Bleeding-rez

Addressed Issues

* [556](https://github.com/nerdvegas/rez/issues/556) rez-cp briefly copies original package definition in non-varianted packages
* [555](https://github.com/nerdvegas/rez/issues/555) rez-cp inconsistent symlinking when --shallow=true
* [554](https://github.com/nerdvegas/rez/issues/554) rez-cp doesn't keep file metadata in some cases

Notes

There were various minor issues related to copying non-varianted packages.

Addressed Issues

* [551](https://github.com/nerdvegas/rez/issues/551) package copy fails if symlinks in root dir

Notes

This was failing when symlinks were present within a non-varianted package being copied. Now, these
symlinks are retained in the target package, unless `--follow-symlinks` is specified.

Addressed Issues

* [549](https://github.com/nerdvegas/rez/issues/549) '--build-system' rez-build option not always
available

Notes

To fix this issue:
* The '--build-system' rez-build option is now always present.
* To provide further control over the build system type, the package itself can now specify its build
system - see https://github.com/nerdvegas/rez/wiki/Package-Definition-Guidebuild_system

COMPATIBILITY ISSUE!

Unfortunately, the 'cmake' build system had its own '--build-system' commandline option also. This
was possible because previous rez versions suppressed the standard '--build-system' option if only
one valid build system was present for a given package working directory. **This option has been
changed to '--cmake-build-system'**.

Addressed Issues

* [433](https://github.com/nerdvegas/rez/issues/433): "package_definition_build_python_paths" defined
paths are not available from top level in package.py
* [442](https://github.com/nerdvegas/rez/issues/442): "rez-depends" and "private_build_requires"
* [416](https://github.com/nerdvegas/rez/issues/416): Need currently-building-variant build variables
* [547](https://github.com/nerdvegas/rez/issues/547): rez-cp follows symlinks within package payload

Notes

The biggest update in this release is the introduction of new variables accessible at early-bind time:
building, build_variant_index and build_variant_requires. This allows you to do things like define
different private_build_requires per-variant, or a requires that is different at runtime than it is
at build time. In order to get this to work, a package.py is now re-evaluated multiple times when a
build occurs - once pre-build (where 'building' is set to False), and once per variant build. Please
see the updated wiki for more details: https://github.com/nerdvegas/rez/wiki/Package-Definition-Guideavailable-objects

A new build-time env-var, REZ_BUILD_VARIANT_REQUIRES, has been added. This mirrors the new
build_variant_requires var mentioned above.

rez-depends has been updated to only include the private_build_requires of the package being queried
(previously, all packages' private build reqs were included, which is not useful). Recall that the
previous release fixes the issue where private_build_requires was being stripped from released
packages.

The entirety of a package definition file can now see the extra build-time modules available via the
package_definition_build_python_paths config setting. Previously, only early bound functions could
see these.

There was an issue with package copying (and thus the rez-cp tool) where symlinks within a package's
payload were expanded out to their source files at copy time. The default now is to keep such symlinks
intact - but hte previous behavior can still be accessed with the rez-cp --follow-symlinks option.

This release adds a new tool, rez-cp, for copying packages/variants from one package repository to
another, with optional renaming/reversioning. The associated API can be found in src/package_copy.py.

Addressed Issues

* 541
* 510
* 477

Notes

* Package definition file writes are now atomic;
* private_build_requires is kept in installed/released packages;
* Fixes include modules not being copied into released packages;
* File lock is no longer created when variant installation happens in dry mode.

Addressed Issues

* 532

Notes

Bug was introduced in: https://github.com/nerdvegas/rez/releases/tag/2.20.0