This fixes a regression from a couple of commits ago; breaking from the
`else` block of a loop to the loop's tag should be allowed when explicitly
targeting the label by name.
This commit aims to simplify and de-duplicate the logic required for
semantically analyzing `switch` expressions.
The core logic has been moved to `analyzeSwitchBlock`, `resolveSwitchBlock`
and `finishSwitchBlock` and has been rewritten around the new iterator-based
API exposed by `Zir.UnwrappedSwitchBlock`.
All validation logic and switch prong item resolution have been moved to
`validateSwitchBlock`, which produces a `ValidatedSwitchBlock` containing
all the necessary information for further analysis.
`Zir.UnwrappedSwitchBlock`, `ValidatedSwitchBlock` and `SwitchOperand`
replace `SwitchProngAnalysis` while adding more flexibility, mainly for
better integration with `switch_block_err_union`.
`analyzeSwitchBlock` has an explicit code path for OPV types which lowers
them to either a `block`-`br` or a `loop`-`repeat` construct instead of a
switch. Backends expect `switch` to actually have an operand that exists
at runtime, so this is a bug fix and avoids further special cases in the
rest of the switch logic.
`resolveSwitchBlock` and `finishSwitchBr` exclusively deal with operands
which can have more than one value, at comptime and at runtime respectively.
This commit also reworks `RangeSet` to be an unmanaged container and adds
`Air.SwitchBr.BranchHints` to offload some complexity from Sema to there
and save a few bytes of memory in the process.
Additionally, some new features have been implemented:
- decl literals and everything else requiring a result type (`@enumFromInt`!)
may now be used as switch prong items
- union tag captures are now allowed for all prongs, not just `inline` ones
- switch prongs may contain errors which are not in the error set being
switched on, if these prongs contain `=> comptime unreachable`
and some bugs have been fixed:
- lots of issues with switching on OPV types are now fixed
- the rules around unreachable `else` prongs when switching on errors now
apply to *any* switch on an error, not just to `switch_block_err_union`,
and are applied properly based on the AST
- switching on `void` no longer requires an `else` prong unconditionally
- lazy values are properly resolved before any comparisons with prong items
- evaluation order between all kinds of switch statements is now the same,
with or without label
When switching on an error, using the captured value instead of the original
one is always preferable since its error set has been narrowed to only
contain errors which haven't already been handled by other switch prongs.
The subsequent commits will disallow this form as an unreachable `else` prong.
This makes `is_non_err` and `unwrap_errunion_err[_ptr]` friendlier towards
being emitted into comptime blocks. Also, `analyzeIsNonErr` now actually
attempts to do something at comptime.
Moved to a more linear layout which lends itself well to exposing an iterator.
Consumers of this iterator now just have to keep track of an index into a
homogenous sequence of bodies.
The new ZIR layout also enables giving switch prong items result locations
by storing the bodies of all items inside of the switch encoding itself.
There are some deliberate exceptions to this: enum literals and error values
are directly encoded as strings and number literals are resolved to comptime
values outside of the switch block. These special encodings exist to save
space and can easily be resolved during semantic analysis.
This commit also re-implements `AstGen` and `print_zir` for switch based on
the new layout and adds some additional information to the ZIR text repr.
Notably `switchExprErrUnion` has been merged into `switchExpr` to reduce
code duplication.
The rules around allowing an unreachable `else` prong in error switches are
also refined by this commit, and enforced properly based on the actual AST.
The special cases are listed exhaustively below:
`else => unreachable,`
`else => return,`
`else => |e| return e,` (where `e` is any identifier)
Additionally `{...} => comptime unreachable,` prongs are marked to support
future features (refer to next couple of commits).
Also fixes 'value with comptime-only type depends on runtime control flow'
error for labeled error switch statements by surrounding the entire expr
with a common block to break to (see previous commits for details).
Adds `Scope.Unwrapped`, a simple union of pointers to already-casted scopes
with `Scope.Tag` as its tag enum. This pairs very nicely with labeled switch
and gets rid of almost every `scope.cast(...).?`, improving developer QOL :)
Enhances `GenZir` to allow labels to provide separate `break` and `continue`
target blocks and adds some more information on continue targets to
communicate whether the target is a switch block or cannot be targeted by
`continue` at all.
The main motivation is enabling this:
```
const result: u32 = operand catch |err| label: switch (err) {
else => continue :label error.MyError,
error.MyError => break :label 1,
};
```
to be lowered to something like this:
```
%1 = block({
%2 = is_non_err(%operand)
%3 = condbr(%2, {
%4 = err_union_payload_unsafe(%operand)
%5 = break(%1, result) // targets enclosing `block`
}, {
%6 = err_union_code(%operand)
%7 = switch_block(%6,
else => {
%8 = switch_continue(%7, "error.MyError") // targets `switch_block`
},
"error.MyError" => {
%9 = break(%1, @one) // targets enclosing `block`
},
)
%10 = break(%1, @void_value)
})
})
```
which makes the non-error case and all breaks from switch prongs, but not
continues from switch prongs, peers.
This is required to avoid the problems described in gh#11957 for labeled
switches without having to introduce a fairly complex special case to the
`switch_block_err_union` logic. Since this construct is very rare in practice,
introducing this additional complexity just to save a few ZIR bytes is
likely not worth it, so the simplified lowering described above will be
used instead.
As a nice bonus, AstGen can now also detect a `continue` trying to target
a labeled block and emit an appropriate error message.
Previously Zig allowed you to write something like,
```zig
switch (x) {
.y => |_| {
```
This seems a bit strange because in other cases, such as when
capturing the tag in a switch case,
```zig
switch (x) {
.y => |_, _| {
```
this produces an error.
The only usecase I can think of for the previous behaviour is
if you wanted to assert that all union payloads are able
to coerce,
```zig
const X = union(enum) { y: u8, z: f32 };
switch (x) {
.y, .z => |_| {
```
This will compile-error with the `|_|` and pass without it.
I don't believe this usecase is strong enough to keep the current
behaviour; it was never used in the Zig codebase and I cannot
find a single usage of this behaviour in the real world, searching
through Sourcegraph.
This reverts commit 867501d9d2.
It seems that the increased run time was a result of the regressed
test-incremental step and that we are now back to normal.
If the float can store all possible values of the integer without
rounding, coercion is allowed. The integer's precision must be less than
or equal to the float's significand precision.
Closes#18614
Since we ignore this flag in `clang_options_data.zig`, it makes
sense to ignore it for Nix as well. One thing I've been thinking about
is if it would make sense to somehow use `clang_options_data.zig` as
source of truth for handling Nix cflags too rather than slap more
hard-coded escape hatches.
