Trailing comma in a dict in function call split all parameters

[char101]

Describe the style change

When passing dict as a function parameter I often prefer than the dict is split in multiple lines while keeping other parameters in the same line.

Original code:

db.insert('table', {'a': 10, 'b': 11})

Examples in the current Black style

Adding a trailing comma in the dict results in all parameters split, consuming 7 lines, which feel too excessive in the vertical space usage.

db.insert(
    'table',
    {
        'a': 10,
        'b': 11,
    },
)

Desired style

A more compact format could be this which only consumes 3 lines.

db.insert('table', {
    'a': 10,
    'b': 11,
})

Which is, black could only split the dictionary without affecting the function parameters.

[felix-hilden]

Definitely related to #1811, although this is a case of manually applying the magic trailing comma.

[ehiggs]

This is a regression somewhere between 19.10b0 and 22.1.0 and affects a lot of users using mongo.

In:

db.my_collection.update({"_id": some_id}, {"$set": {"cool_field": 123}})

Out (unchanged):

db.my_collection.update({"_id": some_id}, {"$set": {"cool_field": 123}})

In (trailing argument comma):

db.my_collection.update({"_id": some_id}, {"$set": {"cool_field": 123}},) 

Out:

db.my_collection.update(                                                        
    {"_id": some_id},                                                           
    {"$set": {"cool_field": 123}},                                              
)

In (trailing comma in the dicts):

db.my_collection.update({"_id": some_id,}, {"$set": {"cool_field": 123,}})

Out:

db.my_collection.update(                                                        
    {                                                                           
        "_id": some_id,                                                         
    },                                                                          
    {                                                                           
        "$set": {                                                               
            "cool_field": 123,                                                  
        }                                                                       
    },                                                                          
)    

I say this is a regression because the purpose of black is to make one true formatting ™️ but the trailing commas influence the formatting a great deal.

[JelleZijlstra]

@ehiggs that's the magic trailing comma, which for better or for worse is Black's documented behavior now. It's separate from the original request in this issue.

[hauntsaninja]

I think OP's request is basically not to have the magic trailing comma. You can accomplish this by using --skip-magic-trailing-comma. The rest of OP's request is a duplicate of #1811