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Polysquare CI Scripts

Polysquare CI Scripts (common to a few modules).

A redirect to the raw version of these scripts exists at You can curl them to a python interpreter.

$(curl -LSs |
  python /dev/stdin -s setup/project/


Travis CI AppVeyor Coverage
Travis AppVeyor Coverage


The idea behind these scripts is that their output is intended to be evaluated by the parent shell. The main work is done inside the script itself (eg, in python) and then we rely on the parent shell to save environment variables and other state between script steps.

What these scripts do is set up a "container" with installations of various programming languages or libraries in a self-contained manner. They can be re-used across builds by adding the specified container to the cache key of your /.travis.yml file.

/ is responsible for creating or re-using a container and then executing a script which makes use of that container in some fashion.

Bootstrap CI Scripts

optional arguments:
  -h, --help            show this help message and exit
  -d DIRECTORY, --directory DIRECTORY
                        Directory to store language runtimes, scripts and
                        other script details in
  -s SCRIPT, --script SCRIPT
                        Script to pass control to
  -e, --eval-output     Evaluate output
                        Directory where scripts are already stored in

The script passed to --script is expressed as a path relative to the current directory, or, if such a file does not exist, then a path relative to the ciscripts directory as hosted on Scripts are downloaded on-the-fly if they don't exist. This means that if you have a project using a particular language that doesn't differ from the way most projects using that language works, you can just refer to that language's setup script and run it.

Scripts passed to --script must have a function named run defined as follows:

def run(container, util, parent_shell, **kwargs):

Scripts and their functions

Bootstrap script

This script passes control to other scripts. It also defines a function in the parent shell called polysquare_run which provides a shorthand way of calling itself in future.

Setup scripts

Setup scripts are located at /ciscripts/setup/language/ where language indicates the language-type of the project which should be set up. The output of a setup script should be evaluated as it will set environment variables in the parent scope. Usually these environment variables will be set in order to 'activate' a certain language installation in the container.

Setup scripts ensure that a project's dependencies are installed.

Check scripts

Check scripts are located at /ciscripts/check/language/ where language indicates the language-type of the project which will be checked. This step is responsible for running both static analysis, builds and any linters. The output of these scripts does not need to be evaluated.

Clean script

The clean script is located at /ciscripts/ and is responsible for cleaning out any set up language installations before the container directory is compressed and uploaded for caching. Usually the various language installations will register themselves in a text file upon installation and this script will get a handle for their container and call its clean method.

The files cleaned are usually temporary files, source code, static libraries, documentation and other files which are not necessary for installing any additional programs or libraries in that language installation.

Deploy script

Usually most languages will not provide this. However, in the case where something from a language container is required for the deploy step, this script can be evaluated and called from the bootstrap script in order to set that thing up. It cannot be called with polysquare_run in the deploy step as environment variables and functions are not defined at this point.

Writing your own scripts

Generally speaking, scripts are designed to be called from other scripts and / They should have a run function with the signature as discussed earlier.

Scripts should never use any functionality that is not in the python standard library, as there is no opportunity to install dependencies safely with pip.

The parent shell

Scripts should never print anything to the standard output, except by using the parent_shell variable passed to them. The standard output is evaluated by the parent shell, but the standard error is displayed on screen.

The parent_shell variable defines the following functions:

  • overwrite_environment_variable: Causes environment variable key to be overwritten with value.
  • remove_from_environment_variable: Removes value from an environment variable list specified at key.
  • prepend_environment_variable: Prepend value to environment variable list at key.
  • define_command: Define a function which calls a specified command with its arguments key.
  • exit: Causes the shell to exit with a certain status.

Generally speaking you wouldn't use any of these functions directly, but you would pass the parent_shell to an equivalent function on the util object, which will also set environment variables in the current scope too.


Dependencies between scripts must be expressed as passing modules around as keyword arguments to the run function of those scripts. Fetch a module using the fetch_and_import function on a container object. This will ensure that the script is downloaded or re-used appropriately. Never express dependencies as imports.

The container object

The ContainerDir object is responsible for managing the "container" directory specified on the command-line to / It manages three internal directories:

  • _languages: For all installations of programming languages which are not the language being used as the project language on travis-ci.
  • _scripts: A local mirror of downloaded scripts.
  • _cache: Both "named" and temporary cache directories.

The idea is that these directories are preserved between builds, to avoid expensive re-installation of dependencies that we've already installed.

Language directories

Any language directory expressed as a subclass of LanguageBase functions in a similar way to the parent container directory. Language installations are "activatable" in the sense that they all export the activate, deactivate, activated and deactivated functions and context managers. These functions set environment variables both in the local scope and parent scope to ensure that dependencies are installed in to this language installation and that any interpreters and compilers are launched from this language installation.

In order to implement a new type of language directory, you should subclass the LanguageBase class. The main assumption is that any language subclass will be created for a directory that already has that language installed, so you will need to handle that yourself before creating the class.

Usually the subclass will implement the following functions:

  • clean: This function is responsible for cleaning out the language directory such that it would be a suitable candidate for being cached. This means that all temporary files, documentation, build files and unneeded source code are removed.
  • _active_environment: This function specifies the values that certain environment variables will have when the language installation is considered "active". It returns a tuple as specified in its tuple_type argument with the overwrite member set to a dictionary of environment variables and their new values (overwriting the old ones) and the prepend value set to a dictionary of environment variables and values to prepend to their existing value.

Indicating which task is being run

Usually you wouldn't print anything to the standard error by yourself, but instead use the Task API to specify when a task is being run. Tasks are printed in a nested fashion. When task A is still running and task B starts, it is considered a "sub-task" of task A and printed as indented within it.

In order to indicate that a certain task is running for a set of commands use Task as a context manager, for example:

with util.Task("Performing some action"):
    with util.Task("Performing sub-action one"):
    with util.Task("Performing sub-action two"):

Executing commands

Some wrappers around the subprocess module are provided to execute certain tasks and manage their output and return code.

The main function is the execute function in the util module. This takes a ContainerDir and an output-management mode as its first two arguments, with its remaining arguments being the arguments to pass to the command itself.

The output management modes are as follows:

  • util.output_on_fail: Suppress all output unless there is an error, showing it on the correct indent level.
  • util.running_output: Show output by default, on the correct indent level.
  • util.long_running_suppressed_output(N): Like util.output_on_fail but prints dots every N seconds while the command is running. This ensures that for long running commands travis-ci will not time out waiting for additional output.

Functional programming constructs

The util module also provides some functions which simplify a number of operations across files:

  • util.where_unavailable: Runs function with *args and **kwargs where executable is not found in the system's PATH.
  • util.apply_to_files: Apply func to all files in tree_node which match patterns in matching and do not match patterns in not_matching, recursively.
  • util.apply_to_directories: Apply func to all directories in tree_node which match patterns in matching and do not match patterns in not_matching, recursively.


Polysquare CI Scripts (common to a few modules)







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