[matcher] Add type check in pairwiseCompare

pkgs/matcher/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 0.12.19-wip
 
 * Improve speed of pretty printing for large collections.
+* Improve output of pairwiseCompare with mismatched types.
 
 ## 0.12.18
 

pkgs/matcher/lib/src/iterable_matchers.dart

@@ -297,7 +297,8 @@ class _PairwiseCompare<S, T> extends _IterableMatcher {
     var i = 0;
     for (var e in _expected) {
       iterator.moveNext();
-      if (!_comparator(e, iterator.current as T)) {
+      var current = iterator.current;
+      if (current is! T || !_comparator(e, current)) {
         addStateInfo(matchState, {
           'index': i,
           'expected': e,

pkgs/matcher/test/iterable_matchers_test.dart

@@ -422,6 +422,17 @@ void main() {
     );
   });
 
+  test('pairwiseCompare with mismatched types', () async {
+    final notInts = ['notInt'];
+    shouldFail(
+      notInts,
+      pairwiseCompare([1], (int e, int a) => a <= e, 'less than or equal'),
+      'Expected: pairwise less than or equal [1] '
+      "Actual: ['notInt'] "
+      "Which: has 'notInt' which is not less than or equal <1> at index 0",
+    );
+  });
+
   test('isEmpty', () {
     var d = SimpleIterable(0);
     var e = SimpleIterable(1);