Global import of modules

[Petar]

On Thursday, 31 March 2022 at 08:45:45 UTC, user1234 wrote:
> On Thursday, 31 March 2022 at 06:47:46 UTC, ryuukk_ wrote:
>> https://forum.dlang.org/post/csnqfrweyiplmuhofojw@forum.dlang.org
>>
>> That is a nice idea, but i think it is better if it is 
>> supported by the compiler directly, so even if you don't use 
>> dub, you get to use the feature
>>
>>
>>    dmd hello.d --global-module=first.d,second.d,third.d
>>
>> This would allow me to do that: 
>> https://github.com/dlang/druntime/pull/3790
>>
>> What is everyone's opinion?
>
> I think it's bad because in theory that can break 3rd part 
> libraries.
> object.d is special, it's a fair exception, it's the runtime.
>
> Everything else should use imports + modules to have names 
> resolved consistently.

If we're serious about pay-as-you-go runtime/stdlib, perhaps 
libraries should be required to explicitly import the things they 
use from druntime? This could be an opt-in breaking change, say 
`--preview=pay-as-you-go-runtime`. I think that would be an 
improvement over the current status quo of all or nothing 
(betterC).

How about the following:

* applications/libraries can opt-in to using pay-as-you-go runtime
* to do so, they need to define their own `prelude.d` file
   * if it's empty that would be roughly the same as using the 
`-betterC` compiler flag
* `prelude.d` publicly imports the parts of druntime/phobos (or a 
custom runtime for embedded devices) that the library needs
   * if a library doesn't use exceptions, it will simply not 
import `Throwable`, `Exception`, `Error` and related functions.
   * if it needs `ModuleInfo`, but not `TypeInfo`, it will only 
import `ModuleInfo`
   * and so on
* The build system of the library will pass 
`--prelude=./src/prelude.d` to the compiler
   * E.g. in `dub.sdl` this could be `preludeModules 
"src/prelude.d"`
* The `--prelude` option affects only the current compilation 
unit - applications or other libraries that depend on library A 
can each have their own prelude, and library A's prelude won't 
affect them and vice-versa.