptionalBar!.foo()
       (.regexPoundDelimiter, .regexSlash),  // opening extended regex delimiter should never be separate by a space
+      (.identifier, .colonColon),
       (.identifier, .leftAngle),  // MyType<Int>
       (.identifier, .leftSquare),  // myArray[1]
       (.identifier, .period),  // a.b

Sources/SwiftParser/Attributes.swift

@@ -325,7 +325,12 @@ extension Parser {
         unexpectedBeforeAtSign,
         atSign: atSign,
         unexpectedBeforeAttributeName,
-        attributeName: RawIdentifierTypeSyntax(name: attributeName, genericArgumentClause: nil, arena: self.arena),
+        attributeName: RawIdentifierTypeSyntax(
+          moduleSelector: nil,
+          name: attributeName,
+          genericArgumentClause: nil,
+          arena: self.arena
+        ),
         leftParen: nil,
         arguments: nil,
         rightParen: nil,
@@ -349,7 +354,9 @@ extension Parser {
 
 extension RawLabeledExprSyntax {
   fileprivate init(
-    _ unexpectedBeforeIdentifier: RawUnexpectedNodesSyntax? = nil,
+    _ unexpectedBeforeModuleSelector: RawUnexpectedNodesSyntax? = nil,
+    moduleSelector: RawModuleSelectorSyntax?,
+    _ unexpectedBetweenModuleSelectorAndIdentifier: RawUnexpectedNodesSyntax? = nil,
     identifier: RawTokenSyntax,
     _ unexpectedBetweenIdentifierAndTrailingComma: RawUnexpectedNodesSyntax? = nil,
     trailingComma: RawTokenSyntax? = nil,
@@ -359,7 +366,9 @@ extension RawLabeledExprSyntax {
       label: nil,
       colon: nil,
       expression: RawDeclReferenceExprSyntax(
-        unexpectedBeforeIdentifier,
+        unexpectedBeforeModuleSelector,
+        moduleSelector: moduleSelector,
+        unexpectedBetweenModuleSelectorAndIdentifier,
         baseName: identifier,
         argumentNames: nil,
         arena: arena
@@ -381,6 +390,7 @@ extension Parser {
     let roleTrailingComma = self.consume(if: .comma)
 
     let roleElement = RawLabeledExprSyntax(
+      moduleSelector: nil,
       unexpectedBeforeRole,
       identifier: role,
       trailingComma: roleTrailingComma,
@@ -410,7 +420,12 @@ extension Parser {
       unexpectedBeforeAtSign,
       atSign: atSign,
       unexpectedBeforeDifferentiable,
-      attributeName: RawIdentifierTypeSyntax(name: differentiable, genericArgumentClause: nil, arena: self.arena),
+      attributeName: RawIdentifierTypeSyntax(
+        moduleSelector: nil,
+        name: differentiable,
+        genericArgumentClause: nil,
+        arena: self.arena
+      ),
       unexpectedBeforeLeftParen,
       leftParen: leftParen,
       arguments: .differentiableArguments(argument),
@@ -551,8 +566,13 @@ extension Parser {
     return RawAttributeSyntax(
       unexpectedBeforeAtSign,
       atSign: atSign,
-      unexpectedBeforeDerivative,
-      attributeName: RawIdentifierTypeSyntax(name: derivative, genericArgumentClause: nil, arena: self.arena),
+      attributeName: RawIdentifierTypeSyntax(
+        moduleSelector: nil,
+        unexpectedBeforeDerivative,
+        name: derivative,
+        genericArgumentClause: nil,
+        arena: self.arena
+      ),
       unexpectedBeforeLeftParen,
       leftParen: leftParen,
       arguments: .derivativeRegistrationArguments(argument),
@@ -574,7 +594,12 @@ extension Parser {
       unexpectedBeforeAtSign,
       atSign: atSign,
       unexpectedBeforeTranspose,
-      attributeName: RawIdentifierTypeSyntax(name: transpose, genericArgumentClause: nil, arena: self.arena),
+      attributeName: RawIdentifierTypeSyntax(
+        moduleSelector: nil,
+        name: transpose,
+        genericArgumentClause: nil,
+        arena: self.arena
+      ),
       unexpectedBeforeLeftParen,
       leftParen: leftParen,
       arguments: .derivativeRegistrationArguments(argument),
@@ -809,6 +834,7 @@ extension Parser {
     let (unexpectedBeforeIsolationKind, isolationKind) =
       self.expectIdentifier(allowKeywordsAsIdentifier: true)
     let isolationKindElement = RawLabeledExprSyntax(
+      moduleSelector: nil,
       unexpectedBeforeIsolationKind,
       identifier: isolationKind,
       arena: self.arena
@@ -939,6 +965,7 @@ extension Parser {
     let declName: RawDeclReferenceExprSyntax
     if label.isMissing && colon.isMissing && self.atStartOfLine {
       declName = RawDeclReferenceExprSyntax(
+        moduleSelector: nil,
         baseName: RawTokenSyntax(missing: .identifier, arena: self.arena),
         argumentNames: nil,
         arena: self.arena

Sources/SwiftParser/Declarations.swift

@@ -610,6 +610,7 @@ extension Parser {
             unexpectedBeforeInherited = RawUnexpectedNodesSyntax([classKeyword], arena: self.arena)
             inherited = RawTypeSyntax(
               RawIdentifierTypeSyntax(
+                moduleSelector: nil,
                 name: missingToken(.identifier, text: "AnyObject"),
                 genericArgumentClause: nil,
                 arena: self.arena
@@ -2246,6 +2247,7 @@ extension Parser {
       modifiers: attrs.modifiers,
       unexpectedBeforePound,
       pound: pound,
+      moduleSelector: nil,
       unexpectedBeforeMacro,
       macroName: macro,
       genericArgumentClause: generics,

Sources/SwiftParser/Expressions.swift

@@ -652,6 +652,7 @@ extension Parser {
     if skipMemberName {
       let missingIdentifier = missingToken(.identifier)
       let declName = RawDeclReferenceExprSyntax(
+        moduleSelector: nil,
         baseName: missingIdentifier,
         argumentNames: nil,
         arena: self.arena
@@ -664,6 +665,7 @@ extension Parser {
     if let indexOrSelf = self.consume(if: .integerLiteral, .keyword(.self)) {
       // Handle "x.42" - a tuple index.
       declName = RawDeclReferenceExprSyntax(
+        moduleSelector: nil,
         baseName: indexOrSelf,
         argumentNames: nil,
         arena: self.arena
@@ -1276,6 +1278,7 @@ extension Parser {
       let poundAvailable = self.parsePoundAvailableConditionElement()
       return RawExprSyntax(
         RawDeclReferenceExprSyntax(
+          moduleSelector: nil,
           RawUnexpectedNodesSyntax([poundAvailable], arena: self.arena),
           baseName: missingToken(.identifier),
           argumentNames: nil,
@@ -1429,6 +1432,7 @@ extension Parser {
     return RawMacroExpansionExprSyntax(
       unexpectedBeforePound,
       pound: pound,
+      moduleSelector: nil,
       unexpectedBeforeMacroName,
       macroName: macroName,
       genericArgumentClause: generics,
@@ -1743,6 +1747,7 @@ extension Parser {
   mutating func parseAnonymousClosureArgument() -> RawDeclReferenceExprSyntax {
     let (unexpectedBeforeBaseName, baseName) = self.expect(.dollarIdentifier)
     return RawDeclReferenceExprSyntax(
+      moduleSelector: nil,
       unexpectedBeforeBaseName,
       baseName: baseName,
       argumentNames: nil,
@@ -2396,7 +2401,12 @@ extension Parser {
       unknownAttr = RawAttributeSyntax(
         atSign: at,
         unexpectedBeforeIdent,
-        attributeName: RawIdentifierTypeSyntax(name: ident, genericArgumentClause: nil, arena: self.arena),
+        attributeName: RawIdentifierTypeSyntax(
+          moduleSelector: nil,
+          name: ident,
+          genericArgumentClause: nil,
+          arena: self.arena
+        ),
         leftParen: nil,
         arguments: nil,
         rightParen: nil,