fix Issue 11039 - Undefined instantiation from circular imports

[WalterBright]

Fix http://d.puremagic.com/issues/show_bug.cgi?id=11039

[9rnsr]

To compile test11039.d and imports/test11039b.d separately, you need to add // COMPILE_SEPARATELY option here.

[WalterBright]

done.

[9rnsr]

OK, looks good.

[MartinNowak]

If mi imports any root modules, we still need to generate the code.

What's the logic behind this?

[WalterBright]

It happens when a non-root module circularly imports a root one. Somebody has to instantiate it.

[9rnsr]

And, in the test code, SomeStruct!string is instantiated in both module, then merged on link-time.

[MartinNowak]

It happens when a non-root module circularly imports a root one. Somebody has to instantiate it.

I see, when you later compile the non-root module the roles inverted so both would delegate the instantiation to some other module.
You could try to improve this fix in two ways.

• Restrict the "imports any root" module search to those root modules that also instantiate the template.
• Use a fixed method to determine the module of a circular import chain that is responsible for the instantiation, e.g. take the module with the lexically smallest module name.