=== Why
* More speed
In debug mode, the server should regenerate the startup manifest
on each page view to ensure immediate effect of changes. But,
this also means more version recomputation work on the server.
For most modules, this was already quite fast on repeat views
because of OS-level file caches, and our file-hash caches and
LESS compile caches in php-apcu from ResourceLoader.
But, this makes it even faster.
* Better integration with browser devtools.
Breakpoints stay more consistently across browsers when the
URL stays the same even after you have changed the file and
reloaded the page. For static files, I believe most browsers ignore
query parameters. But for package files that come from load.php,
this was harder for browsers to guess correctly which old script URL
is logically replaced by a different one on the next page view.
=== How
Change Module::getVersionHash to return empty strings in debug mode.
I considered approaching this from StartupModule::getModuleRegistrations
instead to make the change apply only to the client-side manifest.
I decided against this because we have other calls to getVersionHash
on the server-side (such as for E-Tag calculation, and formatting
cross-wiki URLs) which would then not match the version queries that
mw.loader formats in debug mode.
Also, those calls would still be incurring some the avoidable costs.
=== Notes
* The two test cases for verifying the graceful fallback in production
if version hash computations throw an exception, were moved to a
non-debug test case as no longer happen now during the debug
(unminified) test cases.
* Avoid "PHP Notice: Undefined offset 0" in testMakeModuleResponseStartupError
by adding a fallback to empty string so that if the test fails,
it fails in a more useful way instead of aborting with this error
before the assertion happens. (Since PHPUnit generally stops on the
first error.)
* In practice, there are still "version" query parameters and E-Tag
headers in debug mode. These are not module versions, but URL
"combined versions" crafted by getCombinedVersion() in JS and PHP.
These return the constant "ztntf" in debug mode, which is the hash
of an empty string. We could alter these methods to special-case
when all inputs are and join to a still-empty string, or maybe we
just leave them be. I've done the latter for now.
Bug: T235672
Bug: T85805
Change-Id: I0e63eef4f85b13089a0aa3806a5b6f821d527a92
008b6528b6