I recently landed changes (
https://bugzilla.mozilla.org/show_bug.cgi?id=1879329) to how Glean
generates C++ headers from metrics defined in metrics.yaml files.
It used to generate a single GleanMetrics.h file that every C++ file using
Glean had to include, which meant that any change to any Glean metric
caused a change of that big header, which triggered broad rebuilds of
platform code.
It will now generate a header file per metrics.yaml file allowing C++ code
to include only relevant subsets of metric definitions.
The names of header files are based on the path to the metrics.yaml file
(inspired from what is done for StaticPrefs headers). The folder
separators, - and _ characters are replaced with an uppercase letter in the
path.
For example, to include metric definitions from
toolkit/profile/metrics.yaml, the C++ code will now #include
"mozilla/glean/ToolkitProfileMetrics.h"
Some exceptions were made to the general rule to make file names shorter
and nicer:
- The ‘/base/‘ folders are ignored. (ie. the header is named
BrowserContentMetrics.h rather than BrowserBaseContentMetrics.h)
- {browser,toolkit}/components/componentname/metrics.yaml is treated as if
it was just componentname/metrics.yaml (ie. include PlacesMetrics.h rather
than BrowserComponentsPlacesMetrics.yaml)
To see the full list of exceptions or if you need to add more, you can find
the code generating header names in
https://searchfox.org/mozilla-central/source/toolkit/components/glean/build_scripts/glean_parser_ext/metrics_header_names.py
All the existing includes of GleanMetrics.h have been rewritten.
--
Florian Quèze
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