charles
2806772fd1
Gate generated code behind feature flags so consumers can build in no_std/no_alloc environments: - Runtime: gate RotoMessage, RotoOwned, BufMutBuilder behind alloc - Codegen: split DATA_IMPORTS, gate Owned* structs + service code - Fix RevBuilder::with() to iterate forward without Vec allocation - Wire up bytes/std via alloc feature (Bytes requires Arc) - Update consumer Cargo.toml files with proper feature chains - Add no_std_test example for embedded validation
110 lines
4.4 KiB
Markdown
110 lines
4.4 KiB
Markdown
# Task: Verify Generated Code Works in `no_std` / `no_alloc`
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**Goal:** Ensure all generated protobuf code compiles and runs in `no_std` + `no_alloc` environments. Features requiring `alloc` must be gated behind feature flags in the proto generator's output.
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**Status:** ✅ COMPLETE
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---
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## Findings
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**Already clean (no_std + no_alloc):**
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- All reader structs (`Message<'a>`) — zero-copy accessors over `&[u8]`
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- All field accessors, enums, builders (`MessageBuilder<'b>`), typed iterators
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- Core runtime: `ProtoAccessor`, `ProtoBuilder`, `RevBuilder`, `read_varint`, `write_varint`, all iterators
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**Needs `alloc` feature gate:**
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- `RotoMessage` trait — uses `bytes::Bytes` (has `Arc` internally)
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- `RotoOwned` trait — same issue
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- `OwnedMessage` structs generated by codegen
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- `RevBuilder::with()` — uses `Vec<_>` to collect raw fields
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- `Bytes`, `BytesMut` imports in `DATA_IMPORTS`
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**Needs `std` feature gate:**
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- All service code (`SERVICE_IMPORTS`) — uses `std::sync::Arc`, `std::pin::Pin`, `String`, etc.
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- `std::error::Error for RotoError` (already gated)
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---
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## Plan
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### Phase 1: Runtime (`runtime/src/lib.rs`, `runtime/Cargo.toml`) ✅
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1. ~~**Gate `RotoMessage` and `RotoOwned`** behind `#[cfg(feature = "alloc")]`~~
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2. ~~**Gate `BufMutBuilder`** behind `#[cfg(feature = "alloc")]`~~
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3. ~~**Gate `use bytes::BufMut`** — only import it conditionally~~
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4. ~~**Wire up `bytes` features in Cargo.toml:**~~
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**Note:** `bytes::Bytes` requires `Arc` internally, which is in `std`. Since `bytes` only has a `std` feature (no separate `alloc`), our `alloc` feature implies `std`:
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```toml
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[features]
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default = ["std", "alloc"]
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std = []
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alloc = ["std", "bytes/std"]
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```
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### Phase 2: Codegen — `DATA_IMPORTS` & Generated Data Code (`codegen/src/generator/mod.rs`) ✅
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5. ~~**Split `DATA_IMPORTS`** into unconditional + gated sections~~
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6. ~~**Gate `OwnedMessage` structs + `RotoMessage` impls** with `#[cfg(feature = "alloc")]`~~
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7. ~~**Fix `RevBuilder::with()`** — replaced `Vec::collect()` + `.rev()` with forward iteration~~
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### Phase 3: Codegen — Service Code (`codegen/src/generator/mod.rs`) ✅
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8. ~~**Gate `SERVICE_IMPORTS`** with `#[cfg(feature = "std")]`~~
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9. ~~**Gate all service traits, server impls, and `*Server` structs** with `#[cfg(feature = "std")]`~~
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### Phase 4: Generated Consumer Setup ✅
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10. ~~**Emit a `Cargo.toml`** (or instruct consumers) with the right feature setup~~
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Updated consumer `Cargo.toml` files:
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- `examples/hello_world/Cargo.toml`
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- `roto-tonic/Cargo.toml`
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- `benches/Cargo.toml`
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```toml
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[features]
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default = ["std"]
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std = ["roto-runtime/std", "alloc"]
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alloc = ["roto-runtime/alloc"]
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```
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### Phase 5: Validation ✅
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11. ~~**Update `examples/no_std_test`** to build with `--no-default-features`~~
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12. ~~**Run existing tests** with default features~~
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13. ~~**Add a compile-test** that verifies `--no-default-features` builds succeed~~
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---
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## Dependency Graph
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```
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no_std + no_alloc → readers, enums, builders, iterators
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↓ alloc → + OwnedMessage, RotoMessage trait (implies std via bytes::Bytes)
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↓ std → + service code, std::error::Error
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```
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## Files Modified
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| File | Changes |
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|------|---------|
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| `runtime/src/lib.rs` | Gated `RotoMessage`, `RotoOwned`, `BufMutBuilder`, `use bytes::BufMut` behind `#[cfg(feature = "alloc")]` |
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| `runtime/Cargo.toml` | Made `bytes` optional, wired `alloc` → `bytes/std` |
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| `codegen/src/generator/mod.rs` | Split `DATA_IMPORTS`, gated `Owned*` structs, gated service code, fixed `RevBuilder::with()` |
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| `examples/hello_world/Cargo.toml` | Added `std`/`alloc` feature wiring |
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| `roto-tonic/Cargo.toml` | Added `std`/`alloc` feature wiring |
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| `benches/Cargo.toml` | Added `std`/`alloc` feature wiring, `bytes` dependency |
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| `examples/no_std_test/Cargo.toml` | Updated for `no_std` target, added feature wiring |
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| `examples/no_std_test/src/lib.rs` | Added panic handler for embedded target |
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| `examples/no_std_test/src/helloworld.rs` | Rewrote as minimal gated example |
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## Validation
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- ✅ `cargo build` — all packages build with default features
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- ✅ `cargo build --package roto-runtime --no-default-features` — runtime builds without alloc
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- ✅ `cargo test --all` — 38 tests pass (runtime + codegen + integration)
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- ✅ `examples/no_std_test` builds with `--no-default-features` on `thumbv7em-none-eabihf` target
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- ✅ Generated code from integration test (`test_helloworld_build`) compiles successfully |