commit 03e748680c6539c36afc0d9d1782714240e2212d
author Damien Neil <dneil@google.com> Sun Apr 07 18:18:31 2019 -0700
committer Damien Neil <dneil@google.com> Mon Apr 08 05:14:36 2019 +0000
tree cfbed00416167eedfd13d960395c5ae857d0cb3f
parent 3016b733824758fd0d28eca876005d714c2e600b

proto: replace CachedSize fast-path method with UseCachedSize option

Using an option instead of a separate method has several useful properties:

It makes it explicit whether the fast-path AppendMarshal is expected to use
cached sizes or not.

It properly plumbs the decision to use cached sizes through the call stack.
Consider the case where message A includes B includes C: If A and C support
cached sizes but B does not, we would like to use the size cache in all
messages which support it. Placing this decision in the options allows this
to work properly with no additional effort.

Placing this option in MarshalOptions permits users to request use of
existing cached sizes. This is a two-edged sword: There are places where
this ability can permit substantial efficiencies, but this is also an
exceedingly sharp-edged API. I believe that on balance the benefits
outweigh the risks, especially since the prerequisites for using
cached sizes are intuitively obvious. (You must have called Size, and
you must not have changed the message.)

This CL adds a Size method to MarshalOptions, rather than adding a SizeOptions
type. Future additions to MarshalOptions may affect the size of the encoded
output (e.g., an option to skip encoding unknown fields) and using the same
options for both Marshal and Size makes it easier to use a consistent
configuration for each.

Change-Id: I6adbb55b717dd03d39f067e1d0b7381945000976
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/171119
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>