[ASTGen] MacroExpansionExpr at top-level can be decl

Author: rintaro

lib/ASTGen/Sources/ASTGen/ASTGen.swift

@@ -128,9 +128,17 @@ struct ASTGenVisitor {
           case .generated(let generated):
             return generated
           case .ignored:
-            // Let regular 'self.generate(expr:)' generate the macro expansions.
             break
           }
+
+          // In non-script files, macro expansion at top-level must be a decl.
+          if !declContext.parentSourceFile.isScriptMode {
+            return withDeclContext(parentDC) {
+              return .decl(self.generateMacroExpansionDecl(macroExpansionExpr: node).asDecl)
+            }
+          }
+
+          // Otherwise, let regular 'self.generate(expr:)' generate the macro expansions.
         }
         return .expr(self.generate(expr: node))
       }

lib/ASTGen/Sources/ASTGen/Decls.swift

@@ -855,6 +855,21 @@ extension ASTGenVisitor {
 
     return decl
   }
+
+  func generateMacroExpansionDecl(macroExpansionExpr node: MacroExpansionExprSyntax) -> BridgedMacroExpansionDecl {
+    let info = self.generate(freestandingMacroExpansion: node)
+    return .createParsed(
+      self.declContext,
+      poundLoc: info.poundLoc,
+      macroNameRef: info.macroNameRef,
+      macroNameLoc: info.macroNameLoc,
+      leftAngleLoc: info.leftAngleLoc,
+      genericArgs: info.genericArgs,
+      rightAngleLoc: info.rightAngleLoc,
+      args: info.arguments
+    )
+  }
+
 }
 
 // MARK: - OperatorDecl