claude@clouddev1
cb8ff8a7c2
F1/F2/F3 from the whole-Phase-4 /runda (handoff-42 §3):
- F3: drop an anonymous composite UNIQUE via a derived, engine-neutral
name `unique_<cols>` — recomputed live, nothing persisted, reusing the
existing `DROP CONSTRAINT <name>` grammar (no new syntax/metadata, the
§4g anonymity decision intact). A name matching more than one UNIQUE is
refused as ambiguous, never guessed. One undo step. `describe`
annotates each composite UNIQUE with its name.
- F1: dropping a column a composite UNIQUE covers is refused up-front
with the derived name + the actionable drop command (was an unhelpful
generic engine refusal).
- F2: contextless friendly_message() no longer leaks a literal `{table}`
in the generic hint (new `error.generic.hint_no_table`, selected when
no table is in context). The table-ful path is unchanged.
Docs: ADR-0035 Amendment 1 + Status + README index + plan
docs/plans/20260526-adr-0035-composite-unique-drop-f1f2f3.md.
Tests: +5 (drop-by-name, ambiguous-refused, one-undo-step, F1 guard,
F2 no-leak) + a describe-render assertion. 1922 pass / 0 fail / 0 skip;
clippy clean.
111 lines
6.0 KiB
Markdown
111 lines
6.0 KiB
Markdown
# Plan — ADR-0035 Phase-4 `/runda` follow-ups F1 / F2 / F3 (2026-05-26)
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Bundle of the three error-message / capability follow-ups surfaced by the
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whole-Phase-4 `/runda` (handoff-42 §3). All three live on the **safe**
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composite-UNIQUE edge (dropping a UNIQUE-covered column is correctly
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*refused* today — no corruption); the work improves messaging and adds a
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way to drop the constraint itself.
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## Phase 1 — requirements
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- **F1 — friendly refusal for dropping a composite-UNIQUE column.**
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`do_drop_column`'s covering-index guard reads `read_table_indexes`,
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which filters to `origin='c'` (explicit `CREATE INDEX`) and excludes
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the UNIQUE-constraint auto-index (`origin='u'`). So `drop column c`
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when `unique (b, c)` spans `c` skips the guard, reaches the engine, and
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is refused with an unhelpful generic message. Add an up-front guard
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detecting the column in `schema.unique_constraints` (composite only —
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`read_unique_constraints` routes single-column UNIQUEs to the column
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flag, multi-column to `unique_constraints`), refusing with the
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constraint's **derived name** (F3) + the drop command. Behaviour stays
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"refused"; only the message improves. **Message-only — no `--cascade`
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extension** (the SQL drop-column has no `--cascade` spelling; dropping
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a constraint via cascade is a larger semantic change, out of scope
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unless the user asks).
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- **F2 — literal `{table}` leak in contextless `friendly_message()`.**
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`Verbosity` defaults to `Verbose`, so `friendly_message()` (which uses
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`TranslateContext::default()`, no table) renders the generic hint
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`"…current state of `{table}`."` with the literal placeholder via
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`ctx_table()`'s `"{table}"` fallback. Hits every contextless
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`friendly_message()` callsite whose error lands in the **generic
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bucket**: replay, undo, rebuild-from-text, export. Fix: a tableless
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generic-hint variant selected when `ctx.table` is `None`. **Broader
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finding** (DA): the same `{name}`-marker fallbacks leak in *other*
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templates (e.g. a replayed UNIQUE violation → `error.unique.*`) when
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reached contextless. The documented F2 is the generic case; the broader
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leak is surfaced for the user to scope, not silently expanded/narrowed.
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- **F3 — a way to drop an anonymous composite UNIQUE (user-raised).**
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By design (§4a.2/§4g) a composite `UNIQUE(a,b)` is anonymous —
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PRAGMA-detected, a bare column-list, no name — so `DROP CONSTRAINT
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<name>` can't target it and recreating the table is the only escape.
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Add a way to drop it. **(Amends ADR-0035 — see Amendment 1.)**
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Baseline: `cargo test` → 1917 pass / 0 fail / 0 skip / 1 ignored doctest;
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`cargo clippy --all-targets -- -D warnings` clean.
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## Phase 2/3 — F3 design (the genuine fork; user-decided)
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Composite UNIQUE has no name. Options considered:
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- **A — name composite UNIQUEs (user-supplied):** reverse the §4g
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anonymity decision; needs a new `__rdbms_*` table + YAML round-trip +
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rebuild-arrival migration (the cost §4a.3 deliberately avoided). Most
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SQL-standard, largest.
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- **B — positional drop by column-list** (`drop … unique (cols)`):
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preserves anonymity, no metadata, but needs a *new* grammar form.
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- **C — auto-assigned, engine-neutral *derived* name (chosen).** The
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name is a deterministic function of the columns (`unique_<cols>`),
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recomputed live wherever shown or matched. Storage stays a bare
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column-list (anonymity preserved); the name is purely a
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presentation/addressing label. **Reuses the existing `DROP CONSTRAINT
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<name>` grammar — no new syntax at all.** Zero metadata, zero
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migration, round-trips for free. Tracks column renames.
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**User decisions (2026-05-26):** approach **C / derived (no storage)**;
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name format **`unique_<cols>`**; doc vehicle **amend ADR-0035**; scope
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**advanced-SQL only** (matching the 4g `ADD` form — no simple-mode verb).
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### DA critique (written down)
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1. **Ambiguous derived names** (e.g. a column literally named `b_c` vs
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`UNIQUE (b, c)`): drop-by-name must **detect ambiguity and refuse**,
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never guess. *In scope.*
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2. **Collision with a user-named CHECK/FK** of the same string: the
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`do_drop_constraint_by_name` order is CHECK → FK → UNIQUE, so a
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CHECK/FK shadows a derived UNIQUE name. Acceptable given the
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distinctive `unique_` prefix; **document the order**.
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3. **F1 `--cascade`**: not extended to drop a covering UNIQUE
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(constraint, not index). Refuse-only. *Flagged.*
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4. **F2 breadth**: the leak is broader than `error.generic.hint`. Fix the
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documented generic case; **surface** the broader leak. *Flagged.*
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5. **Single-column UNIQUE column drop**: a parallel gap (a single-column
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UNIQUE column drop also reaches the engine with a poor message) exists
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but is **outside the documented F1 scope** (different mechanism —
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ADR-0029 column-level `drop constraint`). Noted, not fixed here.
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## Phase 4 — execution (order: F3 → F1 → F2)
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1. **F3.** `unique_constraint_name(cols) -> "unique_<cols>"` helper
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(`db.rs`, `pub(crate)`). Extend `do_drop_constraint_by_name` with a
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third step: match each composite UNIQUE's derived name; >1 match →
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refuse (ambiguous); 1 match → `rebuild_table` with that entry removed
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from `unique_constraints` (mirrors `do_alter_add_unique` in reverse) +
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`do_describe_table`. Annotate the describe "Table constraints:"
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section: `unique_b_c: UNIQUE (b, c)`.
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2. **F1.** Up-front guard in `do_drop_column` after the index-covering
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guard: column in any `schema.unique_constraints` entry → refuse with
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the derived name + `alter table T drop constraint <name>`.
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3. **F2.** `error.generic.hint_no_table` catalog entry; in
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`translate_generic`, pick it when `ctx.table` is `None`.
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Test-first for each (reproduce → fail → fix → pass), across the worker
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API (Tier-1/3) and the friendly-layer unit tests + insta snapshots.
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## Phase 5 — verification
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Full `cargo test` + clippy; compare to baseline; every checklist item
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addressed; engine-neutral vocab held (no SQLite/STRICT/PRAGMA in new
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user-facing strings); ADR + README + this plan lockstep.
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