82b46bc412
xx args with a slice target now bridges a comptime pack to a runtime slice: []Any boxes each element to Any; []P xx-erases each to the protocol (reusing the slice-of-protocol erasure from 0052). New lowerPackToSlice; the unary-op arm intercepts xx <pack> before the pack-as-value diagnostic. This is the working forward to a runtime []Any/[]P helper -- log_count(xx args) -> 3 -- so the 2.7 pack-as-value diagnostics now suggest xx <name> for the call case. examples/204-pack-xx-to-slice.sx (both []Any and []P paths); 203 help text updated. issue 0053 FIXED. 239 examples + unit green.
74 lines
2.9 KiB
Markdown
74 lines
2.9 KiB
Markdown
**FIXED** via the `xx <pack>` bridge (the preferred fix below), not by changing
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the `..args` spread. `xx args` with a slice target now materializes the pack
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into a runtime `[]Any`/`[]P` — see [examples/204-pack-xx-to-slice.sx](../examples/204-pack-xx-to-slice.sx).
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`lowerXX`/the unary-op arm intercepts `xx <pack>` before the pack-as-value
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check and calls the new `lowerPackToSlice` ([src/ir/lower.zig](../src/ir/lower.zig)).
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The bare `..args` spread into a non-variadic `[]Any` param is still unsupported
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(use `xx args`); left as-is.
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# Symptom
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Spreading a comptime pack `..$args` into a `[]Any` parameter — `f(..args)` where
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`f` takes `items: []Any` — fails LLVM verification:
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```
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LLVM verification failed: Incorrect number of arguments passed to called function!
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%call = call i64 @log_count(ptr %0, { ptr, i64 }, { ptr, i64 }, double ...)
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```
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The spread passes the pack's N elements as N separate positional args instead of
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materialising a single `[]Any` slice for the one `items` parameter.
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# Reproduction
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```sx
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#import "modules/std.sx";
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log_count :: (items: []Any) -> s64 { return items.len; }
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forward :: (..$args) -> s64 { return log_count(..args); }
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main :: () -> s32 { print("{}\n", forward(1, "hi", 2.5)); return 0; }
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```
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Expected: `3` (the pack spreads into the `[]Any` slice, like calling
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`log_count(1, "hi", 2.5)` against a `[]Any` variadic would).
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# Preferred fix — `xx args` (pack → slice materialization)
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Rather than make the splat-y `..args` spread collapse into a single slice arg,
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the cleaner spelling is an **`xx` cast**, which already means "erase/convert to
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the expected type":
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```sx
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forward :: (..$args) -> s64 { return log_count(xx args); } // target: []Any
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```
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`xx args` (target-typed) should materialize the pack into the expected slice:
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- target `[]Any` → box each pack element to `Any`, build `[N]Any` → `[]Any`;
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- target `[]P` → `xx`-erase each element to the protocol `P`, build `[N]P`
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→ `[]P` (reuse the slice-of-protocol erasure landed in `packVariadicCallArgs`,
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issue 0052).
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This reuses the existing `xx`/protocol machinery, reads naturally, and keeps
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`..xs` reserved for true spreads into pack/variadic callees.
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**Currently `xx args` errors** ("pack 'args' has no runtime value") because the
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Step 2.7 pack-as-value check fires on the bare `args` operand before `xx` is
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considered. The fix: in `xx` (unary_op `.xx`) lowering, intercept a pack operand
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*before* the pack-as-value diagnostic and, when the target type is a slice,
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materialize as above.
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# Workaround today
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Declare the forwarder as the **slice** variadic instead of a pack — then it's
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already a runtime `[]Any` and forwards directly:
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```sx
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forward :: (..args: []Any) -> s64 { return log_count(args); } // works -> 3
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```
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This is what `examples/162-pack-bare-args.sx` demonstrates.
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# Verification
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After the fix, `log_count(xx args)` (and the original `..args` form, if also
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fixed) should print `3` and pass `sx ir` LLVM verification.
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