v2 spec: an expression the INSERT evaluates never sees the schema's own settings (lands with the library build)

[EricAndrechek]

Hold: this lands with the first dev build whose library does it (the artifact producer names the build). Until then the published library still layers the schema's own settings under INSERT-time expressions. Prose only, so the fingerprint doesn't move.

What

spec/abi-v2/docs.md:

• "Settings." (the layering): at the INSERT, the schema's own settings reach only the parse, as a server's CREATE-time settings never reach its INSERT.
  • The parse class keeps all five layers: the settings ClickHouse's own FormatFactory::getFormatSettings reads (input_format_*, date_time_input_format, input_format_allow_errors_*, …). A type gate among them (Nullable(Tuple)'s, for one) is the exception; it binds the CREATE only.
  • Everything else the INSERT does runs under the call's own settings, the server profile and chs_set_defaults only, over the build's own. Every type gate stays at the build's default unless one of those three sets it. That covers:
    • every expression it evaluates: a DEFAULT or MATERIALIZED fill, a CHECK, a TTL, a partition key the server rebuilds at INSERT (one with a modulo), a projection, a Values body's expressions, and any aggregate function's creator in them;
    • its limits, max_partitions_per_insert_block and throw_on_max_partitions_per_insert_block among them.
  • The sorting key and skip indices, which a server builds under its global context, run under the server profile and chs_set_defaults only. An aggregate function's creator there still reads the call's settings.
  • The consequence: a gated CAST or a gated aggregate function in such an expression (a Values body's included), gated only in the schema's own settings, is refused as the server refuses it (455, 44 or 63). A schema-level partition limit doesn't reach the INSERT. A caller whose real INSERT session carries such a setting passes it in the call's settings or the server profile.
  • Measured by the artifact producer, against the server and the library:
    • FORMAT Values (CAST(1 AS LowCardinality(UInt32))), with the gate only in the schema's settings, is refused 455;
    • a 2-partition body under a schema-level limit of 1 is stored;
    • a 101-partition body under a schema-level throw_on_max_partitions_per_insert_block=0 is refused 252, at the server's default limit of 100.
  • Unchanged: session_timezone keeps the zone path.
• chs_filter_create, chs_filter_eval_body, chs_block_create: an evaluation's settings are the INSERT session's. They govern parsing the body AND the expressions the INSERT evaluates, and still never reach the WHERE.

Not changed here: docs/guides/settings.md describes generation 1's precedence, and the ABI v1 reference is unchanged.

Measured

• Fingerprint: unchanged, sha256:d60a681ea0e249ab9e2c83b50640ad9cef040261ddf61805106c93e2c68774e4.
• include/v2/chtypes.h: a509580c… → 9ccd5716f64eb26b3c9e0982765c589ded8f139b162d3bc9de50edd825848227 (prose).
• Gates, each exit 0:
  • gen.py --selftest;
  • --major 2 --check and --major 1 --check;
  • check-no-hand-decls.py --scope all;
  • lint-spelling and lint-cited-paths;
  • markdownlint-cli2@0.18.1 and dprint@0.57.4 check;
  • lint-public (last): ok — no pointers into the private repository, its private notes, or a local filesystem.

🤖 Generated with Claude Code

[EricAndrechek]

Landing checklist (handoff 2026-10-13; #633 item 2):

1. Trigger: the artifact producer reports that the dev build which makes INSERT-time evaluation stop reading the schema's own settings is on staging (its batch 17). Until then, the published library still layers the schema's settings under those expressions, so this stays a draft.

2. If v2 spec: rule r8 — no input crashes the process (lands with the next spec batch) #630 landed first: merge v2 in, then run scripts/abi-v1/gen.py --major 2 --write and --check. Both PRs move include/v2/chtypes.h. The fingerprint stays d60a681e….

3. Merge on the maintainers' clearance, once the required checks are green.

4. The consumer notice for that build names the behaviour change:

   • a gated CAST or aggregate function in a DEFAULT, MATERIALIZED, CHECK or Values body, gated only in the schema's settings, is refused (455/44/63);
   • a schema-level max_partitions_per_insert_block / throw_on_max_partitions_per_insert_block no longer reaches the INSERT.

   A caller whose real INSERT session carries such a setting passes it in the call's settings or the server profile.