Bug 1547115 - Memoize breakableLines to avoid resetting in editor often. r=jlast

Differential Revision: https://phabricator.services.mozilla.com/D29245

--HG--
extra : moz-landing-system : lando

devtools/client/debugger/src/components/Editor/EmptyLines.js

@@ -6,7 +6,7 @@
 
 import { connect } from "../../utils/connect";
 import { Component } from "react";
-import { getSelectedSource, getBreakableLines } from "../../selectors";
+import { getSelectedSource, getSelectedBreakableLines } from "../../selectors";
 import type { Source } from "../../types";
 import { fromEditorLine } from "../../utils/editor";
 
@@ -64,9 +64,7 @@ const mapStateToProps = state => {
   if (!selectedSource) {
     throw new Error("no selectedSource");
   }
-  const breakableLines = new Set(
-    getBreakableLines(state, selectedSource.id) || []
-  );
+  const breakableLines = getSelectedBreakableLines(state);
 
   return {
     selectedSource,

devtools/client/debugger/src/reducers/sources.js

@@ -881,4 +881,12 @@ export function getBreakableLines(state: OuterState, sourceId: string) {
   return state.sources.breakableLines[sourceId];
 }
 
+export const getSelectedBreakableLines: Selector<Set<number>> = createSelector(
+  state => {
+    const sourceId = getSelectedSourceId(state);
+    return sourceId && state.sources.breakableLines[sourceId];
+  },
+  breakableLines => new Set(breakableLines || [])
+);
+
 export default update;