Allow assignment to globals in other modules

[cstjean]

Currently, SomeModule.variable = 5 yields cannot assign variables in other modules. I get that globals aren't recommended in general, but they are occasionally convenient for specifying things like verbosity level, or the color of the output. Could we allow them, when qualified with the module? The alternatives (Ref/accessors) are a bit verbose.

[vtjnash]

verbosity level, or the color of the output

These should be specified using an IOContext

The alternatives

The primary recommended alternative (which is missing from your list) is to eschew globals in favor of using locally scoped constructs (aka local variables / arguments)

But since there's already a number of ways to do this, (notably @eval, although also accessors), I could be convinced either way.

[StefanKarpinski]

This can always be allowed later, so I would not be in a hurry to do this.

[cstjean]

These should be specified using an IOContext

TIL, thank you. AFAICT, there is no way to permanently specify a value (eg. the color of some object's pretty-printing) when it would be tiring and redundant to specify it to print each object in the REPL. (#20509)

If I have a deeply-nested warn("Low accuracy in foo() computation") warning in my package, and I want to offer a way to disable it, is there a recommended non-global way to do that without passing a warn_on_foo_accuracy keyword argument throughout my codebase?

Common Lisp has the following built-in global variables, in addition to vendor-specific extensions:

*break-on-signals* *compile-file-pathname* *compile-file-truename* *compile-print* 
*compile-verbose* *debug-io* *debugger-hook* *default-pathname-defaults* *error-output*
*features* *gensym-counter* *load-pathname* *load-print* *load-truename* *load-verbose* 
*macroexpand-hook* *modules* *package* *print-array* *print-base* *print-case* *print-circle* 
*print-escape* *print-gensym* *print-length* *print-level* *print-lines* *print-miser-width*
*print-pprint-dispatch* *print-pretty* *print-radix* *print-readably* *print-right-margin* 
*query-io* *random-state* *read-base* *read-default-float-format* *read-eval* *read-suppress*
*readtable* *standard-input* *standard-output* *terminal-io* *trace-output*

I can get, set, or temporarily change (dynamic scope) each of these with setf and let. It's a really clean, simple interface. I understand that Julia has type-stability concerns that preclude doing the same in Base, but it would be nice to have globals for performance-insensitive "customization" of my packages.

[cstjean]

On second thought, if #20509 is implemented, that would cover most of my use cases.

[cstjean]

Fixed by #44137, AFAICT.