Can now use a discriminator to walk into a complex extension (for R3)

src/Hl7.Fhir.Specification.Tests/DiscriminatorInterpreterTests.cs

@@ -129,6 +129,22 @@ public async T.Task WalkToInlineExtensionConstraints()
             Assert.AreEqual("hi!", ((FhirString)elem.Current.Current.Fixed).Value);
         }
 
+        [TestMethod]
+        public async T.Task WalkToInlineComplexExtensionConstraints()
+        {
+            var sd = await _source.FindStructureDefinitionAsync("http://unittest.com/StructureDefinition/patient-sliced-complex-extension");
+            var nav = ElementDefinitionNavigator.ForSnapshot(sd);
+            nav.JumpToFirst("Patient.communication");
+            nav.MoveToNextSlice();
+            var walker = new StructureDefinitionWalker(nav, _source);
+
+            var elem = walker.Walk("extension('http://hl7.org/fhir/StructureDefinition/patient-proficiency').extension('type').value").Single();
+            var pattern = elem.Current.Current.Pattern;
+
+            Assert.IsTrue(pattern is Coding c && c.Code == "RSP");
+        }
+
+
         [TestMethod]
         public async T.Task ParseInvalidDiscriminatorExpressions()
         {

src/Hl7.Fhir.Specification.Tests/Hl7.Fhir.Specification.Tests.csproj

@@ -43,12 +43,7 @@
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
   </ItemGroup>  
-
-  <ItemGroup>
-    <None Remove="TestData\validation\list-with-profile-slicing.xml" />
-    <None Remove="TestData\validation\observation-profile-for-discriminator-test.xml" />
-  </ItemGroup>
-
+
   <ItemGroup>
     <Content Include="..\Hl7.Fhir.Specification\data\profiles-resources.xml" Link="TestData\snapshot-test\profiles-resources.xml">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>

src/Hl7.Fhir.Specification.Tests/StructureDefinitionWalkerTests.cs

@@ -1,7 +1,8 @@
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using Hl7.Fhir.Specification.Source;
 using Hl7.Fhir.Model;
+using Hl7.Fhir.Serialization;
 using Hl7.Fhir.Specification.Navigation;
+using Hl7.Fhir.Specification.Source;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using System.Linq;
 using T = System.Threading.Tasks;
 
@@ -112,6 +113,24 @@ public async T.Task WalkAcrossReference()
             var elem = walker.Child("performer").Resolve().OfType("Practitioner").Child("name").Single();
             Assert.AreEqual("Practitioner.name", elem.Current.Path);
         }
+
+        [TestMethod]
+        public async T.Task WalkAcrossInlineExtension()
+        {
+            var sd = await _source.FindStructureDefinitionAsync("http://unittest.com/StructureDefinition/patient-sliced-complex-extension");
+            var nav = ElementDefinitionNavigator.ForSnapshot(sd);
+            nav.JumpToFirst("Patient.communication");
+            nav.MoveToNextSlice();
+
+            var fortest = nav.StructureDefinition.ToXml();
+            var walker = new StructureDefinitionWalker(nav, _source);
+
+            var elem = walker.Extension("http://hl7.org/fhir/StructureDefinition/patient-proficiency");
+            elem = elem.Extension("type");
+
+            Assert.IsNotNull(elem);
+            Assert.AreEqual("Patient.communication:languageControlListening.extension:languageControlListening-proficiency.extension:type", elem.Current.Current.ElementId);
+        }
     }
 }
 

src/Hl7.Fhir.Specification.Tests/TestData/validation/observation-profile-for-discriminator-test.xml

@@ -19,24 +19,6 @@
         <rules value="open"/>
       </slicing>
     </element>
-    <element id="Observation.identifier.extension">
-      <path value="Observation.identifier.extension"/>
-      <slicing>
-        <discriminator>
-          <type value="value"/>
-          <path value="url"/>
-        </discriminator>
-        <rules value="open"/>
-      </slicing>
-    </element>
-    <element id="Observation.identifier.extension:myExtension">
-      <path value="Observation.identifier.extension"/>
-      <sliceName value="myExtension"/>
-      <type>
-        <code value="Extension"/>
-        <profile value="http://example.org/fhir/StructureDefinition/string-extension-for-discriminator-test"/>
-      </type>
-    </element>
     <element id="Observation.identifier:someCustomIdentifier">
       <path value="Observation.identifier"/>
       <sliceName value="someCustomIdentifier"/>

src/Hl7.Fhir.Specification.Tests/TestData/validation/patient-sliced-complex-extension.xml

@@ -0,0 +1,140 @@
+<?xml version="1.0" encoding="utf-8"?>
+<StructureDefinition xmlns="http://hl7.org/fhir">
+  <id value="zib-Patient"/>
+  <url value="http://unittest.com/StructureDefinition/patient-sliced-complex-extension"/>
+  <version value="0.0.1"/>
+  <name value="ZibPatient"/>
+  <title value="zib Patient"/>
+  <status value="draft"/>
+  <experimental value="false"/>
+  <publisher value="Nictiz"/>
+  <contact>
+    <name value="Nictiz"/>
+    <telecom>
+      <system value="email"/>
+      <value value="info@nictiz.nl"/>
+      <use value="work"/>
+    </telecom>
+  </contact>
+  <description value="A person who receives medical, psychological, paramedical or nursing care. In some care settings, the term client or participant is used instead of the term patient.&#xD;&#xA;Nationality is used as an indication of the country of citizenship. &#xD;&#xA;Marital status is a person’s formal position as defined by the Dutch civil code. There is a distinction between marriage and civil union."/>
+  <purpose value="This Patient resource represents the Dutch zib ('Zorginformatiebouwsteen', i.e. Health and Care Information Model) [Patient v3.2 (2020)](https://zibs.nl/wiki/Patient-v3.2(2020EN)), [Nationality v3.0 (2020)](https://zibs.nl/wiki/Nationality-v3.0(2020EN)) and [MaritalStatus v3.1 (2020)](https://zibs.nl/wiki/MaritalStatus-v3.1(2020EN))."/>
+  <copyright value="Copyright and related rights waived via CC0, https://creativecommons.org/publicdomain/zero/1.0/. This does not apply to information from third parties, for example a medical terminology system. The implementer alone is responsible for identifying and obtaining any necessary licenses or authorizations to utilize third party IP in connection with the specification or otherwise."/>
+  <fhirVersion value="4.0.1"/>
+  <mapping>
+    <identity value="zib-patient-v3.2-2020EN"/>
+    <uri value="https://zibs.nl/wiki/Patient-v3.2(2020EN)"/>
+    <name value="zib Patient-v3.2(2020EN)"/>
+  </mapping>
+  <mapping>
+    <identity value="zib-nationality-v3.0-2020EN"/>
+    <uri value="https://zibs.nl/wiki/Nationality-v3.0(2020EN)"/>
+    <name value="zib Nationality-v3.0(2020EN)"/>
+  </mapping>
+  <mapping>
+    <identity value="zib-maritalstatus-v3.1-2020EN"/>
+    <uri value="https://zibs.nl/wiki/MaritalStatus-v3.1(2020EN)"/>
+    <name value="zib MaritalStatus-v3.1(2020EN)"/>
+  </mapping>
+  <mapping>
+    <identity value="zib-languageproficiency-v3.2-2020EN"/>
+    <uri value="https://zibs.nl/wiki/LanguageProficiency-v3.2(2020EN)"/>
+    <name value="zib LanguageProficiency-v3.2(2020EN)"/>
+  </mapping>
+  <mapping>
+    <identity value="zib-contactinformation-v1.2-2020EN"/>
+    <uri value="https://zibs.nl/wiki/ContactInformation-v1.2(2020EN)"/>
+    <name value="zib ContactInformation-v1.2(2020EN)"/>
+  </mapping>
+  <mapping>
+    <identity value="zib-contactperson-v3.4-2020EN"/>
+    <uri value="https://zibs.nl/wiki/ContactPerson-v3.4(2020EN)"/>
+    <name value="zib ContactPerson-v3.4(2020EN)"/>
+  </mapping>
+  <kind value="resource"/>
+  <abstract value="true"/>
+  <type value="Patient"/>
+  <baseDefinition value="http://hl7.org/fhir/StructureDefinition/Patient"/>
+  <derivation value="constraint"/>
+  <differential>
+    <element id="Patient">
+      <path value="Patient"/>
+      <short value="Patient"/>
+      <alias value="Patient"/>
+      <mapping>
+        <identity value="zib-patient-v3.2-2020EN"/>
+        <map value="NL-CM:0.1.1"/>
+        <comment value="Patient"/>
+      </mapping>
+    </element>
+    <element id="Patient.communication">
+      <path value="Patient.communication"/>
+      <short value="LanguageProficiency"/>
+      <definition value="Root concept of the LanguageProficiency information model. This concept contains all data elements of the LanguageProficiency information model."/>
+      <alias value="Taalvaardigheid"/>
+      <mapping>
+        <identity value="zib-languageproficiency-v3.2-2020EN"/>
+        <map value="NL-CM:7.12.1"/>
+        <comment value="LanguageProficiency"/>
+      </mapping>
+    </element>
+    <element id="Patient.communication">
+      <path value="Patient.communication"/>
+      <slicing>
+        <discriminator>
+          <type value="value"/>
+          <path value="extension('http://hl7.org/fhir/StructureDefinition/patient-proficiency').extension('type').value"/>
+        </discriminator>
+        <rules value="open"/>
+      </slicing>
+    </element>
+    <element id="Patient.communication:languageControlListening">
+      <path value="Patient.communication"/>
+      <sliceName value="languageControlListening"/>
+    </element>
+    <element id="Patient.communication:languageControlListening.extension">
+      <path value="Patient.communication.extension"/>
+      <sliceName value="languageControlListening-proficiency" />
+      <short value="LanguageControlListening"/>
+      <definition value="The ability to understand spoken text in the language in question."/>
+      <alias value="TaalvaardigheidBegrijpen"/>
+      <max value="1"/>
+      <type>
+        <code value="Extension"/>
+        <profile value="http://hl7.org/fhir/StructureDefinition/patient-proficiency"/>
+      </type>
+      <mapping>
+        <identity value="zib-languageproficiency-v3.2-2020EN"/>
+        <map value="NL-CM:7.12.6"/>
+        <comment value="LanguageControlListening"/>
+      </mapping>
+    </element>
+    <element id="Patient.communication:languageControlListening.extension:languageControlListening-proficiency.extension:level">
+      <path value="Patient.communication.extension.extension"/>
+      <sliceName value="level"/>
+      <min value="1"/>
+    </element>
+    <element id="Patient.communication:languageControlListening.extension:languageControlListening-proficiency.extension:level.value[x]">
+      <path value="Patient.communication.extension.extension.value[x]"/>
+      <comment value="The zib ValueSet TaalvaardigheidBegrijpenCodelijst is equal to the default FHIR ValueSet."/>
+      <binding>
+        <strength value="required"/>
+      </binding>
+    </element>
+    <element id="Patient.communication:languageControlListening.extension:languageControlListening-proficiency.extension:type">
+      <path value="Patient.communication.extension.extension"/>
+      <sliceName value="type"/>
+      <min value="1"/>
+      <max value="1"/>
+    </element>
+    <element id="Patient.communication:languageControlListening.extension:languageControlListening-proficiency.extension:type.value[x]">
+      <path value="Patient.communication.extension.extension.value[x]"/>
+      <patternCoding>
+        <system value="http://terminology.hl7.org/CodeSystem/v3-LanguageAbilityMode"/>
+        <code value="RSP"/>
+      </patternCoding>
+      <binding>
+        <strength value="required"/>
+      </binding>
+    </element>
+  </differential>
+</StructureDefinition>

src/Hl7.Fhir.Specification/Specification/Navigation/StructureDefinitionWalker.cs

@@ -99,7 +99,7 @@ private IEnumerable<ElementDefinitionNavigator> childDefinitions(string childNam
 
             // Take First(), since we have determined above that there's just one distinct result to expect.
             // (this will be the case when Type=R
-            var expanded = Expand().Single();           
+            var expanded = Expand().Single();
             var nav = expanded.Current.ShallowCopy();
 
             if (!nav.MoveToFirstChild()) yield break;
@@ -233,20 +233,35 @@ public IEnumerable<StructureDefinitionWalker> Resolve()
         public StructureDefinitionWalker Extension(string url)
         {
             // find the extension children of the current node
-            var extensionChildren = childDefinitions("extension");
+            var extensionChildren = childDefinitions("extension").ToList();
             var selection = extensionChildren.Where(c => isExtensionFor(c, url)).ToList();
 
-            // No children in the current profile -> we can still continue in the definition
-            // of the extension itself.
-            if (selection.Count == 0)
-                return FromCanonical(url);
-            else if (selection.Count == 1)
-                return new StructureDefinitionWalker(selection.Single(), _resolver);
-            else
-                throw new StructureDefinitionWalkerException($"extension('{url}') found multiple extension slices constraining the same extension, with is not allowed for the discriminator at '{Current.CanonicalPath()}'.");
+            return selection switch
+            {
+                // No children in the current profile -> we can still continue in the definition
+                // of the extension itself.
+                { Count: 0 } when isAbsoluteUri(url) => FromCanonical(url),
+
+                // No matching child extensions at all -> invalid discriminator.
+                { Count: 0 } => throw new StructureDefinitionWalkerException($"extension('{url}') found no extension slices constraining the same extension, with is not allowed for the discriminator at '{Current.CanonicalPath()}'."),
+
+                { Count: 1 } => new StructureDefinitionWalker(selection.Single(), _resolver),
+
+                // Too many matching child extensions, no discriminating power -> illegal
+                _ => throw new StructureDefinitionWalkerException($"extension('{url}') found multiple extension slices constraining the same extension, with is not allowed for the discriminator at '{Current.CanonicalPath()}'.")
+            };
+
+
+            static bool isExtensionFor(ElementDefinitionNavigator nav, string u)
+            {
+                //  nav.Current.Type.Any(tr => tr.Code == FHIRAllTypes.Extension.GetLiteral() && tr.Profile == u);
+                var childNav = nav.ShallowCopy();
+                if (!childNav.MoveToChild("url")) return false;
+                return childNav.Current.Fixed is FhirUri fu && fu.Value == u;
+            }
 
-            bool isExtensionFor(ElementDefinitionNavigator nav, string u) =>
-                nav.Current.Type.Any(tr => tr.Code == FHIRAllTypes.Extension.GetLiteral() && tr.Profile == u);
+            static bool isAbsoluteUri(string uri) =>
+                 new Uri(uri, UriKind.RelativeOrAbsolute).IsAbsoluteUri;
         }
     };