There are a few reasons that this is a desirable move to take:
1. Proof of concept that a third party event loop is possible
2. Clear separation of responsibility between rt::io and the uv-backend
3. Enforce in the future that the event loop is "pluggable" and replacable
Here's a quick summary of the points of this pull request which make this
possible:
* Two new lang items were introduced: event_loop, and event_loop_factory.
The idea of a "factory" is to define a function which can be called with no
arguments and will return the new event loop as a trait object. This factory
is emitted to the crate map when building an executable. The factory doesn't
have to exist, and when it doesn't then an empty slot is in the crate map and
a basic event loop with no I/O support is provided to the runtime.
* When building an executable, then the rustuv crate will be linked by default
(providing a default implementation of the event loop) via a similar method to
injecting a dependency on libstd. This is currently the only location where
the rustuv crate is ever linked.
* There is a new #[no_uv] attribute (implied by #[no_std]) which denies
implicitly linking to rustuv by default
Closes#5019
Namely, switched in many places to using GNU make provided functions
for directory listing and text processing, rather than spawning a
shell process to do that work.
In the process of the revision, learned about Target-specific
variables, which were very applicable to INSTALL_LIB (which, on a
per-recipe basis, was always receiving the same actual arguments for
its first two formal parameters in every invocation).
http://www.gnu.org/software/make/manual/html_node/Target_002dspecific.html
(We might be able to make use of those in future refactorings.)
----
Also adds a cleanup pass to get-snapshot.py as well, since the same
problem arises when we unpack libraries from the snapshot archive into
a build directory with a prior snapshot's artifacts. (I put this step
into the python script rather than the makefile because I wanted to
delay the cleanup pass until after we have at least successfully
downloaded the tarball. That way, if the download fails, you should
not destroy the previous unarchived snapshot libraries and build
products.)
----
Also reverted whitespace changes to minimize diff.
I plan to put them back in in a dedicated commit elsewhere.
When building Rust libraries (e.g. librustc, libstd, etc), checks for
and verbosely removes previous build products before invoking rustc.
(Also, when Make variable VERBOSE is defined, it will list all of the
libraries matching the object library's glob after the rustc
invocation has completed.)
When installing Rust libraries, checks for previous libraries in
target install directory, but does not remove them.
The thinking behind these two different modes of operation is that the
installation target, unlike the build tree, is not under the control
of this infrastructure and it is not up to this Makefile to decide if
the previous libraries should be removed.
This is an attempt to address Issue #3326 by adding [*order-only*][1]
prerequsites of each build product on the directory where it is to go.
It is important that the prerequisites be order-only, since the
timestamp on a parent directory is not relevant to whether a product
is out of date; the parent directory merely needs to exist.
(This use case of generating target directories was provided as an
[example][2] of how order-only prequisites are used.)
[1]: http://www.gnu.org/software/make/manual/html_node/Prerequisite-Types.html
[2]: http://www.kolpackov.net/pipermail/notes/2004-January/000001.html
This splits mk/stageN.mk into host.mk and target.mk and makes
the build rules somewhat simpler - there's no more building from stageN
into stageN+1; instead we always build from stageN(host) to
stageN(target) then promote from stageN(target) to stageN+1(host).
Add a big honkin explaination right at the top of Makefile.in
