fix: Proper data validation in findNearestContainer (#754)

This prevents a thrown when the statement map needs to be processed for
container hits, because the statement map entries do not contain a "loc"
field, they just have this inforation at the top level.

Fix: #753

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

@@ -45,13 +45,21 @@ function assertValidObject(obj) {
 const keyFromLoc = ({ start, end }) =>
     `${start.line}|${start.column}|${end.line}|${end.column}`;
 
+const isObj = o => !!o && typeof o === 'object';
+const isLineCol = o =>
+    isObj(o) && typeof o.line === 'number' && typeof o.column === 'number';
+const isLoc = o => isObj(o) && isLineCol(o.start) && isLineCol(o.end);
+const getLoc = o => (isLoc(o) ? o : isLoc(o.loc) ? o.loc : null);
+
 // When merging, we can have a case where two ranges cover
 // the same block of code with `hits=1`, and each carve out a
 // different range with `hits=0` to indicate it's uncovered.
 // Find the nearest container so that we can properly indicate
 // that both sections are hit.
 // Returns null if no containing item is found.
 const findNearestContainer = (item, map) => {
+    const itemLoc = getLoc(item);
+    if (!itemLoc) 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
@@ -62,8 +70,8 @@ const findNearestContainer = (item, map) => {
     let containerDistance = null;
     let containerKey = null;
     for (const [i, mapItem] of Object.entries(map)) {
-        const mapLoc = mapItem.loc;
-        const itemLoc = item.loc;
+        const mapLoc = getLoc(mapItem);
+        if (!mapLoc) continue;
         // contained if all of line distances are > 0
         // or line distance is 0 and col dist is >= 0
         const distance = [

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

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