[Buildbot-devel] Discussion on source steps

[Dustin J. Mitchell]

So I think this gets to the crux of the matter.  There *are* two
choices to make, although if I may I'd like to adjust their
presentation slightly.

The first choice, I think should be binary and should be the same for
every VC.  The second choice should specify behaviors, and thus be
somewhat VC-specific.

On Mon, May 16, 2011 at 4:30 AM, A.T.Hofkamp <a.t.hofkamp at tue.nl> wrote:
> Maybe it is my lack of understanding your other modes, but in my view there are 2 choices to make.
> The main one is:
>
> 1. Throw away everything each time, or
> 2. Keep existing directory.

How about
 1. Build from a pristine directory with no leftovers from previous builds
 2. Build from an already-used directory with some/all files left intact

Let's refer to 1 as "clean" and 2 as "incremental" (although every
project seems to have its own names - Mozilla uses "clobber" and
"objdir")

> In 2, you then have a second choice, namely
>
> 2a. Keep all files
> 2c. Throw away *all* files not in the current revision of the VCS, and revert any changed source.
> (yep, 2b is missing, but it is on purpose, see below.)

Actually, in both cases you have a number of choices in how to
implement this behavior; those choices differ from VCS to VCS.  For
example:

1a. Delete the directory and re-checkout (or re-clone, or whatever)
1b. Keep a pristine 'source' directory, delete the build directory,
copy from source to build, and update
1c. Use '$vcs clean' with appropriately harsh (delete it all!) options

These may differ in efficiency in terms of filesystem access speed,
disk space, and network bandwidth, and as such should be
user-selectable, but that selection is basically an optimization and
not part of the high-level clean vs. incremental choice.  Note that by
this analysis, your 2a falls under "clean", not "incremental"

For incremental, I'm sure there are subtle per-vc behaviors that may
need to be adjusted.  For example,

2b. Remove non-ignored files (as Amber suggested is sometimes desirable)
2d. if the branch has changed, do $some_other_behavior (e.g., for
broken svn switches)
 others?

Dustin