adjust 'one-of/c' and 'symbols' so they just use or/c (when possible)
improve or/c's stronger check so that, in the case that or/c is
getting eq or equal contracts, or/c's stronger check is as good as
'symbols'/'one-of/c's stronger check is.
This distinction is important after the introduction of chaperones and
impersonators, since accessing a key and accessing its corresponding value
may have different effects, and hash-keys should only trigger the former.
The immediate symptom was that `(provide (all-defined-out))'
didn't work in a `module+'-based submodule, but there were
also non-submodule ways to expose the problem.
The bug happens with n-ary uses of arithmetic operations that
have constant arguments but couldn't be constant-folded ---
maybe due to a divide-by-zero.
Previously, sandbox creation used `gui?', which is the result of
`gui-available?' at the time that `racket/sandbox' is instanited.
This change makes sandbox behavior less sensitive tothe order in
which modules `require'd into a program are intiantiated.
The change depends on a new `sandbox-make-namespace' default
function for `sandbox-namespace-specs'. The new function uses
either `make-base-namespace' or `make-gui-namespace', depending
on whether the GUI library is available at that point.
A new `sandbox-gui-enabled' parameter can disable use of the
GUI library even if it is available.
The `gui?' binding is still exported for backward compatibility,
but it shouldn't be used anymore.
Mostly for amusement, including the contrast between
the benefits of closure compilation for a host interpreter
versus the benefits for a host compiler.
The old implementation could cause deadlock by blocking on a semaphore
while waiting for the original place to run a callback, but a master
GC might be needed (and the blocked place wouldn't get the signal).
Beside fixing that problem, a potential memory leak is fixed in
calling an ffi funcition and having a Racket->C unmarshaling fail.
Also, the GC marking routine for a `place' value didn't reference the
place's underlying `place_obj' value.
The bug is triggered by unsafe flonum operations, a
conversion that tries to make the arguments more unboxable,
and a `lambda' form within an argument to the unsafe
operation.
Closes PR 12587
