fix: do not throw on missing range locations

Fix: #753

packages/istanbul-lib-coverage/lib/file-coverage.js

@@ -52,6 +52,7 @@ const keyFromLoc = ({ start, end }) =>
 // that both sections are hit.
 // Returns null if no containing item is found.
 const findNearestContainer = (item, map) => {
+    if (!item.loc) return null;
     // the B item is not an identified range in the A set, BUT
     // it may be contained by an identified A range. If so, then
     // any hit of that containing A range counts as a hit of this
@@ -63,6 +64,7 @@ const findNearestContainer = (item, map) => {
     let containerKey = null;
     for (const [i, mapItem] of Object.entries(map)) {
         const mapLoc = mapItem.loc;
+        if (!mapLoc) continue;
         const itemLoc = item.loc;
         // contained if all of line distances are > 0
         // or line distance is 0 and col dist is >= 0

packages/istanbul-lib-coverage/test/file.test.js

@@ -1123,3 +1123,22 @@ describe('addNearestContainerHits unit coverage', () => {
         );
     });
 });
+
+describe('findNearestContainer missing loc defense', () => {
+    it('does not throw if loc is missing', () => {
+        const loc = (sl, sc, el, ec) => ({
+            loc: {
+                start: { line: sl, column: sc },
+                end: { line: el, column: ec }
+            }
+        });
+        const map = {
+            0: loc(1, 1, 100, 100),
+            1: {},
+            2: loc(10, 10, 50, 50),
+            3: loc(20, 20, 40, 40)
+        };
+        assert.equal(findNearestContainer({ no: 'loc' }, map), null);
+        assert.equal(findNearestContainer(loc(30, 30, 35, 35), '3'));
+    });
+});