Beginning support for library prefixes in the dart API.

Beginning support for library prefixes in the dart API.

This is a request for comments. Do we want to expose library
prefixes like this? Is there a way to import with a prefix already
and lookup members?

The reason why I would like to do this is so that I can import the
user-supplied builtins library under a prefix. This will be a useful
first step to move the print function to corelib while preserving
the ability to patch in a print implementation via the builtins
library.

R=iposva@google.com,turnidge@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=11494

[Mads Ager (google), 2012-08-23 13:58:56]

Here is a sketch of how I would like to use this to move print to corelib using
patching:

https://chromiumcodereview.appspot.com/10868043

The only thing I actually need for this is the change to take a prefix in
Dart_LibraryImportLibrary.

[Mads Ager (google), 2012-08-27 09:39:55]

I have cut this down to what is actually needed to support the 'print' corelib
unification.

Ivan and Todd, could you have a look at this?

[Ivan Posva, 2012-08-27 23:55:00]

https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/include/dar...
File runtime/include/dart_api.h (right):

https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/include/dar...
runtime/include/dart_api.h:2540: 
?

https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/vm/dart_api...
File runtime/vm/dart_api_impl.cc (right):

https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/vm/dart_api...
runtime/vm/dart_api_impl.cc:4050: if (prefix_vm.IsNull()) {
I would expect that an empty prefix is equivalent to an empty string. Although
Todd has a better overview of the API.

[Ivan Posva, 2012-08-27 23:55:35]

On 2012/08/27 23:55:00, Ivan Posva wrote:
>
https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/include/dar...
> File runtime/include/dart_api.h (right):
> 
>
https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/include/dar...
> runtime/include/dart_api.h:2540: 
> ?
> 
>
https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/vm/dart_api...
> File runtime/vm/dart_api_impl.cc (right):
> 
>
https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/vm/dart_api...
> runtime/vm/dart_api_impl.cc:4050: if (prefix_vm.IsNull()) {
> I would expect that an empty prefix is equivalent to an empty string. Although
> Todd has a better overview of the API.

With empty prefix I obviously meant a handle containing a null.

[Mads Ager (google), 2012-08-28 05:58:31]

https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/include/dar...
File runtime/include/dart_api.h (right):

https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/include/dar...
runtime/include/dart_api.h:2540: 
On 2012/08/27 23:55:00, Ivan Posva wrote:
> ?

Done.

https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/vm/dart_api...
File runtime/vm/dart_api_impl.cc (right):

https://chromiumcodereview.appspot.com/10867032/diff/3001/runtime/vm/dart_api...
runtime/vm/dart_api_impl.cc:4050: if (prefix_vm.IsNull()) {
On 2012/08/27 23:55:00, Ivan Posva wrote:
> I would expect that an empty prefix is equivalent to an empty string. Although
> Todd has a better overview of the API.

I'll be happy to do it either way. Let me know what you guys want so I can move
forward with this change (and coordinate with Dartium changes as well).

[Ivan Posva, 2012-08-28 23:22:02]

LGTM with comments.

-Ivan

https://chromiumcodereview.appspot.com/10867032/diff/9001/runtime/bin/builtin.cc
File runtime/bin/builtin.cc (right):

https://chromiumcodereview.appspot.com/10867032/diff/9001/runtime/bin/builtin...
runtime/bin/builtin.cc:83: prefix));
Siva and I discussed this and we feel that being able to pass Dart_Null()
instead of allocating an empty string is the right choice here.

https://chromiumcodereview.appspot.com/10867032/diff/9001/runtime/vm/dart_api...
File runtime/vm/dart_api_impl_test.cc (right):

https://chromiumcodereview.appspot.com/10867032/diff/9001/runtime/vm/dart_api...
runtime/vm/dart_api_impl_test.cc:5299: "#library('library2_name');";
Also add a test that something in the prefixed library can be found for example:

foobar() => bar.foo();

[Mads Ager (google), 2012-08-29 05:52:10]

Thanks Ivan.

I will prepare the corresponding Dartium change and land.

https://chromiumcodereview.appspot.com/10867032/diff/9001/runtime/bin/builtin.cc
File runtime/bin/builtin.cc (right):

https://chromiumcodereview.appspot.com/10867032/diff/9001/runtime/bin/builtin...
runtime/bin/builtin.cc:83: prefix));
On 2012/08/28 23:22:02, Ivan Posva wrote:
> Siva and I discussed this and we feel that being able to pass Dart_Null()
> instead of allocating an empty string is the right choice here.

Sounds good. I updated the code to allow both Dart_Null as well as an empty
string to act as no prefix. Additionally, I added a bit of documentation to the
API.

https://chromiumcodereview.appspot.com/10867032/diff/9001/runtime/vm/dart_api...
File runtime/vm/dart_api_impl_test.cc (right):

https://chromiumcodereview.appspot.com/10867032/diff/9001/runtime/vm/dart_api...
runtime/vm/dart_api_impl_test.cc:5299: "#library('library2_name');";
On 2012/08/28 23:22:02, Ivan Posva wrote:
> Also add a test that something in the prefixed library can be found for
example:
> 
> foobar() => bar.foo();

Done.