Improve error message for ValueSet compose component without any concept

src/export/ValueSetExporter.ts

@@ -457,7 +457,15 @@ export class ValueSetExporter {
           });
         }
       }
-
+      if (conceptIndex == null) {
+        logger.error(
+          `Cannot process caret assignment rule for code ${system}#${code} because ` +
+            'this value set does not explicitly include or exclude this code in its ' +
+            'rules. To fix this error, add a rule that specifically includes or excludes ' +
+            'this code for the value set.'
+        );
+        return;
+      }
       if (conceptIndex !== -1) {
         if (rule.isInstance) {
           const instanceExporter = new InstanceExporter(this.tank, this.pkg, this.fisher);

test/export/ValueSetExporter.test.ts

@@ -754,6 +754,34 @@ describe('ValueSetExporter', () => {
     });
   });
 
+  it('should throw error for caret rule on valueset compose component without any concept', () => {
+    // ValueSet: SomeVS
+    // * include codes from system http://example.org/CS
+    // * http://example.org/CS#"some-code" ^designation.value = "some value"
+
+    const valueSet = new FshValueSet('SomeVS');
+
+    const component = new ValueSetConceptComponentRule(true);
+    component.from.system = 'http://example.org/CS';
+
+    const cvRule = new CaretValueRule('');
+    cvRule.pathArray = ['http://example.org/CS#"some-code"'];
+    cvRule.caretPath = 'designation.value';
+    cvRule.value = 'some value';
+
+    valueSet.rules.push(component, cvRule);
+    doc.valueSets.set(valueSet.name, valueSet);
+    const exported = exporter.export().valueSets;
+    expect(exported.length).toBe(1);
+    expect(loggerSpy.getAllMessages('error')).toHaveLength(1);
+    expect(loggerSpy.getLastMessage('error')).toBe(
+      'Cannot process caret assignment rule for code http://example.org/CS#"some-code" ' +
+        'because this value set does not explicitly include or exclude this code in its ' +
+        'rules. To fix this error, add a rule that specifically includes or excludes this ' +
+        'code for the value set.'
+    );
+  });
+
   it('should export a value set with a contained resource created on the value set', () => {
     // ValueSet: DinnerVS
     // * ^contained.resourceType = "Observation"