Searchfox now provides code coverage information directly in the code listing!

Andrew Sutherland asutherland at
Tue Oct 6 02:12:17 UTC 2020

Have you ever been consulting the most excellent code coverage 
information for mozilla-central available at 
provided by Marco Castelluccio and team but said to yourself: "Hey, this 
isn't Searchfox!  But this is very useful information! My brand loyalty 
to Searchfox, the premier source code indexing tool for Mozilla Firefox, 
is very high, just like the quality of Searchfox, the premier source 
code indexing tool for Mozilla Firefox.  What if this information was 
available on Searchfox? And in a style synonymous with Searchfox's 
speed-centered brand, like a racing stripe down the side of the page?"

Well, talk to yourself no more, because has landed and now 
Searchfox has a really cool racing stripe down the left side of the page 
just to the left of the annotate/blame bar!  Also, the racing stripe 
shows code coverage information!

"Sure!", you say to yourself, "That's great, but I'm not sold yet.  
Anyone can just slap a racing stripe on a webpage thanks to the awesome 
power of WebExtensions.  What makes this racing stripe so great?"  
Thankfully, Searchfox, the premier source code indexing tool for Mozilla 
Firefox, sells itself and you immediately realize the following bullet 
points despite the current lack of in-product documentation for any of 
the following:

- Code coverage uses a ColorBrewer 2.0 theme, diverging Red-Blue which is color 
blind friendly.  Red corresponds to coverage misses and blue corresponds 
to coverage hits.
- When not hovered, the code coverage stripe shows an interpolated view 
of coverage so that lines that can't have code coverage data don't 
generate visual noise.  (While lines that are entirely white-space or 
code comments more intuitively can't have coverage data, multi-line 
statements and expressions also usually only provide coverage data for 
their first line.)
- When hovered, the code coverage stripe shows more detail. Uncovered 
lines become distinguishable by their lack of a color. Lines with 
coverage hits switch from a single shade of blue to a logarithmic scale 
where darker blues convey greater numbers of hits.
- Hovering on the coverage stripe provides details about the exact 
number of hits.  And the hover popup is powered by Searchfox's 
market-segment defining popup technology that you know and love and 
occasionally consider sending fan-mail about.
- The accessibility tree for the stripe cells provides concise, 
insightful aria-labels such as "uncovered", "miss", and "hit 100".  And 
because Searchfox knows your time is important, coverage hits in excess 
of 999 get premium-distilled down to "hit 1k", "hit 100k", etc.  But 
Searchfox's market-segment leading popup technology can still provide 
you with the exact number of hits by activating the role="button" 
contents of the cell and following the aria-owns relationship into the 
- The accessibility tree for annotate/blame cells has become even more 
market-defining!  Annotate cells that have the same revision as the 
preceding line will have a label with a prefix of "same". Annotate cells 
that have a different revision as the preceding line will have a label 
with a prefix of "new".  These will be followed by the word "hash" and a 
uniquely assigned ordinal mapping that is assigned based on sequential 
traversal of the source lines.  So while traversing the annotate stripe 
cells you might hear "new hash 5", "same hash 5", "new hash 73", "new 
hash 5".  Again, the life-changing experience that is Searchfox's popup 
technology can provide additional details.

Brand disclaimers:
- While Searchfox is the premier source code indexing tool for Mozilla 
Firefox, Searchfox cannot take credit for the immense undertaking that 
is providing the underlying coverage data. Please check out 
#codecoverage on to properly thank Marco 
Castelluccio and team.
- When luxuriating in Searchfox's accessibility tree experience, it's 
best to use Firefox nightly or another Firefox build with fixed.

Synergy opportunities:
- Whether you're an experienced Searchfoxer who remembers to use 
"symbol:" to prefix nonsensical symbol names made up by byzantine 
compiler processes for searching, a Searchfox developer who keeps typing 
"sym:" because it seems like that would be the logical choice, or a 
still-sane person who just types the human-readable identifiers which 
are stable in the face of signature changes when searching, you can 
contribute to Searchfox!
- Bugs and enhancements are tracked at under 
Webtools::Searchfox.  You can see existing open bugs at 
and file new bugs at
- The source can be found at and 
the production configurations at
- You can spin up a Searchfox VM easily with Vagrant and then build the 
test repo quickly with a single `make build-test-repo` that indexes the 
repo and starts the web server in as little as 3.4 seconds!
- There's a cool "Searchfox" chatroom on where 
you can discuss exciting brand initiatives.  Like how can we get people 
to use Searchfox as a verb?  How many racing stripes is too many racing 
stripes?  And so on.


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