Confusing message when pip wheel is used with --(global|build)-option

[sbidoul]

When pip wheel is used with --build-option or --global-option, it emits the following message: UserWarning: Disabling all use of wheels due to the use of --build-option / --global-option / --install-option..

This is confusing because the command will generate wheels nevertheless.

What it really does is disable binaries via FormatControl (which is normally used for --no-binary, --only-binary).

This in turn has the side effect of forcing build from source for all dependencies of the packages being built.

Describe the solution you'd like

Deprecate this behaviour of disabling binaries, by mentioning that in a future pip version, --(global|build)-option will only apply to the build of non-PEP 517 source distributions, and if the user intended to apply the options to all distributions, --no-binary :all: should be used.

This would have the advantage of a better separation of concerns and put more control in the hands of users.

This is however a backward incompatible change in some situations.

Alternative Solutions

Keep the existing behaviour and clarify the warning message by saying, e.g. that --(build|option)-option implies --no-binary :all:. (we'd need to check what happens if --only-binary` is used in the same command).

This would have the advantage of keeping full backward compatibility.

Additional context

#2677 (comment)

[pradyunsg]

I want us instead add proper PEP 517 config_settings support, get rid of --global/build-option, and be done with this mess. >.<

</rant>