Remove choice type specifier type if empty.

Src/java/cql-to-elm/src/main/java/org/cqframework/cql/cql2elm/CqlCompiler.java

@@ -17,6 +17,7 @@
 import org.antlr.v4.runtime.*;
 import org.antlr.v4.runtime.tree.ParseTree;
 import org.cqframework.cql.cql2elm.elm.ElmEdit;
+import org.cqframework.cql.cql2elm.elm.ElmEditEnum;
 import org.cqframework.cql.cql2elm.elm.ElmEditor;
 import org.cqframework.cql.cql2elm.model.CompiledLibrary;
 import org.cqframework.cql.cql2elm.preprocessor.CqlPreprocessor;
@@ -232,9 +233,10 @@ public Library run(CharStream is) {
         // Phase 5: ELM optimization/reduction (this is where result types, annotations, etc. are removed
         // and there will probably be a lot of other optimizations that happen here in the future)
         var edits = allNonNull(
-                !options.contains(EnableAnnotations) ? ElmEdit.REMOVE_ANNOTATION : null,
-                !options.contains(EnableResultTypes) ? ElmEdit.REMOVE_RESULT_TYPE : null,
-                !options.contains(EnableLocators) ? ElmEdit.REMOVE_LOCATOR : null);
+                !options.contains(EnableAnnotations) ? ElmEditEnum.REMOVE_ANNOTATION : null,
+                !options.contains(EnableResultTypes) ? ElmEditEnum.REMOVE_RESULT_TYPE : null,
+                !options.contains(EnableLocators) ? ElmEditEnum.REMOVE_LOCATOR : null,
+                ElmEditEnum.REMOVE_CHOICE_TYPE_SPECIFIER_TYPE_IF_EMPTY);
 
         new ElmEditor(edits).edit(library);
 

Src/java/cql-to-elm/src/main/java/org/cqframework/cql/cql2elm/elm/ElmEdit.java

@@ -1,44 +1,7 @@
 package org.cqframework.cql.cql2elm.elm;
 
-import org.hl7.cql_annotations.r1.Annotation;
 import org.hl7.elm.r1.Element;
 
-public enum ElmEdit {
-    REMOVE_LOCATOR {
-        @Override
-        public void edit(Element element) {
-            element.setLocator(null);
-        }
-    },
-    REMOVE_ANNOTATION {
-        @Override
-        public void edit(Element element) {
-            element.setLocalId(null);
-            if (element.getAnnotation() != null) {
-                for (int i = 0; i < element.getAnnotation().size(); i++) {
-                    var x = element.getAnnotation().get(i);
-                    if (x instanceof Annotation) {
-                        var a = (Annotation) x;
-                        // TODO: Remove narrative but _not_ tags
-                        // Tags are necessary for `allowFluent` compiler resolution
-                        // to work correctly
-                        a.setS(null);
-                        if (a.getT().isEmpty()) {
-                            element.getAnnotation().remove(i);
-                            i--;
-                        }
-                    }
-                }
-            }
-        }
-    },
-    REMOVE_RESULT_TYPE {
-        @Override
-        public void edit(Element element) {
-            element.setResultTypeName(null);
-            element.setResultTypeSpecifier(null);
-        }
-    };
-
-    public abstract void edit(Element element);
+public interface ElmEdit {
+    void edit(Element element);
 }

Src/java/cql-to-elm/src/main/java/org/cqframework/cql/cql2elm/elm/ElmEditEnum.java

@@ -0,0 +1,58 @@
+package org.cqframework.cql.cql2elm.elm;
+
+import org.hl7.cql_annotations.r1.Annotation;
+import org.hl7.elm.r1.ChoiceTypeSpecifier;
+import org.hl7.elm.r1.Element;
+
+public enum ElmEditEnum implements ElmEdit {
+    REMOVE_LOCATOR {
+        public void edit(Element element) {
+            element.setLocator(null);
+        }
+    },
+    REMOVE_ANNOTATION {
+        public void edit(Element element) {
+            element.setLocalId(null);
+            if (element.getAnnotation() != null) {
+                for (int i = 0; i < element.getAnnotation().size(); i++) {
+                    var x = element.getAnnotation().get(i);
+                    if (x instanceof Annotation) {
+                        var a = (Annotation) x;
+                        // TODO: Remove narrative but _not_ tags
+                        // Tags are necessary for `allowFluent` compiler resolution
+                        // to work correctly
+                        a.setS(null);
+                        if (a.getT().isEmpty()) {
+                            element.getAnnotation().remove(i);
+                            i--;
+                        }
+                    }
+                }
+            }
+        }
+    },
+    REMOVE_RESULT_TYPE {
+        public void edit(Element element) {
+            element.setResultTypeName(null);
+            element.setResultTypeSpecifier(null);
+        }
+    },
+    REMOVE_CHOICE_TYPE_SPECIFIER_TYPE_IF_EMPTY {
+        // The ChoiceTypeSpecifier ELM node has a deprecated `type` element which, if not null, clashes with the
+        // `"type" : "ChoiceTypeSpecifier"` field in the JSON serialization of the node. This does not happen in the XML
+        // serialization which nests <type> tags inside <ChoiceTypeSpecifier>.
+        // Because the `type` element is deprecated, it is not normally populated by the compiler anymore and
+        // stays null in the ChoiceTypeSpecifier instance. It is however set to an empty list if you just call
+        // ChoiceTypeSpecifier.getType() (which we do during the ELM optimization stage in the compiler), so
+        // this edit is needed to "protect" the downstream JSON serialization if it can be done without data loss.
+
+        public void edit(Element element) {
+            if (element instanceof ChoiceTypeSpecifier) {
+                var choice = (ChoiceTypeSpecifier) element;
+                if (choice.getType().isEmpty()) {
+                    choice.setType(null);
+                }
+            }
+        }
+    };
+}

Src/java/cql-to-elm/src/main/java/org/cqframework/cql/cql2elm/elm/ElmEditor.java

@@ -11,26 +11,24 @@
 public class ElmEditor {
 
     private final List<ElmEdit> edits;
-    private final FunctionalElmVisitor<Void, List<ElmEdit>> visitor;
+    private final FunctionalElmVisitor<Trackable, Void> visitor;
 
     public ElmEditor(List<ElmEdit> edits) {
         this.edits = Objects.requireNonNull(edits);
-        this.visitor = Visitors.from(ElmEditor::applyEdits);
+        this.visitor = Visitors.from((elm, context) -> elm, this::applyEdits);
     }
 
     public void edit(Library library) {
-        this.visitor.visitLibrary(library, edits);
+        this.visitor.visitLibrary(library, null);
     }
 
-    protected static Void applyEdits(Trackable trackable, List<ElmEdit> edits) {
-        if (!(trackable instanceof Element)) {
-            return null;
+    protected Trackable applyEdits(Trackable aggregate, Trackable nextResult) {
+        if (nextResult instanceof Element) {
+            for (ElmEdit edit : edits) {
+                edit.edit((Element) nextResult);
+            }
         }
 
-        for (ElmEdit edit : edits) {
-            edit.edit((Element) trackable);
-        }
-
-        return null;
+        return aggregate;
     }
 }

Src/java/cql-to-elm/src/test/java/org/cqframework/cql/cql2elm/elm/ElmEditTest.java

@@ -0,0 +1,32 @@
+package org.cqframework.cql.cql2elm.elm;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.List;
+import org.hl7.elm.r1.ChoiceTypeSpecifier;
+import org.hl7.elm.r1.NamedTypeSpecifier;
+import org.hl7.elm.r1.TypeSpecifier;
+import org.junit.jupiter.api.Test;
+
+class ElmEditTest {
+
+    @Test
+    void removeChoiceTypeSpecifierTypeIfEmpty() {
+        var extChoiceTypeSpecifier = new ExtChoiceTypeSpecifier();
+
+        extChoiceTypeSpecifier.setType(List.of());
+        ElmEditEnum.REMOVE_CHOICE_TYPE_SPECIFIER_TYPE_IF_EMPTY.edit(extChoiceTypeSpecifier);
+        assertNull(extChoiceTypeSpecifier.getType());
+
+        var typeSpecifiers = List.of((TypeSpecifier) new NamedTypeSpecifier());
+        extChoiceTypeSpecifier.setType(typeSpecifiers);
+        ElmEditEnum.REMOVE_CHOICE_TYPE_SPECIFIER_TYPE_IF_EMPTY.edit(extChoiceTypeSpecifier);
+        assertSame(typeSpecifiers, extChoiceTypeSpecifier.getType());
+    }
+
+    private static class ExtChoiceTypeSpecifier extends ChoiceTypeSpecifier {
+        public List<TypeSpecifier> getType() {
+            return type;
+        }
+    }
+}

Src/java/cql-to-elm/src/test/java/org/cqframework/cql/cql2elm/elm/ElmEditorTest.java

@@ -0,0 +1,32 @@
+package org.cqframework.cql.cql2elm.elm;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.List;
+import org.hl7.elm.r1.ChoiceTypeSpecifier;
+import org.hl7.elm.r1.Element;
+import org.junit.jupiter.api.Test;
+
+class ElmEditorTest {
+    boolean editCalled = false;
+
+    @Test
+    void applyEdits() {
+        editCalled = false;
+        var editCounter = new ElmEdit() {
+            public void edit(Element element) {
+                editCalled = true;
+            }
+        };
+        var edits = List.of((ElmEdit) editCounter);
+        ElmEditor editor = new ElmEditor(edits);
+
+        editCalled = false;
+        editor.applyEdits(null, null);
+        assertFalse(editCalled);
+
+        editCalled = false;
+        editor.applyEdits(null, new ChoiceTypeSpecifier());
+        assertTrue(editCalled);
+    }
+}