On Thursday, 31 May 2018 at 23:17:20 UTC, Steven Schveighoffer
wrote:
Hm... I just had a crazy idea: what if D had a switch that
allowed it to store a dependency graph of constructors into a
json file, and then when you link, there is a wrapper which
consumes all these files, runs the cycle detection and sort,
and then compiles a perfectly sorted moduleinfo section to be
included in the binary (obviously, written in D and compiled by
the compiler).
This is how languages get custom object formats and custom
linkers.
A fly in the ointment is .di files. This works today and does the
right thing:
// bar.d
import modulewithstaticctor;
shared static this() {}
string something = modulewithstaticctor.someValue;
// bar.di
// no static ctor, no imports
string something;
// foo.d
import bar, std.stdiod;
void main()
{
writefln(something);
}
So mixing that dependency graph with .di files is "here be
dragons" territory.
If the dependency data were inserted into the object files
instead (which it should be? that's what ModuleInfo is), then the
compiler could potentially read this out before linking, and we
could be sure that the resulting order is correct. Like, insert a
weak symbol into each normal object file saying there's no
dependency graph, and then the compiler can run on a set of
object files to produce a new object file with the complete
dependency graph as a strong symbol.
But that's more work.
