Hide UndefVarError if the upstream cell errored

[HirumalPriyashan]

• Addresses Hide UndefVarError if the upstream cell errored #1179

Implementation details

• check whether the current is erred due to a UndefVarError.
• find that undefined variable and check whether its due to an error in an upstream cell
• if the err is due to an err in upstream cell, replace the current cell output with upstream cell's erred output

New behavior

[github-actions]

Try this Pull Request!

Open Julia and type:

julia> import Pkg
julia> Pkg.activate(temp=true)
julia> Pkg.add(url="https://github.com/HirumalPriyashan/Pluto.jl", rev="fix-1179")
julia> using Pluto

[fonsp]

Do you think that it is possible to implement this in https://github.com/fonsp/Pluto.jl/blob/main/frontend/components/ErrorMessage.js instead? And always be sure to give a (short) description to you PR: how is it implemented, maybe explain why you chose this implementation, and show screenshots/videos of the new behaviour.

[HirumalPriyashan]

@fonsp

Do you think that it is possible to implement this in https://github.com/fonsp/Pluto.jl/blob/main/frontend/components/ErrorMessage.js instead?

I have taken this approach as we don't have access to cell result of errored upstream cell (notebook.cell_results[upstream_cell_id]) in ErrorMessage.js

But seems like we can get those values through pluto_actions.get_notebook() in ErrorMessage.js. Will check the possibility of that approach and update the PR.

And always be sure to give a (short) description to you PR: how is it implemented, maybe explain why you chose this implementation, and show screenshots/videos of the new behaviour.

Updated the PR description.

[HirumalPriyashan]

@fonsp

Updated the PR using https://github.com/fonsp/Pluto.jl/blob/main/frontend/components/ErrorMessage.js .
Since there is no point of showing upstream error body in the current cell, updated the msg with a new error msg.

New behavior

[fonsp]

Some ideas:

• Can you make it recursive? i.e. if you have three cells, x = sqrt(-1), y = x, z = y, then the last two cells should show the redirect message instead of an undefvarerror.
• What happens when there are multiple upstream variables? E.g. a = b = sqrt(-1), a + b.
• Can you insert a clickable link to the upstream variable(s)?
• Let's remove the stack trace

[HirumalPriyashan]

• Can you make it recursive? i.e. if you have three cells, x = sqrt(-1), y = x, z = y, then the last two cells should show the redirect message instead of an undefvarerror.
• Let's remove the stack trace

At the moment, these two are already available with the changes. Please let me know if I did not understand it correctly. But I think we can point error in the third cell to a since the error is due to failure of computing of a not b.

• What happens when there are multiple upstream variables? E.g. a = b = sqrt(-1), a + b.

Right now, it just displays the first upstream cell which identified as errored. But sure, we can update it for multiple variables.

• Can you insert a clickable link to the upstream variable(s)?

Sounds cool, yes we can do that.

[HirumalPriyashan]

New behavior

• Added a clickable link for upstream variables
• Notice for the fifth cell errors are produced for the root cause, since c is errored due to a and b.

Edit:
Update after commit 8e0aaee

• Removed the stacktrace

[fonsp]

This is great, thanks @HirumalPriyashan !!

I made some small changes, including:

• dd0a631 (#2057): this is not really internal state (you don't want this value to persist across renders)
• 1bb4aae (#2057) this fixes this issue, which could be confusing/frustrating in a large cell with multiple errors.

[HirumalPriyashan]

Awesome, thanks.

[KronosTheLate]

I am late to the party, but want to give a huge appreciation for this fix <3