Allow specifying simple diagnostic messages in an enum

Author: ahoppen

Sources/SwiftParser/Diagnostics/ParseDiagnosticsGenerator.swift

@@ -47,6 +47,11 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     diagnostics.append(Diagnostic(node: Syntax(node), message: message))
   }
 
+  /// Produce a diagnostic.
+  private func addDiagnostic<T: SyntaxProtocol>(_ node: T, _ message: StaticParserError) {
+    addDiagnostic(node, message as DiagnosticMessage)
+  }
+
   /// If a diagnostic is generated that covers multiple syntax nodes, mark them as handles so they don't produce the generic diagnostics anymore.
   private func markNodesAsHandled(_ nodes: SyntaxIdentifier...) {
     handledNodes.append(contentsOf: nodes)
@@ -95,7 +100,7 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     if let unexpectedCondition = node.body.unexpectedBeforeLeftBrace {
       // Detect C-style for loops based on two semicolons which could not be parsed between the 'for' keyword and the '{'
       if unexpectedCondition.tokens(withKind: .semicolon).count == 2 {
-        addDiagnostic(node, CStyleForLoopError())
+        addDiagnostic(node, .cStyleForLoop)
         markNodesAsHandled(node.inKeyword.id, unexpectedCondition.id)
       }
     }
@@ -108,7 +113,7 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     }
     if let output = node.output, let unexpectedBeforeReturnType = output.unexpectedBetweenArrowAndReturnType {
       if let throwsInReturnPosition = unexpectedBeforeReturnType.tokens(withKind: .throwsKeyword).first {
-        addDiagnostic(throwsInReturnPosition, ThrowsInReturnPositionError())
+        addDiagnostic(throwsInReturnPosition, .throwsInReturnPosition)
         markNodesAsHandled(unexpectedBeforeReturnType.id, throwsInReturnPosition.id)
         return .visitChildren
       }

Sources/SwiftParser/Diagnostics/ParserDiagnosticMessages.swift

@@ -55,12 +55,24 @@ public extension ParserError {
   }
 }
 
-// MARK: - Diagnostics (please sort alphabetically)
+// MARK: - Static diagnostics
+
+/// Please order the cases in this enum alphabetically by case name.
+public enum StaticParserError: String, DiagnosticMessage {
+  case cStyleForLoop = "C-style for statement has been removed in Swift 3"
+  case throwsInReturnPosition = "'throws' may only occur before '->'"
+
+  public var message: String { self.rawValue }
+
+  public var diagnosticID: MessageID {
+    MessageID("\(type(of: self)).\(self)")
+  }
 
-public struct CStyleForLoopError: ParserError {
-  public var message = "C-style for statement has been removed in Swift 3"
+  public var severity: DiagnosticSeverity { .error }
 }
 
+// MARK: - Diagnostics (please sort alphabetically)
+
 public struct MissingTokenError: ParserError {
   public let missingToken: TokenSyntax
 
@@ -84,10 +96,6 @@ public struct MissingTokenError: ParserError {
   }
 }
 
-public struct ThrowsInReturnPositionError: ParserError {
-  public let message = "'throws' may only occur before '->'"
-}
-
 public struct UnexpectedNodesError: ParserError {
   public let unexpectedNodes: UnexpectedNodesSyntax
 

Tests/SwiftParserTest/DiagnosticInfrastructureTests.swift

@@ -12,5 +12,8 @@ public class DiagnosticInfrastructureTests: XCTestCase {
     XCTAssertEqual(diag.diagnosticID, MessageID("TestDiagnostic"))
     XCTAssertEqual(diag.message, "My test diagnostic")
     XCTAssertEqual(diag.severity, .error)
+
+    XCTAssertEqual(StaticParserError.throwsInReturnPosition.diagnosticID, MessageID("StaticParserError.throwsInReturnPosition"))
+    XCTAssertEqual(StaticParserError.throwsInReturnPosition.severity, .error)
   }
 }