Add Append to Generated pdata Structs (#1157)

This makes it a bit more convenient to assemble data structures.

It is also congruent with the existing Go slice functionality with
the same name.

cmd/pdatagen/internal/base_structs.go

@@ -132,6 +132,14 @@ func (es ${structName}) Resize(newLen int) {
  oldOrig = append(oldOrig, &extraOrigs[i])
  }
  (*es.orig) = oldOrig
+}
+
+// Append will increase the length of the ${structName} by one and set the
+// given ${elementName} at that new position. The original ${elementName}
+// could still be referenced so do not reuse it after passing it to this
+// method.
+func (es ${structName}) Append(e *${elementName}) {
+ (*es.orig) = append((*es.orig), *e.orig)
 }`
 
 const sliceTestTemplate = `func Test${structName}(t *testing.T) {
@@ -233,6 +241,23 @@ func Test${structName}_Resize(t *testing.T) {
  // Test Resize 0 elements.
  es.Resize(0)
  assert.EqualValues(t, New${structName}(), es)
+}
+
+func Test${structName}_Append(t *testing.T) {
+ es := generateTest${structName}()
+ emptyVal := New${elementName}()
+ emptyVal.InitEmpty()
+
+ es.Append(&emptyVal)
+ assert.EqualValues(t, *(es.At(7)).orig, *emptyVal.orig)
+
+ emptyVal2:= New${elementName}()
+ emptyVal2.InitEmpty()
+
+ es.Append(&emptyVal2)
+ assert.EqualValues(t, *(es.At(8)).orig, *emptyVal2.orig)
+
+ assert.Equal(t, 9, es.Len())
 }`
 
 const sliceGenerateTest = `func generateTest${structName}() ${structName} {