Handle missing func keyword

Author: kimdv

Sources/SwiftParser/Declarations.swift

@@ -208,6 +208,10 @@ extension Parser {
       modifiers: self.parseDeclModifierList()
     )
 
+    if atFunctionDeclarationWithoutFuncKeyword() {
+      return RawDeclSyntax(self.parseFuncDeclaration(attrs, .missing(.keyword(.func))))
+    }
+
     // If we are inside a memberDecl list, we don't want to eat closing braces (which most likely close the outer context)
     // while recovering to the declaration start.
     let recoveryPrecedence = inMemberDeclList ? TokenPrecedence.closingBrace : nil
@@ -283,10 +287,7 @@ extension Parser {
         )
       }
 
-      let isPossibleFuncIdentifier = self.at(.identifier, .wildcard)
-      let isPossibleFuncParen = self.peek(isAt: .leftParen, .binaryOperator)
-      // Treat operators specially because they're likely to be functions.
-      if (isPossibleFuncIdentifier && isPossibleFuncParen) || self.at(anyIn: Operator.self) != nil {
+      if atFunctionDeclarationWithoutFuncKeyword() {
         return RawDeclSyntax(self.parseFuncDeclaration(attrs, .missing(.keyword(.func))))
       }
     }
@@ -298,6 +299,17 @@ extension Parser {
       )
     )
   }
+
+  /// Returns `true` if it looks like the parser is positioned at a function declaration that’s missing the `func` keyword.
+  fileprivate mutating func atFunctionDeclarationWithoutFuncKeyword() -> Bool {
+    if self.at(.identifier) && (self.peek(isAt: .leftParen) || self.peek().tokenText.hasPrefix("<")) {
+      return true
+    }
+    if self.at(anyIn: Operator.self) != nil {
+      return true
+    }
+    return false
+  }
 }
 
 extension Parser {

Tests/SwiftParserTest/DeclarationTests.swift

@@ -452,18 +452,20 @@ final class DeclarationTests: ParserTestCase {
 
     assertParse(
       """
-      private(1️⃣+
-        set
+      private(1️⃣+2️⃣
+        set3️⃣
       ) var a = 0
       """,
       diagnostics: [
-        DiagnosticSpec(message: "expected 'set)' to end modifier", fixIts: ["insert 'set)'"]),
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected 'set)' to end modifier", fixIts: ["insert 'set)'"]),
+        DiagnosticSpec(locationMarker: "1️⃣", message: "expected 'func' in function", fixIts: ["insert 'func'"]),
+        DiagnosticSpec(locationMarker: "2️⃣", message: "expected '(' to start parameter clause", fixIts: ["insert '('"]),
         // FIXME: It should print `+` as detail of text.
-        DiagnosticSpec(message: "unexpected code in variable"),
+        DiagnosticSpec(locationMarker: "3️⃣", message: "expected ':' and type in parameter", fixIts: ["insert ':' and type"]),
       ],
       fixedSource: """
-        private(set) +
-          set
+        private(set) func + (
+          set: <#type#>
         ) var a = 0
         """
     )

Tests/SwiftParserTest/translated/RecoveryTests.swift

@@ -2107,13 +2107,7 @@ final class RecoveryTests: ParserTestCase {
     )
   }
 
-  func testRecovery120() {
-    assertParse(
-      """
-      //===--- Recovery for wrong decl introducer keyword.
-      """
-    )
-  }
+  // MARK: - Recovery for wrong decl introducer keyword.
 
   func testRecovery121() {
     assertParse(
@@ -2125,20 +2119,36 @@ final class RecoveryTests: ParserTestCase {
       }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 2: expected 'func' keyword in instance method declaration
-        DiagnosticSpec(message: "unexpected code 'notAKeyword() {}' before function")
-      ]
+        DiagnosticSpec(message: "expected 'func' in function", fixIts: ["insert 'func'"])
+      ],
+      fixedSource: """
+        class WrongDeclIntroducerKeyword1 {
+          func notAKeyword() {}
+          func foo() {}
+          class func bar() {}
+        }
+        """
     )
-  }
 
-  func testRecovery122() {
     assertParse(
       """
-      //===--- Recovery for wrong inheritance clause.
-      """
+      class WrongDeclIntroducerKeyword1 {
+        1️⃣notAKeyword() {}
+        var x: Int
+      }
+      """,
+      diagnostics: [DiagnosticSpec(message: "expected 'func' in function", fixIts: ["insert 'func'"])],
+      fixedSource: """
+        class WrongDeclIntroducerKeyword1 {
+          func notAKeyword() {}
+          var x: Int
+        }
+        """
     )
   }
 
+  // MARK: - Recovery for wrong inheritance clause.
+
   func testRecovery123() {
     assertParse(
       """