Don't check type on add_column via column_exists?`

[eileencodes]

I originally added the type to the column_exists? check in
add_column because I thought it would be useful to still raise if you
tried to add a column with a different type. It seemed bad to silently
ignore.

The type check works fine for standard, non-type casted types like
string, but migrations that use types like blob in mysql/sqlite3 or
char in postgres cast these to other types. When c.type == type.to_sym is called in those cases they won't match. For example
c.type for a blob column will return binary so the comparison
won't match. I attempted to cast the type passed in but that's error
prone because for dbs like postgres we need a lot more information
than just a type to determine how to cast it. I also tried going the
other way but the column doesn't store the original type, just the type
casted type (as type) and the sql type which is a string representation
of type that doesn't always match the original.

This functionality was originally extracted from GitHub and when I
looked back at our old implementation I found that we originally weren't
passing type. This came up in a migration for enterprise that wasn't
properly handling the if_not_exists because our type check was
comparing binary to mediumblob. I think it makes the most sense to
leave the public column_exists? method as is and remove the type
check from column_exists? in the add_column method.

[eileencodes]

Welp that didn't work for postgres - looking into that.

[eileencodes]

I reimplemented this differently than my original commit said. I dropped the casting altogether and am just checking for the same column name on the table. This has a slight behavior change in that we no longer will raise if you try to add the same column name with a different type, but I think that's rare.

[federicoaldunate]

I reimplemented this differently than my original commit said. I dropped the casting altogether and am just checking for the same column name on the table. This has a slight behavior change in that we no longer will raise if you try to add the same column name with a different type, but I think that's rare.

I agree with what you did. Also, I think it's consistent with the remove_column with if_exists option in true.

def remove_column(table_name, column_name, type = nil, **options)
  return if options[:if_exists] == true && !column_exists?(table_name, column_name)
  .
  .
  .

Note: I don't like the naming of the option if_not_exists, I think it's confusing.

[eileencodes]

Note: I don't like the naming of the option if_not_exists, I think it's confusing.

I followed existing options on create/drop table when I implemented this. It doesn't make sense to have different options.