Add contextual diagnostic message if colon is missing in ternary expression

rdar://98745337

Author: ahoppen

Sources/SwiftParser/Diagnostics/ParseDiagnosticsGenerator.swift

@@ -169,5 +169,16 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     }
     return .visitChildren
   }
+
+  public override func visit(_ node: UnresolvedTernaryExprSyntax) -> SyntaxVisitorContinueKind {
+    if shouldSkip(node) {
+      return .skipChildren
+    }
+    if node.colonMark.presence == .missing {
+      addDiagnostic(node.colonMark, .missingColonInTernaryExprDiagnostic)
+      markNodesAsHandled(node.colonMark.id)
+    }
+    return .visitChildren
+  }
 }
 

Sources/SwiftParser/Diagnostics/ParserDiagnosticMessages.swift

@@ -76,6 +76,7 @@ public extension ParserFixIt {
 /// Please order the cases in this enum alphabetically by case name.
 public enum StaticParserError: String, DiagnosticMessage {
   case cStyleForLoop = "C-style for statement has been removed in Swift 3"
+  case missingColonInTernaryExprDiagnostic = "Expected ':' after '? ...' in ternary expression"
   case missingFunctionParameterClause = "Expected argument list in function declaration"
   case throwsInReturnPosition = "'throws' may only occur before '->'"
 

Tests/SwiftParserTest/DiagnosticTests.swift

@@ -93,4 +93,16 @@ public class DiagnosticTests: XCTestCase {
 
     XCTAssertSingleDiagnostic(in: classDecl, line: 2, column: 25, message: "Expected argument list in function declaration")
   }
+
+  func testMissingColonInTernary() throws {
+    let source = """
+      foo ? 1
+      """
+
+    let node = withParser(source: source) {
+      Syntax(raw: $0.parseExpression().raw)
+    }
+
+    XCTAssertSingleDiagnostic(in: node, line: 1, column: 8, message: "Expected ':' after '? ...' in ternary expression")
+  }
 }