[Issue 14680] Investigate the use of .di files for Phobos

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14680

Andrei Alexandrescu <andrei at erdani.com> changed:

           What    |Removed                     |Added
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         Depends on|14687                       |

--- Comment #1 from Andrei Alexandrescu <andrei at erdani.com> ---
I made a brief first pass, with encouraging results. The build speed for this
program decreased from 0.172s to 0.149s:

import std.stdio, std.algorithm, std.range;
void main(string[] args) {
}

That includes linking. Difference in compilation alone is quite a bit higher
(2x from 0.07 to 0.036) but of course it's expected that these margins will
degrade once semantic analysis starts to dominate.

Sadly I was unable to actually call any function because the generated .di
files have a number of issues, which I'll file separately.

Files in std/*.d have a total of 8,564,957 bytes, whereas the .di generated
files have 2,922,494 bytes. On the face of it it makes a lot of sense to not
distribute for importing the source files with all comments, unittests etc. in
them. So I think we should pursue this.

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