Fix a laundry list of warnings involving unused imports that glutted
up compilation output. There are more, but there seems to be some
false positives (where 'remedy' appears to break the build), but this
particular set of fixes seems safe.
These commits perform a variety of actions:
1. The linting of missing documentation has been consolidated under one `missing_doc` attribute, and many more things are linted about.
2. A test was added for linting missing documentation, which revealed a large number of corner cases in both linting and the `missing_doc` lint pass. Some notable edge cases:
* When compiling with `--test`, all `missing_doc` warnings are suppressed
* If any parent of the current item has `#[doc(hidden)]`, then the `missing_doc` warning is suppressed
3. Both the std and extra libraries were modified to `#[deny(missing_doc)]` by default.
I believe that the libraries are getting to the point where they're fairly well documented, and they should definitely stay that way. If developing a particular new module, it's easy enough to add `#[allow(missing_doc)]` at the top, but those should definitely be flags for removal in favor of actual documentation.
I added as much documentation as I could throughout std/extra, although I avoided trying to document things that I knew nothing about. I can't say that this lint pass will vouch for the quality of the documentation of std/extra, but it will certainly make sure that there's at least some describing words.
That being said, I may have a different opinion, so I don't mind amending these commits to turn off the lint by default for std/extra if people think otherwise.
This refactors pass handling to use the argument names, so it can be used
in a similar manner to `opt`. This may be slightly less efficient than the
previous version, but it is much easier to maintain.
It also adds in the ability to specify a custom pipeline on the command
line, this overrides the normal passes, however. This should completely
close#2396.
Fix#6805: add --enable-ccache configure option to prefix compiler invocations with `ccache` to attempt to reuse common results, e.g. for LLVM (re)builds.
The information at developer [Note-ccache](../../wiki/Note-ccache) and at [ccache and clang concerns](http://petereisentraut.blogspot.fr/2011/09/ccache-and-clang-part-2.html) were what drove my introduction of the `-Qunused-arguments` and `CCACHE_CPP2` options. (Though I did confirm first-hand that at least the first really is necessary.)
Yes, one certainly can re-route how `gcc` and `clang` are resolved in one's PATH and use that as a way to invoke `ccache`. But I personally do not want to introduce that change to my own PATH, and this seems like a small enough change that it does not hurt to add it, at least for now. (I don't know what form it would take when we move over to `rustpkg`.)
