29a4891374
Impl blocks are anonymous (no declName), so a parameterised-protocol impl in a module reached via a diamond import was appended once per path and registered twice — 'duplicate impl Into for source s64'. mergeFlat and the directory-import merge loop now also dedup by node pointer; a physical AST node is lowered once regardless of how many import paths reach it. Regression: examples/issue-0056-diamond-param-impl.sx.
80 lines
2.6 KiB
Markdown
80 lines
2.6 KiB
Markdown
# 0056 — parameterised-protocol impl not deduped across a diamond import
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**FIXED** (`examples/issue-0056-diamond-param-impl.sx`, helpers in
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`examples/issue-0056/`). The flat decl list in
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[src/imports.zig](../src/imports.zig) now dedups by **node identity** as well
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as by name. `ResolvedModule.mergeFlat` and the directory-import merge loop each
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carry a `seen_nodes: std.AutoHashMap(*Node, void)` alongside the existing
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`seen_in_list` name set, and skip a decl whose pointer was already appended.
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## Symptom
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A module containing a parameterised-protocol impl (`impl Into(T) for S`) could
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not be imported through more than one path. Under a diamond —
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```
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main ─┬─ mid_a ─┐
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└─ mid_b ─┴─ common (holds `impl Into(Wrapped) for s64`)
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```
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— compilation failed with:
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```
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error: duplicate impl 'Into' for source 's64' in .../common.sx
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```
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This bit the moment `modules/std/objc.sx` (imported by `main.sx`,
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`platform/uikit.sx`, and `gpu/metal.sx` — a diamond) gained an
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`impl Into(*NSString) for string`.
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## Root cause
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`mergeFlat`/`addOwnDecl` dedup the global flat decl list by
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`decl.data.declName()`. Named decls (structs, fns, foreign classes) dedup
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fine across diamonds. But `impl_block` is anonymous — `declName()` returns
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`null` (see [src/ast.zig](../src/ast.zig) `Data.declName`) — so the dedup
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guard was skipped and the **same cached** impl node (modules are cached in
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`ModuleCache`, so both paths share one node pointer) was appended once per
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path. `registerParamImpl` in [src/ir/lower.zig](../src/ir/lower.zig) then saw
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two entries with the same `defining_module` and raised the same-file
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"duplicate impl" diagnostic.
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The pre-existing `impl Into(Block) for Closure(...)` in
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`modules/std/objc_block.sx` never tripped this because that module is not
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imported through any diamond.
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## Reproduction
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`examples/issue-0056/common.sx`:
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```sx
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Wrapped :: struct { v: s64; }
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impl Into(Wrapped) for s64 {
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convert :: (self: s64) -> Wrapped {
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return .{ v = self };
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}
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}
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```
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`mid_a.sx` / `mid_b.sx` each `#import "common.sx";`. The diamond main:
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```sx
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#import "modules/std.sx";
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#import "issue-0056/mid_a.sx";
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#import "issue-0056/mid_b.sx";
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main :: () -> s32 {
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w : Wrapped = xx 7; // pre-fix: duplicate impl 'Into' for source 's64'
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print("{}\n", w.v); // post-fix: prints 7
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0;
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}
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```
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## Fix
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Dedup the flat decl list by node identity in addition to name — a physical
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AST node must be lowered once regardless of how many import paths reach it.
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Named-decl first-wins behaviour is unchanged. Regression test:
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`examples/issue-0056-diamond-param-impl.sx` (in `tests/run_examples.sh`).
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