Diagnostics: teach the parser API to listen to diagnostics emitted from the compiler(parser).

Sources/SwiftSyntax/Diagnostic.swift

@@ -14,7 +14,8 @@
 
 /// A FixIt represents a change to source code in order to "correct" a
 /// diagnostic.
-public enum FixIt: Codable {
+public enum FixIt: Codable, CustomDebugStringConvertible {
+
   /// Remove the characters from the source file over the provided source range.
   case remove(SourceRange)
 
@@ -32,6 +33,10 @@ public enum FixIt: Codable {
     case string
   }
 
+  public var debugDescription: String {
+    return "Fixit: \(range.debugDescription) Text: \"\(text)\""
+  }
+
   public init(from decoder: Decoder) throws {
     let container = try decoder.container(keyedBy: CodingKeys.self)
     let type = try container.decode(String.self, forKey: .type)
@@ -119,8 +124,14 @@ public struct Note: Codable {
 }
 
 /// A Diagnostic message that can be emitted regarding some piece of code.
-public struct Diagnostic: Codable {
-  public struct Message: Codable {
+public struct Diagnostic: Codable, CustomDebugStringConvertible {
+
+  public struct Message: Codable, CustomDebugStringConvertible {
+
+    public var debugDescription: String {
+      return "\(severity): \(text)"
+    }
+
     /// The severity of diagnostic. This can be note, error, or warning.
     public let severity: Severity
 
@@ -157,6 +168,16 @@ public struct Diagnostic: Codable {
   /// An array of possible FixIts to apply to this diagnostic.
   public let fixIts: [FixIt]
 
+  public var debugDescription: String {
+    var lines: [String] = []
+    let loc = location == nil ? "" : "\(location!) "
+    lines.append("\(loc)\(message.debugDescription)")
+    fixIts.forEach { lines.append("\($0.debugDescription)") }
+    highlights.forEach { lines.append("Highlight: \($0.debugDescription)") }
+    lines.append(contentsOf: notes.map({ loc + $0.asDiagnostic().debugDescription}))
+    return lines.joined(separator: "\n")
+  }
+
   /// A diagnostic builder that exposes mutating operations for notes,
   /// highlights, and FixIts. When a Diagnostic is created, a builder
   /// will be provided in a closure where the user can conditionally

Sources/SwiftSyntax/DiagnosticConsumer.swift

@@ -15,10 +15,19 @@
 /// An object that intends to receive notifications when diagnostics are
 /// emitted.
 public protocol DiagnosticConsumer {
+
+  /// Whether the collected diagnostics should calculate line:column pair; true
+  /// by default.
+  var needsLineColumn: Bool { get }
+
   /// Handle the provided diagnostic which has just been registered with the
   /// DiagnosticEngine.
   func handle(_ diagnostic: Diagnostic)
 
   /// Finalize the consumption of diagnostics, flushing to disk if necessary.
   func finalize()
 }
+
+public extension DiagnosticConsumer  {
+  var needsLineColumn: Bool { return true }
+}

Sources/SwiftSyntax/DiagnosticEngine.swift

@@ -26,6 +26,11 @@ public class DiagnosticEngine {
 
   public private(set) var diagnostics = [Diagnostic]()
 
+  internal var needsLineColumn: Bool {
+    // Check if any consumer is interested in line and column.
+    return consumers.first { $0.needsLineColumn } != nil
+  }
+
   /// Adds the provided consumer to the consumers list.
   public func addConsumer(_ consumer: DiagnosticConsumer) {
     consumers.append(consumer)
@@ -36,6 +41,13 @@ public class DiagnosticEngine {
     }
   }
 
+  internal func diagnose(_ diagnostic: Diagnostic) {
+    diagnostics.append(diagnostic)
+    for consumer in consumers {
+      consumer.handle(diagnostic)
+    }
+  }
+
   /// Registers a diagnostic with the diagnostic engine.
   /// - parameters:
   ///   - message: The message for the diagnostic. This message includes
@@ -44,12 +56,7 @@ public class DiagnosticEngine {
   public func diagnose(_ message: Diagnostic.Message,
                        location: SourceLocation? = nil,
                        actions: ((inout Diagnostic.Builder) -> Void)? = nil) {
-    let diagnostic = Diagnostic(message: message, location: location,
-                                actions: actions)
-    diagnostics.append(diagnostic)
-    for consumer in consumers {
-      consumer.handle(diagnostic)
-    }
+    diagnose(Diagnostic(message: message, location: location, actions: actions))
   }
 
   /// If any of the diagnostics in this engine have the `error` severity.

Sources/SwiftSyntax/SourceLocation.swift

@@ -12,7 +12,7 @@
 
 /// Represent the user-facing part of SourceLocation that can be calculated
 /// on demand.
-struct ComputedLocation: Codable {
+struct ComputedLocation: Codable, CustomDebugStringConvertible {
   /// The line in the file where this location resides. 1-based.
   let line: Int
 
@@ -23,6 +23,11 @@ struct ComputedLocation: Codable {
   /// The file in which this location resides.
   let file: String
 
+  var debugDescription: String {
+    // Print file name?
+    return "\(line):\(column)"
+  }
+
   init(line: Int, column: Int, file: String) {
     self.line = line
     self.column = column
@@ -38,7 +43,7 @@ struct ComputedLocation: Codable {
 }
 
 /// Represents a source location in a Swift file.
-public struct SourceLocation: Codable {
+public struct SourceLocation: Codable, CustomDebugStringConvertible {
 
   /// Line and column that can be computed on demand.
   private var compLoc: ComputedLocation?
@@ -62,6 +67,13 @@ public struct SourceLocation: Codable {
     return compLoc?.file
   }
 
+  public var debugDescription: String {
+    guard let compLoc = compLoc else {
+      return "\(offset)"
+    }
+    return compLoc.debugDescription
+  }
+
   public init(line: Int, column: Int, offset: Int, file: String) {
     self.offset = offset
     self.compLoc = ComputedLocation(line: line, column: column, file: file)
@@ -79,13 +91,18 @@ public struct SourceLocation: Codable {
 }
 
 /// Represents a start and end location in a Swift file.
-public struct SourceRange: Codable {
+public struct SourceRange: Codable, CustomDebugStringConvertible {
+
   /// The beginning location in the source range.
   public let start: SourceLocation
 
   /// The beginning location in the source range.
   public let end: SourceLocation
 
+  public var debugDescription: String {
+    return "(\(start.debugDescription),\(end.debugDescription))"
+  }
+
   public init(start: SourceLocation, end: SourceLocation) {
     self.start = start
     self.end = end
@@ -111,6 +128,15 @@ public final class SourceLocationConverter {
     assert(tree.byteSize == endOfFile.utf8Offset)
   }
 
+  /// - Parameters:
+  ///   - file: The file path associated with the syntax tree.
+  ///   - source: The source code to convert positions to line/columns for.
+  public init(file: String, source: String) {
+    self.file = file
+    (self.lines, endOfFile) = computeLines(source)
+    assert(source.lengthOfBytes(using: .utf8) == endOfFile.utf8Offset)
+  }
+
   /// Convert a `AbsolutePosition` to a `SourceLocation`. If the position is
   /// exceeding the file length then the `SourceLocation` for the end of file
   /// is returned. If position is negative the location for start of file is
@@ -305,6 +331,22 @@ fileprivate func computeLines(
   return (lines, position)
 }
 
+fileprivate func computeLines(_ source: String) ->
+    ([AbsolutePosition], AbsolutePosition) {
+  var lines: [AbsolutePosition] = []
+  // First line starts from the beginning.
+  lines.append(.startOfFile)
+  var position: AbsolutePosition = .startOfFile
+  let addLine = { (lineLength: SourceLength) in
+    position += lineLength
+    lines.append(position)
+  }
+  var curPrefix: SourceLength = .zero
+  curPrefix = source.forEachLineLength(prefix: curPrefix, body: addLine)
+  position += curPrefix
+  return (lines, position)
+}
+
 fileprivate extension String {
   /// Walks and passes to `body` the `SourceLength` for every detected line,
   /// with the newline character included.