Respond to review feedback

Author: ApolloZhu

Sources/SwiftSyntaxMacroExpansion/MacroArgument.swift

@@ -1,3 +1,15 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
 import SwiftDiagnostics
 import SwiftSyntax
 
@@ -20,7 +32,9 @@ enum DeclReferenceError: DiagnosticMessage {
   }
 }
 
-class CheckDeclReferenceVisitor: SyntaxAnyVisitor {
+/// Check sub-expressions to ensure all expressions are literals, and call
+/// `diagnoseNonLiteral` for all other expressions.
+class OnlyLiteralExprChecker: SyntaxAnyVisitor {
   var diagnostics: [Diagnostic] = []
 
   init() {
@@ -127,8 +141,14 @@ class CheckDeclReferenceVisitor: SyntaxAnyVisitor {
 }
 
 extension MacroExpansionExprSyntax {
+  /// For compiler to check a macro expression used as default argument.
+  ///
+  /// Only literals are permitted as arguments to these expressions.
+  ///
+  /// If there are diagnostics, they will be wrapped into an error and thrown.
+  @_spi(Compiler)
   public func checkDefaultArgumentMacroExpression() throws {
-    let visitor = CheckDeclReferenceVisitor()
+    let visitor = OnlyLiteralExprChecker()
     visitor.walk(arguments)
 
     if !visitor.diagnostics.isEmpty {

Sources/SwiftSyntaxMacroExpansion/MacroReplacement.swift

@@ -93,7 +93,7 @@ extension MacroDefinition {
   }
 }
 
-fileprivate class ParameterReplacementVisitor: CheckDeclReferenceVisitor {
+fileprivate class ParameterReplacementVisitor: OnlyLiteralExprChecker {
   let macro: MacroDeclSyntax
   var replacements: [MacroDefinition.Replacement] = []
   var genericReplacements: [MacroDefinition.GenericArgumentReplacement] = []

Tests/SwiftSyntaxMacroExpansionTest/MacroArgumentTests.swift

@@ -13,7 +13,7 @@
 import SwiftDiagnostics
 import SwiftSyntax
 import SwiftSyntaxBuilder
-import SwiftSyntaxMacroExpansion
+@_spi(Compiler) import SwiftSyntaxMacroExpansion
 import XCTest
 import _SwiftSyntaxTestSupport
 
@@ -34,22 +34,21 @@ final class MacroArgumentTests: XCTestCase {
       #otherMacro(first: b, second: "\(false)", third: 1 + 2)
       """#
 
-    let diags: [Diagnostic]
-    do {
-      try macro.as(MacroExpansionExprSyntax.self)!
-        .checkDefaultArgumentMacroExpression()
-      XCTFail("should have failed with an error")
-      fatalError()
-    } catch let diagError as DiagnosticsError {
-      diags = diagError.diagnostics
-    }
+    XCTAssertThrowsError(try macro.as(MacroExpansionExprSyntax.self)!
+      .checkDefaultArgumentMacroExpression()) { error in
+        guard let diagError = error as? DiagnosticsError else {
+          XCTFail("should have failed with a diagnostics error")
+          return
+        }
+        let diags = diagError.diagnostics
 
-    XCTAssertEqual(diags.count, 3)
-    for diag in diags {
-      XCTAssertEqual(
-        diag.diagMessage.message,
-        "only literals are permitted"
-      )
-    }
+        XCTAssertEqual(diags.count, 3)
+        for diag in diags {
+          XCTAssertEqual(
+            diag.diagMessage.message,
+            "only literals are permitted"
+          )
+        }
+      }
   }
 }