Bug when passing getAllContexts() to new Component({ context })

[hgiesel]

Describe the bug

Some contexts are unexplicably removed from the map object when passing it to new Component().

From #6447 it seems like this was it's intended usage.

Reproduction

https://svelte.dev/repl/178ba9c6c46a43b9bcd8376262f1d021?version=3.42.6.
(note: In production, I would not render in a normal div, but rather in a shadow DOM)

Logs

No response

System Info

System:
    OS: macOS 11.5.2
    CPU: (8) x64 Intel(R) Core(TM) i7-1060NG7 CPU @ 1.20GHz
    Memory: 213.38 MB / 8.00 GB
    Shell: 5.1.4 - /usr/local/bin/bash
  Binaries:
    Node: 16.0.0 - /usr/local/bin/node
    Yarn: 1.22.5 - ~/.yarn/bin/yarn
    npm: 7.10.0 - /usr/local/bin/npm
  Browsers:
    Chrome: 93.0.4577.82
    Firefox: 92.0
    Safari: 14.1.2
  npmPackages:
    svelte: ^3.25.0 => 3.42.6

Severity

blocking all usage of svelte;
after this comment, it's just an annoyance (and pitfall)

[hgiesel]

It seems like the context you pass in is completely ignored, which is because of this line:

svelte/src/runtime/internal/Component.ts

Line 127 in dad0284

context: new Map(parent_component ? parent_component.$$.context : options.context || []),

which would need to be changed to give preference to options.context, something like this:

context: new Map(options.context || (parent_component ? parent_component.$$.context : [])),

[Conduitry]

Preferring options.context makes sense, I think, but I haven't thought through all of the implications of that. For now, to make sure parent_component isn't set, you can just avoid synchronously instantiating a component inside another one. Adding a setTimeout around the new GetContext makes this behave in the way you want.

[Conduitry]

This is fixed in 3.43.0 - https://svelte.dev/repl/178ba9c6c46a43b9bcd8376262f1d021?version=3.43.0