Support construction of DeclSyntax subtypes from string interpolation

Allow the creation of e.g. an `ExtensionDeclSyntax` as

```swift
let extension = try ExtensionDeclSyntax("extension Foo: Proto {}")
```

The initializer throws if the string describes a declaration other than an 'extension'. If the string can get parsed as an extension but contains syntax errors, we return a node that contains syntax errors. This matches the behavior of the `HasTrailingCodeBlock` intializers that take a header + result builder.

Author: ahoppen

Sources/SwiftSyntaxBuilder/CMakeLists.txt

@@ -8,6 +8,7 @@
 
 add_swift_host_library(SwiftSyntaxBuilder
   ConvenienceInitializers.swift
+  DeclSyntaxParseable.swift
   Indenter.swift
   ResultBuilderExtensions.swift
   SwiftSyntaxBuilderCompatibility.swift

Sources/SwiftSyntaxBuilder/DeclSyntaxParseable.swift

@@ -0,0 +1,57 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftSyntax
+
+/// Adds an initializer that allows the creation of declaration from string
+/// interpolations.
+///
+/// - Warning: This protocol is considered an implementation detail. Do not rely
+///   on it, only the initializer that it adds.
+public protocol DeclSyntaxParseable: DeclSyntaxProtocol {}
+public extension DeclSyntaxParseable {
+  /// Create a syntax node from the given string interpolation.
+  ///
+  /// This initializer throws if the syntax node was not able to be parsed as
+  /// this type, e.g. when calling `ClassDeclSyntax("actor Foo {})`.
+  ///
+  /// If there are syntax errors in the string, the initializer will return a
+  /// node that contains errors without throwing.
+  init(_ stringInterpolation: SyntaxNodeString) throws {
+    let node: DeclSyntax = "\(stringInterpolation)"
+    if let castedDecl = node.as(Self.self) {
+      self = castedDecl
+    } else {
+      throw SyntaxStringInterpolationError.producedInvalidNodeType(expectedType: Self.self, actualNode: node)
+    }
+  }
+}
+
+// These are all the declarations that get parsed from `parseDecl`
+extension ActorDeclSyntax: DeclSyntaxParseable {}
+extension AssociatedTypeDeclSyntax: DeclSyntaxParseable {}
+extension EnumCaseDeclSyntax: DeclSyntaxParseable {}
+extension ClassDeclSyntax: DeclSyntaxParseable {}
+extension DeinitializerDeclSyntax: DeclSyntaxParseable {}
+extension EnumDeclSyntax: DeclSyntaxParseable {}
+extension ExtensionDeclSyntax: DeclSyntaxParseable {}
+extension FunctionDeclSyntax: DeclSyntaxParseable {}
+extension ImportDeclSyntax: DeclSyntaxParseable {}
+extension VariableDeclSyntax: DeclSyntaxParseable {}
+extension MacroDeclSyntax: DeclSyntaxParseable {}
+extension OperatorDeclSyntax: DeclSyntaxParseable {}
+extension MacroExpansionDeclSyntax: DeclSyntaxParseable {}
+extension PrecedenceGroupDeclSyntax: DeclSyntaxParseable {}
+extension ProtocolDeclSyntax: DeclSyntaxParseable {}
+extension StructDeclSyntax: DeclSyntaxParseable {}
+extension SubscriptDeclSyntax: DeclSyntaxParseable {}
+extension TypeAliasDeclSyntax: DeclSyntaxParseable {}

Sources/SwiftSyntaxBuilder/SyntaxNodeWithBody.swift

@@ -14,13 +14,18 @@ import SwiftSyntax
 
 // MARK: - PartialSyntaxNode
 
+@available(*, deprecated, renamed: "SyntaxNodeString")
+public typealias PartialSyntaxNodeString = SyntaxNodeString
+
 /// A type that is expressible by string interpolation the same way that syntax
 /// nodes are, but instead of producing a node, it stores the string interpolation
-/// text. Used to represent partial syntax nodes in initializers that take a
+/// text.
+///
+/// Used to represent partial syntax nodes in initializers that take a
 /// trailing code block.
 ///
 /// This type should always be constructed using string interpolation.
-public struct PartialSyntaxNodeString: SyntaxExpressibleByStringInterpolation {
+public struct SyntaxNodeString: SyntaxExpressibleByStringInterpolation {
   let sourceText: [UInt8]
 
   public init(stringInterpolation: SyntaxStringInterpolation) {
@@ -29,7 +34,7 @@ public struct PartialSyntaxNodeString: SyntaxExpressibleByStringInterpolation {
 }
 
 extension SyntaxStringInterpolation {
-  public mutating func appendInterpolation(_ value: PartialSyntaxNodeString) {
+  public mutating func appendInterpolation(_ value: SyntaxNodeString) {
     sourceText.append(contentsOf: value.sourceText)
     self.lastIndentation = nil
   }
@@ -59,11 +64,11 @@ public protocol HasTrailingCodeBlock {
   /// ```
   ///
   /// Throws an error if `header` defines a different node type than the type the initializer is called on. E.g. if calling `try IfStmtSyntax("while x < 5") {}`
-  init(_ header: PartialSyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) rethrows
+  init(_ header: SyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) rethrows
 }
 
 public extension HasTrailingCodeBlock where Self: StmtSyntaxProtocol {
-  init(_ header: PartialSyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) throws {
+  init(_ header: SyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) throws {
     let stmt = StmtSyntax("\(header) {}")
     guard let castedStmt = stmt.as(Self.self) else {
       throw SyntaxStringInterpolationError.producedInvalidNodeType(expectedType: Self.self, actualNode: stmt)
@@ -74,7 +79,7 @@ public extension HasTrailingCodeBlock where Self: StmtSyntaxProtocol {
 }
 
 extension CatchClauseSyntax: HasTrailingCodeBlock {
-  public init(_ header: PartialSyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) rethrows {
+  public init(_ header: SyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) rethrows {
     self = CatchClauseSyntax("\(header) {}")
     self.body = try CodeBlockSyntax(statements: bodyBuilder())
   }
@@ -109,11 +114,11 @@ public protocol HasTrailingOptionalCodeBlock {
   /// ```
   ///
   /// Throws an error if `header` defines a different node type than the type the initializer is called on. E.g. if calling `try FunctionDeclSyntax("init") {}`
-  init(_ header: PartialSyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) throws
+  init(_ header: SyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) throws
 }
 
 public extension HasTrailingOptionalCodeBlock where Self: DeclSyntaxProtocol {
-  init(_ header: PartialSyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) throws {
+  init(_ header: SyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax) throws {
     let decl = DeclSyntax("\(header) {}")
     guard let castedDecl = decl.as(Self.self) else {
       throw SyntaxStringInterpolationError.producedInvalidNodeType(expectedType: Self.self, actualNode: decl)
@@ -154,11 +159,11 @@ public protocol HasTrailingMemberDeclBlock {
   /// ```
   ///
   /// Throws an error if `header` defines a different node type than the type the initializer is called on. E.g. if calling `try StructDeclSyntax("class MyClass") {}`
-  init(_ header: PartialSyntaxNodeString, @MemberBlockItemListBuilder membersBuilder: () throws -> MemberBlockItemListSyntax) throws
+  init(_ header: SyntaxNodeString, @MemberBlockItemListBuilder membersBuilder: () throws -> MemberBlockItemListSyntax) throws
 }
 
 public extension HasTrailingMemberDeclBlock where Self: DeclSyntaxProtocol {
-  init(_ header: PartialSyntaxNodeString, @MemberBlockItemListBuilder membersBuilder: () throws -> MemberBlockItemListSyntax) throws {
+  init(_ header: SyntaxNodeString, @MemberBlockItemListBuilder membersBuilder: () throws -> MemberBlockItemListSyntax) throws {
     let decl = DeclSyntax("\(header) {}")
     guard let castedDecl = decl.as(Self.self) else {
       throw SyntaxStringInterpolationError.producedInvalidNodeType(expectedType: Self.self, actualNode: decl)
@@ -198,7 +203,7 @@ public extension IfExprSyntax {
   ///
   /// Throws an error if `header` does not start an `if` expression. E.g. if calling `try IfExprSyntax("while true") {}`
   init(
-    _ header: PartialSyntaxNodeString,
+    _ header: SyntaxNodeString,
     @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax,
     @CodeBlockItemListBuilder `else` elseBuilder: () throws -> CodeBlockItemListSyntax? = { nil }
   ) throws {
@@ -246,7 +251,7 @@ public extension IfExprSyntax {
   /// ```
   ///
   /// Throws an error if `header` does not start an `if` expression. E.g. if calling `try IfExprSyntax("while true", bodyBuilder: {}, elseIf: {})`
-  init(_ header: PartialSyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax, elseIf: IfExprSyntax) throws {
+  init(_ header: SyntaxNodeString, @CodeBlockItemListBuilder bodyBuilder: () throws -> CodeBlockItemListSyntax, elseIf: IfExprSyntax) throws {
     let expr = ExprSyntax("\(header) {}")
     guard let ifExpr = expr.as(Self.self) else {
       throw SyntaxStringInterpolationError.producedInvalidNodeType(expectedType: Self.self, actualNode: expr)
@@ -279,7 +284,7 @@ extension SwitchCaseSyntax {
   /// ```
   ///
   /// Throws an error if `header` does not start a switch case item. E.g. if calling `try SwitchCaseSyntax("func foo") {}`
-  public init(_ header: PartialSyntaxNodeString, @CodeBlockItemListBuilder statementsBuilder: () throws -> CodeBlockItemListSyntax) rethrows {
+  public init(_ header: SyntaxNodeString, @CodeBlockItemListBuilder statementsBuilder: () throws -> CodeBlockItemListSyntax) rethrows {
     self = SwitchCaseSyntax("\(header)")
     self.statements = try statementsBuilder()
   }
@@ -313,7 +318,7 @@ public extension SwitchExprSyntax {
   /// ```
   ///
   /// Throws an error if `header` does not start a switch expression. E.g. if calling `try SwitchExprSyntax("if x < 42") {}`
-  init(_ header: PartialSyntaxNodeString, @SwitchCaseListBuilder casesBuilder: () throws -> SwitchCaseListSyntax = { SwitchCaseListSyntax([]) }) throws {
+  init(_ header: SyntaxNodeString, @SwitchCaseListBuilder casesBuilder: () throws -> SwitchCaseListSyntax = { SwitchCaseListSyntax([]) }) throws {
     let expr = ExprSyntax("\(header) {}")
     guard let switchExpr = expr.as(Self.self) else {
       throw SyntaxStringInterpolationError.producedInvalidNodeType(expectedType: Self.self, actualNode: expr)
@@ -347,7 +352,7 @@ public extension VariableDeclSyntax {
   /// ```
   ///
   /// Throws an error if `header` does not start a variable declaration. E.g. if calling `try VariableDeclSyntax("func foo") {}`
-  init(_ header: PartialSyntaxNodeString, @CodeBlockItemListBuilder accessor: () throws -> CodeBlockItemListSyntax) throws {
+  init(_ header: SyntaxNodeString, @CodeBlockItemListBuilder accessor: () throws -> CodeBlockItemListSyntax) throws {
     let decl = DeclSyntax("\(header) {}")
     guard let castedDecl = decl.as(Self.self) else {
       throw SyntaxStringInterpolationError.producedInvalidNodeType(expectedType: Self.self, actualNode: decl)

Sources/SwiftSyntaxBuilder/SyntaxParsable+ExpressibleByStringInterpolation.swift

@@ -20,14 +20,31 @@ import SwiftParserDiagnostics
 import OSLog
 #endif
 
+fileprivate var suppressStringInterpolationParsingErrors = false
+
+/// Run the body, disabling any runtime warnings about syntax error in string
+/// interpolation inside the body.
+///
+/// Used to test the behavior of string interpolation with syntax errors.
+@_spi(Testing)
+public func withStringInterpolationParsingErrorsSuppressed<T>(_ body: () throws -> T) rethrows -> T {
+  suppressStringInterpolationParsingErrors = true
+  defer {
+    suppressStringInterpolationParsingErrors = false
+  }
+  return try body()
+}
+
 extension SyntaxParseable {
   public typealias StringInterpolation = SyntaxStringInterpolation
 
   /// Assuming that this node contains a syntax error, log it using OSLog if we
   /// are on a platform that supports OSLog, otherwise don't do anything.
   private func logStringInterpolationParsingError() {
     #if canImport(OSLog) && !SWIFTSYNTAX_NO_OSLOG_DEPENDENCY
-    if #available(macOS 11.0, iOS 14.0, tvOS 14.0, watchOS 7.0, macCatalyst 14.0, *) {
+    if #available(macOS 11.0, iOS 14.0, tvOS 14.0, watchOS 7.0, macCatalyst 14.0, *),
+      !suppressStringInterpolationParsingErrors
+    {
       let diagnostics = ParseDiagnosticsGenerator.diagnostics(for: self)
       let formattedDiagnostics = DiagnosticsFormatter().annotatedSource(tree: self, diags: diagnostics)
       Logger(subsystem: "SwiftSyntax", category: "ParseError").fault(

Tests/SwiftBasicFormatTest/BasicFormatTests.swift

@@ -12,7 +12,7 @@
 
 import SwiftBasicFormat
 import SwiftParser
-import SwiftSyntaxBuilder
+@_spi(Testing) import SwiftSyntaxBuilder
 import SwiftSyntax
 
 import XCTest
@@ -491,15 +491,17 @@ final class BasicFormatTest: XCTestCase {
   }
 
   func testUnexpectedIsNotFormatted() {
-    let expr: ExprSyntax = """
-      let foo=1
-      """
-
-    assertFormatted(
-      tree: expr,
-      expected: """
+    withStringInterpolationParsingErrorsSuppressed {
+      let expr: ExprSyntax = """
         let foo=1
         """
-    )
+
+      assertFormatted(
+        tree: expr,
+        expected: """
+          let foo=1
+          """
+      )
+    }
   }
 }

Tests/SwiftSyntaxBuilderTest/StringInterpolationTests.swift

@@ -12,7 +12,7 @@
 
 import _SwiftSyntaxTestSupport
 import SwiftSyntax
-import SwiftSyntaxBuilder
+@_spi(Testing) import SwiftSyntaxBuilder
 import SwiftParser
 import SwiftBasicFormat
 
@@ -500,4 +500,16 @@ final class StringInterpolationTests: XCTestCase {
       )
     }
   }
+
+  func testExtensionDeclFromStringInterpolation() throws {
+    let extensionDecl = try ExtensionDeclSyntax("extension Foo {}")
+    XCTAssertFalse(extensionDecl.hasError)
+
+    try withStringInterpolationParsingErrorsSuppressed {
+      let extensionWithError = try ExtensionDeclSyntax("extension Foo {")
+      XCTAssert(extensionWithError.hasError)
+    }
+
+    XCTAssertThrowsError(try ExtensionDeclSyntax("class Foo {}"))
+  }
 }