QuantitiesGenerator emits a factory for only the first availableUnit

[matt-edmondson]

Summary

The QuantitiesGenerator produces a single From{Unit}(T value) static factory per quantity type, regardless of how many entries availableUnits has in dimensions.json. As a result, generated quantities expose only the SI base unit factory and there is no way to construct values from any of the other declared units.

Evidence

Semantics.SourceGenerators/Generators/QuantitiesGenerator.cs:369-385 only iterates the first unit when emitting From* factories.

Confirmed in generated output, e.g. Semantics.Quantities/Generated/.../Mass.g.cs:

public static Mass<T> FromKilogram(T value) => Create(value);

There is no FromGram, FromMilligram, FromTonne, etc. Same pattern across every generated file (e.g. Length only emits FromMeter, with no FromCentimeter, FromKilometer, FromFoot, FromInch, FromYard, FromMile).

Impact

• The user-facing API documented in docs/strategy-unified-vector-quantities.md (e.g. Speed.FromMetersPerSecond(...), Force1D.FromNewtons(...)) is partially missing for any non-base unit.
• Forces consumers to manually convert before calling From{BaseUnit}, defeating a core ergonomics goal of the library.

Suggested next step

Update the generator to emit a From{Unit} factory for every entry in availableUnits, applying the unit's conversion factor (read from the units metadata / ConversionsGenerator) so the value is normalised to the SI base unit inside the factory.

Area / Severity

SourceGenerators · bug

[matt-edmondson]

Status check, not closing.

Confirmed still present after the #70 regenerate: every V0 base, V0 overload and V1 base type only emits From{firstUnit}. The factory loop in QuantitiesGenerator.cs (EmitV0BaseType ~L394–413, EmitV1BaseType ~L493–511, EmitOverloadType ~L684–698) just reads dim.AvailableUnits[0] and stops.

Threading per-unit factories through end-to-end requires the generator to load units.json + magnitudes.json + conversions.json (it currently only reads dimensions.json), then for each unit compute the to-base factor:

• system: SIBase → factor 1, offset 0
• magnitude: <Name> → factor 10^exponent from magnitudes.json
• conversionFactor: <Name> → lookup in conversions.json
• temperature units need the additive offset (Celsius, Fahrenheit) — these compose with the V0 non-negativity guard so Temperature.FromCelsius(-300) should still throw

Combined with #49 (singular vs plural) this is a single, coherent change — recommend they ship together with one new factoryName field on UnitDefinition (default = unit name + "s"; explicit string for irregular plurals like Foot→Feet).

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Generated by Claude Code