On 2014-08-25, 1:54 PM, Nathan Froyd wrote:
----- Original Message -----
Often my workflow looks something like this:
change files in directory D
rebuild only D, get a list of errors to fix
...iterate until no more errors
try to rebuild a few related directories, fixing errors there
then rebuild the entire tree, hopefully without errors
Often the changes to directory D are to header files that are included all
over the tree. If I could only do full rebuilds, I would have to wait for a
bunch of unrelated files to compile before I could see if the directory I'm
interested in works. Then, if fixing an error required making a change to
one of the header files again, I would have to wait for a ton of files to
recompile again. A process that would have taken 20 minutes could be drawn
out into an hour.
This happens really often when changing the JS engine or xpconnect, since
files like jsapi.h, jsfriendapi.h, and xpcpublic.h are included almost
everywhere.
Strawman idea: add support for:
mach check-syntax <directory>...
which runs the compiler with -fsyntax-only (GCCish) or /Zs (MSVC) on the source
files in the given directory(ies). This sort of thing should be fairly
straightforward, given that we already support something similar for generating
preprocessed files in a given directory. Then you get to keep the fast
workflow, the build folks get to ignore single-directory rebuilds, and
everybody winds up happy--well, as soon as people adjust to typing new commands
for their workflow, of course...
(This obviously doesn't address linking errors, but AIUI, the workflow above
isn't about linking errors, but build errors.)
That will do nothing to reduce the overhead of the build system. Most
of the errors that Bill is talking about can be found the first time the
code is exercised by the compiler, so removing the codegen won't help
all that much.
Personally I find 15s of overhead for full builds bad enough to want to
have a way to build only one directory. Also, I wonder if the numbers
that Gregory was suggesting are on our slowest platform: Windows. If
not, they will probably translate to minutes on Windows, which is
unacceptable IMO.
Cheers,
Ehsan
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