Avoid printing the full token stream and doing line/column position calculations when extracting th…

runtime/lib/mirrors.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "lib/invocation_mirror.h"
 #include "vm/bootstrap_natives.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
 #include "vm/exceptions.h"
@@ skipping 2027 matching lines @@
   const Function& func = Function::Handle(ref.GetFunctionReferent());
   if (func.IsImplicitConstructor() || func.IsSignatureFunction()) {
     // We may need to handle more cases when the restrictions on mixins are
     // relaxed. In particular we might start associating some source with the
     // forwarding constructors when it becomes possible to specify a particular
     // constructor from the mixin to use.
     return Instance::null();
   }
   const Script& script = Script::Handle(func.script());
   const TokenStream& stream = TokenStream::Handle(script.tokens());
+  if (!script.HasSource()) {
+    // When source is not available, avoid printing the whole token stream and
+    // doing expensive position calculations.

[hausner, 2014/02/10 16:49:53]

Maybe mention in the comment why it makes no sense to do the calculation below:
column positions are not available.

Maybe this faster path is good enough even when we have sources? What would we
lose?

+    return stream.GenerateSource(func.token_pos(), func.end_token_pos() + 1);
+  }
+
   const TokenStream::Iterator tkit(stream, func.end_token_pos());
   intptr_t from_line;
   intptr_t from_col;
   intptr_t to_line;
   intptr_t to_col;
   script.GetTokenLocation(func.token_pos(), &from_line, &from_col);
   script.GetTokenLocation(func.end_token_pos(), &to_line, &to_col);
   intptr_t last_tok_len = String::Handle(tkit.CurrentLiteral()).Length();
   // Handle special cases for end tokens of closures (where we exclude the last
   // token):
@@ skipping 40 matching lines @@
 
 DEFINE_NATIVE_ENTRY(VariableMirror_type, 2) {
   GET_NON_NULL_NATIVE_ARGUMENT(MirrorReference, ref, arguments->NativeArgAt(0));
   const Field& field = Field::Handle(ref.GetFieldReferent());
   GET_NATIVE_ARGUMENT(AbstractType, instantiator, arguments->NativeArgAt(1));
   const AbstractType& type = AbstractType::Handle(field.type());
   return InstantiateType(type, instantiator);
 }
 
 }  // namespace dart