Merge pull request #2219 from DougGregor/typed-throws

Typed throws

Author: DougGregor

CodeGeneration/Sources/SyntaxSupport/Child.swift

@@ -82,6 +82,10 @@ public class Child {
   /// Whether this child is optional and can be `nil`.
   public let isOptional: Bool
 
+  /// The experimental feature the child represents, or `nil` if this isn't
+  /// for an experimental feature.
+  public let experimentalFeature: ExperimentalFeature?
+
   /// A name of this child that can be shown in diagnostics.
   ///
   /// This is used to e.g. describe the child if all of its tokens are missing in the source file.
@@ -110,6 +114,10 @@ public class Child {
   /// The first line of the child's documentation
   public let documentationAbstract: String
 
+  /// If `true`, this is for an experimental language feature, and any public
+  /// API generated should be SPI.
+  public var isExperimental: Bool { experimentalFeature != nil }
+
   public var syntaxNodeKind: SyntaxNodeKind {
     switch kind {
     case .node(kind: let kind):
@@ -218,6 +226,15 @@ public class Child {
     }
   }
 
+  /// The attributes that should be printed on any API for the this child.
+  ///
+  /// This is typically used to mark APIs as SPI when the keyword is part of
+  /// an experimental language feature.
+  public var apiAttributes: AttributeListSyntax {
+    guard isExperimental else { return "" }
+    return AttributeListSyntax("@_spi(ExperimentalLanguageFeatures)").with(\.trailingTrivia, .newline)
+  }
+
   /// If a classification is passed, it specifies the color identifiers in
   /// that subtree should inherit for syntax coloring. Must be a member of
   /// ``SyntaxClassification``.
@@ -227,6 +244,7 @@ public class Child {
     name: String,
     deprecatedName: String? = nil,
     kind: ChildKind,
+    experimentalFeature: ExperimentalFeature? = nil,
     nameForDiagnostics: String? = nil,
     documentation: String? = nil,
     isOptional: Bool = false
@@ -236,6 +254,7 @@ public class Child {
     self.name = name
     self.deprecatedName = deprecatedName
     self.kind = kind
+    self.experimentalFeature = experimentalFeature
     self.nameForDiagnostics = nameForDiagnostics
     self.documentationSummary = SwiftSyntax.Trivia.docCommentTrivia(from: documentation)
     self.documentationAbstract = String(documentation?.split(whereSeparator: \.isNewline).first ?? "")

CodeGeneration/Sources/SyntaxSupport/CommonNodes.swift

@@ -79,6 +79,34 @@ public let COMMON_NODES: [Node] = [
     ]
   ),
 
+  Node(
+    kind: .thrownTypeClause,
+    base: .syntax,
+    nameForDiagnostics: "thrown type clause",
+    documentation: "The specific error type that a function can throw.",
+    traits: [
+      "Parenthesized"
+    ],
+    children: [
+      Child(
+        name: "leftParen",
+        kind: .token(choices: [.token(.leftParen)]),
+        documentation: "The '(' to open the thrown type clause."
+      ),
+      Child(
+        name: "type",
+        kind: .node(kind: .type),
+        nameForDiagnostics: "thrown type",
+        documentation: "The thrown error type."
+      ),
+      Child(
+        name: "rightParen",
+        kind: .token(choices: [.token(.rightParen)]),
+        documentation: "The ')' to closure the thrown type clause."
+      ),
+    ]
+  ),
+
   Node(
     kind: .accessorEffectSpecifiers,
     base: .syntax,
@@ -99,6 +127,13 @@ public let COMMON_NODES: [Node] = [
         documentation: "The `throws` keyword.",
         isOptional: true
       ),
+      Child(
+        name: "thrownError",
+        kind: .node(kind: .thrownTypeClause),
+        experimentalFeature: .typedThrows,
+        documentation: "The specific error type thrown by this accessor.",
+        isOptional: true
+      ),
     ]
   ),
 
@@ -122,6 +157,13 @@ public let COMMON_NODES: [Node] = [
         documentation: "The `throws` or `rethrows` keyword.",
         isOptional: true
       ),
+      Child(
+        name: "thrownError",
+        kind: .node(kind: .thrownTypeClause),
+        experimentalFeature: .typedThrows,
+        documentation: "The specific error type thrown by this function.",
+        isOptional: true
+      ),
     ]
   ),
 
@@ -324,6 +366,13 @@ public let COMMON_NODES: [Node] = [
         kind: .token(choices: [.keyword(.throws)]),
         isOptional: true
       ),
+      Child(
+        name: "thrownError",
+        kind: .node(kind: .thrownTypeClause),
+        experimentalFeature: .typedThrows,
+        documentation: "The specific error type thrown by this function type.",
+        isOptional: true
+      ),
     ]
   ),
 

CodeGeneration/Sources/SyntaxSupport/ExperimentalFeatures.swift

@@ -15,6 +15,7 @@ import SwiftSyntax
 public enum ExperimentalFeature: String, CaseIterable {
   case referenceBindings
   case thenStatements
+  case typedThrows
 
   /// The name of the feature, which is used in the doc comment.
   public var featureName: String {
@@ -23,6 +24,8 @@ public enum ExperimentalFeature: String, CaseIterable {
       return "reference bindings"
     case .thenStatements:
       return "'then' statements"
+    case .typedThrows:
+      return "typed throws"
     }
   }
 

CodeGeneration/Sources/SyntaxSupport/SyntaxNodeKind.swift

@@ -268,6 +268,7 @@ public enum SyntaxNodeKind: String, CaseIterable {
   case switchExpr
   case ternaryExpr
   case thenStmt
+  case thrownTypeClause
   case throwStmt
   case tryExpr
   case tupleExpr

CodeGeneration/Sources/SyntaxSupport/Traits.swift

@@ -56,7 +56,15 @@ public let TRAITS: [Trait] = [
       Child(name: "asyncSpecifier", kind: .token(choices: [.keyword(.async), .keyword(.reasync)]), isOptional: true),
       Child(name: "unexpectedBetweenAsyncSpecifierAndThrowsSpecifier", kind: .node(kind: .unexpectedNodes), isOptional: true),
       Child(name: "throwsSpecifier", kind: .token(choices: [.keyword(.throws), .keyword(.rethrows)]), isOptional: true),
-      Child(name: "unexpectedAfterThrowsSpecifier", kind: .node(kind: .unexpectedNodes), isOptional: true),
+      Child(name: "unexpectedBetweenThrowsSpecifierAndThrownError", kind: .node(kind: .unexpectedNodes), isOptional: true),
+      Child(
+        name: "thrownError",
+        kind: .node(kind: .thrownTypeClause),
+        experimentalFeature: .typedThrows,
+        documentation: "The specific thrown error type.",
+        isOptional: true
+      ),
+      Child(name: "unexpectedAfterThrownError", kind: .node(kind: .unexpectedNodes), isOptional: true),
     ]
   ),
   Trait(

CodeGeneration/Sources/generate-swift-syntax/templates/swiftsyntax/SyntaxNodesFile.swift

@@ -138,7 +138,7 @@ func syntaxNode(nodesStartingWith: [Character]) -> SourceFileSyntax {
           try! VariableDeclSyntax(
             """
             \(child.documentation)
-            public var \(child.varOrCaseName.backtickedIfNeeded): \(type)
+            \(child.apiAttributes)public var \(child.varOrCaseName.backtickedIfNeeded): \(type)
             """
           ) {
             AccessorDeclSyntax(accessorSpecifier: .keyword(.get)) {

CodeGeneration/Sources/generate-swift-syntax/templates/swiftsyntax/SyntaxTraitsFile.swift

@@ -31,7 +31,7 @@ let syntaxTraitsFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
         DeclSyntax(
           """
           \(child.documentation)
-          var \(child.varOrCaseName): \(child.syntaxNodeKind.syntaxType)\(questionMark) { get set }
+          \(child.apiAttributes)var \(child.varOrCaseName): \(child.syntaxNodeKind.syntaxType)\(questionMark) { get set }
           """
         )
       }

Release Notes/510.md

@@ -50,6 +50,9 @@
 
 ## API-Incompatible Changes
 
+- Effect specifiers:
+  - Description: The `unexpectedAfterThrowsSpecifier` node of the various effect specifiers has been removed.
+  - Pull request: https://github.com/apple/swift-syntax/pull/2219
 
 ## Template
 

Sources/SwiftParser/Specifiers.swift

@@ -128,6 +128,13 @@ public enum EffectSpecifier: TokenSpecSet {
     case .throwsSpecifier(let underlyingKind): return underlyingKind.spec
     }
   }
+
+  var isThrowsSpecifier: Bool {
+    switch self {
+    case .asyncSpecifier: return false
+    case .throwsSpecifier: return true
+    }
+  }
 }
 
 // MARK: - EffectSpecifiersTrait
@@ -153,10 +160,12 @@ protocol RawMisplacedEffectSpecifiersTrait {
 
   var asyncSpecifier: RawTokenSyntax? { get }
   var throwsSpecifier: RawTokenSyntax? { get }
+  var thrownError: RawThrownTypeClauseSyntax? { get }
 
   init(
     asyncSpecifier: RawTokenSyntax?,
     throwsSpecifier: RawTokenSyntax?,
+    thrownError: RawThrownTypeClauseSyntax?,
     arena: __shared SyntaxArena
   )
 
@@ -166,14 +175,17 @@ protocol RawMisplacedEffectSpecifiersTrait {
 protocol RawEffectSpecifiersTrait: RawMisplacedEffectSpecifiersTrait {
   var unexpectedBeforeAsyncSpecifier: RawUnexpectedNodesSyntax? { get }
   var unexpectedBetweenAsyncSpecifierAndThrowsSpecifier: RawUnexpectedNodesSyntax? { get }
-  var unexpectedAfterThrowsSpecifier: RawUnexpectedNodesSyntax? { get }
-
+  var unexpectedBetweenThrowsSpecifierAndThrownError: RawUnexpectedNodesSyntax? { get }
+  var thrownError: RawThrownTypeClauseSyntax? { get }
+  var unexpectedAfterThrownError: RawUnexpectedNodesSyntax? { get }
   init(
     _ unexpectedBeforeAsyncSpecifier: RawUnexpectedNodesSyntax?,
     asyncSpecifier: RawTokenSyntax?,
     _ unexpectedBetweenAsyncSpecifierAndThrowsSpecifier: RawUnexpectedNodesSyntax?,
     throwsSpecifier: RawTokenSyntax?,
-    _ unexpectedAfterThrowsSpecifier: RawUnexpectedNodesSyntax?,
+    _ unexpectedBetweenThrowsSpecifierAndThrownError: RawUnexpectedNodesSyntax?,
+    thrownError: RawThrownTypeClauseSyntax?,
+    _ unexpectedAfterThrownError: RawUnexpectedNodesSyntax?,
     arena: __shared SyntaxArena
   )
 }
@@ -182,6 +194,7 @@ extension RawEffectSpecifiersTrait {
   init(
     asyncSpecifier: RawTokenSyntax?,
     throwsSpecifier: RawTokenSyntax?,
+    thrownError: RawThrownTypeClauseSyntax?,
     arena: __shared SyntaxArena
   ) {
     self.init(
@@ -190,6 +203,8 @@ extension RawEffectSpecifiersTrait {
       nil,
       throwsSpecifier: throwsSpecifier,
       nil,
+      thrownError: thrownError,
+      nil,
       arena: arena
     )
   }
@@ -200,7 +215,9 @@ extension RawEffectSpecifiersTrait {
       asyncSpecifier: self.asyncSpecifier ?? misplacedAsyncKeyword,
       self.unexpectedBetweenAsyncSpecifierAndThrowsSpecifier,
       throwsSpecifier: self.throwsSpecifier ?? misplacedThrowsKeyword,
-      self.unexpectedAfterThrowsSpecifier,
+      self.unexpectedBetweenThrowsSpecifierAndThrownError,
+      thrownError: thrownError,
+      self.unexpectedAfterThrownError,
       arena: arena
     )
   }
@@ -521,10 +538,12 @@ extension RawDeinitializerEffectSpecifiersSyntax: RawMisplacedEffectSpecifiersTr
   }
 
   var throwsSpecifier: RawTokenSyntax? { nil }
+  var thrownError: RawThrownTypeClauseSyntax? { nil }
 
   init(
     asyncSpecifier: RawTokenSyntax?,
     throwsSpecifier: RawTokenSyntax?,
+    thrownError: RawThrownTypeClauseSyntax?,
     arena: __shared SwiftSyntax.SyntaxArena
   ) {
     // `throwsSpecifier` should never be present because `parseMisplacedEffectSpecifiers()` only creates missing tokens
@@ -577,12 +596,28 @@ extension TokenConsumer {
 // MARK: - Parsing effect specifiers
 
 extension Parser {
+  private mutating func parseThrownTypeClause() -> RawThrownTypeClauseSyntax {
+    let (unexpectedBeforeLeftParen, leftParen) = self.expect(.leftParen)
+    let type = self.parseType()
+    let (unexpectedBeforeRightParen, rightParen) = self.expect(.rightParen)
+    return RawThrownTypeClauseSyntax(
+      unexpectedBeforeLeftParen,
+      leftParen: leftParen,
+      type: type,
+      unexpectedBeforeRightParen,
+      rightParen: rightParen,
+      arena: self.arena
+    )
+  }
+
   private mutating func parseEffectSpecifiers<S: RawEffectSpecifiersTrait>(_: S.Type) -> S? {
     var unexpectedBeforeAsync: [RawSyntax] = []
     var asyncKeyword: RawTokenSyntax? = nil
     var unexpectedBeforeThrows: [RawSyntax] = []
     var throwsKeyword: RawTokenSyntax?
-    var unexpectedAfterThrows: [RawSyntax] = []
+    var thrownError: RawThrownTypeClauseSyntax?
+    var unexpectedAfterThrownError: [RawSyntax] = []
+
     while let misspelledAsync = self.consume(ifAnyIn: S.MisspelledAsyncTokenKinds.self) {
       unexpectedBeforeAsync.append(RawSyntax(misspelledAsync))
       if asyncKeyword == nil {
@@ -617,26 +652,32 @@ extension Parser {
       let (unexpected, throwsKw) = self.eat(handle)
       unexpectedBeforeThrows.append(contentsOf: unexpected?.elements ?? [])
       throwsKeyword = throwsKw
+
+      if self.at(.leftParen) && experimentalFeatures.contains(.typedThrows) {
+        thrownError = parseThrownTypeClause()
+      }
     }
 
-    var unexpectedAfterThrowsLoopProgress = LoopProgressCondition()
-    while self.hasProgressed(&unexpectedAfterThrowsLoopProgress) {
+    var unexpectedAfterThrownErrorLoopProgress = LoopProgressCondition()
+    while self.hasProgressed(&unexpectedAfterThrownErrorLoopProgress) {
       if let (_, handle, _) = self.at(anyIn: S.MisspelledAsyncTokenKinds.self, or: S.CorrectAsyncTokenKinds.self) {
         let misspelledAsync = self.eat(handle)
-        unexpectedAfterThrows.append(RawSyntax(misspelledAsync))
+        unexpectedAfterThrownError.append(RawSyntax(misspelledAsync))
         if asyncKeyword == nil {
           // Handle `async` after `throws`
           asyncKeyword = missingToken(.keyword(.async))
         }
       } else if let (_, handle, _) = self.at(anyIn: S.MisspelledThrowsTokenKinds.self, or: S.CorrectThrowsTokenKinds.self) {
         let misspelledThrows = self.eat(handle)
-        unexpectedAfterThrows.append(RawSyntax(misspelledThrows))
+        unexpectedAfterThrownError.append(RawSyntax(misspelledThrows))
       } else {
         break
       }
     }
 
-    if unexpectedBeforeAsync.isEmpty && asyncKeyword == nil && unexpectedBeforeThrows.isEmpty && throwsKeyword == nil && unexpectedAfterThrows.isEmpty {
+    if unexpectedBeforeAsync.isEmpty && asyncKeyword == nil && unexpectedBeforeThrows.isEmpty && throwsKeyword == nil && thrownError == nil
+      && unexpectedAfterThrownError.isEmpty
+    {
       return nil
     }
 
@@ -645,7 +686,9 @@ extension Parser {
       asyncSpecifier: asyncKeyword,
       RawUnexpectedNodesSyntax(unexpectedBeforeThrows, arena: self.arena),
       throwsSpecifier: throwsKeyword,
-      RawUnexpectedNodesSyntax(unexpectedAfterThrows, arena: self.arena),
+      nil,
+      thrownError: thrownError,
+      RawUnexpectedNodesSyntax(unexpectedAfterThrownError, arena: self.arena),
       arena: self.arena
     )
   }
@@ -749,6 +792,7 @@ extension Parser {
         effectSpecifiers = S(
           asyncSpecifier: synthesizedAsync,
           throwsSpecifier: synthesizedThrows,
+          thrownError: nil,
           arena: self.arena
         )
       }

Sources/SwiftParser/Types.swift

@@ -800,11 +800,18 @@ extension Parser.Lookahead {
       return true
     }
 
-    if self.at(anyIn: EffectSpecifier.self) != nil {
+    if let effect = self.at(anyIn: EffectSpecifier.self) {
       if self.peek().rawTokenKind == .arrow {
         return true
       }
 
+      if effect.spec.isThrowsSpecifier && self.peek().rawTokenKind == .leftParen {
+        var backtrack = self.lookahead()
+        backtrack.consumeAnyToken()
+        backtrack.skipSingle()
+        return backtrack.atFunctionTypeArrow()
+      }
+
       if peek(isAtAnyIn: EffectSpecifier.self) != nil {
         var backtrack = self.lookahead()
         backtrack.consumeAnyToken()