This allows the dependency queue to properly handle packages with the same
name but from different sources.
A test was added which exercieses this functionality by depending on two
different revs of the same git repo.
* Add a convenience method bin() for generating the name of a binary. On windows
this remembers to append `.exe`.
* Stop executing relative paths to binaries and relying on PATH. This is
suffering from rust-lang/rust#15149 and failing to spawn processes on windows.
Additionally, this allows the tests to work with a pre-installed cargo becuase
the freshly built executables are precisely specified.
* A new function, escape_path(), was added for tests. When generated source
files with paths, this function needs to be called to properly escape the
\-character that appears in windows path names. Without this function we would
be generating invalid TOML and rust.
This commit adds support for recognizing "fingerprints" of upstream
dependencies. When a dependency's fingerprint change, it must be rebuilt.
Currently the fingerprint unconditionally includes the version of the compiler
you're using as well as a specialized version depending on the type of source
you're compiling from:
- git sources return their fingerprint as the current SHA. This will
disregard any local changes.
- path sources return their fingerprint as the maximum mtime of any file found
at the location. This is a little too coarse and may rebuild packages too
often (due to sub-packages), but this should get the job done for now.
When executing `cargo compile`, dependencies are not rebuilt if their
fingerprint remained constant.
