Alerting: Fix state reason (#101530)

---------

Signed-off-by: Yuri Tseretyan <yuriy.tseretyan@grafana.com>

pkg/services/ngalert/state/state.go

@@ -832,9 +832,9 @@ func (a *State) transition(alertRule *models.AlertRule, result eval.Result, extr
 }
 
 func resultStateReason(result eval.Result, rule *models.AlertRule) string {
-	if rule.ExecErrState == models.KeepLastErrState || rule.NoDataState == models.KeepLast {
+	if result.State == eval.Error && rule.ExecErrState == models.KeepLastErrState ||
+		result.State == eval.NoData && rule.NoDataState == models.KeepLast {
 		return models.ConcatReasons(result.State.String(), models.StateReasonKeepLast)
 	}
-
 	return result.State.String()
 }

pkg/services/ngalert/state/state_test.go

@@ -1132,3 +1132,61 @@ func TestPatch(t *testing.T) {
 		assert.EqualValues(t, orig.Annotations, state.Annotations)
 	})
 }
+
+func TestResultStateReason(t *testing.T) {
+	gen := ngmodels.RuleGen
+	tests := []struct {
+		name     string
+		result   eval.Result
+		rule     *ngmodels.AlertRule
+		expected string
+	}{
+		{
+			name: "Error state with KeepLast",
+			result: eval.Result{
+				State: eval.Error,
+			},
+			rule:     gen.With(ngmodels.RuleMuts.WithErrorExecAs(ngmodels.KeepLastErrState)).GenerateRef(),
+			expected: "Error, KeepLast",
+		},
+		{
+			name: "Error state without KeepLast",
+			result: eval.Result{
+				State: eval.Error,
+			},
+			rule:     gen.With(ngmodels.RuleMuts.WithErrorExecAs(ngmodels.ErrorErrState)).GenerateRef(),
+			expected: "Error",
+		},
+		{
+			name: "NoData state with KeepLast state",
+			result: eval.Result{
+				State: eval.NoData,
+			},
+			rule:     gen.With(ngmodels.RuleMuts.WithNoDataExecAs(ngmodels.KeepLast)).GenerateRef(),
+			expected: "NoData, KeepLast",
+		},
+		{
+			name: "NoData state without KeepLast",
+			result: eval.Result{
+				State: eval.NoData,
+			},
+			rule:     gen.With(ngmodels.RuleMuts.WithNoDataExecAs(ngmodels.NoData)).GenerateRef(),
+			expected: "NoData",
+		},
+		{
+			name: "Normal state",
+			result: eval.Result{
+				State: eval.NoData,
+			},
+			rule:     gen.With(ngmodels.RuleMuts.WithErrorExecAs(ngmodels.ErrorErrState), ngmodels.RuleMuts.WithNoDataExecAs(ngmodels.NoData)).GenerateRef(),
+			expected: "NoData",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			result := resultStateReason(tc.result, tc.rule)
+			assert.Equal(t, tc.expected, result)
+		})
+	}
+}