tree 3625e032abf15fc532890a7b2182ce4df8318d84
parent ce2f0cff74c384f56457b1959fac40e9bab1b16a
author Oliver Newman <olivernewman@google.com> 1694619535 +0000
committer CQ Bot <fuchsia-internal-scoped@luci-project-accounts.iam.gserviceaccount.com> 1694619535 +0000

[engine] Expose runtime-configurable variables to checks

Makes a new `ctx.vars.get()` field available to checks that is used to
retrieve optional runtime-configurable values passed into shac via
`--var name=value` command-line flags.

In order to be set at runtime, a var must be declared beforehand in
shac.textproto with an optional default value. Centralizating the list
of allowed variables differs from the strategies taken by lucicfg and
GN, which both allow any file to declare arbitrary runtime-configurable
variables. However, that approach makes it much harder to discover the
list of allowed variables, and makes it much easier to add new
runtime-configurable variables.

A proliferation of runtime-configurable variables is not desired for
shac because it would open the door to divergence between local
workflows and CI, e.g. if CI sets many variables to non-default values
then it would become difficult to accurately reproduce CI results
locally. Therefore, vars should only be used when absolutely necessary
and only for passing through opaque parameters rather than tweaking
behavior. The most immediate use case is for passing in the path to a
repository's build directory into shac so shac can run executables and
read artifacts from the build directory.

Bug: 82386
Change-Id: I18cacfc8d9800e4d784c108389e697b5d6b12bc1
Reviewed-on: https://fuchsia-review.googlesource.com/c/shac-project/shac/+/915494
Reviewed-by: Anthony Fandrianto <atyfto@google.com>
Fuchsia-Auto-Submit: Oliver Newman <olivernewman@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>