This enforces our use of a consistent style in how we access Python
modules; "from os.path import dirname" is a particularly popular
abbreviation inconsistent with our style, and so it deserves a lint
rule.
Commit message and error text tweaked by tabbott.
Fixes#6543.
Modify `generate_sha1sum_node_modules()` such that it can calculate
the hash for a particular installation.
Tweaked by tabbott to use os.path.realpath in the setup_dir
calculation, to ensure it's consistent.
Since we can use both perfer_offline=True and False in a since build
prefer_offline shouldn't be used as a cache key or it will confuse the
cleanup script. Since yarn install (if successful) should be idempotent.
This will probably be ok.
Basically we just seperate out the sha1sum generation for the
node modules so that it can be reused later for cache clearance
logic. This is achieved by adding a function which returns the
sha1sum based HEX digest.
Previously, success_stamp was touched whenever we used a particular
node_modules version; it makes more sense to only touch it when the
node_modules directory has actually changed.