For generic code, it is far more useful to consider this equivalent to
`unreachable`. Meanwhile, it is difficult to accidentally write concrete
code which performs this operation, so very little is actually lost from
not having a compile error.
If we accept that this operation does not trigger a compile error, then
it already has the potential to invoke Illegal Behavior today, because
uninstantiable types have an unspecified size in memory, so the
dereference always potentially exceeds the pointer's provenance. (That
said, this only means it is *possible* for the operation to invoke IB,
so the langspec should nonetheless explicitly specify that dereferencing
a pointer to an uninstantiable type is itself Illegal Behavior.)
Storing uninstantiable types into memory does not require any specific
language rules, because that operation can never be reached anyway due
to it requiring an operand (the RHS of `a = b`) whose type is the store
type, which is (by definition) impossible for uninstantiable types.
Resolves: https://codeberg.org/ziglang/zig/issues/36247
`castTruncatedData` was a poorly worded error (all shrinking casts
"truncate bits", it's just that we assume those bits to be zext/sext of
the other bits!), and `negativeToUnsigned` was a pointless distinction
which forced the compiler to emit worse code (since two separate safety
checks were required for casting e.g. 'i32' to 'u16') and wasn't even
implemented correctly. This commit combines those safety panics into one
function, `integerOutOfBounds`. The name maybe isn't perfect, but that's
not hugely important; what matters is the new default message, which is
clearer than the old ones: "integer does not fit in destination type".
* `std.builtin.Panic` -> `std.builtin.panic`, because it is a namespace.
* `root.Panic` -> `root.panic` for the same reason. There are type
checks so that we still allow the legacy `pub fn panic` strategy in
the 0.14.0 release.
* `std.debug.SimplePanic` -> `std.debug.simple_panic`, same reason.
* `std.debug.NoPanic` -> `std.debug.no_panic`, same reason.
* `std.debug.FormattedPanic` is now a function `std.debug.FullPanic`
which takes as input a `panicFn` and returns a namespace with all the
panic functions. This handles the incredibly common case of just
wanting to override how the message is printed, whilst keeping nice
formatted panics.
* Remove `std.builtin.panic.messages`; now, every safety panic has its
own function. This reduces binary bloat, as calls to these functions
no longer need to prepare any arguments (aside from the error return
trace).
* Remove some legacy declarations, since a zig1.wasm update has
happened. Most of these were related to the panic handler, but a quick
grep for "zig1" brought up a couple more results too.
Also, add some missing type checks to Sema.
Resolves: #22584
formatted -> full
Meghan Denny