Simplify _build_prepared

[Julian-O]

Versions

• Buildozer: 2.2.1

Description

The _build_prepared code is overly complicated, and should be refactored.

The Buildozer instance wants to make sure if doesn't prepare a build twice for the same target.

In the current implementation, it attaches its own attribute, _build_prepared to the Target instance. It sets it to True when it has finished prepare_for_build, but the value is ignored. It checks for its existence at the beginning of prepare_for_build and build.

[Note: This triggers style-checkers that don't like attributes with leading underscores being accessed from outside the class.]

Meanwhile, the osx target has a check_build_prepared(), which has four weird behaviours:

• It is only called after prepare_for_build(), so we know the build has been prepared. It appears to be a pointless check.
• It is only called in the case of a debug build, not a release build, which is an unexplained inconsistency.
• Despite its name, it doesn't check the value of _build_prepared. Instead, it sets the value, thus (re)declaring it built.
• It sets the value to False. The value is never used, so this is functionally equivalent to setting it to True, but it isn't clear if some difference was intended.

[Note: This triggers style-checkers that don't like attributes being set in methods that aren't declared in the __init__ methods]

My recommendation:

• In the base class, Target.__init__(), add an instance attribute called is_build_prepared` and set it to False. (No leading underscore - it is a public attribute,)
• Modify the Buildozer class to assume its existence and use it as a Boolean.
• Remove check_build_prepare() from osx.

[I am raising this as a bug report rather than a simple PR, because I am aware I haven't figured out why the osx target is behaving this way, and that can make refactoring more dangerous.]