[mgmt] release: 0.0.20 (function values/lambdas)

[James]

I've just released version 0.0.20 of mgmt!

> 295 files changed, 8585 insertions(+), 1413 deletions(-)

This was a very challenging release but it includes many useful changes
since 0.0.19, including:

* Function values / lambdas exist and are first-class
* Over 70 new tests have been added!
* Core functions, classes, and globals can now be written in mcl code
* A new compiler "Ordering" step was added

And much more...

DOWNLOAD

Prebuilt binaries are available here:
https://github.com/purpleidea/mgmt/releases/tag/0.0.20

NEWS

* After a long and challenging road, I finally got function values and
lambdas merged. If you find any bugs, please let me know! You can now
treat functions as first-class values, and even use them as closures by
capturing variable state.

* Over 70 new tests were added, most of which test the behaviour of the
new functions.

* Core packages always allowed you to write new functions in pure
golang, but now you can implement new functions, classes, and even
variables in native mcl code! It's still desirable and perhaps
efficient in some cases to want native golang implementations, but all
good programs self-host some of their stdlib in their own language
eventually.

* A new compiler step called "Ordering" was added. It's hidden inside
the SetScope step, but now lets us generate code ordering graphs and
determine exactly what to run first.

* Light copying of Node's allows more correct and efficient function
graphs that can share common vertices and edges. For example, if two
different closures capture a variable $x, they'll both use the same
copy when running the function, since the compiler can prove if they're
identical.

* Improved the type system slightly to allow advanced type comparisons.

* The type unification algorithm was improved. Hopefully it should
solve all scenarios without needing the recursive solver which was very
slow. If you find a case that isn't speedy, please let us know!

* Added subtest listing by using -short and -v in a test. This lets you
know what's available and how to run individual sub tests easily.

* Support for the systemd STATE_DIRECTORY and xdg cache dir was added
by new contributor John! Thanks!

* New contributor Adam added a pgraph test.

* A bug in the systemd mount resource was fixed. Hopefully it should
work correctly now.

* A bug that prevented us from allowing nested system imports was
fixed. Nest away! This will pave the way for us to automatically import
most of the golang standard library by doing: import "golang/regexp" or
golang/whatever".

* Added an example showing that unicode is allowed in strings.

* Fixed a rare race in the engine.

* Added some new core functions including math.mod and datetime
improvements.

* Changed the API to remove the use of --lang. This avoids the
stuttering.

* Moved to golang 1.11 and etcd 3.3.13. The later includes a fix for an
un-catchable error scenario which we fixed in etcd.

* Improved the pgraph library significantly so that we can generate
better graphs with accurate vertices based on the vertex pointers.

* Added ArchLinux OS family detection.

* We're looking for help writing Amazon, Google, DigitalOcean, etc
resources if anyone is interested, reach out to us. Particularly if
there is support from those organizations as well.

* Many other bug fixes, changes, etc...

* See the git log for more NEWS, and for anything notable I left out!

BUGS

* There are a few known issues with some disabled code paths in the new
function value code. These issues don't *need* to be fixed, but if they
are, then we should see a slight performance increase. Happy to have
someone dig into these, and they shouldn't bother anyone.

* Some of the pre-built binaries might not work on your system. We need
to start building them with the right dependencies so that `ldd`
related things are happy. For now, please try building yourself if the
build doesn't work for you, or help improve our build system.

TALKS

I'll be giving a talk at an upcoming mini-conference in Montreal. If
you're interested in attending, please let me know.
If you'd like to give an mgmt talk somewhere, please let me know!

MISC

We're still looking for new contributors, and there are easy, medium
and hard issues available! You're also welcome to suggest your own!
Please join us in #mgmtconfig on Freenode IRC, or ping this list if
you'd like help getting started! For details please see:

https://github.com/purpleidea/mgmt/blob/master/docs/faq.md#how-do-i-con
tribute-to-the-project-if-i-dont-know-golang

Many tagged #mgmtlove issues exist:
https://github.com/purpleidea/mgmt/issues?q=is%3Aissue+is%3Aopen+label%
3Amgmtlove

MENTORING

We offer mentoring for new golang/mgmt hackers who want to get
involved. This is fun and friendly! You get to improve your skills,
and we get some patches in return. Ping me off-list for details.

THANKS

Thanks (alphabetically) to everyone who contributed to the latest
release:
Adam Sigal, Christian Rebischke, Felix Frank, James Shubin, Jan
Martens, Johan Bloemberg, John Hooks, Ward Vandewege
We had 8 unique committers since 0.0.19, and have had 67 overall.
run 'git log 0.0.19..0.0.20' to see what has changed since 0.0.19


Happy hacking,
James
@purpleidea

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