[tor-commits] [sbws/maint-1.1] fix: doc: Document why ersioneer to obtain version

[juga@xxxxxxxxxxxxxx]

commit cba9671ea52e3e2eda880d46fbca02fad01af5f6
Author: juga0 <juga@xxxxxxxxxx>
Date:   Thu Feb 27 16:54:15 2020 +0000

    fix: doc: Document why ersioneer to obtain version
---
 docs/source/implementation.rst | 98 ++++++++++++++++++++++++++++++++++++++++++
 docs/source/index.rst          |  1 +
 2 files changed, 99 insertions(+)

diff --git a/docs/source/implementation.rst b/docs/source/implementation.rst
new file mode 100644
index 0000000..7470b62
--- /dev/null
+++ b/docs/source/implementation.rst
@@ -0,0 +1,98 @@
+Implementation decissions
+=========================
+
+Dependencies
+------------
+
+When a needed feature is already implemented in some other software, there're
+usually some things to consider whether to use that software as dependency or
+re-implement the feature:
+
+Possible advantages using other software:
+
+- zero maintainance
+- not reinventing the wheel
+
+Possible disadvantages using other software:
+
+- maybe too big
+- maybe introduce security issues
+- maybe is not maintaned
+
+sbws version
+````````````
+
+Because some bwauths install sbws from the git repository, it is useful to
+know from which git revision they install it from.
+We'd prefer to do not see the git revision when it is installed from a git
+tag or Debian package (which is usually built from a git tag or git archive
+release).
+
+A first solution would be to obtain the git revision at runtime, but:
+
+- sbws is not usually running from the same directory as the git repository,
+  as the installation might install it in other directory.
+- if some other git repository is the current path, sbws might be obtaining
+  the git revision of that other repository.
+
+So next solution was to obtain the git revision at build/install time.
+To achive this, an script should be call from the installer or at runtime
+whenever `__version__` needs to be read.
+
+While it could be implemented by us, there're two external tools that achive
+this.
+
+setuptools_scm
+~~~~~~~~~~~~~~
+
+https://github.com/pypa/setuptools_scm/
+
+Advantages:
+
+- does what we want, for 19 commits after 1.1.0 tag it'd add an string like
+  `'1.1.1.dev19+g76ef2fe0.d20200221`.
+  We don't need the date, but it can probably be removed and it does not hurt.
+- we don't need to maintain it.
+
+Disadvantages:
+
+- it adds the extra dependency setuptools_scm.
+- it does not obtain the version from a git archive, though there's other tool
+  that does that.
+- the version reported comes only from build time, so if we make a commit
+  without running `setup.py`, sbws will not report the new version.
+
+versioneer
+~~~~~~~~~~
+
+https://github.com/warner/python-versioneer
+
+Advantages:
+
+- it does not add any extra dependency. The first time, versioneer needs to
+  be installed. When run, it will generate `versioneer.py` and `_version.py`,
+  which are created from versioneer itself.  Then it can be uninstall
+- does what we want, for 19 commits after 1.1.0 tag it'd add an string like
+  `1.1.0+19.g76ef2fe0`. Note the difference with `1.1.0` from he `1.1.1`
+  generated by
+- we don't need to maintain it.
+- it is also capable to obtain the version from a git archive.
+- the version reported at build time and runtime is the same.
+
+Disadvantages:
+
+- it adds extra code to sbws and it's quite a lot
+- the generated code is independent from the upstream and loses the tests.
+- does not seem maintained.
+
+Conclussion
+~~~~~~~~~~~
+
+Because `setuptools_scm` gives only the version at build time, we decided to
+use `versioneer`.
+We might need to change it in the future if starts giving problems with other
+git or python versions or we find a way to make `setuptools_scm` to detect
+the same version at buildtime and runtime.
+
+See `<https://github.com/MartinThoma/MartinThoma.github.io/blob/1235fcdecda4d71b42fc07bfe7db327a27e7bcde/content/2018-11-13-python-package-versions.md>`_
+for other comparative versioning python packages.
\ No newline at end of file
diff --git a/docs/source/index.rst b/docs/source/index.rst
index 9806ef3..342e857 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -45,6 +45,7 @@ Included in the
    config
    config_tor
    sbws
+   implementation
    bandwidth_distribution
    tor_bandwidth_files
    bandwidth_authorities

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