dowel

Open questions

In priority order. The higher an item, the more it constrains later design.

Q1. The `cfg` namespace vocabulary

Status: not started. The next item to pin down.

The shared foundation referenced by when predicates in dowel.toml, match / when in dowel.build, toolchain selection, and ABI labels.

Working draft:

cfg.opt        configuration (debug / release / …)
cfg.target     target triple
host.os        build host OS
host.arch      build host architecture
feature.<name> feature flag
tc.c           the selected C toolchain

To decide:

Which dimensions belong in cfg (these become candidate components of the ABI label)
Predicate composition rules (allow anything beyond implicit AND?)
Whether the vocabulary is fixed or extensible by toolchains

The provisional vocabulary used by the implementation

To make progress, the implementation adopts the draft above verbatim as a closed vocabulary (crates/dowel-eval/src/config.rs). This is a placeholder until Q1 is decided, not the decision itself. The live version is available from dowel schema dump.

Namespace	Implemented keys	Domain
`cfg`	`opt`	`debug` / `release`
`cfg`	`target`	target triple (free-form string)
`host`	`os` / `arch`	build host values
`feature`	`<name>`	boolean (only names declared in `[features]` of `dowel.toml`)
`tc`	`c`	identifier of the selected C toolchain
`tc`	`cxx`	identifier of the selected C++ toolchain

Predicate composition is implicit AND only. Exhaustiveness checking of match applies to keys with finite domains (cfg.opt / host.os / host.arch); cfg.target has an unbounded domain and requires a _ arm. This asymmetry will be revisited when Q1 is decided.

Q2. ABI label composition

Status: deferred. Depends on the outcome of Q1.

The counterpart of Conan’s package_id. Granularity dominates the design.

Too coarse → verification becomes meaningless (the vcpkg triplet limit)
Too fine → cache hit rates collapse

Candidate components: toolchain ID, C++ standard version, standard library implementation, _GLIBCXX_USE_CXX11_ABI, MSVC runtime kind, sanitizers, LTO, exception model, floating-point model.

The Phase 0 verification (how many real mismatches are detected) will indicate the required granularity.

Q4. Store format details

Status: skeleton only (20-architecture.md section 5).

Record structure and index layout
What goes into the fingerprint (what is hashed)
GC policy (generations / size cap / reachability)
Migration across version changes (when a format change discards the store)

Q6. What to do when `import` output is rejected

Configurations extracted from an existing project may fail this system’s verification (ABI mismatch, error_on_conflict, and so on).

Options:

A mode that downgrades to warnings (limited to a migration window)
Fail and require fixes
Mark extracted output “unverified” and enable verification incrementally

The third is favored. The current implementation carries the mark as an UNVERIFIED header comment on the generated files (human-facing, pointing at migrate verify); whether a machine-readable mark should gate verification per target — and what clears it — remains undecided.

Q7. C++20 modules

The plan is to make scan actions first-class in the graph, but parts of this depend on the state of clangd support. Re-survey when Phase 2 starts.

Q8. Verifying the current state of Meson

The statements about Meson in 00-overview.md are based on prior knowledge. The wrap and lock behavior in particular may have changed in recent releases; confirmation against the official documentation has not been done.

Q10. Prebuilt distribution for dowelup

Status: not started. ADR-0013 defined source builds only.

Building from source assumes a Rust toolchain. Widening the audience requires distributing prebuilt binaries. To decide:

Where to publish (GitHub Releases or a separate endpoint)
How to verify (SHA-256 comparison; whether signatures are required)
How binaries map back to the sha source of truth (recording and checking which commit a binary was built from)

Fetching itself can be delegated to curl, but verification has to be owned here.

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