ad7200c196
registerTopLevelGlobal's init_val switch serialized only literal / array- literal / struct-literal initializers. An identifier initializer (`K : A : 42; g : A = K;`) fell through to `else => null`, so the global was emitted with no payload and silently zero-initialized (printed g=0). Extract the initializer serialization into globalInitValue and add an .identifier arm that materializes the global's static value from ProgramIndex.module_const_map (typed module consts are registered in the same scanDecls pass-2 just before, via registerTypedModuleConst). An identifier that names no usable constant now emits a diagnostic instead of silently zeroing — a global has no run site for a dynamic initializer. Other initializer shapes (enum-literal shorthand, etc.) keep their established static-lowering behavior; enum-literal globals' zero-init is load-bearing for `inline if OS == ...` in the stdlib, so it stays out of scope here. This pass only closes the identifier/module-const hole. Regression: examples/0134-types-global-init-from-module-const.sx (g=42, exit 42). Gate: zig build, zig build test, run_examples.sh -> 355/0.
118 lines
3.9 KiB
Markdown
118 lines
3.9 KiB
Markdown
# 0071 — global initialized from module const silently zero-initializes
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> **RESOLVED.** Root cause: `Lowering.registerTopLevelGlobal`'s init_val switch
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> serialized only literal / array-literal / struct-literal initializers; an
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> identifier initializer (`g : A = K;`) fell through to `else => null`, so the
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> global was emitted with no payload and silently zero-initialized.
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> Fix: extracted the initializer serialization into `Lowering.globalInitValue`
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> and added an `.identifier` arm that materializes the global's static value from
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> `ProgramIndex.module_const_map` (typed module consts are registered in the same
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> pass-2 just before, via `registerTypedModuleConst`). An identifier that names no
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> usable constant now emits a diagnostic instead of silently zeroing. Other
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> initializer shapes (enum-literal shorthand, etc.) keep their established
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> static-lowering behavior — this pass only closes the identifier/module-const
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> hole. Regression: `examples/0134-types-global-init-from-module-const.sx`
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> (`g=42` / exit 42).
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## Symptom
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A top-level global initialized from a module constant compiles but is
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zero-initialized instead of receiving the constant's value.
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Observed:
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```text
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g=0
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```
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Expected: `g` should be initialized to `42`, or the compiler should reject the
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initializer loudly if identifier/module-const global initializers are not
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supported.
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## Reproduction
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```sx
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#import "modules/std.sx";
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A :: B;
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B :: s32;
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K : A : 42;
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g : A = K;
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main :: () -> s32 {
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print("g={}\n", g);
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return g;
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}
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```
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Run:
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```sh
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./zig-out/bin/sx run .sx-tmp/probe-0070-global-init-from-const.sx
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```
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The repro is standalone; the inline source above is sufficient to recreate the
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scratch file under `.sx-tmp/`.
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## Investigation prompt
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Fix issue 0071: a top-level global initialized from a module constant must not
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silently become zero.
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Context:
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- This surfaced during Codex re-review of `932cdfa`, the issue-0070 fix.
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- `932cdfa` correctly defers top-level global and typed-module-const annotation
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resolution until after the forward-alias fixpoint.
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- The remaining bug is in the global initializer path, not the annotation path:
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`K : A : 42; g : A = K;` resolves `A` correctly, registers `K` in
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`ProgramIndex.module_const_map`, but `g` is emitted as zero.
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Suspected area:
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- `src/ir/lower.zig`, `Lowering.registerTopLevelGlobal`.
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- Its `init_val` switch serializes literal / array / struct-literal initializers,
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but an identifier initializer falls through to `else => null`, and the global
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is emitted with no initializer payload. That silently becomes zero-initialized.
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- Related facts: `ProgramIndex.module_const_map` already records typed module
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constants via `registerTypedModuleConst`, now in pass 2 after alias convergence.
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Likely fix:
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- Add explicit handling for identifier initializers that name a module constant,
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converting the recorded constant value into the global's `ConstantValue` with
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the global's declared type.
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- If some initializer shape cannot be represented as a global constant yet, emit
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a diagnostic instead of returning `null` / zero-initializing.
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- Do not regress issue 0070: `A :: B; B :: s32; g : A = 7;` and
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`K : A : 35;` must still resolve through the converged alias map.
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- Preserve literal, array literal, struct literal, and foreign-global behavior.
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Verification:
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- Add a focused regression, likely in the `01xx` types block:
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```sx
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#import "modules/std.sx";
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A :: B;
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B :: s32;
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K : A : 42;
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g : A = K;
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main :: () -> s32 { print("g={}\n", g); return g; }
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```
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- Keep these green:
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- `examples/0133-types-forward-alias-global.sx`
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- `examples/0132-types-forward-type-alias.sx`
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- `examples/0116-types-type-alias-size-align.sx`
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- `examples/0201-generics-generic-struct.sx`
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- `examples/1117-diagnostics-value-const-as-type-rejected.sx`
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- Run:
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```sh
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zig build
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zig build test
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bash tests/run_examples.sh
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```
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Expected result: the new regression prints `g=42` and exits `42`; unsupported
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global initializer shapes no longer silently zero-initialize; the full suite
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passes.
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