Guess Erlang Application Scattering

Geas : (In Irish folklore) an obligation or prohibition magically imposed on a person.

By extension, obligation or prohibition imposed by an Erlang application or module, which may modify its scattering.

Geas is a tool detecting the runnable official Erlang release window for your project.

Geas will tell you also :

• what are the offending functions in the beam/source files that reduce the available window.
• if some beam files are compiled native.
• the installed patches and recommend patches that should be installed depending your code.

For example , if a dependency is using application:ensure_all_started/1 your project can only be used starting R16B02 or if maps is used somewhere, starting 17.0. On contrary, pg module cannot be used after 17.5 but is back again in 23.0.

For more details, see Wiki.

Geas is also available on hex.pm.

Help this project to be maintained ! If you find this project useful, please donate to:

Bitcoin: 1Ep9VoyNtnNiGoXM52V6NwcMh4SZ9bxkAG
Ethereum: 0xfac5e46ffe12ec1fc2830d95c22e6583d163d7f9 

• Each time you prepare a project release or update a dependency.
• When you plan to add a dependency to your project
• When writing your README, to inform your project's users on possible release window
• To limit test of CI tools on only possible release window

geas is available as a module, but you will probably prefer to use geas plugins with your usual build tool.

Plugin is available for erlang.mk and rebar .

Example on a test project using cowboy :

   R15                   26.1       Geas database                      2.7.14
---Min--------Arch-------Max----------------------------------------------------
   R16B                  23.3       cowboy                              1.0.4
                         19.3       cowlib                              1.0.2
                         23.3       ranch                               1.2.1
   R16B03                18.1       test                                0.0.1
--------------------------------------------------------------------------------
   R16B03                18.1       Global project                      0.0.1

C : 26.0
T : >=R16B03 <=18.1

./_build/default/lib/cowboy/ebin/cowboy_clock.beam
R16B      erlang:integer_to_binary/1

./_build/default/lib/cowboy/ebin/cowboy_handler.beam
23.3      erlang:get_stacktrace/0

./_build/default/lib/cowboy/ebin/cowboy_req.beam
R16B      erlang:integer_to_binary/1

./_build/default/lib/cowboy/ebin/cowboy_rest.beam
23.3      erlang:get_stacktrace/0

./_build/default/lib/cowboy/ebin/cowboy_static.beam
R16B      erlang:integer_to_binary/1

./_build/default/lib/cowboy/ebin/cowboy_websocket.beam
R15B02    crypto:hash/2

23.3      erlang:get_stacktrace/0

./_build/default/lib/cowlib/ebin/cow_multipart.beam
19.3      crypto:rand_bytes/1

./_build/default/lib/ranch/ebin/ranch_ssl.beam
23.3      ssl:cipher_suites/0, ssl:ssl_accept/2

./_build/default/lib/test/ebin/test.beam
R16B03    ssh_message:encode_host_key/1

18.1      ssh_message:encode_host_key/1
===> Current Erlang/OTP release is incompatible with project release window

Current (C) Erlang release found is 26.0 and no patches (P) was detected. The global project can run starting R16B03 up to 18.1 in such case, due to use of a function introduced in R16B03 and another one removed in 18.2. No native compilation was detected on any module. Recommended patches (R) is optionally proposed when an application used in code is referenced in a not installed patche, even if in this example, current Erlang release cannot run the project.

Output can be tuned depending some environment variables.

Note : starting version 2.6, variables can be set in rebar.config.

Environment variables cheatsheet :

Under compat table output, some information can be shown depending those environment variables and analyze result. A single capital letter is used as tag for each information.

• C = Current : Current Erlang major.minor release used (for example 20.2)
• P = Patches : List of patches detected to be installed on current release, if any (for example 20.2.2)
• T = Total : All releases inside computed release window GEAS_MY_RELS=""
• L = Local : All local releases given by user inside computed window GEAS_MY_RELS="18.1 19.0"
• D = Discarded : Show releases that was automatically discarded GEAS_DISC_RELS=1
• E = Excluded : User excluded release list GEAS_EXC_RELS="R16B03"
• R = Recommended : Patches that should be applied, because code is using module impacted by a patch for current version GEAS_TIPS=1

git clone git://github.com/crownedgrouse/geas.git
cd geas
make
make shell

Contributions are welcome. Please use pull-requests.