Add documentation

Author: liufengyun

compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala

@@ -627,6 +627,14 @@ class ClassfileParser(
       None // ignore malformed annotations
   }
 
+  /** A completer for attributes
+   *
+   *  Top-level classes complete attributes eagerly, while members complete azily.
+   *
+   *  Note that we cannot simply store the bytes of attributes, as the bytes may
+   *  contain references to the constant pool, where the constants are loaded
+   *  lazily.
+   */
   class AttributeCompleter(sym: Symbol) {
     var sig: String = null
     var constant: Constant = null
@@ -659,7 +667,6 @@ class ClassfileParser(
     }
   }
 
-  // invariant: `in` and `ctx` should not be captured inside the result function
   def parseAttributes(sym: Symbol)(using ctx: Context, in: DataReader): AttributeCompleter = {
     val res = new AttributeCompleter(sym)