Document that changing pcommon.Map invalidates Value references

Signed-off-by: Bogdan Drutu <[email protected]>

Author: bogdandrutu

.chloggen/document-13073.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
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Document that changing pcommon.Map (Remove/removeIf/Put*) invalidates Value references obtained via Get.
+
+# One or more tracking issues or pull requests related to the change
+issues: [13073]
+
+# (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/pcommon/map.go

@@ -55,12 +55,14 @@ func (m Map) EnsureCapacity(capacity int) {
 	copy(*m.getOrig(), oldOrig)
 }
 
-// Get returns the Value associated with the key and true. Returned
+// Get returns the Value associated with the key and true. The returned
 // Value is not a copy, it is a reference to the value stored in this map.
 // It is allowed to modify the returned value using Value.Set* functions.
 // Such modification will be applied to the value stored in this map.
+// Accessing the returned value after modifying the underlying map
+// (removing or adding new values) is an undefined behavior.
 //
-// If the key does not exist returns a zero-initialized KeyValue and false.
+// If the key does not exist, returns a zero-initialized KeyValue and false.
 // Calling any functions on the returned invalid instance may cause a panic.
 func (m Map) Get(key string) (Value, bool) {
 	for i := range *m.getOrig() {

pdata/plog/logs_test.go

@@ -172,3 +172,31 @@ func BenchmarkLogsUsage(b *testing.B) {
 		}
 	}
 }
+
+func Test_minimal_reproducer(t *testing.T) {
+	logs := NewLogs()
+	resourceLogs1 := logs.ResourceLogs().AppendEmpty()
+	attrs1 := resourceLogs1.Resource().Attributes()
+	attrs1.PutStr("attr.to.move", "mover")
+	attrs1.PutStr("service.name", "dummy-service")
+	attrs1.PutStr("service.namespace", "dash0")
+
+	// Create a second Resource
+	resourceLogs2 := logs.ResourceLogs().AppendEmpty()
+	attrs2 := resourceLogs2.Resource().Attributes()
+	attrs2.PutStr("service.name", "another-dummy-service")
+	attrs2.PutStr("service.namespace", "dash0")
+
+	// Now we pick up the attribute and remove from the first Resource, then add to the second Resource
+	// Normally this would happen e.g. in some loop or other logic, but shortened just to make the issue clear
+	if v, ok := logs.ResourceLogs().At(0).Resource().Attributes().Get("attr.to.move"); ok {
+		// !! the Remove happens FIRST !!
+		logs.ResourceLogs().At(0).Resource().Attributes().Remove("attr.to.move")
+
+		logs.ResourceLogs().At(1).Resource().Attributes().PutStr("attr.to.move", v.AsString())
+	}
+
+	movedValue, ok := logs.ResourceLogs().At(1).Resource().Attributes().Get("attr.to.move")
+	assert.True(t, ok)
+	assert.Equal(t, "mover", movedValue.AsString()) // FAILS, value is "dash0" from the service.namespace
+}