[processor/metricsgeneration] Fix panic when using a sum metric for c…

…alculations (open-telemetry#35428)

**Description:** 
The metrics generation processor would previously hit a panic when the
calculation rule was operating on a `sum` metric, instead of a `gauge`.
The [component
proposal](open-telemetry#2722),
[initial
implementation](open-telemetry#3433),
nor the
[README](https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/processor/metricsgenerationprocessor)
state that it's a requirement for the metric to be a `gauge`, nor do I
think this requirement makes sense.

I've updated the logic to account for sum metrics being used and added a
test.

**Testing:** 
Added a test for this situation, the test panics before the change and
passes after.

.chloggen/metricsgeneration_relax_type_req.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: metricsgenerationprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Allow metric calculations to be done on sum metrics
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35428]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

processor/metricsgenerationprocessor/README.md

@@ -16,12 +16,14 @@
 
 ## Description
 
-The metrics generation processor (`experimental_metricsgenerationprocessor`) can be used to create new metrics using existing metrics following a given rule. Currently it supports following two approaches for creating a new metric.
+The metrics generation processor (`experimental_metricsgenerationprocessor`) can be used to create new metrics using existing metrics following a given rule. This processor currently supports the following two approaches for creating a new metric.
 
-1. It can create a new metric from two existing metrics by applying one of the following arithmetic operations: add, subtract, multiply, divide and percent. One use case is to calculate the `pod.memory.utilization` metric like the following equation-
+1. It can create a new metric from two existing metrics by applying one of the following arithmetic operations: add, subtract, multiply, divide, or percent. One use case is to calculate the `pod.memory.utilization` metric like the following equation-
 `pod.memory.utilization` = (`pod.memory.usage.bytes` / `node.memory.limit`)
 1. It can create a new metric by scaling the value of an existing metric with a given constant number. One use case is to convert `pod.memory.usage` metric values from Megabytes to Bytes (multiply the existing metric's value by 1,048,576)
 
+Note: The created metric's type is inherited from the metric configured as `metric1`.
+
 ## Configuration
 
 Configuration is specified through a list of generation rules. Generation rules find the metrics which 
@@ -43,10 +45,10 @@ processors:
               # type describes how the new metric will be generated. It can be one of `calculate` or `scale`.  calculate generates a metric applying the given operation on two operand metrics. scale operates only on operand1 metric to generate the new metric.
               type: {calculate, scale}
 
-              # This is a required field.
+              # This is a required field. This must be a gauge or sum metric.
               metric1: <first_operand_metric>
 
-              # This field is required only if the type is "calculate".
+              # This field is required only if the type is "calculate". When required, this must be a gauge or sum metric.
               metric2: <second_operand_metric>
 
               # Operation specifies which arithmetic operation to apply. It must be one of the five supported operations.

processor/metricsgenerationprocessor/go.mod

@@ -3,6 +3,8 @@ module github.com/open-telemetry/opentelemetry-collector-contrib/processor/metri
 go 1.22.0
 
 require (
+	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/golden v0.110.0
+	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest v0.110.0
 	github.com/stretchr/testify v1.9.0
 	go.opentelemetry.io/collector/component v0.110.0
 	go.opentelemetry.io/collector/confmap v1.16.0
@@ -15,6 +17,7 @@ require (
 )
 
 require (
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-logr/logr v1.4.2 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
@@ -29,6 +32,7 @@ require (
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
+	github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatautil v0.110.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/rogpeppe/go-internal v1.12.0 // indirect
 	go.opentelemetry.io/collector/component/componentstatus v0.110.0 // indirect
@@ -59,3 +63,9 @@ retract (
 	v0.76.1
 	v0.65.0
 )
+
+replace github.com/open-telemetry/opentelemetry-collector-contrib/pkg/golden => ../../pkg/golden
+
+replace github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest => ../../pkg/pdatatest
+
+replace github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatautil => ../../pkg/pdatautil

processor/metricsgenerationprocessor/processor_test.go

@@ -5,15 +5,21 @@ package metricsgenerationprocessor
 
 import (
 	"context"
+	"fmt"
+	"path/filepath"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/collector/confmap/confmaptest"
 	"go.opentelemetry.io/collector/consumer/consumertest"
 	"go.opentelemetry.io/collector/pdata/pcommon"
 	"go.opentelemetry.io/collector/pdata/pmetric"
 	"go.opentelemetry.io/collector/processor/processortest"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/golden"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/pdatatest/pmetrictest"
 )
 
 type testMetric struct {
@@ -384,3 +390,107 @@ func getOutputForIntGaugeTest() pmetric.Metrics {
 
 	return intGaugeOutputMetrics
 }
+
+func TestSumCalculateNewMetric(t *testing.T) {
+	next := new(consumertest.MetricsSink)
+	cfg := &Config{
+		Rules: []Rule{
+			{
+				Name:      "system.filesystem.capacity",
+				Unit:      "bytes",
+				Type:      "calculate",
+				Metric1:   "system.filesystem.usage",
+				Metric2:   "system.filesystem.utilization",
+				Operation: "divide",
+			},
+		},
+	}
+	factory := NewFactory()
+	mgp, err := factory.CreateMetricsProcessor(
+		context.Background(),
+		processortest.NewNopSettings(),
+		cfg,
+		next,
+	)
+	assert.NotNil(t, mgp)
+	assert.NoError(t, err)
+
+	assert.True(t, mgp.Capabilities().MutatesData)
+	require.NoError(t, mgp.Start(context.Background(), nil))
+
+	inputMetrics, err := golden.ReadMetrics(filepath.Join("testdata", "filesystem_metrics_input.yaml"))
+	assert.NoError(t, err)
+
+	err = mgp.ConsumeMetrics(context.Background(), inputMetrics)
+	assert.NoError(t, err)
+
+	got := next.AllMetrics()
+	// golden.WriteMetrics(t, filepath.Join(".", "testdata", "filesystem_metrics_expected.yaml"), got[0])
+	expected, err := golden.ReadMetrics(filepath.Join("testdata", "filesystem_metrics_expected.yaml"))
+	assert.NoError(t, err)
+	assert.Len(t, got, 1)
+	err = pmetrictest.CompareMetrics(expected, got[0],
+		pmetrictest.IgnoreMetricDataPointsOrder(),
+		pmetrictest.IgnoreStartTimestamp(),
+		pmetrictest.IgnoreTimestamp())
+	assert.NoError(t, err)
+}
+
+func TestResultingMetricTypes(t *testing.T) {
+	testCaseNames := []string{
+		"add_sum_sum",
+		"add_gauge_gauge",
+		"add_gauge_sum",
+		"add_sum_gauge",
+		"multiply_gauge_sum",
+		"multiply_sum_gauge",
+		"divide_gauge_sum",
+		"divide_sum_gauge",
+		"subtract_gauge_sum",
+		"subtract_sum_gauge",
+		"percent_sum_gauge",
+		"percent_gauge_sum",
+	}
+
+	cm, err := confmaptest.LoadConf(filepath.Join("testdata", "metric_types", "gauge_sum_metrics_config.yaml"))
+	assert.NoError(t, err)
+
+	for _, testCase := range testCaseNames {
+		next := new(consumertest.MetricsSink)
+		factory := NewFactory()
+		cfg := factory.CreateDefaultConfig()
+
+		sub, err := cm.Sub(fmt.Sprintf("%s/%s", "experimental_metricsgeneration", testCase))
+		require.NoError(t, err)
+		require.NoError(t, sub.Unmarshal(cfg))
+
+		mgp, err := factory.CreateMetricsProcessor(
+			context.Background(),
+			processortest.NewNopSettings(),
+			cfg,
+			next,
+		)
+		assert.NotNil(t, mgp)
+		assert.NoError(t, err)
+
+		assert.True(t, mgp.Capabilities().MutatesData)
+		require.NoError(t, mgp.Start(context.Background(), nil))
+
+		inputMetrics, err := golden.ReadMetrics(filepath.Join("testdata", "metric_types", "gauge_sum_metrics_input.yaml"))
+		assert.NoError(t, err)
+
+		err = mgp.ConsumeMetrics(context.Background(), inputMetrics)
+		assert.NoError(t, err)
+
+		got := next.AllMetrics()
+		// golden.WriteMetrics(t, filepath.Join("testdata", "metric_types", fmt.Sprintf("%s_%s", testCase, "expected.yaml")), got[0])
+		expected, err := golden.ReadMetrics(filepath.Join("testdata", "metric_types", fmt.Sprintf("%s_%s", testCase, "expected.yaml")))
+		assert.NoError(t, err)
+		assert.Len(t, got, 1)
+		err = pmetrictest.CompareMetrics(expected, got[0],
+			pmetrictest.IgnoreMetricDataPointsOrder(),
+			pmetrictest.IgnoreStartTimestamp(),
+			pmetrictest.IgnoreTimestamp())
+		assert.NoError(t, err)
+	}
+}