Add diagnostics for missing modifier in operator declaration

Author: StevenWong12

Sources/SwiftParser/Declarations.swift

@@ -1964,9 +1964,16 @@ extension Parser {
     } else {
       unexpectedAtEnd = nil
     }
+
+    var modifiers: RawModifierListSyntax? = attrs.modifiers
+    if modifiers == nil {
+      let missedModifier = RawDeclModifierSyntax(name: self.missingToken(.prefix), detail: nil, arena: self.arena)
+      modifiers = RawModifierListSyntax(elements: [missedModifier], arena: self.arena)
+    }
+
     return RawOperatorDeclSyntax(
       attributes: attrs.attributes,
-      modifiers: attrs.modifiers,
+      modifiers: modifiers,
       unexpectedBeforeOperatorKeyword,
       operatorKeyword: operatorKeyword,
       unexpectedBeforeName,

Sources/SwiftParserDiagnostics/ParseDiagnosticsGenerator.swift

@@ -855,6 +855,17 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     if shouldSkip(node) {
       return .skipChildren
     }
+
+    if let modifier = node.modifiers,
+      modifier.contains(where: { $0.isMissingAllTokens })
+    {
+      addDiagnostic(
+        modifier,
+        .missingModifierForOperatorDecl,
+        handledNodes: [modifier.id]
+      )
+    }
+
     if let unexpected = node.unexpectedAfterOperatorPrecedenceAndTypes,
       unexpected.contains(where: { $0.is(PrecedenceGroupAttributeListSyntax.self) }) == true
     {

Sources/SwiftParserDiagnostics/ParserDiagnosticMessages.swift

@@ -164,6 +164,9 @@ extension DiagnosticMessage where Self == StaticParserError {
   public static var missingConformanceRequirement: Self {
     .init("expected ':' or '==' to indicate a conformance or same-type requirement")
   }
+  public static var missingModifierForOperatorDecl: Self {
+    .init("operator must be declared as 'prefix', 'postfix', or 'infix'")
+  }
   public static var misspelledAsync: Self {
     .init("expected async specifier; did you mean 'async'?")
   }

Tests/SwiftParserTest/translated/OperatorDeclTests.swift

@@ -117,34 +117,34 @@ final class OperatorDeclTests: XCTestCase {
   func testOperatorDecl6() {
     AssertParse(
       """
-      operator ++*** : A
+      1️⃣operator ++*** : A
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 1: operator must be declared as 'prefix', 'postfix', or 'infix'
+        DiagnosticSpec(message: "operator must be declared as 'prefix', 'postfix', or 'infix'")
       ]
     )
   }
 
   func testOperatorDecl7() {
     AssertParse(
       """
-      operator +*+++ 1️⃣{ }
+      1️⃣operator +*+++ 2️⃣{ }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 1: operator must be declared as 'prefix', 'postfix', or 'infix'
-        DiagnosticSpec(message: "operator should not be declared with body")
+        DiagnosticSpec(locationMarker: "1️⃣", message: "operator must be declared as 'prefix', 'postfix', or 'infix'"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "operator should not be declared with body"),
       ]
     )
   }
 
   func testOperatorDecl8() {
     AssertParse(
       """
-      operator +*++* : A 1️⃣{ }
+      1️⃣operator +*++* : A 2️⃣{ }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 1: operator must be declared as 'prefix', 'postfix', or 'infix'
-        DiagnosticSpec(message: "operator should not be declared with body")
+        DiagnosticSpec(locationMarker: "1️⃣", message: "operator must be declared as 'prefix', 'postfix', or 'infix'"),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "operator should not be declared with body"),
       ]
     )
   }