Highlight destructive operations in makemigrations output

[Tom Forbes]

Makemigrations should highlight destructive and potentially destructive operations in the console output. We advise that makemigrations is only a code generator people sometimes apply them without looking. Highlighting dangerous operations in the output will make them stand out, and might help them notice issues before they blindly apply.

For example:

$ ./manage.py makemigrations ...
Migrations for 'some_app':
  some_app/migrations/0002_delete.py
    - Delete model SomeModel
    + Add model AnotherModel
    ~ Alter field X on Y

We can use - as a prefix for known destructive operations, + for "safe" operations and ~ for possibly-destructive operations, colour coded as red, green and yellow respectively.

Mailing list discussion: ​https://groups.google.com/d/msg/django-developers/A0m8YkPKpZo/Yx8l2P8EAQAJ

[Carlton Gibson]

I'm not sure about this: seems like visual noise for (I suspect) little benefit. I commented on the mailing list discussion: let's see how that goes.

[Carlton Gibson]

A similar example of a dangerous migration with a rename involving verbose_name has come up in #32206 and #24157. That looks like a case where a warning would come in handy.

​Tobias McNulty had a suggestion on the mailing list thread:

I'm +1 to doing *something.* Absent a louder reminder, I think it's unrealistic to expect everyone to read the output of makemigrations all the time.

As others have said, I'm not sure manage.py migrate is the right time. I think it's too late. The code may have already been committed, who knows what machine the migrations are being run on, etc.

During makemigrations, on the other hand, I don't see anything wrong with formatted text or +/-, but I might go a step further. We already prompt for things like renames and merges. Why not forcibly gain user acceptance before creating a migration that deletes something? ...

Let's take this as an opportunity to give users better warnings to check twice here.

[Ramon Saraiva]

Looking at the implementation for this output, it feels like the + for addition, - for deletion, and ~ for modification approach might be easier to accomplish. Could potentially add a prefix based on the "operation type".

Sounds like all operations follow this same structure of (Add|Remove|Alter){suffix} so I could possibly use that to identify what type of prefix I'd be using. The other way would be explicitly configuring an operation type in each operation.

Adding colors to each operation might be a little too much, but I like the warning approach in the end (and maybe that can be colored somehow).

What do you guys think?

[Bhuvnesh]

Anyone working on this issue?

[Bhuvnesh]

Colored migration operations

[Bhuvnesh]

should i prepare a patch?

[Ramon Saraiva]

Not sure, I'll deassign myself so you can take this one if you have a patch.

[Amir Karimi]

I'd like to work on this issue. I have implemented it in the +/-/~ way. I can add coloring too. I'll create its PR soon.

[Amir Karimi]

I have prepared the feature. I wasn't sure coloring as highlighting is a good idea so I added both prefixes (+,-,~) and colors.

[Natalia Bidart]

Amir, in order for the PR to appear in the review queue, the flag "has patch" needs to be set (I'm setting it now). There are more details about how to proceed with PRs and review feedback in [​https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/submitting-patches/#patch-style this link[.

[Amir Karimi]

Replying to Natalia Bidart:

Amir, in order for the PR to appear in the review queue, the flag "has patch" needs to be set (I'm setting it now). There are more details about how to proceed with PRs and review feedback in [​https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/submitting-patches/#patch-style this link[.

Thnx Natalia for your notice. As it's kinda new feature, I just wanted to add some docs about it, but I didn't find any post related to such a feature that might be better to consider the community's opinion on the Django forum. I wanna add a new topic about such a feature, and find out if people see it as interesting or noisy.

[Mariusz Felisiak]

Marking as "needs improvement" per ​Adam's comment.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 27a3eee7:

Fixed #31700 -- Made makemigrations command display meaningful symbols for each operation.