introduce the Equal method on Stack (#13952)

This introduces `Stack.Equal()`, to help with profiles merging.
See #13928

Author: dmathieu

.chloggen/stack-equal.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: pdata/pprofile
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Introduce `Equal` method on the `Stack` type
+
+# One or more tracking issues or pull requests related to the change
+issues: [13952]
+
+# (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:
+
+# 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: [api]

pdata/pprofile/stack.go

@@ -0,0 +1,19 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package pprofile // import "go.opentelemetry.io/collector/pdata/pprofile"
+
+// Equal checks equality with another Stack
+func (ms Stack) Equal(val Stack) bool {
+	if ms.LocationIndices().Len() != val.LocationIndices().Len() {
+		return false
+	}
+
+	for i := range ms.LocationIndices().Len() {
+		if ms.LocationIndices().At(i) != val.LocationIndices().At(i) {
+			return false
+		}
+	}
+
+	return true
+}

pdata/pprofile/stack_test.go

@@ -0,0 +1,72 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package pprofile
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestStackEqual(t *testing.T) {
+	for _, tt := range []struct {
+		name string
+		orig Stack
+		dest Stack
+		want bool
+	}{
+		{
+			name: "with empty stacks",
+			orig: NewStack(),
+			dest: NewStack(),
+			want: true,
+		},
+		{
+			name: "with non-empty equal stacks",
+			orig: func() Stack {
+				s := NewStack()
+				s.LocationIndices().Append(1)
+				return s
+			}(),
+			dest: func() Stack {
+				s := NewStack()
+				s.LocationIndices().Append(1)
+				return s
+			}(),
+			want: true,
+		},
+		{
+			name: "with different location indices lengths",
+			orig: func() Stack {
+				s := NewStack()
+				s.LocationIndices().Append(1)
+				return s
+			}(),
+			dest: NewStack(),
+			want: false,
+		},
+		{
+			name: "with non-equal location indices",
+			orig: func() Stack {
+				s := NewStack()
+				s.LocationIndices().Append(2)
+				return s
+			}(),
+			dest: func() Stack {
+				s := NewStack()
+				s.LocationIndices().Append(1)
+				return s
+			}(),
+			want: false,
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.want {
+				assert.True(t, tt.orig.Equal(tt.dest))
+			} else {
+				assert.False(t, tt.orig.Equal(tt.dest))
+			}
+		})
+	}
+}