Generate no lookup conf for an unnamed variable

dashboard/src/pages/StudyConfPage/forms/destinations/Destination.test.tsx

@@ -88,6 +88,54 @@ describe('a destination saved before ref_mode existed', () => {
   });
 });
 
+describe('a destination saved with an explicit mode', () => {
+  const stored: any = {
+    type: 'messenger',
+    name: 'fly messenger',
+    initial_shortcode: 'mnchweek',
+    welcome_message: 'Welcome!',
+    button_text: 'OK',
+    additional_metadata: null,
+    ref_mode: 'encoded',
+  };
+
+  it('preserves that mode through an unrelated edit', () => {
+    // The counterpart of the absent case: a conf that states a mode keeps it,
+    // because the forms spread `...data` rather than rebuilding the conf.
+    const update = jest.fn();
+
+    render(
+      <Destination
+        data={{ ...stored }}
+        index={0}
+        update={update}
+        savedDestinations={[{ ...stored }]}
+      />
+    );
+
+    fireEvent.change(screen.getByDisplayValue('Welcome!'), {
+      target: { name: 'welcome_message', value: 'Hello!' },
+    });
+
+    const [conf] = update.mock.calls[update.mock.calls.length - 1];
+    expect(conf.welcome_message).toBe('Hello!');
+    expect(conf.ref_mode).toBe('encoded');
+  });
+
+  it('does not warn while the mode still matches what was loaded', () => {
+    render(
+      <Destination
+        data={{ ...stored }}
+        index={0}
+        update={jest.fn()}
+        savedDestinations={[{ ...stored }]}
+      />
+    );
+
+    expect(screen.queryByText(/rewrites every ad/i)).toBeNull();
+  });
+});
+
 describe('a destination being added now', () => {
   it('states its mode, because it is a new conf', () => {
     const update = jest.fn();

dashboard/src/pages/StudyConfPage/forms/inferenceData/extraction.test.ts

@@ -300,6 +300,25 @@ describe('extraction', () => {
     it('gives a fly source with no variables one blank row', () => {
       expect(generateLookupConfs('fly', [])).toHaveLength(1);
     });
+
+    it('skips a variable the researcher has not named yet', () => {
+      // `name` is both the output name and the key into the ad's frozen row, so
+      // a lookup without one reads nothing off the row while presenting itself
+      // as configured.
+      const confs = generateLookupConfs('fly', ['gender', '', 'Age']);
+
+      expect(confs.map(c => c.name)).toEqual(['gender', 'Age']);
+    });
+
+    it('falls back to a blank row when no variable is named', () => {
+      // One unnamed variable is length 1, so a length check lets it through.
+      const confs = generateLookupConfs('fly', ['']);
+
+      expect(confs).toHaveLength(1);
+      expect(confs[0].name).toBe('');
+      expect(confs[0].mapping).toBe('raw');
+      expect(confs[0].location).toBe('');
+    });
   });
 
   describe('round trip into what swoosh reads', () => {

dashboard/src/pages/StudyConfPage/forms/inferenceData/generateLookupConfs.ts

@@ -57,9 +57,18 @@ export const generateLookupConfs = (
   source: string,
   variables: string[]
 ): Extraction[] => {
-  if (source !== FLY_SOURCE || variables.length === 0) {
+  if (source !== FLY_SOURCE) {
     return [blankConf()];
   }
 
-  return variables.map(lookupConf);
+  // An unnamed variable produces no conf. `name` is both the output name and
+  // the key into the ad's frozen row, so a lookup without one reads nothing off
+  // the row while presenting itself as configured — the researcher sees a
+  // filled-in row that can only ever yield nothing.
+  //
+  // Filtered rather than counted: one unnamed variable is length 1, so a
+  // `variables.length === 0` guard lets it straight through.
+  const named = variables.filter(name => !!name);
+
+  return named.length ? named.map(lookupConf) : [blankConf()];
 };