Site eligibility

Works out which Smart Forms components actually read an expression, so a rule reports only what Smart Forms would act on. readBy(ctx, site) returns the selected components that read a site, each with how it handles the language there, or nothing when none does.

A component reads a site when both of these hold for its selected version:

1. It reads the location. It has a language fact for the site's extension, such as the renderer for a calculatedExpression.
2. Every prerequisite holds there. A prerequisite is what a component needs beyond the location, for example:
   • populate reads an itemPopulationContext only on an item with child items, only the first one on the item, and only with a name and text. A later one with the same name anywhere in the form replaces it.
   • the renderer reads an initialExpression, enableWhenExpression or answerExpression only when no earlier one of the same kind on the item is text/fhirpath.
   • the renderer builds a targetConstraint only with a key, a severity and a human-readable message, and keeps one per key.

The answer does not depend on the site's own language. That way unsupported-expression-language can report exactly the sites a component reads but ignores because of their language. A prerequisite never depends on the language either; how a component handles the language is a separate fact.

The answer is per component. For example, the renderer can read an initialExpression that population does not, because it re-reads the first text/fhirpath one to repopulate a form. A rule that cares about one component filters on it.

Nothing reads an uncatalogued site, a query fragment, or a location no component reads, such as candidateExpression, contextExpression, itemExtractionContext, the root _title and a root itemPopulationContext.

storesVariable builds on readBy: whether a component stores a value under a variable's name, because it evaluates the variable in a language it stores a name for. The Population model and stored names use it.

Site eligibility in the design plan lists every prerequisite with its source.

Schema

7 of the 9 rules call readBy. variable-name-collision uses it through stored names, and unsupported-template-extract-context works from the templates instead.

Code

• src/eligibility.ts: readBy and the Reader it returns, storesVariable, and requireCompat and templateExtractVersion, which read the selected versions.
• src/facts/prerequisites.ts: the prerequisites of each component version, each with a requires description for maintainers and its evidence, and prerequisitesHold. It also has helpers that answer why populate does not read an itemPopulationContext, and which targetConstraint the renderer keeps.
• src/facts/languages.ts: languageFactAt, the locations each component reads.