fix legend line point style not showing the dataset dash

src/plugins/plugin.legend.js

@@ -679,19 +679,25 @@ export default {
         return chart._getSortedDatasetMetas().map((meta) => {
           const style = meta.controller.getStyle(usePointStyle ? 0 : undefined);
           const borderWidth = toPadding(style.borderWidth);
+          const itemPointStyle = pointStyle || style.pointStyle;
+          // a line symbol stands for the dataset line but the point scope has no dash
+          // on it so read that off the dataset element instead, markers stay solid
+          const dashStyle = usePointStyle && itemPointStyle === 'line'
+            ? meta.controller.getStyle(undefined)
+            : style;
 
           return {
             text: datasets[meta.index].label,
             fillStyle: style.backgroundColor,
             fontColor: color,
             hidden: !meta.visible,
             lineCap: style.borderCapStyle,
-            lineDash: style.borderDash,
-            lineDashOffset: style.borderDashOffset,
+            lineDash: dashStyle.borderDash,
+            lineDashOffset: dashStyle.borderDashOffset,
             lineJoin: style.borderJoinStyle,
             lineWidth: (borderWidth.width + borderWidth.height) / 4,
             strokeStyle: style.borderColor,
-            pointStyle: pointStyle || style.pointStyle,
+            pointStyle: itemPointStyle,
             rotation: style.rotation,
             textAlign: textAlign || style.textAlign,
             borderRadius: useBorderRadius && (borderRadius || style.borderRadius),

test/specs/plugin.legend.tests.js

@@ -189,6 +189,67 @@ describe('Legend block tests', function() {
     }]);
   });
 
+  it('should take the dataset dash for a line point style', function() {
+    var chart = window.acquireChart({
+      type: 'line',
+      data: {
+        labels: [],
+        datasets: [{
+          label: 'solid',
+          data: []
+        }, {
+          label: 'dashed',
+          borderDash: [6, 3],
+          borderDashOffset: 4,
+          data: []
+        }]
+      },
+      options: {
+        plugins: {
+          legend: {
+            labels: {
+              usePointStyle: true,
+              pointStyle: 'line'
+            }
+          }
+        }
+      }
+    });
+
+    expect(chart.legend.legendItems.map(function(item) {
+      return item.lineDash;
+    })).toEqual([[], [6, 3]]);
+    expect(chart.legend.legendItems.map(function(item) {
+      return item.lineDashOffset;
+    })).toEqual([0, 4]);
+  });
+
+  it('should leave other point styles solid', function() {
+    var chart = window.acquireChart({
+      type: 'line',
+      data: {
+        labels: [],
+        datasets: [{
+          label: 'dashed',
+          borderDash: [6, 3],
+          data: []
+        }]
+      },
+      options: {
+        plugins: {
+          legend: {
+            labels: {
+              usePointStyle: true,
+              pointStyle: 'circle'
+            }
+          }
+        }
+      }
+    });
+
+    expect(chart.legend.legendItems[0].lineDash).toBeUndefined();
+  });
+
   it('should reverse correctly', function() {
     var chart = window.acquireChart({
       type: 'line',