Set the preview selection to null when there is no selection (#5568)

We are currently using a "no preview selection" object of the shape `{
hasSelection: false, isModifying: false }` when there is no preview
selection. We can instead just use null, it's more idiomatic.

I recommend reviewing commits individually.

Author: mstange

src/actions/profile-view.ts

@@ -1749,13 +1749,17 @@ export function changeShowJsTracerSummary(
 }
 
 export function updatePreviewSelection(
-  previewSelection: PreviewSelection
+  previewSelection: PreviewSelection | null
 ): ThunkAction<void> {
   return (dispatch, getState) => {
+    // Only dispatch if the selection changes. This function can fire in a tight loop,
+    // and this check saves a dispatch.
     const currentPreviewSelection = getPreviewSelection(getState());
-    if (!objectShallowEquals(currentPreviewSelection, previewSelection)) {
-      // Only dispatch if the selection changes. This function can fire in a tight loop,
-      // and this check saves a dispatch.
+    if (
+      !currentPreviewSelection ||
+      !previewSelection ||
+      !objectShallowEquals(currentPreviewSelection, previewSelection)
+    ) {
       dispatch({
         type: 'UPDATE_PREVIEW_SELECTION',
         previewSelection,

src/components/app/BottomBox.tsx

@@ -28,7 +28,7 @@ import {
   getSourceViewCode,
   getAssemblyViewCode,
 } from 'firefox-profiler/selectors/code';
-import { getPreviewSelection } from 'firefox-profiler/selectors/profile';
+import { getPreviewSelectionIsBeingModified } from 'firefox-profiler/selectors/profile';
 import explicitConnect from 'firefox-profiler/utils/connect';
 
 import type { ConnectedProps } from 'firefox-profiler/utils/connect';
@@ -295,7 +295,7 @@ export const BottomBox = explicitConnect<{}, StateProps, DispatchProps>({
       selectedNodeSelectors.getAssemblyViewAddressTimings(state),
     assemblyViewScrollGeneration: getAssemblyViewScrollGeneration(state),
     assemblyViewIsOpen: getAssemblyViewIsOpen(state),
-    disableOverscan: getPreviewSelection(state).isModifying,
+    disableOverscan: getPreviewSelectionIsBeingModified(state),
   }),
   mapDispatchToProps: {
     closeBottomBox,

src/components/app/ProfileFilterNavigator.tsx

@@ -187,7 +187,7 @@ export const ProfileFilterNavigator = explicitConnect<
     const items = getCommittedRangeLabels(state);
     const previewSelection = getPreviewSelection(state);
     const profileTimelineUnit = getProfileTimelineUnit(state);
-    const uncommittedItem = previewSelection.hasSelection
+    const uncommittedItem = previewSelection
       ? getFormattedTimelineValue(
           previewSelection.selectionEnd - previewSelection.selectionStart,
           profileTimelineUnit

src/components/calltree/CallTree.tsx

@@ -16,7 +16,7 @@ import {
 import {
   getScrollToSelectionGeneration,
   getFocusCallTreeGeneration,
-  getPreviewSelection,
+  getPreviewSelectionIsBeingModified,
   getCategories,
   getCurrentTableViewOptions,
 } from 'firefox-profiler/selectors/profile';
@@ -410,7 +410,7 @@ export const CallTree = explicitConnect<{}, StateProps, DispatchProps>({
     expandedCallNodeIndexes:
       selectedThreadSelectors.getExpandedCallNodeIndexes(state),
     searchStringsRegExp: getSearchStringsAsRegExp(state),
-    disableOverscan: getPreviewSelection(state).isModifying,
+    disableOverscan: getPreviewSelectionIsBeingModified(state),
     invertCallstack: getInvertCallstack(state),
     implementationFilter: getImplementationFilter(state),
     // Use the filtered call node max depth, rather than the preview filtered call node

src/components/flame-graph/FlameGraph.tsx

@@ -74,7 +74,7 @@ type StateProps = {
   readonly ctssSampleIndexOffset: number;
   readonly maxStackDepthPlusOne: number;
   readonly timeRange: StartEndRange;
-  readonly previewSelection: PreviewSelection;
+  readonly previewSelection: PreviewSelection | null;
   readonly flameGraphTiming: FlameGraphTiming;
   readonly callTree: CallTree;
   readonly callNodeInfo: CallNodeInfo;

src/components/js-tracer/Canvas.tsx

@@ -608,7 +608,6 @@ class JsTracerCanvasImpl extends React.PureComponent<Props, State> {
     // const { markers, updatePreviewSelection } = this.props;
     // const marker = markers[eventIndex];
     // updatePreviewSelection({
-    //   hasSelection: true,
     //   isModifying: false,
     //   selectionStart: marker.start,
     //   selectionEnd: marker.start + marker.dur,

src/components/js-tracer/Chart.tsx

@@ -53,7 +53,7 @@ type StateProps = {
   readonly stringTable: StringTable;
   readonly timeRange: StartEndRange;
   readonly threadsKey: ThreadsKey;
-  readonly previewSelection: PreviewSelection;
+  readonly previewSelection: PreviewSelection | null;
 };
 
 type Props = ConnectedProps<OwnProps, StateProps, DispatchProps>;

src/components/marker-chart/Canvas.tsx

@@ -775,7 +775,6 @@ class MarkerChartCanvasImpl extends React.PureComponent<Props> {
     );
 
     updatePreviewSelection({
-      hasSelection: true,
       isModifying: false,
       selectionStart: start,
       selectionEnd: end,

src/components/marker-chart/index.tsx

@@ -56,7 +56,7 @@ type StateProps = {
   readonly markerListLength: number;
   readonly timeRange: StartEndRange;
   readonly threadsKey: ThreadsKey;
-  readonly previewSelection: PreviewSelection;
+  readonly previewSelection: PreviewSelection | null;
   readonly rightClickedMarkerIndex: MarkerIndex | null;
   readonly selectedMarkerIndex: MarkerIndex | null;
 };

src/components/network-chart/index.tsx

@@ -19,7 +19,7 @@ import {
 
 import {
   getScrollToSelectionGeneration,
-  getPreviewSelection,
+  getPreviewSelectionIsBeingModified,
   getPreviewSelectionRange,
 } from '../../selectors/profile';
 import { selectedThreadSelectors } from '../../selectors/per-thread';
@@ -422,7 +422,7 @@ export const NetworkChart = explicitConnect<
     hoveredMarkerIndexFromState:
       selectedThreadSelectors.getHoveredMarkerIndex(state),
     timeRange: getPreviewSelectionRange(state),
-    disableOverscan: getPreviewSelection(state).isModifying,
+    disableOverscan: getPreviewSelectionIsBeingModified(state),
     threadsKey: getSelectedThreadsKey(state),
   }),
   mapDispatchToProps: {