Special case error messages if a single keyword is unexpected

Sources/SwiftParser/Diagnostics/SyntaxExtensions.swift

@@ -83,6 +83,10 @@ extension SyntaxProtocol {
       } else {
         return "braces"
       }
+    } else if let token = Syntax(self).as(UnexpectedNodesSyntax.self)?.onlyTokens(satisfying: { $0.tokenKind.isKeyword })?.only {
+      return "'\(token.text)' keyword"
+    } else if let token = Syntax(self).as(TokenSyntax.self) {
+      return "'\(token.text)' keyword"
     } else if contentWithoutTrivia.contains("\n") || contentWithoutTrivia.count > 100 {
       return "code"
     } else {

Tests/SwiftParserTest/Types.swift

@@ -55,7 +55,7 @@ final class TypeTests: XCTestCase {
         print("closure with empty capture list")
       }
       """)
-    
+
     AssertParse("""
                 { ()
                 throws -> Void in }
@@ -71,7 +71,7 @@ final class TypeTests: XCTestCase {
                 { $0.parseClosureExpression() },
                 diagnostics: [
                   DiagnosticSpec(locationMarker: "1️⃣", message: "expected identifier in closure capture item"),
-                  DiagnosticSpec(locationMarker: "1️⃣", message: "unexpected code 'class' in closure capture signature"),
+                  DiagnosticSpec(locationMarker: "1️⃣", message: "unexpected 'class' keyword in closure capture signature"),
                   DiagnosticSpec(locationMarker: "2️⃣", message: "expected '}' to end closure"),
                 ])
 

Tests/SwiftParserTest/translated/EnumTests.swift

@@ -385,7 +385,7 @@ final class EnumTests: XCTestCase {
       """,
       diagnostics: [
         DiagnosticSpec(locationMarker: "1️⃣", message: "keyword 'Self' cannot be used as an identifier here"),
-        DiagnosticSpec(locationMarker: "2️⃣", message: "unexpected code 'Self' in enum"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "unexpected 'Self' keyword in enum"),
       ]
     )
   }

Tests/SwiftParserTest/translated/ErrorsTests.swift

@@ -187,7 +187,7 @@ final class ErrorsTests: XCTestCase {
       diagnostics: [
         // TODO: Old parser expected error on line 1: 'rethrows' may only occur before '->', Fix-It replacements: 43 - 43 = 'rethrows ', 46 - 55 = ''
         DiagnosticSpec(locationMarker: "1️⃣", message: "expected 'rethrows' in function signature"),
-        DiagnosticSpec(locationMarker: "2️⃣", message: "unexpected code 'rethrows' in function signature"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "unexpected 'rethrows' keyword in function signature"),
       ]
     )
   }
@@ -263,7 +263,7 @@ final class ErrorsTests: XCTestCase {
       diagnostics: [
         // TODO: Old parser expected error on line 3: consecutive statements on a line must be separated by ';'
         // TODO: Old parser expected error on line 3: expected expression
-        DiagnosticSpec(message: "unexpected code 'throws' in function"),
+        DiagnosticSpec(message: "unexpected 'throws' keyword in function"),
       ]
     )
   }

Tests/SwiftParserTest/translated/IfconfigExprTests.swift

@@ -142,7 +142,7 @@ final class IfconfigExprTests: XCTestCase {
       }
       """,
       diagnostics: [
-        DiagnosticSpec(message: "unexpected code 'return' in conditional compilation block"),
+        DiagnosticSpec(message: "unexpected 'return' keyword in conditional compilation block"),
       ]
     )
   }