feat: Add issue message formatting

Author: effigies

src/schema/applyRules.ts

@@ -1,7 +1,7 @@
 import type { GenericRule, GenericSchema, SchemaFields, SchemaTypeLike } from '../types/schema.ts'
 import type { Severity } from '../types/issues.ts'
 import type { BIDSContext } from './context.ts'
-import { contextFunction, prepareContext } from './expressionLanguage.ts'
+import { contextFunction, formatter, prepareContext } from './expressionLanguage.ts'
 import { logger } from '../utils/logger.ts'
 import { compile } from '../validators/json.ts'
 import type { DefinedError } from '@ajv'
@@ -166,12 +166,13 @@ function _evalRuleChecks(
 ): boolean {
   if (rule.checks && !mapEvalCheck(rule.checks, context)) {
     if (rule.issue?.code && rule.issue?.message) {
+      const format = formatter(rule.issue.message)
       context.dataset.issues.add({
         code: rule.issue.code,
         location: context.path,
         rule: schemaPath,
         severity: rule.issue.level as Severity,
-      }, rule.issue.message)
+      }, format(context))
     } else {
       context.dataset.issues.add(
         { code: 'CHECK_ERROR', location: context.path, rule: schemaPath },

src/schema/expressionLanguage.ts

@@ -140,6 +140,24 @@ function _contextFunction(expr: string): (context: BIDSContext) => any {
  */
 export const contextFunction = memoize(_contextFunction)
 
+function _formatter(format: string): (context: BIDSContext) => string {
+  if (!format.includes('{')) {
+    return (context: BIDSContext) => format
+  }
+  const template = format.replace(/{/g, '${').replace(/\\/g, '\\\\').replace(/`/g, '\\`')
+  return new Function('context', `with (context) { return \`${template}\` }`) as (
+    context: BIDSContext,
+  ) => string
+}
+
+/**
+ * Generate a function that formats a string using the BIDS context.
+ *
+ * Strings are expected to use Python-style formatting,
+ * e.g., "sub-{entities.sub}/ses-{entities.ses}".
+ */
+export const formatter = memoize(_formatter)
+
 function safeContext(context: BIDSContext): BIDSContext {
   return new Proxy(context, {
     has: () => true,