hakorune/docs/archive/proposals/issue_62_update_proposal.md

Issue 62 Update Proposal: Enable String Constants in WASM Backend First

Status: Historical

This is a concrete request to implement minimal string support in the WASM backend so that Issue #62 can proceed. It reflects the current repo state.

Background

• As noted in Issue #61, the current WASM backend does not support string constants yet.
• Issue #62 depends on string support and cannot be completed without it.
• Current state:
  • src/backend/wasm/codegen.rs → generate_const handles only Integer/Bool/Void; String is not implemented.
  • src/backend/wasm/memory.rs already defines a basic layout for StringBox:
    • Header: [type_id:i32][ref_count:i32][field_count:i32]
    • Fields: [data_ptr:i32][length:i32]
    • StringBox type_id = 0x1001.

Goal

Add minimal string constant support to the WASM backend:

• Allow ConstValue::String in codegen by embedding UTF-8 string bytes and constructing a StringBox with [data_ptr,length].
• Provide a minimal debugging import env.print_str(ptr,len) to verify strings at runtime.
• Unblock Issue #62 implementation and tests that require strings.

Scope

Minimal features required:

1. Data segments for string literals

   • Extend WasmModule (in codegen.rs) with a data_segments: Vec<String> field.
   • Update to_wat() to emit (data ...) after memory/globals and before functions/exports.
   • For each string constant, create a unique offset and emit a (data (i32.const <offset>) "...bytes...") entry.

2. Codegen for ConstValue::String

   • In generate_const, when encountering ConstValue::String(s),
     • Allocate a data segment for s (UTF-8 bytes) and get its offset and length.
     • Allocate a StringBox using existing helpers (see MemoryManager), then set its fields: data_ptr and length.
     • Return the StringBox pointer (i32) in the destination local.

3. Helper for StringBox allocation

   • Either:
     • Provide a dedicated WAT helper function $alloc_stringbox that calls $malloc, writes header (type_id=0x1001, ref_count=1, field_count=2), and returns the box pointer, then inline store data_ptr/length.
   • Or:
     • Use $box_alloc with (type_id=0x1001, field_count=2) and then store data_ptr/length via generated i32.store sequences.

4. Runtime import for string output (for verification)

   • Extend RuntimeImports (src/backend/wasm/runtime.rs) with:
     • (import "env" "print_str" (func $print_str (param i32 i32)))
   • In host (Node/Browser), implement importObject.env.print_str = (ptr,len) => { decode UTF-8 from memory; console.log(...) }.

5. E2E test

   • Add a tiny program that produces/prints a string (e.g., Const String → call env.print_str(ptr,len) via a minimal MIR program) and verify it logs the correct text.
   • Option: update test_runner.js to include print_str and decode from memory using TextDecoder('utf-8').

Out of Scope (for this change)

• String operations (concat/substr/compare), normalization, encoding conversions.
• GC/RC or freeing memory (current allocator is bump-only).
• Returning StringBox directly from main (keep verification via print_str).

Acceptance Criteria

• Generated WAT includes (data ...) segments for string literals and correct offsets.
• ConstValue::String codegen constructs a valid StringBox with proper [data_ptr,length].
• env.print_str correctly prints UTF-8 strings in both Browser and Node runners.
• Issue #62 tasks that rely on strings can proceed.

References (repo paths)

• String unsupported path: src/backend/wasm/codegen.rs (generate_const)
• Memory/layout: src/backend/wasm/memory.rs (StringBox, type_id=0x1001)
• Runtime imports: src/backend/wasm/runtime.rs (currently only env.print(i32))
• Node runner: test_runner.js (has env.print; extend with print_str)

Notes

• Data segment approach is the simplest for initial support; future work may add constant pooling and deduplication.
• Keeping verification via print_str(ptr,len) avoids complicating function return types for now.
• UTF-8 decoding is available in hosts via TextDecoder('utf-8').