Adding methods to `eval` or `include` throws in v1.12

[nickrobinson251]

...if the function name isn't fully qualified or explicity imported

e.g.

> julia +nightly -q --startup-file=no
julia> VERSION
v"1.12.0-DEV.1898"

julia> eval(::Int) = 42
ERROR: cannot define function eval; it already has a value
Stacktrace:
 [1] top-level scope
   @ none:0
 [2] top-level scope
   @ REPL[2]:1

julia> include(::Int) = 0
ERROR: cannot define function include; it already has a value
Stacktrace:
 [1] top-level scope
   @ none:0
 [2] top-level scope
   @ REPL[3]:1

julia> Base.eval(::Int) = 42  # works

julia> Base.include(::Int) = 0  # works

Note the error message is different from trying to extend other methods without qualification e.g.

julia> VERSION
v"1.12.0-DEV.1898"

julia> 1+2  # so Base.+ has been used
3

julia> +(::String) = 42
ERROR: invalid method definition in Main: function Base.+ must be explicitly imported to be extended
Stacktrace:
 [1] top-level scope
   @ none:0
 [2] top-level scope
   @ REPL[3]:1

Whereas in v1.11

nickr@RAI-Mac ~/r/r/p/Tropea> julia +1.11 -q --startup-file=no
julia> VERSION
v"1.11.2"

julia> eval(::Int) = 42
eval (generic function with 2 methods)

julia> include(::Int) = 0
include (generic function with 3 methods)

Was this a deliberate change?

It broke some of our code that happened to use the name eval (not meaning to extend Base.eval), so wanted to check the new behaviour was intended

[mbauman]

This is certainly due to #55949. Unlike +, eval and include are (and have been) local definitions in the module. Previously, you were modifying the function table for that module's machinery and not doing any shadowing as you may have expected.

[NHDaly]

🤔 so technically #55949 was a breaking change then, since it has now essentially made eval and include into reserved names, and a package cannot provide functions called eval or include.

This is maybe okay, but it's a breaking change. Eval, in particular, could be a useful name for packages like solvers?
For example: DACE.eval

[nsajko]

a package cannot provide functions called eval or include

Not true, it's still possible to define a new function named eval or include. This is as before, by using baremodule in place of module:

julia> baremodule M
           function eval end
           function include end
       end
Main.M

[Keno]

Yes, the change was intentional

It broke some of our code that happened to use the name eval (not meaning to extend Base.eval), so wanted to check the new behaviour was intended

And this was basically one of the primary reasons. It was unclear what the scope of such overloads is and in fact it changed several times over different Julia versions. This has now been cleaned up.