Slight diagnostics cleanup for incorrect infix and prefix operators

Author: DougGregor

Sources/SwiftIfConfig/IfConfigError.swift

@@ -35,6 +35,7 @@ enum IfConfigError: Error, CustomStringConvertible {
   case macabiIsMacCatalyst(syntax: ExprSyntax)
   case expectedModuleName(syntax: ExprSyntax)
   case badInfixOperator(syntax: ExprSyntax)
+  case badPrefixOperator(syntax: ExprSyntax)
 
   var description: String {
     switch self {
@@ -97,6 +98,9 @@ enum IfConfigError: Error, CustomStringConvertible {
 
     case .badInfixOperator:
       return "expected '&&' or '||' expression"
+
+    case .badPrefixOperator:
+      return "expected unary '!' expression"
     }
   }
 
@@ -120,7 +124,8 @@ enum IfConfigError: Error, CustomStringConvertible {
       .endiannessDoesNotMatch(syntax: let syntax, argument: _),
       .macabiIsMacCatalyst(syntax: let syntax),
       .expectedModuleName(syntax: let syntax),
-      .badInfixOperator(syntax: let syntax):
+      .badInfixOperator(syntax: let syntax),
+      .badPrefixOperator(syntax: let syntax):
       return Syntax(syntax)
 
     case .unsupportedVersionOperator(name: _, operator: let op):

Sources/SwiftIfConfig/IfConfigEvaluation.swift

@@ -107,9 +107,12 @@ func evaluateIfConfig(
   }
 
   // Logical '!'.
-  if let prefixOp = condition.as(PrefixOperatorExprSyntax.self),
-    prefixOp.operator.text == "!"
-  {
+  if let prefixOp = condition.as(PrefixOperatorExprSyntax.self) {
+    // If this isn't '!', complain.
+    guard prefixOp.operator.text == "!" else {
+      return recordError(.badPrefixOperator(syntax: condition))
+    }
+
     let (innerActive, innerSyntaxErrorsAllowed, innerDiagnostics) = evaluateIfConfig(
       condition: prefixOp.expression,
       configuration: configuration,
@@ -121,9 +124,14 @@ func evaluateIfConfig(
 
   // Logical '&&' and '||'.
   if let binOp = condition.as(InfixOperatorExprSyntax.self),
-    let op = binOp.operator.as(BinaryOperatorExprSyntax.self),
-    (op.operator.text == "&&" || op.operator.text == "||")
+    let op = binOp.operator.as(BinaryOperatorExprSyntax.self)
   {
+    // If this is neither && nor ||, it was already diagnosed as part of
+    // operator folding. Just return this as inactive.
+    guard op.operator.text == "&&" || op.operator.text == "||" else {
+      return (active: false, syntaxErrorsAllowed: true, diagnostics: extraDiagnostics)
+    }
+
     // Check whether this was likely to be a check for targetEnvironment(simulator).
     if outermostCondition,
       let targetEnvironmentDiag = diagnoseLikelySimulatorEnvironmentTest(binOp)

Tests/SwiftIfConfigTest/EvaluateTests.swift

@@ -158,12 +158,19 @@ public class EvaluateTests: XCTestCase {
           message: "expected '&&' or '||' expression",
           line: 1,
           column: 3
-        ),
+        )
+      ]
+    )
+
+    assertIfConfig(
+      "^DEBUG",
+      .unparsed,
+      diagnostics: [
         DiagnosticSpec(
-          message: "invalid conditional compilation expression",
+          message: "expected unary '!' expression",
           line: 1,
           column: 1
-        ),
+        )
       ]
     )
   }