Code review comment for lp://staging/~gagern/bzr/bug396819-lazy_import-threadsafe

Sorry we've not managed to get this reviewed MvG. Your analysis here and in the bug about the previous change seem correct to me, but I'm unconvinced about making further changes to lazy_import in this regard.

I can't offer useful suggestions for improving the branch, only complain about the state of the pitch:

* There's no way to disable lazy imports for things like loggerhead that care about threading not startup time.

* Telling whether a given lazy import is actually doing anything useful is far too hard.

  * It's not uncommon to see an object get imported then unconditionally used further down in the module.

  * Many parts of bzrlib are lazily imported somewhere, but end up always being required anyway.

  * The import tariff tests are nice, but very heavy compared to say, a lint style check.

* Parsing import statements out of strings is silly in many respects.

What I'd like to see would be a replacement with fewer features bzrlib could move to instead. I'm imagining it would:

* Use the import statement directly.

* Only works on module objects.

* Use a proxy that remains in place but gains attributes.

Since bzrlib.lazy_import was introduced we've gained a bunch of other lazy mechanisms which take over some of the work, but it's all very ad hoc.