b710a0a42a
`xx <struct-typed local>` used to heap-copy the value through context.allocator.
The protocol value's `ctx` pointed at the heap copy; the original local was
left behind, untouched. Mutations through the protocol never reached the
original, and direct reads of the original never saw protocol mutations.
Two-fork bug, silent, easy to write by mistake.
New rule (Option 3 in the discussion):
- `xx <lvalue>` — identifier, field access, index expression, deref —
borrows the operand's storage. No heap copy, no `free` needed.
- `xx <rvalue>` — struct literal, function-call result, arithmetic, etc. —
heap-copies through context.allocator. Unchanged from today.
- `xx @ptr` and `xx <pointer-typed value>` — borrows the pointee. Unchanged.
Single switch in `buildProtocolErasure` ([lower.zig:10334](src/ir/lower.zig#L10334))
gated by a new `isLvalueExpr` helper ([lower.zig:10322](src/ir/lower.zig#L10322)).
Struct-typed operand: if the AST shape is identifier/field/index/deref,
emit `lowerExprAsPtr(operand_node)` and skip the heap-copy; otherwise
keep the alloca-store-heap_copy path.
specs.md §3 ownership table extended to three rows (rvalue, lvalue,
pointer) with examples and rationale per row.
Regressions:
- `examples/130-xx-value-routes-through-context-allocator.sx` — the
Phase 1.1 witness for heap-copy-via-context-allocator. Previous shape
(`xx <local-value>`) is now a borrow under Option 3 and no longer
exercises the heap-copy path. Rewritten to use a struct literal
(`xx ByValue.{...}`) which still heap-copies through context.allocator
— Tracer.count = 1 as before.
- `examples/135-xx-lvalue-borrows.sx` — new test. Dereferences a
TrackingAllocator into a stack value, does `xx tracker` inside a
push Context, and asserts alloc_count/dealloc_count on the LOCAL go
up. Under old semantics this would have stayed at 0 (heap copy got
the increments, local stayed stale).
157/157 example tests pass; chess clean on macOS / iOS sim / Android
(`tools/verify-step.sh` ran green immediately before this work).
45 lines
1.3 KiB
Plaintext
45 lines
1.3 KiB
Plaintext
// Phase 1.1 — the compiler-internal heap-copy that backs `xx <rvalue>`
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// protocol erasure must dispatch through `context.allocator`, not call
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// libc malloc directly. So when a `push Context.{ allocator = tracer }`
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// block is active, a `xx StructLiteral.{}` inside it MUST be allocated
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// by the tracker.
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//
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// Note: `xx` only heap-copies for RVALUES (struct literals, call results).
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// `xx <lvalue>` (an identifier, field access, index, or deref) borrows
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// the operand's storage, so it never allocates and never reaches this
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// path. See specs.md §3 — Protocol value ownership and lifetime.
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#import "modules/std.sx";
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Tracer :: struct {
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count: s64;
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init :: () -> *Tracer {
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t : *Tracer = xx malloc(size_of(Tracer));
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t.count = 0;
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t;
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}
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}
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impl Allocator for Tracer {
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alloc :: (self: *Tracer, size: s64) -> *void {
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self.count += 1;
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return malloc(size);
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}
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dealloc :: (self: *Tracer, ptr: *void) {
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free(ptr);
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}
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}
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ByValue :: struct { x: s64; y: s64; }
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main :: () -> s32 {
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tracer := Tracer.init();
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push Context.{ allocator = xx tracer, data = null } {
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// Struct-literal operand: rvalue → heap-copy through context.allocator.
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ignore : Allocator = xx ByValue.{ x = 1, y = 2 };
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_ = ignore;
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}
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print("Tracer.count = {}\n", tracer.count);
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0;
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}
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