[pdata] Add SetLen method to primitive slices

CHANGELOG.md

@@ -31,7 +31,7 @@
 - Deprecate `*DataPoint.[Set]FlagsImmutable()` funcs in favor of `*DataPoint.[Set]Flags()`. (#6017)
 - Deprecate `LogRecord.FlagsStruct()` and `LogRecord.SetFlagsStruct()` in favor of `LogRecord.Flags()` and `LogRecord.SetFlags()`. (#6007)
 - Deprecate `config.Unmarshallable` in favor of `confmap.Unmarshaler`. (#6031)
-- Primitive slice wrapper are now mutable (#5971):
+- Primitive slice wrapper are now mutable (#5971, #6053):
   - `pcommon.ImmutableByteSlice` is deprecated in favor of `pcommon.ByteSlice`
   - `pcommon.ImmutableFloat64Slice` is deprecated in favor of `pcommon.Float64Slice`
   - `pcommon.ImmutableUInt64Slice` is deprecated in favor of `pcommon.UInt64Slice`

pdata/internal/cmd/pdatagen/internal/primitive_slice_structs.go

@@ -61,6 +61,18 @@ func (ms ${structName}) SetAt(i int, val ${itemType}) {
 	(*ms.getOrig())[i] = val
 }
 
+// SetLen sets length of ${structName}.
+func (ms ${structName}) SetLen(l int) {
+	switch {
+	case l < len(*ms.getOrig()):	
+		*ms.getOrig() = (*ms.getOrig())[:l]
+	case len(*ms.getOrig()) < l:
+		buf := *ms.getOrig()
+		*ms.getOrig() = make([]${itemType}, l)
+		copy(*ms.getOrig(), buf)
+	}
+}
+
 // MoveTo moves ${structName} to another instance.
 func (ms ${structName}) MoveTo(dest ${structName}) {
 	*dest.getOrig() = *ms.getOrig()
@@ -111,6 +123,18 @@ const immutableSliceTestTemplate = `func TestNew${structName}(t *testing.T) {
 	ms.MoveTo(mv)
 	assert.Equal(t, 3, mv.Len())
 	assert.Equal(t, ${itemType}(1), mv.At(0))
+}
+
+func Test${structName}SetLen(t *testing.T) {
+	ms := New${structName}()
+	ms.FromRaw([]${itemType}{1, 2, 3})
+	ms.SetLen(1)
+	assert.Equal(t, 1, ms.Len())
+	assert.Equal(t, ${itemType}(1), ms.At(0))
+	ms.SetLen(3)
+	assert.Equal(t, 3, ms.Len())
+	assert.Equal(t, ${itemType}(1), ms.At(0))
+	assert.Equal(t, ${itemType}(0), ms.At(2))
 }`
 
 const primitiveSliceInternalTemplate = `