This reverts commit b461d07a5464aec86c533434dab0b58edfffb331.
After some discussion in the team, we've decided that this is too disruptive,
especially because the linker errors are less than helpful. That's a fixable
problem, so we might reconsider this in the future, but revert it for now.
Wow, *lots* of backends were reliant on Sema doing the heavy lifting for
them. CBE, Wasm, and SPIR-V have all regressed in places now that they
actually need to, like, initialize unions and such.
This logic predates certain Sema enhancements whose behavior it
essentially tries to emulate in one specific case in a problematic way.
In particular, this logic handled initializing comptime-known `const`s
through RLS, which was reworked a few years back in 644041b to not rely
on this logic, and catching runtime fields in comptime-only
initializers, which has since been *correctly* fixed with better checks
in `Sema.storePtr2`. That made the highly complex logic in
`validateStructInit`, `validateUnionInit`, and `zirValidatePtrArrayInit`
entirely redundant. Worse, it was also causing some tracked bugs, as
well as a bug which I have identified and fixed in this PR (a
corresponding behavior test is added).
This commit simplifies union initialization by bringing the runtime
logic more in line with the comptime logic: the tag is now always
populated by `Sema.unionFieldPtr` based on `initializing`, where this
previously happened only in the comptime case (with `validateUnionInit`
instead handling it in the runtime case). Notably, this means that
backends are now able to consider getting a pointer to an inactive union
field as Illegal Behavior, because the `set_union_tag` instruction now
appears *before* the `struct_field_ptr` instruction as you would
probably expect it to.
Resolves: #24520Resolves: #24595
Also check that FileNotFound is consistently returned when the path is missing.
The new `run_relative` step will test spawning paths like:
child_path: ../84385e7e669db0967d7a42765011dbe0/child
missing_child_path: ../84385e7e669db0967d7a42765011dbe0/child_intentionally_missing
besides simply being redundant work, the now removed normalize call would cause
spawn to errantly fail (BadPath) when passing a relative path which traversed
'above' the current working directory. This case is already handled by leaving
normalization to the windows.wToPrefixedFileW call in
windowsCreateProcessPathExt
