Some selectors, such as fuzzy and syntax, allow saving and loading presets from a file. This is a good way to reuse a selection, either at a later date or by sharing with others. Look for a ‘preset’ section in mach <selector> --help to determine whether the selector supports this functionality.

Using Presets

To save a preset, run:

$ mach try <selector> --save <name> <args>

For example, to save a preset that selects all Windows mochitests:

$ mach try fuzzy --save all-windows-mochitests --query "'win 'mochitest"
preset saved, run with: --preset=all-windows-mochitests

Then run that saved preset like this:

$ mach try --preset all-windows-mochitests

To see a list of all available presets run:

$ mach try --list-presets

Editing and Sharing Presets

Presets can be defined in one of two places, in your home directory or in a file checked into mozilla-central.

Local Presets

These are defined in your $MOZBUILD_STATE_DIR, typically ~/.mozbuild/try_presets.yml. Presets defined here are your own personal collection of presets. You can modify them by running:

$ ./mach try --edit-presets

Shared Presets

You can also check presets into mozilla-central in tools/tryselect/try_presets.yml. These presets will be available to all users of mach try, so please be mindful when editing this file. Make sure the name of the preset is scoped appropriately (i.e doesn’t contain any team or module specific terminology). It is good practice to prefix the preset name with the name of the team or module that will get the most use out of it.

Preset Format

Presets are simple key/value objects, with the name as the key and a metadata object as the value. For example, the preset saved above would look something like this in try_presets.yml:

    selector: fuzzy
    description: >-
        Runs all windows mochitests.
        - "'win 'mochitest"

The selector key (required) allows mach try to determine which subcommand to dispatch to. The description key (optional in user presets but required for shared presets) is a human readable string describing what the preset selects and when to use it. All other values in the preset are forwarded to the specified selector as is.