fix: don't pass a non-positive pinch scale to math.log

lib/src/gestures/map_interactive_viewer.dart

@@ -647,10 +647,13 @@ class MapInteractiveViewerState extends State<MapInteractiveViewer>
     var newZoom = _camera.zoom;
 
     // Handle pinch zoom.
-    if (hasPinchZoom && details.scale > 0.0) {
+    // After a gesture-race win, _scaleCorrector is 1 - lastScale, so this
+    // sum can be <= 0 even when details.scale itself is positive.
+    final scale = details.scale + _scaleCorrector;
+    if (hasPinchZoom && scale > 0.0) {
       newZoom = _getZoomForScale(
         _mapZoomStart,
-        details.scale + _scaleCorrector,
+        scale,
       );
 
       // Handle starting of pinch zoom.
@@ -1401,10 +1404,19 @@ class MapInteractiveViewerState extends State<MapInteractiveViewer>
 
   // Utilities
 
+  /// Converts a pinch [scale] into a zoom level starting from [startZoom].
+  ///
+  /// Returns [startZoom] when [scale] is not a positive finite number.
+  /// `math.log` is undefined for those inputs and would produce `NaN` or
+  /// `-Infinity`, which then poison the camera.
+  @visibleForTesting
+  static double zoomForScale(double startZoom, double scale) {
+    if (scale <= 0.0 || !scale.isFinite) return startZoom;
+    return scale == 1.0 ? startZoom : startZoom + math.log(scale) / math.ln2;
+  }
+
   double _getZoomForScale(double startZoom, double scale) {
-    final resultZoom =
-        scale == 1.0 ? startZoom : startZoom + math.log(scale) / math.ln2;
-    return _camera.clampZoom(resultZoom);
+    return _camera.clampZoom(zoomForScale(startZoom, scale));
   }
 
   Offset _rotateOffset(Offset offset) {

test/gestures/map_interactive_viewer_test.dart

@@ -46,4 +46,42 @@ void main() {
       },
     );
   });
+
+  group('MapInteractiveViewerState.zoomForScale', () {
+    test('adds log2(scale) to the start zoom', () {
+      expect(MapInteractiveViewerState.zoomForScale(13, 2), 14);
+      expect(MapInteractiveViewerState.zoomForScale(13, 1), 13);
+      expect(MapInteractiveViewerState.zoomForScale(13, 0.5), 12);
+    });
+
+    test(
+      'returns the start zoom when the corrected pinch scale is not '
+      'positive (regression: details.scale + _scaleCorrector can be '
+      '<= 0 after a gesture-race win, and math.log of that is NaN - '
+      'https://github.com/fleaflet/flutter_map/issues/2237)',
+      () {
+        // _scaleCorrector = 1.0 - _lastScale, with _lastScale == 2.5
+        const scaleCorrector = 1.0 - 2.5;
+        const detailsScale = 1;
+        final scale = detailsScale + scaleCorrector;
+
+        expect(scale, lessThanOrEqualTo(0));
+
+        final zoom = MapInteractiveViewerState.zoomForScale(13, scale);
+
+        expect(zoom, 13);
+        expect(zoom.isFinite, isTrue);
+        expect(zoom.isNaN, isFalse);
+      },
+    );
+
+    test('returns the start zoom for zero, NaN, and infinite scale', () {
+      expect(MapInteractiveViewerState.zoomForScale(13, 0), 13);
+      expect(MapInteractiveViewerState.zoomForScale(13, double.nan), 13);
+      expect(
+        MapInteractiveViewerState.zoomForScale(13, double.negativeInfinity),
+        13,
+      );
+    });
+  });
 }