Add diagnostic message for identifier editor placeholder

Sources/SwiftParser/Lexer/Cursor.swift

@@ -2044,6 +2044,7 @@ extension Lexer.Cursor {
 extension Lexer.Cursor {
   mutating func tryLexEditorPlaceholder(sourceBufferStart: Lexer.Cursor) -> Lexer.Result {
     precondition(self.is(at: "<") && self.is(offset: 1, at: "#"))
+    let start = self
     var ptr = self
     let leftAngleConsumed = ptr.advance(matching: "<")
     let poundConsumed = ptr.advance(matching: "#")
@@ -2058,7 +2059,10 @@ extension Lexer.Cursor {
         let closingAngleConsumed = ptr.advance(matching: ">")
         precondition(closingAngleConsumed)
         self = ptr
-        return Lexer.Result(.identifier)
+        return Lexer.Result(
+          .identifier,
+          error: LexingDiagnostic(.editorPlaceholder, position: start)
+        )
       default:
         break
       }

Sources/SwiftParserDiagnostics/LexerDiagnosticMessages.swift

@@ -38,6 +38,7 @@ public extension TokenError {
 
 /// Please order the cases in this enum alphabetically by case name.
 public enum StaticTokenError: String, DiagnosticMessage {
+  case editorPlaceholder = "editor placeholder in source file"
   case expectedBinaryExponentInHexFloatLiteral = "hexadecimal floating point literal must end with an exponent"
   case expectedClosingBraceInUnicodeEscape = #"expected '}' in \u{...} escape sequence"#
   case expectedDigitInFloatLiteral = "expected a digit in floating point exponent"
@@ -132,6 +133,7 @@ public extension SwiftSyntax.TokenDiagnostic {
     }
 
     switch self.kind {
+    case .editorPlaceholder: return StaticTokenError.editorPlaceholder
     case .expectedBinaryExponentInHexFloatLiteral: return StaticTokenError.expectedBinaryExponentInHexFloatLiteral
     case .expectedClosingBraceInUnicodeEscape: return StaticTokenError.expectedClosingBraceInUnicodeEscape
     case .expectedDigitInFloatLiteral: return StaticTokenError.expectedDigitInFloatLiteral

Sources/SwiftSyntax/TokenDiagnostic.swift

@@ -22,6 +22,7 @@ public struct TokenDiagnostic: Hashable {
   public enum Kind {
     // Please order these alphabetically
 
+    case editorPlaceholder
     case expectedBinaryExponentInHexFloatLiteral
     case expectedClosingBraceInUnicodeEscape
     case expectedDigitInFloatLiteral
@@ -94,6 +95,7 @@ public struct TokenDiagnostic: Hashable {
 
   public var severity: Severity {
     switch kind {
+    case .editorPlaceholder: return .error
     case .expectedBinaryExponentInHexFloatLiteral: return .error
     case .expectedClosingBraceInUnicodeEscape: return .error
     case .expectedDigitInFloatLiteral: return .error

Tests/SwiftParserTest/Assertions.swift

@@ -87,7 +87,7 @@ private func assertTokens(
   var lexemeStartOffset = 0
   for (actualLexeme, expectedLexeme) in zip(actual, expected) {
     defer {
-      lexemeStartOffset = actualLexeme.byteLength
+      lexemeStartOffset += actualLexeme.byteLength
     }
     if actualLexeme.rawTokenKind != expectedLexeme.rawTokenKind {
       XCTFail(

Tests/SwiftParserTest/DeclarationTests.swift

@@ -1379,12 +1379,15 @@ final class DeclarationTests: XCTestCase {
     assertParse(
       """
       class Foo {
-        <#code#>
+        1️⃣<#code#>
       }
       """,
       substructure: Syntax(
         MemberDeclListItemSyntax(decl: EditorPlaceholderDeclSyntax(identifier: .identifier("<#code#>")))
-      )
+      ),
+      diagnostics: [
+        DiagnosticSpec(message: "editor placeholder in source file")
+      ]
     )
   }
 

Tests/SwiftParserTest/ExpressionTests.swift

@@ -838,9 +838,28 @@ final class ExpressionTests: XCTestCase {
   }
 
   func testCodeCompletionExpressions() {
-    assertParse("if !<#b1#> && !<#b2#> {}")
-    assertParse("if <#test#> {}")
-    assertParse("if <#b1#>, <#b2#> {}")
+    assertParse(
+      "if !1️⃣<#b1#> && !2️⃣<#b2#> {}",
+      diagnostics: [
+        DiagnosticSpec(locationMarker: "1️⃣", message: "editor placeholder in source file"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "editor placeholder in source file"),
+      ]
+    )
+
+    assertParse(
+      "if 1️⃣<#test#> {}",
+      diagnostics: [
+        DiagnosticSpec(locationMarker: "1️⃣", message: "editor placeholder in source file")
+      ]
+    )
+
+    assertParse(
+      "if 1️⃣<#b1#>, 2️⃣<#b2#> {}",
+      diagnostics: [
+        DiagnosticSpec(locationMarker: "1️⃣", message: "editor placeholder in source file"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "editor placeholder in source file"),
+      ]
+    )
   }
 
   func testKeywordApplyExpression() {

Tests/SwiftParserTest/LexerTests.swift

@@ -663,20 +663,20 @@ public class LexerTests: XCTestCase {
 
   func testEditorPlaceholders() {
     assertLexemes(
-      "!<#b1#> && !<#b2#>",
+      "!1️⃣<#b1#> && !2️⃣<#b2#>",
       lexemes: [
         LexemeSpec(.prefixOperator, text: "!"),
-        LexemeSpec(.identifier, text: "<#b1#>", trailing: " "),
+        LexemeSpec(.identifier, text: "<#b1#>", trailing: " ", errorLocationMarker: "1️⃣", diagnostic: "editor placeholder in source file"),
         LexemeSpec(.binaryOperator, text: "&&", trailing: " "),
         LexemeSpec(.prefixOperator, text: "!"),
-        LexemeSpec(.identifier, text: "<#b2#>"),
+        LexemeSpec(.identifier, text: "<#b2#>", errorLocationMarker: "2️⃣", diagnostic: "editor placeholder in source file"),
       ]
     )
 
     assertLexemes(
-      "<##>",
+      "1️⃣<##>",
       lexemes: [
-        LexemeSpec(.identifier, text: "<##>", trailing: "")
+        LexemeSpec(.identifier, text: "<##>", trailing: "", diagnostic: "editor placeholder in source file")
       ]
     )
   }

Tests/SwiftParserTest/translated/IdentifiersTests.swift

@@ -83,10 +83,10 @@ final class IdentifiersTests: XCTestCase {
     assertParse(
       """
       // Placeholders are recognized as identifiers but with error.
-      func <#some name#>() {}
+      func 1️⃣<#some name#>() {}
       """,
       diagnostics: [
-        // TODO: (good first issue) Old parser expected error on line 2: editor placeholder in source file
+        DiagnosticSpec(message: "editor placeholder in source file")
       ]
     )
   }