This commit changes how we represent comptime-mutable memory
(`comptime var`) in the compiler in order to implement the intended
behavior that references to such memory can only exist at comptime.
It does *not* clean up the representation of mutable values, improve the
representation of comptime-known pointers, or fix the many bugs in the
comptime pointer access code. These will be future enhancements.
Comptime memory lives for the duration of a single Sema, and is not
permitted to escape that one analysis, either by becoming runtime-known
or by becoming comptime-known to other analyses. These restrictions mean
that we can represent comptime allocations not via Decl, but with state
local to Sema - specifically, the new `Sema.comptime_allocs` field. All
comptime-mutable allocations, as well as any comptime-known const allocs
containing references to such memory, live in here. This allows for
relatively fast checking of whether a value references any
comptime-mtuable memory, since we need only traverse values up to
pointers: pointers to Decls can never reference comptime-mutable memory,
and pointers into `Sema.comptime_allocs` always do.
This change exposed some faulty pointer access logic in `Value.zig`.
I've fixed the important cases, but there are some TODOs I've put in
which are definitely possible to hit with sufficiently esoteric code. I
plan to resolve these by auditing all direct accesses to pointers (most
of them ought to use Sema to perform the pointer access!), but for now
this is sufficient for all realistic code and to get tests passing.
This change eliminates `Zcu.tmp_hack_arena`, instead using the Sema
arena for comptime memory mutations, which is possible since comptime
memory is now local to the current Sema.
This change should allow `Decl` to store only an `InternPool.Index`
rather than a full-blown `ty: Type, val: Value`. This commit does not
perform this refactor.
A pointer type already has an alignment, so this information does not
need to be duplicated on the function type. This already has precedence
with addrspace which is already disallowed on function types for this
reason. Also fixes `@TypeOf(&func)` to have the correct addrspace and
alignment.
There is no reason to perform this detection during semantic analysis.
In fact, doing so is problematic, because we wish to utilize detection
of existing decls in a namespace in incremental compilation.
Before this fix, passing an undefined union value to `Sema.switchCond`
returned an undefined value of the union type, not the tag type, since
`Value.unionTag` forwards undefined values unchanged.
This leads us into the `.Union` branch in `Sema.zirSwitchBlock` which is
unreachable, now we take the `.Enum` branch instead.
This logic was previously in Sema, which was unnecessary complexity, and meant the issue was not detected unless the declaration was semantically analyzed. This commit finishes the work which 941090d started.
Resolves: #17916
Previously `@as(i64, undefined) +% 1` would produce `@as(@TypeOf(undefined), undefined)` which now gives `@as(i64, undefined)`.
Previously `@as(i64, undefined) +| 1` would hit an assertion which now gives `@as(i64, undefined)`.
This reverts commit d9d840a33ac8abb0e616de862f592821a7f4a35e, reversing
changes made to a04d4330945565b8d6f298ace993f6954c42d0f3.
This is not an adequate implementation of the missing safety check, as
evidenced by the changes to std.json that are reverted in this commit.
Reopens#18382Closes#18510
This reverts commit f88b523065fbb8afbd723fd6e803ace0334b713c.
Let's please go through the language proposal process for this change. I
don't see any justification for this breaking change even in the commit
message.
In general, I don't like the idea of std.meta.trait, and so I am
providing some guidance by deleting the entire namespace from the
standard library and compiler codebase.
My main criticism is that it's overcomplicated machinery that bloats
compile times and is ultimately unnecessary given the existence of Zig's
strong type system and reference traces.
Users who want this can create a third party package that provides this
functionality.
closes#18051
