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diff --git a/devtools/client/debugger/src/reducers/pending-breakpoints.js b/devtools/client/debugger/src/reducers/pending-breakpoints.js
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * Pending breakpoints reducer.
+ *
+ * Pending breakpoints are a more lightweight version compared to regular breakpoints objects.
+ * They are meant to be persisted across Firefox restarts and stored into async-storage.
+ * This reducer data is saved into asyncStore from bootstrap.js and restored from main.js.
+ *
+ * The main difference with pending breakpoints is that we only save breakpoints
+ * against source with an URL as only them can be restored. (source IDs are different across reloads).
+ * The second difference is that we don't store the whole source object but only the source URL.
+ */
+
+import { isPrettyURL } from "../utils/source";
+import assert from "../utils/assert";
+
+function update(state = {}, action) {
+  switch (action.type) {
+    case "SET_BREAKPOINT":
+      if (action.status === "start") {
+        return setBreakpoint(state, action.breakpoint);
+      }
+      return state;
+
+    case "REMOVE_BREAKPOINT":
+      if (action.status === "start") {
+        return removeBreakpoint(state, action.breakpoint);
+      }
+      return state;
+
+    case "REMOVE_PENDING_BREAKPOINT":
+      return removePendingBreakpoint(state, action.pendingBreakpoint);
+
+    case "CLEAR_BREAKPOINTS": {
+      return {};
+    }
+  }
+
+  return state;
+}
+
+function shouldBreakpointBePersisted(breakpoint) {
+  // We only save breakpoint for source with URL.
+  // Source without URL can only be identified via their source actor ID
+  // which isn't persisted across reloads.
+  return !breakpoint.options.hidden && breakpoint.location.source.url;
+}
+
+function setBreakpoint(state, breakpoint) {
+  if (!shouldBreakpointBePersisted(breakpoint)) {
+    return state;
+  }
+
+  const id = makeIdFromBreakpoint(breakpoint);
+  const pendingBreakpoint = createPendingBreakpoint(breakpoint);
+
+  return { ...state, [id]: pendingBreakpoint };
+}
+
+function removeBreakpoint(state, breakpoint) {
+  if (!shouldBreakpointBePersisted(breakpoint)) {
+    return state;
+  }
+
+  const id = makeIdFromBreakpoint(breakpoint);
+  state = { ...state };
+
+  delete state[id];
+  return state;
+}
+
+function removePendingBreakpoint(state, pendingBreakpoint) {
+  const id = makeIdFromPendingBreakpoint(pendingBreakpoint);
+  state = { ...state };
+
+  delete state[id];
+  return state;
+}
+
+/**
+ * Return a unique identifier for a given breakpoint,
+ * using its original location, or for pretty-printed sources,
+ * its generated location.
+ *
+ * @param {Object} breakpoint
+ */
+function makeIdFromBreakpoint(breakpoint) {
+  const location = isPrettyURL(breakpoint.location.source.url)
+    ? breakpoint.generatedLocation
+    : breakpoint.location;
+
+  const { source, line, column } = location;
+  const sourceUrlString = source.url || "";
+  const columnString = column || "";
+
+  return `${sourceUrlString}:${line}:${columnString}`;
+}
+
+function makeIdFromPendingBreakpoint(pendingBreakpoint) {
+  const { sourceUrl, line, column } = pendingBreakpoint.location;
+  const sourceUrlString = sourceUrl || "";
+  const columnString = column || "";
+
+  return `${sourceUrlString}:${line}:${columnString}`;
+}
+
+/**
+ * Convert typical debugger frontend location (created via location.js:createLocation)
+ * to a more lightweight flavor of it which will be stored in async storage.
+ */
+function createPendingLocation(location) {
+  assert(location.hasOwnProperty("line"), "location must have a line");
+  assert(location.hasOwnProperty("column"), "location must have a column");
+
+  const { source, line, column } = location;
+  assert(source.url !== undefined, "pending location must have a source url");
+  return { sourceUrl: source.url, line, column };
+}
+
+/**
+ * Create a new pending breakpoint, which is a more lightweight version of the regular breakpoint object.
+ */
+function createPendingBreakpoint(bp) {
+  return {
+    options: bp.options,
+    disabled: bp.disabled,
+    location: createPendingLocation(bp.location),
+    generatedLocation: createPendingLocation(bp.generatedLocation),
+  };
+}
+
+export default update;