From 5a83439bdd5f359b808b0e2c414cdc8abef50bd0 Mon Sep 17 00:00:00 2001
From: Lalitha Pranathi Pulavarthy <drprans@icloud.com>
Date: Sat, 10 Oct 2026 02:48:14 -0400
Subject: [PATCH] Use the right default url for ValueSet and CodeSystem
 instances

getUrlFromFshDefinition fell back to a StructureDefinition url for any
Instance, so the tank matched ValueSet and CodeSystem instances on the
wrong url. InstanceExporter gives them {canonical}/ValueSet/{id} and
{canonical}/CodeSystem/{id}, so the fallback uses that now.
---
 src/fhirtypes/common.ts     |  6 ++++++
 test/import/FSHTank.test.ts | 40 +++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/src/fhirtypes/common.ts b/src/fhirtypes/common.ts
index c540a7293..a10926934 100644
--- a/src/fhirtypes/common.ts
+++ b/src/fhirtypes/common.ts
@@ -1438,6 +1438,12 @@ export function getUrlFromFshDefinition(
     fhirType = 'ValueSet';
   } else if (fshDefinition instanceof FshCodeSystem) {
     fhirType = 'CodeSystem';
+  } else if (
+    fshDefinition instanceof Instance &&
+    (fshDefinition.instanceOf === 'ValueSet' || fshDefinition.instanceOf === 'CodeSystem')
+  ) {
+    // match the default URL that the InstanceExporter assigns to definitional instances
+    fhirType = fshDefinition.instanceOf;
   } else {
     fhirType = 'StructureDefinition';
   }
diff --git a/test/import/FSHTank.test.ts b/test/import/FSHTank.test.ts
index e09f2c4d8..0b0e05685 100644
--- a/test/import/FSHTank.test.ts
+++ b/test/import/FSHTank.test.ts
@@ -527,6 +527,15 @@ describe('FSHTank', () => {
       expect(tank.fish('ExtensionInstance|2.0.0', Type.Extension)).toBeUndefined();
     });
 
+    it('should find an extension defined as an instance definition when fishing by its default url', () => {
+      expect(
+        tank.fish(
+          'http://hl7.org/fhir/us/minimal/StructureDefinition/ExtensionInstance',
+          Type.Extension
+        ).name
+      ).toBe('ExtensionInstance');
+    });
+
     it('should only find logical models when logical models are requested', () => {
       expect(tank.fish('log1', Type.Logical).name).toBe('Logical1');
       expect(
@@ -744,6 +753,21 @@ describe('FSHTank', () => {
       expect(tank.fish('ValueSetInstance|2.0.0', Type.ValueSet)).toBeUndefined();
     });
 
+    it('should find a valueset defined as an instance definition when fishing by its default url', () => {
+      expect(
+        tank.fish('http://hl7.org/fhir/us/minimal/ValueSet/ValueSetInstance2', Type.ValueSet).name
+      ).toBe('ValueSetInstance2');
+    });
+
+    it('should not find a valueset defined as an instance definition when fishing by a StructureDefinition url', () => {
+      expect(
+        tank.fish(
+          'http://hl7.org/fhir/us/minimal/StructureDefinition/ValueSetInstance2',
+          Type.ValueSet
+        )
+      ).toBeUndefined();
+    });
+
     it('should only find codesystems when codesystems are requested', () => {
       expect(tank.fish('cs1', Type.CodeSystem).name).toBe('CodeSystem1');
       expect(
@@ -813,6 +837,22 @@ describe('FSHTank', () => {
       expect(tank.fish('CodeSystemInstance|2.0.0', Type.CodeSystem)).toBeUndefined();
     });
 
+    it('should find a codesystem defined as an instance definition when fishing by its default url', () => {
+      expect(
+        tank.fish('http://hl7.org/fhir/us/minimal/CodeSystem/CodeSystemInstance2', Type.CodeSystem)
+          .name
+      ).toBe('CodeSystemInstance2');
+    });
+
+    it('should not find a codesystem defined as an instance definition when fishing by a StructureDefinition url', () => {
+      expect(
+        tank.fish(
+          'http://hl7.org/fhir/us/minimal/StructureDefinition/CodeSystemInstance2',
+          Type.CodeSystem
+        )
+      ).toBeUndefined();
+    });
+
     it('should only find instances when instances are requested', () => {
       expect(tank.fish('inst1', Type.Instance).name).toBe('Instance1');
       expect(