XFA - Always bind root subform on root data

- it partially fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1717805 (on the data side at least but there is still a layout issue).

src/core/xfa/bind.js

@@ -55,12 +55,12 @@ class Binder {
     this.root = root;
     this.datasets = root.datasets;
     if (root.datasets && root.datasets.data) {
-      this.emptyMerge = false;
       this.data = root.datasets.data;
     } else {
-      this.emptyMerge = true;
       this.data = new XmlObject(NamespaceIds.datasets.id, "data");
     }
+    this.emptyMerge = this.data[$getChildren]().length === 0;
+
     this.root.form = this.form = root.template[$clone]();
   }
 
@@ -477,6 +477,23 @@ class Binder {
 
       if (this._mergeMode === undefined && child[$nodeName] === "subform") {
         this._mergeMode = child.mergeMode === "consumeData";
+
+        // XFA specs p. 182:
+        // The highest-level subform and the data node representing
+        // the current record are special; they are always
+        // bound even if their names don't match.
+        const dataChildren = dataNode[$getChildren]();
+        if (dataChildren.length > 0) {
+          this._bindOccurrences(child, [dataChildren[0]], null);
+        } else if (this.emptyMerge) {
+          const dataChild = new XmlObject(
+            dataNode[$namespaceId],
+            child.name || "root"
+          );
+          dataNode[$appendChild](dataChild);
+          this._bindElement(child, dataChild);
+        }
+        continue;
       }
 
       let global = false;
@@ -570,21 +587,29 @@ class Binder {
           }
           match = matches.length > 0 ? matches : null;
         } else {
+          // If we've an empty merge, there are no reason
+          // to make multiple bind so skip consumed nodes.
           match = dataNode[$getRealChildrenByNameIt](
             child.name,
             /* allTransparent = */ false,
-            /* skipConsumed = */ false
+            /* skipConsumed = */ this.emptyMerge
           ).next().value;
           if (!match) {
             // We're in matchTemplate mode so create a node in data to reflect
             // what we've in template.
             match = new XmlObject(dataNode[$namespaceId], child.name);
+            if (this.emptyMerge) {
+              match[$consumed] = true;
+            }
             dataNode[$appendChild](match);
 
             // Don't bind the value in newly created node because it's empty.
             this._bindElement(child, match);
             continue;
           }
+          if (this.emptyMerge) {
+            match[$consumed] = true;
+          }
           match = [match];
         }
       }

test/unit/xfa_tohtml_spec.js

@@ -219,4 +219,55 @@ describe("XFAFactory", function () {
       expect(field2).not.toEqual(null);
     });
   });
+
+  it("should have an input or textarea", function () {
+    const xml = `
+<?xml version="1.0"?>
+<xdp:xdp xmlns:xdp="http://ns.adobe.com/xdp/">
+  <template xmlns="http://www.xfa.org/schema/xfa-template/3.3">
+    <subform name="root" mergeMode="matchTemplate">
+      <pageSet>
+        <pageArea>
+          <contentArea x="123pt" w="456pt" h="789pt"/>
+          <medium stock="default" short="456pt" long="789pt"/>
+          <field y="1pt" w="11pt" h="22pt" x="2pt">
+            <ui>
+              <textEdit multiLine="1"/>
+            </ui>
+          </field>
+        </pageArea>
+      </pageSet>
+      <subform name="first">
+        <field y="1pt" w="11pt" h="22pt" x="2pt" name="hello">
+          <ui>
+            <textEdit/>
+          </ui>
+          <value>
+            <integer/>
+          </value>
+        </field>
+      </subform>
+    </subform>
+  </template>
+  <xfa:datasets xmlns:xfa="http://www.xfa.org/schema/xfa-data/1.0/">
+    <xfa:data>
+      <toto>
+        <first>
+          <hello>123
+          </hello>
+        </first>
+      </toto>
+    </xfa:data>
+  </xfa:datasets>
+</xdp:xdp>
+    `;
+    const factory = new XFAFactory({ "xdp:xdp": xml });
+
+    expect(factory.numberPages).toEqual(1);
+
+    const pages = factory.getPages();
+    const field1 = searchHtmlNode(pages, "name", "input");
+    expect(field1).not.toEqual(null);
+    expect(field1.attributes.value).toEqual("123");
+  });
 });