Improve diagnostic message if unexpected tokens are found at the start of a layout node

This helps us produce better error messages once we implement recovery in front of declarations.

Author: ahoppen

Sources/SwiftParser/Diagnostics/ParserDiagnosticMessages.swift

@@ -16,12 +16,20 @@ import SwiftSyntax
 let diagnosticDomain: String = "SwiftParser"
 
 extension SyntaxProtocol {
-  var nodeTypeNameForDiagnostics: String? {
+  /// Return a name of this syntax node that can be used to describe it in
+  /// diagnostics.
+  /// Nodes that mostly exist for the syntax tree's structure and don't have a
+  /// correspondence in the source code that's meeingful to the user by default
+  /// use the name of the parent node that encloses it. Pass `false` to `inherit`
+  /// to prevent this name inheritance.
+  func nodeTypeNameForDiagnostics(inherit: Bool = true) -> String? {
     if let name = Syntax(self).as(SyntaxEnum.self).nameForDiagnostics {
       return name
     }
-    if let parent = self.parent {
-      return parent.nodeTypeNameForDiagnostics
+    if inherit {
+      if let parent = self.parent {
+        return parent.nodeTypeNameForDiagnostics(inherit: inherit)
+      }
     }
     return nil
   }
@@ -118,7 +126,7 @@ public struct MissingTokenError: ParserError {
   public let missingToken: TokenSyntax
 
   public var message: String {
-    guard let parent = missingToken.parent, let parentTypeName = parent.nodeTypeNameForDiagnostics else {
+    guard let parent = missingToken.parent, let parentTypeName = parent.nodeTypeNameForDiagnostics() else {
       return "Expected '\(missingToken.text)'"
     }
     switch missingToken.tokenKind {
@@ -141,17 +149,17 @@ public struct UnexpectedNodesError: ParserError {
   public let unexpectedNodes: UnexpectedNodesSyntax
 
   public var message: String {
-    let parentTypeName = unexpectedNodes.parent?.nodeTypeNameForDiagnostics
-    let shortContent = unexpectedNodes.contentForDiagnosticsIfShortSingleLine
-    switch (parentTypeName, shortContent) {
-    case (let parentTypeName?, let shortContent?):
-      return "Unexpected text '\(shortContent)' found in \(parentTypeName)"
-    case (let parentTypeName?, nil):
-      return "Unexpected text found in \(parentTypeName)"
-    case (nil, let shortContent?):
-      return "Unexpected text '\(shortContent)'"
-    case (nil, nil):
-      return "Unexpected text"
+    var message = "Unexpected text"
+    if let shortContent = unexpectedNodes.contentForDiagnosticsIfShortSingleLine {
+      message += " '\(shortContent)'"
+    }
+    if let parent = unexpectedNodes.parent {
+      if let parentTypeName = parent.nodeTypeNameForDiagnostics(inherit: false), parent.children(viewMode: .sourceAccurate).first?.id == unexpectedNodes.id {
+        message += " before \(parentTypeName)"
+      } else if let parentTypeName = parent.nodeTypeNameForDiagnostics() {
+        message += " in \(parentTypeName)"
+      }
     }
+    return message
   }
 }

Tests/SwiftParserTest/Declarations.swift

@@ -381,7 +381,7 @@ final class DeclarationTests: XCTestCase {
       "(first second #^DIAG^#third fourth: Int)",
       { $0.parseFunctionSignature() },
       diagnostics: [
-        DiagnosticSpec(message: "Unexpected text 'third fourth' found in function parameter")
+        DiagnosticSpec(message: "Unexpected text 'third fourth' in function parameter")
       ]
     )
   }
@@ -523,7 +523,7 @@ final class DeclarationTests: XCTestCase {
       diagnostics: [
         DiagnosticSpec(
           message: """
-            Unexpected text '/ ###line 25 "line-directive.swift"' found in struct
+            Unexpected text '/ ###line 25 "line-directive.swift"' in struct
             """
         )
       ]
@@ -538,7 +538,7 @@ final class DeclarationTests: XCTestCase {
       }
       """,
       diagnostics: [
-        DiagnosticSpec(message: "Unexpected text 'bogus rethrows set' found in variable")
+        DiagnosticSpec(message: "Unexpected text 'bogus rethrows set' in variable")
       ]
     )
   }
@@ -570,7 +570,7 @@ final class DeclarationTests: XCTestCase {
         trailingComma: nil
       )),
       diagnostics: [
-        DiagnosticSpec(message: "Unexpected text 'third' found in function parameter")
+        DiagnosticSpec(message: "Unexpected text 'third' in function parameter")
       ]
     )
   }
@@ -591,7 +591,7 @@ final class DeclarationTests: XCTestCase {
         trailingComma: nil
       )),
       diagnostics: [
-        DiagnosticSpec(message: "Unexpected text 'third fourth' found in function parameter")
+        DiagnosticSpec(message: "Unexpected text 'third fourth' in function parameter")
       ]
     )
   }
@@ -642,7 +642,7 @@ final class DeclarationTests: XCTestCase {
         trailingComma: nil
       )),
       diagnostics: [
-        DiagnosticSpec(message: "Unexpected text '[third fourth]' found in function parameter")
+        DiagnosticSpec(message: "Unexpected text '[third fourth]' in function parameter")
       ]
     )
   }
@@ -667,7 +667,7 @@ final class DeclarationTests: XCTestCase {
       diagnostics: [
         DiagnosticSpec(locationMarker: "COLON", message: "Expected ':' in function parameter"),
         DiagnosticSpec(locationMarker: "END_ARRAY" , message: "Expected ']' to end array type"),
-        DiagnosticSpec(locationMarker: "END_ARRAY", message: "Unexpected text 'fourth: Int' found in parameter clause")
+        DiagnosticSpec(locationMarker: "END_ARRAY", message: "Unexpected text 'fourth: Int' in parameter clause")
       ]
     )
   }

Tests/SwiftParserTest/Expressions.swift

@@ -202,7 +202,7 @@ final class ExpressionTests: XCTestCase {
       " >> \( abc #^DIAG^#} ) << "
       """#,
       diagnostics: [
-        DiagnosticSpec(message: "Unexpected text '}' found in string literal")
+        DiagnosticSpec(message: "Unexpected text '}' in string literal")
       ]
     )
 
@@ -419,7 +419,7 @@ final class ExpressionTests: XCTestCase {
       "[(Int) -> #^DIAG^#throws Int]()",
       diagnostics: [
         // FIXME: We should suggest to move 'throws' in front of '->'
-        DiagnosticSpec(message: "Unexpected text 'throws Int' found in array")
+        DiagnosticSpec(message: "Unexpected text 'throws Int' in array")
       ]
     )
 
@@ -449,7 +449,7 @@ final class ExpressionTests: XCTestCase {
       let :(#^DIAG_1^#..)->
       """,
       diagnostics: [
-        DiagnosticSpec(locationMarker: "DIAG_1", message: "Unexpected text '..' found in function type"),
+        DiagnosticSpec(locationMarker: "DIAG_1", message: "Unexpected text '..' in function type"),
       ]
     )
   }

Tests/SwiftParserTest/Statements.swift

@@ -14,7 +14,7 @@ final class StatementTests: XCTestCase {
       """,
       diagnostics: [
         DiagnosticSpec(message: "Expected '=' in pattern matching"),
-        DiagnosticSpec(message: "Unexpected text '* ! = x' found in 'if' statement"),
+        DiagnosticSpec(message: "Unexpected text '* ! = x' in 'if' statement"),
       ]
     )
   }
@@ -158,8 +158,8 @@ final class StatementTests: XCTestCase {
       }
       """,
       diagnostics: [
-        DiagnosticSpec(locationMarker: "TEST_1", message: "Unexpected text '@s return' found in function"),
-        DiagnosticSpec(locationMarker: "TEST_2", message: "Unexpected text '@unknown return' found in function")
+        DiagnosticSpec(locationMarker: "TEST_1", message: "Unexpected text '@s return' in function"),
+        DiagnosticSpec(locationMarker: "TEST_2", message: "Unexpected text '@unknown return' in function")
       ]
     )
   }
@@ -177,7 +177,7 @@ final class StatementTests: XCTestCase {
       }
       """,
       diagnostics: [
-        DiagnosticSpec(message: "Unexpected text found in 'switch' statement"),
+        DiagnosticSpec(message: "Unexpected text in 'switch' statement"),
 
       ]
     )
@@ -197,7 +197,7 @@ final class StatementTests: XCTestCase {
       }
       """,
       diagnostics: [
-        DiagnosticSpec(message: "Unexpected text found in 'switch' statement")
+        DiagnosticSpec(message: "Unexpected text in 'switch' statement")
       ]
     )
   }

Tests/SwiftParserTest/Types.swift

@@ -29,7 +29,7 @@ final class TypeTests: XCTestCase {
 
   func testFunctionTypes() throws {
     AssertParse("t as(#^DIAG^#..)->", diagnostics: [
-      DiagnosticSpec(message: "Unexpected text '..' found in function type")
+      DiagnosticSpec(message: "Unexpected text '..' in function type")
     ])
   }
 }