Ensure that we diagnose compound names where they shouldn't be

Author: DougGregor

Sources/SwiftIfConfig/IfConfigEvaluation.swift

@@ -96,10 +96,9 @@ func evaluateIfConfig(
   }
 
   // Declaration references are for custom compilation flags.
-  if let identExpr = condition.as(DeclReferenceExprSyntax.self) {
-    // FIXME: Need a real notion of an identifier.
-    let ident = identExpr.baseName.text
-
+  if let identExpr = condition.as(DeclReferenceExprSyntax.self),
+    let ident = identExpr.simpleIdentifier
+  {
     // Evaluate the custom condition. If the build configuration cannot answer this query, fail.
     return checkConfiguration(at: identExpr) {
       (active: try configuration.isCustomConditionSet(name: ident), syntaxErrorsAllowed: false)
@@ -499,18 +498,6 @@ private func extractImportPath(_ expression: some ExprSyntaxProtocol) throws ->
   throw IfConfigError.expectedModuleName(syntax: ExprSyntax(expression))
 }
 
-extension DeclReferenceExprSyntax {
-  /// If this declaration reference is a simple identifier, return that
-  /// string.
-  fileprivate var simpleIdentifier: String? {
-    guard argumentNames == nil else {
-      return nil
-    }
-
-    return baseName.text
-  }
-}
-
 /// Determine whether the given condition only involves disjunctions that
 /// check the given config function against one of the provided values.
 ///

Sources/SwiftIfConfig/SyntaxLiteralUtils.swift

@@ -36,13 +36,23 @@ extension LabeledExprListSyntax {
 extension ExprSyntax {
   /// Whether this is a simple identifier expression and, if so, what the identifier string is.
   var simpleIdentifierExpr: String? {
-    guard let identExpr = self.as(DeclReferenceExprSyntax.self),
-      identExpr.argumentNames == nil
-    else {
+    guard let identExpr = self.as(DeclReferenceExprSyntax.self) else {
       return nil
     }
 
-    // FIXME: Handle escaping here.
-    return identExpr.baseName.text
+    return identExpr.simpleIdentifier
+  }
+}
+
+extension DeclReferenceExprSyntax {
+  /// If this declaration reference is a simple identifier, return that
+  /// string.
+  var simpleIdentifier: String? {
+    guard argumentNames == nil else {
+      return nil
+    }
+
+    /// FIXME: Make this an Identifier so we handle escaping properly.
+    return baseName.text
   }
 }

Tests/SwiftIfConfigTest/EvaluateTests.swift

@@ -120,6 +120,17 @@ public class EvaluateTests: XCTestCase {
         )
       ]
     )
+    assertIfConfig(
+      "BAR(_:)",
+      .unparsed,
+      diagnostics: [
+        DiagnosticSpec(
+          message: "invalid conditional compilation expression",
+          line: 1,
+          column: 1
+        )
+      ]
+    )
   }
 
   func testBadExpressions() throws {