Jean-Pierre

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Bare #[setting(default)] fields are not marked optional in the schema ​

  • Status: Done
  • Kind: Bug
  • Authors: jp
  • Date: 2026-08-24
  • Label: package=schematic
  • Label: type=bug

FieldArgs::default is an Option<Expr>, and parse_default (crates/contrib/schematic_macros/src/utils.rs) maps the bare #[setting(default)] form to None — the same value an absent default attribute produces. The two are therefore indistinguishable downstream.

Two consequences, both in crates/contrib/schematic_macros/src/common/field.rs:

  • Field::is_optional gates on args.default.is_some(), so a bare-default field reports optional: false in the generated SchemaField.
  • PartialConfig::default_values() contains no entry for the field, so it stays None there.

Neither is a regression: on main the bare form made preserve_str_literal return Err, and FieldArgs::from_attributes(...).unwrap_or_default() swallowed it, leaving args.default = None as well. parse_default reproduces that deliberately so the ~20 existing bare-default fields keep byte-identical generated code.

There is also no resolved-config difference: an unset partial field resolves through Config::from_partial's fallback to the type's Default impl, which is exactly what bare default declares.

Impact today ​

None observable. SchemaField::optional is write-only in this workspace — the macro populates it and nothing reads it. The only two consumers of AppConfig::schema() are AppConfig::fields() (reads the field map) and jp_conversation::compat (reads fields and flatten). There is no JSON Schema export.

So this is metadata that will be wrong for the first consumer that reads it, not a bug anyone can currently hit.

Fix ​

Replace FieldArgs::default: Option<Expr> with a three-state representation — absent / bare / expression:

  • generate_default_value (config/field_value.rs) already treats "absent" and "bare" identically; keep that.
  • is_optional returns true for bare and expression.

Roughly 25 lines in schematic_macros across three call sites (the third is the Expr::Lit inspection in generate_schema_type).

Because nothing reads the flag, the change is safe to make whenever, and equally fine to defer until a schema consumer exists.

Context ​

Raised in review on #887 (comment 3657548560) and dismissed there as out of scope for that PR, which was explicitly behavior-neutral in the macro hunk.