FIX singleton module issue for manager & theme not being set correctly

[ndelangen]

Issue: #5663

What I did

• enforce singleton modules of storybook packages for the manager
• add a safety check for theme

[shilman]

I don't like this safety check. I feel like this is going to hide bugs. Can we fail fast here instead?

[ndelangen]

Fail when anything is missing in the theme?

[shilman]

Yeah, so the stack trace leads you to the error check, rather than in the depths of some component where it's unclear whether it's a bug in the theme or a bug in the component.

[ndelangen]

I agree on your point that it may hide bugs, but I think throwing on a missing property will cause issues later if we're adding something to the theme.

In that scenario, anything we add to the theme object, will break every theme users have made.

I think some grace is appropriate here, likely the worst that is to happen is, some styling inconsistency in someone's storybook, not broken one.

[ndelangen]

My suggestion:

The storybook continues to function with the light theme merged in.

[shilman]

OK, this looks better to me. Thanks!

[codecov]

Codecov Report

Merging #5679 into next will decrease coverage by 0.11%.
The diff coverage is 8.57%.

@@            Coverage Diff             @@
##             next    #5679      +/-   ##
==========================================
- Coverage   33.35%   33.24%   -0.12%     
==========================================
  Files         647      648       +1     
  Lines        9332     9363      +31     
  Branches     1324     1330       +6     
==========================================
  Hits         3113     3113              
- Misses       5604     5635      +31     
  Partials      615      615

Impacted Files	Coverage Δ
lib/ui/src/core/context.js	9.52% <0%> (-0.48%)	⬇️
.../core/src/server/manager/manager-webpack.config.js	0% <0%> (ø)	⬆️
lib/ui/src/index.js	63.63% <0%> (ø)	⬆️
lib/theming/src/index.ts	0% <0%> (ø)	⬆️
lib/theming/src/ensure.ts	0% <0%> (ø)
lib/client-logger/src/index.ts	100% <100%> (ø)	⬆️

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[tmeasday]

I like this, the resolve solution for singletons is about the best we can do.

Also warning on missing theme props is probably what we want.

👍