[dmd-internals] changeset 455

[Robert Clipsham]

On 28/04/10 22:53, Jason House wrote:
> As one who attempted to do quick surgical fixes and failed, I appreciate

That doesn't surprise me, I don't think there's such thing as a quick 
surgical fix in dmd, there's so many things you don't expect to break 
but do with even trivial changes, unless you know the bit of code you're 
working with well.

> your efforts! I'm curious, how long did you spend researching before you
> could start making useful changes?

It took me about 3 or 4 days to reverse engineer various parts of the 
DWARF info[1] to figure out how it worked, figure out how dmd wrote the 
DWARF info, and track down/fix the bug in total. Subsequent DWARF bugs 
took next to no time to track down and fix, as I'm not pretty familiar 
with that part of the codebase.

> Every time I try peeking under the hood of dmd, I wish there was some
> kind of basic overview document. Even a few sentences at the top of a
> file indicating its purpose would be a great help. It's probably 10x
> better still if I stop acting so lazy and dedicate a few hours to
> getting a basic sense of what the code is doing!

An overview document would be nice for a lot of people, it needs someone 
to write it though. I've spent a lot of time in the dmd front end/other 
compiler front ends over the past year or so, so I'm pretty familiar 
with the layout and how things work now, that said, most bugs would 
still take me a few days. I think the best way to figure out what's 
happening is to head to mars.c and read through main(), seeing how it 
works. You can skip the first half that parses options etc. This should 
give you a rough idea of how it all fits together, it will take some 
time though.

--
[1] It was mostly reverse engineered, I used the spec, the gdb source 
and dmd source as a reference... I tried reading the spec, it was going 
in one eye and out the other though... I found it far easier to reverse 
engineer it and use various sources as a reference.