Ruby

The ignored_columns attribute allows the exclusion of certain columns when working with ActiveRecord models in Rails. However, accessing an ignored column from an ActiveRecord model wail raise a NoMethodError.

IO.select statements can get very hard to make them compatible with Ruby 3 scheduler. It is recommended to use wait_readable or wait_writable on an IO object with a given timeout instead of rescuing an IO::WaitReadable or IO::WaitWritable error and using IO.select in the block.

If an unused method argument is intended, it should be prefixed with an underscore.

The rename_column/t.rename migration method in Rails is used to rename a column in a database table. However, if an ActiveRecord model is still accessing the renamed column using its old name, it can lead to errors during runtime.

While the safe navigation operator is generally a good idea, when checking foo&.blank? in a conditional, foo being nil will actually do the opposite of what was intended.

Requiring, or relatively requiring same file/module twice is unnecessary and either of the blocks can be removed as they both serve the same purpose.

The division by zero error in Ruby occurs when an attempt is made to divide a number by zero. This issue arises due to the fundamental mathematical rule that division by zero is undefined. When the division operation encounters a denominator of zero, it leads to an error condition.

When creating a custom value object using Struct.new, be careful as to not have attributes whose names match the built-in methods provided by the Struct class.

Range literal should be enclosed in parentheses when the end of the range is at a line break, otherwise the intention of the code becomes ambigous.

Do not return from an ensure block. If you explicitly return from a method inside an ensure block, the return will take precedence over any exception being raised, and the method will return as if no exception had been raised

You intended to write as rescue StandardError. However, you have written rescue => StandardError. In that case, the result of rescue will overwrite StandardError.

Lambda without a literal block is deprecated since Ruby 3.0, use the proc without lambda instead.

Non-atomic file operations can cause problems that are difficult to reproduce, especially in cases of frequent file operations in parallel, such as test runs with parallel_rspec.

Defining uniqueness: true on an ActiveRecord model can be error prone if the column hasn't been declared unique at the database level.

Starting from Ruby 3.1, include or prepend must not be used within a refine block. These methods are deprecated and should be replaced with Refinement#import_methods.

Having duplicate magic comments can lead to potential bug-risks, as a duplicate magic comment can have a different argument passed to it which can change the behavior of the program or even cause it to crash.

Avoid using "*" on an Arel::Table column reference.

Setting the timezone using Time.zone= should be avoided.