Require \(raw: <expr>) for plain strings

While we want `SyntaxStringInterpolation` to allow the interpolation of values known to be valid syntax into a literal, allowing plain old strings goes a little too far—you don’t know where that string’s been. Require a `raw:` label to indicate that a conversion is required, while also supporting any type (not just `CustomStringConvertible` conformers) now that the behavior is more explicit. Leave the original support in place but deprecated.

Author: beccadax

Sources/SwiftSyntaxBuilder/Syntax+StringInterpolation.swift

@@ -82,13 +82,19 @@ extension SyntaxStringInterpolation: StringInterpolationProtocol {
   }
 
   // Append a value of any CustomStringConvertible type as source text.
+  @available(*, deprecated, renamed: "appendInterpolation(raw:)", message: "use '\\(raw: <value>)' to interpolate a plain string directly into Swift code")
   public mutating func appendInterpolation<T: CustomStringConvertible>(
     _ value: T
   ) {
     sourceText.append(contentsOf: value.description.utf8)
     self.lastIndentation = nil
   }
 
+  public mutating func appendInterpolation<T>(raw value: T) {
+    sourceText.append(contentsOf: String(describing: value).utf8)
+    self.lastIndentation = nil
+  }
+
   // Append a value of any metatype as source text
   public mutating func appendInterpolation<T>(
     _ type: T.Type

Sources/SwiftSyntaxBuilder/SyntaxNodeWithBody.swift

@@ -38,7 +38,7 @@ public protocol HasTrailingCodeBlock {
 
 public extension HasTrailingCodeBlock where Self: SyntaxExpressibleByStringInterpolation {
   init(_ signature: String, @CodeBlockItemListBuilder bodyBuilder: () -> CodeBlockItemListSyntax) {
-    self = "\(signature) {}"
+    self = "\(raw: signature) {}"
     self.body = CodeBlock(statements: bodyBuilder())
   }
 }
@@ -58,7 +58,7 @@ public protocol HasTrailingOptionalCodeBlock {
 
 public extension HasTrailingOptionalCodeBlock where Self: SyntaxExpressibleByStringInterpolation {
   init(_ signature: String, @CodeBlockItemListBuilder bodyBuilder: () -> CodeBlockItemListSyntax) {
-    self = "\(signature) {}"
+    self = "\(raw: signature) {}"
     self.body = CodeBlock(statements: bodyBuilder())
   }
 }
@@ -77,7 +77,7 @@ public protocol HasTrailingMemberDeclBlock {
 
 public extension HasTrailingMemberDeclBlock where Self: SyntaxExpressibleByStringInterpolation {
   init(_ signature: String, @MemberDeclListBuilder membersBuilder: () -> MemberDeclListSyntax) {
-    self = "\(signature) {}"
+    self = "\(raw: signature) {}"
     self.members = MemberDeclBlock(members: membersBuilder())
   }
 }

Sources/_SwiftSyntaxTestSupport/SyntaxProtocol+Initializer.swift

@@ -62,11 +62,11 @@ private extension TriviaPiece {
     let (label, value) = Mirror(reflecting: self).children.first!
     switch value {
     case let value as String:
-      return FunctionCallExpr(callee: ".\(label!)") {
+      return FunctionCallExpr(callee: ".\(raw: label!)") {
         TupleExprElement(expression: StringLiteralExpr(content: value))
       }
     case let value as Int:
-      return FunctionCallExpr(callee: ".\(label!)") {
+      return FunctionCallExpr(callee: ".\(raw: label!)") {
         TupleExprElement(expression: IntegerLiteralExpr(value))
       }
     default:
@@ -131,7 +131,7 @@ extension SyntaxProtocol {
         tokenInitializerName = String(tokenKindStr[..<tokenKindStr.firstIndex(of: "(")!])
         requiresExplicitText = true
       }
-      return FunctionCallExpr(callee: ".\(tokenInitializerName)") {
+      return FunctionCallExpr(callee: ".\(raw: tokenInitializerName)") {
         if requiresExplicitText {
           TupleExprElement(
             expression: StringLiteralExpr(content: token.text)

Tests/SwiftSyntaxBuilderTest/FunctionTests.swift

@@ -37,7 +37,7 @@ final class FunctionTests: XCTestCase {
   func testArguments() {
     let buildable = FunctionCallExpr(callee: "test") {
       for param in (1...5) {
-        TupleExprElement(label: param.isMultiple(of: 2) ? "p\(param)" : nil, expression: "value\(param)")
+        TupleExprElement(label: param.isMultiple(of: 2) ? "p\(param)" : nil, expression: "value\(raw: param)")
       }
     }
     AssertBuildResult(buildable, "test(value1, p2: value2, value3, p4: value4, value5)")

Tests/SwiftSyntaxBuilderTest/StringInterpolation.swift

@@ -77,6 +77,20 @@ final class StringInterpolationTests: XCTestCase {
     let name = "Type"
     let id = 17
 
+    let structNode: DeclSyntax =
+       """
+       struct \(raw: name) {
+         static var id = \(raw: id)
+       }
+       """
+    XCTAssertTrue(structNode.is(StructDeclSyntax.self))
+  }
+
+  @available(*, deprecated)
+  func testStructGeneratorDeprecated() {
+    let name = "Type"
+    let id = 17
+
     let structNode: DeclSyntax =
        """
        struct \(name) {
@@ -117,6 +131,43 @@ final class StringInterpolationTests: XCTestCase {
   }
 
   func testParserBuilderInStringInterpolation() {
+    let cases = SwitchCaseList {
+      for i in 0..<2 {
+        SwitchCase("""
+        case \(raw: i):
+          return \(raw: i + 1)
+        """)
+      }
+      SwitchCase("""
+      default:
+        return -1
+      """)
+    }
+    let plusOne = FunctionDeclSyntax("""
+    func plusOne(base: Int) -> Int {
+      switch base {
+      \(cases, format: TwoSpacesFormat())
+      }
+    }
+    """)
+
+    AssertStringsEqualWithDiff(plusOne.description.trimmingTrailingWhitespace(), """
+    func plusOne(base: Int) -> Int {
+      switch base {
+
+      case 0:
+        return 1
+      case 1:
+        return 2
+      default:
+        return -1
+      }
+    }
+    """)
+  }
+
+  @available(*, deprecated)
+  func testParserBuilderInStringInterpolationDeprecated() {
     let cases = SwitchCaseList {
       for i in 0..<2 {
         SwitchCase("""

Tests/SwiftSyntaxBuilderTest/StructTests.swift

@@ -82,7 +82,7 @@ final class StructTests: XCTestCase {
         if i.isMultiple(of: 2) {
           VariableDecl(letOrVarKeyword: .let) {
             PatternBinding(
-              pattern: IdentifierPattern("var\(i)"),
+              pattern: IdentifierPattern("var\(raw: i)"),
               typeAnnotation: TypeAnnotation(type: Type("String"))
             )
           }