Add a TODO for wasm32 issues

Author: FrancescAlted

plans/wasm32-todo.md

@@ -0,0 +1,79 @@
+# wasm32 TODO: DSL `int(...)` Cast Path
+
+Last updated: 2026-02-19
+
+## Context
+
+In `python-blosc2` on wasm32/Pyodide, DSL kernels that use index symbols with `int(...)` casting still fail in practice for this shape:
+
+- DSL kernel: `return int(_i0 * _n1 + _i1)`
+- Typical integration symptom: `DSL kernels require miniexpr ... miniexpr compilation or execution failed`
+- Current status in python-blosc2: expected-to-fail behavior is still kept for wasm32.
+
+This is likely either:
+- a true miniexpr wasm32 cast/runtime gap, or
+- an integration mismatch between python-blosc2's prefilter setup and miniexpr's supported dtype/cast combinations.
+
+## Goal
+
+Make DSL `int(...)` casting reliable on wasm32 for ND/index-symbol expressions (or explicitly declare and document it as unsupported with precise diagnostics).
+
+## Work Items
+
+1. Reproduce with a minimal miniexpr-only regression
+- Add/extend a wasm-executed test that mirrors python-blosc2 usage:
+  - ND expression with `_i0`, `_i1`, `_n1`
+  - explicit output dtype `ME_INT64`
+  - both no-input and with-input variants
+- Candidate files:
+  - `tests/test_nd.c`
+  - `tests/test_dsl_syntax.c`
+
+2. Confirm whether miniexpr core already passes the scenario
+- If miniexpr tests pass but python-blosc2 fails, classify as integration issue and document expected call contract from miniexpr side.
+- If miniexpr fails on wasm32, keep investigating below items.
+
+3. Audit cast intrinsic lowering and dtype propagation
+- Inspect and validate:
+  - `dsl_cast_int_intrinsic`
+  - `dsl_cast_int_target_dtype`
+  - compile-time dtype selection for DSL statements and return value
+  - ND output write path for integral dtypes
+- Candidate source:
+  - `src/miniexpr.c`
+
+4. Audit wasm32 runtime behavior for cast-heavy DSL
+- Verify interpreter path vs JIT path behavior parity for this kernel.
+- Ensure reserved index symbol handling does not accidentally disable needed runtime path.
+- Confirm no wasm-only narrowing/overflow bugs in writeback for `ME_INT64`.
+
+5. Strengthen diagnostics for unsupported cast combos
+- If a cast combination is intentionally unsupported on wasm32, return an explicit error reason (not generic execution failure).
+- Add tests that assert the exact reason.
+
+6. Add parity tests and CI coverage
+- Native + wasm32 parity for:
+  - `int(3.9)`
+  - `int(_i0 * _n1 + _i1)`
+  - `float(int(x)) + bool(x)`
+  - mixed input dtype to integer output
+- Ensure these tests run in the wasm32 CI lane.
+
+## Validation Commands (suggested)
+
+```bash
+# native
+cmake -S . -B build -DMINIEXPR_BUILD_TESTS=ON
+cmake --build build -j
+ctest --test-dir build --output-on-failure -R "test_nd|test_dsl_syntax|test_dsl_jit_runtime_cache"
+
+# wasm32
+emcmake cmake -S . -B build-wasm32 -DMINIEXPR_BUILD_TESTS=ON
+cmake --build build-wasm32 -j
+ctest --test-dir build-wasm32 --output-on-failure -R "test_nd|test_dsl_syntax|test_dsl_jit_runtime_cache"
+```
+
+## Exit Criteria
+
+- `int(_i0 * _n1 + _i1)` works on wasm32 in miniexpr and in python-blosc2 integration, with deterministic behavior and tests.
+- OR behavior is explicitly unsupported, documented, and enforced by a precise, tested error path.