547148b8b6
A free function called via UFCS (recv.fn(args)) whose first param is *T was passed the receiver by value (LLVM "Call parameter type does not match function signature"), and a function reached only via UFCS was declared but never emitted (undefined symbol at link). The bare-name UFCS fallback now mirrors the qualified-method path: it lazily lowers the target body and calls fixupMethodReceiver + coerceCallArgs, so the value receiver gets the same implicit address-of as a struct-defined method and mutations through *T are visible. Regression: 0039-basic-free-fn-ufcs-pointer-receiver.sx.
64 lines
2.9 KiB
Markdown
64 lines
2.9 KiB
Markdown
# 0063 — free-function UFCS with a pointer first-param passes the struct by value
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> **✅ RESOLVED (2026-06-01).** The free-function UFCS fallback in
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> [src/ir/lower.zig](../src/ir/lower.zig) ("Try to resolve as bare function
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> name") built `method_args` with the value receiver but never called
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> `fixupMethodReceiver`, and never lazily lowered the target — so the receiver
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> was passed by value (LLVM signature mismatch) and a UFCS-only function was
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> declared but never emitted (link error). Fix: that path now (1) lazily lowers
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> `fa.field` if it's a known fn not yet lowered, and (2) calls
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> `fixupMethodReceiver` + `coerceCallArgs` exactly like the qualified-method
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> path. The explicit `bump(@p)` form was always fine. Regression:
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> [examples/0039-basic-free-fn-ufcs-pointer-receiver.sx](../examples/0039-basic-free-fn-ufcs-pointer-receiver.sx).
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## Symptom
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Calling a **free** function via UFCS where the function's first parameter is a
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pointer (`p: *Parser`), on a local struct value, passes the struct BY VALUE
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where the function expects a pointer:
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```
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LLVM verification failed: Call parameter type does not match function signature!
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%load = load { i32, i32 }, ptr %alloca, align 4
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%call = call i32 @bump(ptr @__sx_default_context, { i32, i32 } %load)
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```
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The UFCS auto-address-of (`p.bump()` → `bump(@p)`) does not kick in for free
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functions; the receiver is loaded by value instead of having its address taken.
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The same method defined **inside** the struct works fine — so this is specific
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to free-function UFCS, not method calls in general. Not failable-specific (the
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repro is a plain `-> s32`), so this is orthogonal to ERR.
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Expected: `p.bump()` on a `*Parser`-first-param free function takes `@p`'s
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address, matching the in-struct method behavior.
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## Reproduction
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```sx
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#import "modules/std.sx";
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Parser :: struct { pos: s32; }
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bump :: (p: *Parser) -> s32 { p.pos += 1; return p.pos; } // FREE fn, pointer first param
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main :: () -> s32 {
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p := Parser.{ pos = 0 };
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print("{}\n", p.bump()); // LLVM signature mismatch
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return 0;
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}
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```
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Control (works): move `bump` inside `Parser :: struct { … bump :: (p: *Parser) -> s32 { … } }`.
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Also fails with an explicit `bump(@p)` — so the explicit address-of of a local
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struct into a pointer param is the underlying miscompile, not just the UFCS sugar.
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## Investigation prompt
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Two related call paths in [src/ir/lower.zig](../src/ir/lower.zig): (1) UFCS
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rewrite of `obj.fn(args)` for a free function whose first param is a pointer —
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it must auto-take-address of the receiver (as the in-struct method path does);
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(2) more fundamentally, lowering an explicit `@local_struct` argument into a
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`*T` parameter loads the struct by value instead of passing its slot pointer.
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Compare the in-struct method call lowering (which marshals the `self`/receiver
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correctly) against the free-function call + the address-of-local lowering.
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Verify with the repro (`p.bump()` and `bump(@p)` both compile + print 1, then 2
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if called twice).
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