[v9.3.x] StateTimeline: Fix negative infinity legend/tooltip from thresholds (#60280)

StateTimeline: Fix negative infinity legend/tooltip from thresholds (#60279)

(cherry picked from commit e0eacf1b04)

Co-authored-by: Leon Sorokin <leeoniya@gmail.com>

public/app/plugins/panel/state-timeline/utils.test.ts

@@ -174,7 +174,7 @@ describe('getThresholdItems', () => {
 });
 
 describe('prepareTimelineLegendItems', () => {
-  it('should return legend items', () => {
+  it('should return legend items without crashing when single (base) threshold', () => {
     const frame: any = [
       {
         refId: 'A',

public/app/plugins/panel/state-timeline/utils.ts

@@ -479,10 +479,21 @@ export function getThresholdItems(fieldConfig: FieldConfig, theme: GrafanaTheme2
 
   const fmt = (v: number) => formattedValueToString(disp(v));
 
-  for (let i = 1; i <= steps.length; i++) {
-    const step = steps[i - 1];
+  for (let i = 0; i < steps.length; i++) {
+    let step = steps[i];
+    let value = step.value;
+    let pre = '';
+    let suf = '';
+
+    if (value === -Infinity && i < steps.length - 1) {
+      value = steps[i + 1].value;
+      pre = '< ';
+    } else {
+      suf = '+';
+    }
+
     items.push({
-      label: i === 1 ? `< ${fmt(step.value)}` : `${fmt(step.value)}+`,
+      label: `${pre}${fmt(value)}${suf}`,
       color: theme.visualization.getColorByName(step.color),
       yAxis: 1,
     });
@@ -511,10 +522,9 @@ export function getFieldLegendItem(fields: Field[], theme: GrafanaTheme2): VizLe
   const items: VizLegendItem[] = [];
   const fieldConfig = fields[0].config;
   const colorMode = fieldConfig.color?.mode ?? FieldColorModeId.Fixed;
-  const thresholds = fieldConfig.thresholds;
 
   // If thresholds are enabled show each step in the legend
-  if (colorMode === FieldColorModeId.Thresholds && thresholds?.steps && thresholds.steps.length > 1) {
+  if (colorMode === FieldColorModeId.Thresholds) {
     return getThresholdItems(fieldConfig, theme);
   }