When creation of a syntax node using string interpolation failed, log the diagnostics

From the first feedback of developers starting to build macros, the number one mistake was to build incorrect syntax nodes, e.g. build an `ExprSyntax` for a declaration. Up until recently, these errors weren’t diagnosed at all. By now we at least issue an XCTest assertion if the expanded macro code contains syntax errors. But I think the issues are a lot easier to debug if we can emit an error at the location where the incorrect syntax node is being created.

Since we can’t throw an error from string interpolation, use OSLog to log the parsing error to Xcode or OS console. When OSLog is not available or we are building using CMake (and thus don’t want to introduce any dependency on the SDK), silently accept the error as we do right now. Logging to stderr might be too fragile in case some application is expecting to populate stderr itself.

Author: ahoppen

CodeGeneration/Sources/generate-swiftsyntax/templates/swiftsyntaxbuilder/SyntaxExpressibleByStringInterpolationConformancesFile.swift

@@ -17,41 +17,8 @@ import Utils
 
 let syntaxExpressibleByStringInterpolationConformancesFile = SourceFileSyntax(leadingTrivia: copyrightHeader) {
   DeclSyntax("import SwiftSyntax")
-  DeclSyntax("import SwiftParser")
-  DeclSyntax("import SwiftParserDiagnostics")
-
-  try! ExtensionDeclSyntax("extension SyntaxParseable") {
-    DeclSyntax("public typealias StringInterpolation = SyntaxStringInterpolation")
-
-    DeclSyntax(
-      """
-      public init(stringInterpolation: SyntaxStringInterpolation) {
-        self = performParse(source: stringInterpolation.sourceText, parse: { parser in
-          return Self.parse(from: &parser)
-        })
-      }
-      """
-    )
-  }
 
   for node in SYNTAX_NODES where node.parserFunction != nil {
     DeclSyntax("extension \(node.kind.syntaxType): SyntaxExpressibleByStringInterpolation {}")
   }
-
-  DeclSyntax(
-    """
-    // TODO: This should be inlined in SyntaxParseable.init(stringInterpolation:),
-    // but is currently used in `ConvenienceInitializers.swift`.
-    // See the corresponding TODO there.
-    func performParse<SyntaxType: SyntaxProtocol>(source: [UInt8], parse: (inout Parser) -> SyntaxType) -> SyntaxType {
-      return source.withUnsafeBufferPointer { buffer in
-        var parser = Parser(buffer)
-        // FIXME: When the parser supports incremental parsing, put the
-        // interpolatedSyntaxNodes in so we don't have to parse them again.
-        let result = parse(&parser)
-        return result
-      }
-    }
-    """
-  )
 }

Package.swift

@@ -162,7 +162,7 @@ let package = Package(
 
     .target(
       name: "SwiftSyntaxBuilder",
-      dependencies: ["SwiftBasicFormat", "SwiftParser", "SwiftParserDiagnostics", "SwiftSyntax"],
+      dependencies: ["SwiftBasicFormat", "SwiftParser", "SwiftDiagnostics", "SwiftParserDiagnostics", "SwiftSyntax"],
       exclude: ["CMakeLists.txt"]
     ),
 

Sources/SwiftSyntaxBuilder/CMakeLists.txt

@@ -12,6 +12,7 @@ add_swift_host_library(SwiftSyntaxBuilder
   ResultBuilderExtensions.swift
   Syntax+StringInterpolation.swift
   SyntaxNodeWithBody.swift
+  SyntaxParsable+ExpressibleByStringInterpolation.swift
   ValidatingSyntaxNodes.swift
   WithTrailingCommaSyntax+EnsuringTrailingComma.swift
 

Sources/SwiftSyntaxBuilder/SyntaxParsable+ExpressibleByStringInterpolation.swift

@@ -0,0 +1,56 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 SwiftDiagnostics
+import SwiftSyntax
+import SwiftParser
+import SwiftParserDiagnostics
+// Don't introduce a dependency on OSLog when building SwiftSyntax using CMake
+// for the compiler.
+#if canImport(OSLog) && !CMAKE_BUILD
+import OSLog
+#endif
+
+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) && !CMAKE_BUILD
+    if #available(macOS 11.0, *) {
+      let diagnostics = ParseDiagnosticsGenerator.diagnostics(for: self)
+      let formattedDiagnostics = DiagnosticsFormatter().annotatedSource(tree: self, diags: diagnostics)
+      Logger(subsystem: "SwiftSyntax", category: "ParseError").warning(
+        """
+        Parsing a `\(Self.self)` node from string interpolation produced the following parsing errors.
+        Set a brakpoint in `SyntaxParseable.logStringInterpolationParsingError()` to debug the failure.
+        \(formattedDiagnostics)
+        """
+      )
+    }
+    #endif
+  }
+
+  public init(stringInterpolation: SyntaxStringInterpolation) {
+    self = stringInterpolation.sourceText.withUnsafeBufferPointer { buffer in
+      var parser = Parser(buffer)
+      // FIXME: When the parser supports incremental parsing, put the
+      // interpolatedSyntaxNodes in so we don't have to parse them again.
+      let result = Self.parse(from: &parser)
+      return result
+    }
+    if self.hasError {
+      self.logStringInterpolationParsingError()
+    }
+  }
+}

Sources/SwiftSyntaxBuilder/generated/SyntaxExpressibleByStringInterpolationConformances.swift

@@ -13,18 +13,6 @@
 //===----------------------------------------------------------------------===//
 
 import SwiftSyntax
-import SwiftParser
-import SwiftParserDiagnostics
-
-extension SyntaxParseable {
-  public typealias StringInterpolation = SyntaxStringInterpolation
-  
-  public init(stringInterpolation: SyntaxStringInterpolation) {
-    self = performParse(source: stringInterpolation.sourceText, parse: { parser in
-      return Self.parse(from: &parser)
-    })
-  }
-}
 
 extension AccessorDeclSyntax: SyntaxExpressibleByStringInterpolation {}
 
@@ -57,16 +45,3 @@ extension StmtSyntax: SyntaxExpressibleByStringInterpolation {}
 extension SwitchCaseSyntax: SyntaxExpressibleByStringInterpolation {}
 
 extension TypeSyntax: SyntaxExpressibleByStringInterpolation {}
-
-// TODO: This should be inlined in SyntaxParseable.init(stringInterpolation:),
-// but is currently used in `ConvenienceInitializers.swift`.
-// See the corresponding TODO there.
-func performParse<SyntaxType: SyntaxProtocol>(source: [UInt8], parse: (inout Parser) -> SyntaxType) -> SyntaxType {
-  return source.withUnsafeBufferPointer { buffer in
-    var parser = Parser(buffer)
-    // FIXME: When the parser supports incremental parsing, put the
-    // interpolatedSyntaxNodes in so we don't have to parse them again.
-    let result = parse(&parser)
-    return result
-  }
-}

cmake/modules/AddSwiftHostLibrary.cmake

@@ -56,6 +56,9 @@ function(add_swift_host_library name)
       -emit-module-interface-path;${module_interface_file}
       >)
 
+  target_compile_options("${name}" PRIVATE
+    $<$<COMPILE_LANGUAGE:Swift>:-D;CMAKE_BUILD>)  
+
   if(CMAKE_VERSION VERSION_LESS 3.26.0 AND SWIFT_SYNTAX_ENABLE_WMO_PRE_3_26)
     target_compile_options(${name} PRIVATE
         $<$<COMPILE_LANGUAGE:Swift>:-wmo>)