[pdata] Fix CopyTo to deep-copy bytes oneof values

.chloggen/pdata-copyto-deepcopy-bytes.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. receiver/otlp)
+component: pkg/pdata
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix `pcommon.Value.CopyTo` to deep-copy `ValueTypeBytes` values instead of sharing the backing array
+
+# One or more tracking issues or pull requests related to the change
+issues: [15621]
+
+# (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: |
+  The bytes oneof field in CopyAnyValue was assigned directly, so the copy and source shared the same []byte.
+  This also affected Map.CopyTo and Slice.CopyTo, which delegate to CopyAnyValue.
+
+# 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]

internal/cmd/pdatagen/internal/proto/copy.go

@@ -16,7 +16,11 @@ const copyOther = `{{ if .repeated -}}
 	} else {
 		ov = ProtoPool{{ .oneOfMessageName }}.Get().(*{{ .oneOfMessageName }})
 	}
+	{{ if .isBytes -}}
+	ov.{{ .fieldName }} = append(ov.{{ .fieldName }}[:0], t.{{ .fieldName }}...)
+	{{ else -}}
 	ov.{{ .fieldName }} = t.{{ .fieldName }}
+	{{ end -}}
 	dest.{{ .oneOfGroup }} = ov
 {{ else if .nullable -}}
 	if src.Has{{ .fieldName }}() {

internal/cmd/pdatagen/internal/proto/field.go

@@ -216,6 +216,7 @@ func (pf *Field) getTemplateFields() map[string]any {
 		"oneOfMessageName":  pf.OneOfMessageName,
 		"repeated":          pf.Repeated,
 		"nullable":          pf.Nullable,
+		"isBytes":           pf.Type == TypeBytes,
 		"bitSize":           bitSize,
 		"goType":            pf.GoType(),
 		"defaultValue":      pf.DefaultValue(),

pdata/pcommon/value_test.go

@@ -255,6 +255,19 @@ func TestValue_CopyTo(t *testing.T) {
 	assert.Equal(t, internal.GenTestAnyValue(), dest.getOrig())
 }
 
+func TestValue_CopyToBytesIsDeepCopy(t *testing.T) {
+	src := NewValueBytes()
+	src.Bytes().FromRaw([]byte{1, 2, 3})
+
+	dest := NewValueEmpty()
+	src.CopyTo(dest)
+
+	// mutating the copy must not affect the source, since CopyTo is a deep copy.
+	dest.Bytes().SetAt(0, 99)
+	assert.Equal(t, []byte{1, 2, 3}, src.Bytes().AsRaw())
+	assert.Equal(t, []byte{99, 2, 3}, dest.Bytes().AsRaw())
+}
+
 func TestSliceWithNilValues(t *testing.T) {
 	origWithNil := []internal.AnyValue{
 		{},