I wanted to write an integration test to replace the following unit test:
https://searchfox.org/mozilla-central/source/devtools/client/debugger/src/actions/sources/tests/newSources.spec.js#134-172
Where we assert that a slow loading sourcemap doesn't delay loading the other ones.

But while writing this integration test, I realized that things were broken while sourcemap were loading. You could set a breakpoint on the generated source while the sourcemap was loading. And breakpoints weren't fully functional even if you set them beforehand.

This goal of this bug is to provide this integration test and try to fix the underlying issues, if possible.

We had some unit tests to cover slow-loading source maps,
but they were only covering sources management.
I'm converting them to an integration test, so that we can assert
that the debugger is fully function while the source maps are loading.

We were blocking breakpoint setting and hitting code on the calls to mapLocation/updateFrameLocation,
which were waiting for the sourcemap to load.
Instead we should consider setting the breakpoint only on the generated location.
And when we hit a breakpoint, we should only try to map the frame if
the generated source has an original source already registered.

The severity field is not set for this bug.
:Honza, could you have a look please?

For more information, please visit auto_nag documentation.

There are some r+ patches which didn't land and no activity in this bug for 2 weeks.
:ochameau, could you have a look please?
If you still have some work to do, you can add an action "Plan Changes" in Phabricator.
For more information, please visit auto_nag documentation.

Fixing this particular issue introduces more issues as highligted on phabricator.
We will get back to this after having simplified the debugger some more in bug 1749767 project.