Expression parsing

Reads the text of an expression: FHIRPath with the pinned fhirpath.js, and x-fhir-query with a small scanner. It is not a stage of the run but a set of helpers that the rules and Name analysis call.

FHIRPath. Only a site whose language is exactly text/fhirpath is parsed; CQL and other languages never are. fhirpath.ts is the only file that uses fhirpath.js, pinned to 4.10.1, so the linter parses as the engine does. From the parse tree it reads:

• the syntax error and its position, when the text does not parse, which sdc/parse-error reports, or sdc/fragment-parse-error in a query fragment;
• the function calls, which sdc/unknown-function checks against the functions fhirpath.js implements;
• the %name references, leaving out names that defineVariable binds earlier in the chain. Each says whether it is complete, and whether it is conditional: fhirpath.js may skip it, as in an iif branch;
• the linkId references, written where(linkId = '…');
• whether the expression reads its input other than its linkId, which plugin rules use to tell whether a value can differ between repetitions of a group.

x-fhir-query. Both codes, application/x-fhir-query (R4) and text/x-fhir-query (R5), are read as queries. The scanner finds each {{…}} fragment, which becomes a FHIRPath site of its own, and checks that the query has the shape of a FHIR search. It does not check resource types or search parameters.

Schema

FHIRPath, in fhirpath.ts:

x-fhir-query, in x-fhir-query.ts:

Code

In packages/core/src/analysis/:

• fhirpath.ts: findFhirPathSyntaxProblem, findFunctionCalls, findVariableReferences, findLinkIdReferences and readsInput. Each returns undefined when the text does not parse.
• x-fhir-query.ts: scanQueryFragments and findQueryShapeProblem. isQueryLanguage, which plugins can import, is here too.
• fhirpath-function-catalog.ts: the names of the functions fhirpath.js implements. It is generated by npm run generate:functions --workspace @aehrc/sdc-questionnaire-lint; regenerate it after bumping fhirpath.js, and never edit it by hand.

The analysis helpers in the architecture map have the details.