Consumer Experience Review

Consumer-experience review

You are auditing a library as the people who will cargo add / npm install / pip install it — not as its author. Internal tests pass through the crate's own privacy and import context and therefore cannot see the gaps a real consumer hits (missing root re-exports, trait-import friction, method-name collisions, feature-flag dead-ends, error types you can't name). The only reliable instrument is a separate project that depends on the library externally and uses it the way a reasonable-but-not-omniscient user would.

Core principle

Write the code a competent user would write on their first try — reaching for conventional names and paths — and let it fail. The natural call that doesn't compile is the finding. Do not pre-correct your consumer code with insider knowledge; that hides exactly what you're looking for. Evidence is a captured compiler error, not an assertion.

Procedure

1. Map the public surface (don't trust memory — read it)

Enumerate what a consumer actually sees:

• Crate-root re-exports (self_update::Status, self_update::get_target) vs what's only reachable via deeper paths (self_update::update::*, self_update::backends::github::Update, self_update::errors::Error). Asymmetry here is the #1 source of findings — e.g. is the value/error returned by build() and update() nameable from the root, or only via a deeper module path?
• Traits and every method signature — look for two traits that define the same method name (collides when both are in scope), and for &mut self where a consumer would expect &self.
• Constructors / builders — is the entry Type::configure() returning a builder? Is the fallible path build()? Is it consistent across the four backends (github / gitlab / gitea / s3)? Do the per-backend builders share setter names (url, target, identifier, access_key)?
• Error types — can the error returned by a public function be named via the same path the type came from? (self_update::errors::Error reachable from the root?)
• Feature flags — what's gated, and does a natural feature combination leave a type unreferenceable or a backend unusable? The reqwest and ureq clients are mutually exclusive — confirm the failure mode when a user enables both or neither. Note there is no explicit compile_error! guard today: both yields a confusing duplicate-glob name collision and neither yields undefined-item errors, so the raw clash is the diagnostic the user sees — a candidate finding, not a clean message.
• Macros — re-exported at the crate root (use self_update::cargo_crate_version;)? Ecosystem convention is root.

2. Scaffold a throwaway external consumer

• Put it in $TMPDIR (or another scratch path) — never inside the repo, never in git. Do not pollute the project's examples/, tests/, or working tree. (local/ in this repo is a safe scratch dir if you prefer it, but a path-dependency consumer outside the repo is what proves the gap.)
• Depend on the library by path with a realistic feature set:
  • Rust: self_update = { path = "/abs/path", features = [...] }
  • npm: npm link / file: dependency. Python: pip install -e. Same idea — external module resolution, real package boundary.
• Exercise the breadth: each backend (github, gitlab, gitea, s3), the update() and update_extended() paths, ReleaseList::fetch, the Download/Extract/Move utilities, builder options, and at least one less-common feature combination (e.g. ureq instead of reqwest, or rustls instead of default-tls).

3. Write naive-but-reasonable consumer code

Deliberately reach for conventions first:

• Import the macro from the crate root (use self_update::cargo_crate_version;) before trying submodule paths.
• Bring the obvious traits/types into scope together (or glob use self_update::*;) — exactly what a real user does.
• Name the type returned by build() and the error type returned on failure in a let _: Option<self_update::SomeError> = None; or a function signature.
• Build request headers for Download::set_header the obvious way — does the user have to reach into reqwest/http directly, or does the crate re-export what they need?
• Guess builder method names by convention — a wrong guess that the compiler can't help disambiguate is a discoverability finding.

4. Compile, run, capture exact errors

cargo build/run (or the ecosystem equivalent). For every failure, record the exact diagnostic code and message (error[E0432]: unresolved import, E0599, E0034: multiple applicable items, etc.). That verbatim error is the evidence in your report.

5. Isolate each gap in a minimal probe

For each suspected issue, create a tiny separate binary/module that triggers only that issue with the smallest natural snippet. This (a) proves it's real and not a side effect, and (b) gives you a clean before/after to re-run once a fix is proposed/applied.

6. Severity — weight the release window

Rank findings, and explicitly factor in the version context:

• Pre-1.0 / major bump: a hard compile error on a common operation, or any public-surface inconsistency, is high — this is the only non-breaking window to fix the method/type surface. Say so.
• Post-1.0 minor: a breaking fix is itself a cost; lean toward additive fixes (new re-exports, #[doc(alias)], deprecations) and documentation.
• Always separate: 🔴 blocks/forces ugly workarounds on common paths · 🟠 awkward but workable · 🟡 docs/discoverability.

7. Report — evidence first, fixes proposed not applied

For each finding: the natural code that failed → the exact compiler error → root cause (cite file:line) → concrete proposed fix (and whether it's breaking or additive). Recommend a subset to act on given the release window. Do not implement fixes unless the user asks — this skill produces a review. If asked to fix, re-run the isolated probes (step 5) afterward to prove the natural code now works, and run the project's full check (fmt / clippy / tests / doctests on both the reqwest and ureq clients, plus README drift via ./readme.sh check).

8. Clean up

Remove or abandon the scratch consumer crate. Never leave it in the repo or stage it.

Gap classes to actively check (the checklist that catches the real ones)

• Root re-export gaps / asymmetry — type at root but its builder/error only via self_update::sub::; one sibling backend exports a setter, another doesn't (e.g. identifier, or the endpoint url(...) setter).
• Trait method-name collisions — two in-scope traits with the same method name → E0034, forces UFCS. Settle pre-1.0.
• Unnameable error / return types — build() returns a type the user can't name from the path they imported.
• Constructor/builder inconsistency — entry points and fallible paths that differ across the four backends; a shared setter whose name drifts from the impl_common_builder_setters! macro.
• Macro / helper not at crate root — convention is root.
• Feature-flag dead-ends — a plausible feature set where a needed type/backend is unreferenceable; the reqwest/ureq mutual exclusion not surfaced clearly.
• Header/auth ergonomics — does building a custom download header force a direct dependency on a specific http client crate?
• &mut self for reads — forces a lock/wrapper for shared use; note it even if intentional.
• Discoverability — natural names that don't exist and have no #[doc(alias)]; missing trait-import hints in errors.

Cautions

• Testing from inside the crate (its own tests/, examples/, or doctests) is not a consumer test — it inherits the crate's import/privacy context and will miss the gaps. External path dependency is mandatory.
• Sandboxed builds may hit registry/network errors; this skill only needs the path-dependency and std/tokio-class deps. If a build fails for sandbox/network reasons (not a real API gap), retry with the sandbox disabled before concluding.
• A finding is the user's natural code failing, not "the API is unusable" — the API may work fine once you know the trick. The cost being measured is "knowing the trick."
• Generalize beyond Rust where relevant: npm (root export maps, exports field, dual ESM/CJS), Python (__init__.py re-exports, optional-extra imports) — same methodology, same gap classes.