The tagged sum is Tast.data now and Tast.unions is C's untagged union, which
arrives as a structure whose every field sits at offset zero. That is a
layout, and a layout is the one thing an object has none of here -- two
properties cannot share a run of bytes -- so it is refused with the type's own
name rather than met as "not a struct".
Two hardenings the sweep could not have found. $str built a view onto node's
Buffer pool, where small Buffers share one ArrayBuffer, so a write through one
string literal's slice could have reached another's bytes; native puts a
literal in .rodata where that write is a fault. And copy_of's Option arm named
its argument three times, which evaluates it three times.
SURVEY_FLAGS reaches both sides now, as it does in the x86 sweep, so the
unchecked indexing path -- a bare a[i] with no $at around it, which nothing
had ever run -- is swept too: 23 match, 0 differ.
spike/js/survey.sh is the x86 sweep's shape with one deliberate difference in
what it counts. That backend is behind, so a refusal there is a regression and
its strict mode fails on one. This is a dialect, so a refusal is the design
working -- a pointer, an allocator, a Map, the FFI and conditions are refused
permanently and correctly. What fails the @js alias is a DIFFER, which is a
wrong answer, and a CRASH, which is JS this backend emitted and node would not
run.
Two probes carry the decisions the corpus does not reach. p1-int-semantics
prints wrapping at all eight widths, a multiply past 2^53, truncating division
with a negative operand, shifts whose count is out of range, bitwise over a
u32, f32 that is not a double, and the conversions both ways -- 35 lines, all
identical to the LLVM build. It found two real bugs: >>> binds tighter than &
in JavaScript, so a bit-and on a u32 answered -1; and a 64-bit value through
Number() rounds to 53 bits before it can be truncated, so (i32 i64hi) answered
0 where it must answer -1.
p2-value-copies goes past values.flan to the cases a shallow copy would pass:
a struct inside a struct, a struct returned out of a function, an element read
out of an array of structs, and a global.
Also fixed, and all three were found by the sweep rather than by reading: a
unit-typed call in statement position was compiled to an expression nobody
emitted, so (load-xs) silently did not happen; an arrow body that starts with
a brace is a block, so a zeroed array of structs was a syntax error; and a
bounds message must carry the index expression's location, not the form's,
because that is the one emit.ml passes to check_at.
Render reads an Option's tag as field 0 and a union's as field 0, which is the
LLVM layout and not this one, so both are answered here rather than refused.
fdefers is dropped rather than refused: nothing in the dialect can start a
transfer, so the transfer exit path is unreachable, and refusing it would have
refused every program that writes a plain defer.
