tree ed050b947cac50e0b8b88aa51b207fa14ddb0b9d
parent cfd80493c530afb96ac94dbfbf69fb99d71236ce
author Joe Tsai <joetsai@digital-static.net> 1582943836 -0800
committer Joe Tsai <joetsai@digital-static.net> 1584732302 +0000

internal/msgfmt: use msgfmt package to format messages

Port message formatting logic in testing/protocmp to internal/msgfmt
and improve upon its output.

This formatter is optimized for humanly readable output.
It takes the best parts of both the JSON and proto text formats.

The good of prototext:
	* It supports emitting unknown fields (useful for debugging).
	* It is relatively concise in the common-case since keys do not
	need to be represented as quoted strings (e.g., "key" vs key).

The bad of prototext:
	* Requires relatively large dependency on encoding/prototext.
	* Our implementation lacks support for serializing packed lists.
	* Lacks support for readable maps.
	* Lacks support for readable Timestamp and Duration.

The good of protojson:
	* First-class support for readable maps.
	* First-class support for readable Timestamp and Duration.

The bad of protojson:
	* Requires relatively large dependency on encoding/protojson.
	* Lacks support for emitting unknown fields.
	* More verbose in the common-case as keys are quoted strings.

The msgfmt package has the benefits of both protojson and prototext,
but none of the detriments. It is a relatively simple implementation.

This output is only intended for human consumption with no associated
deserialization implementation.
To avoid any illusion that this is identical to either the proto text
or JSON formats, this always emits surrounding "{}" for
top-level messages and the keys are not quoted strings.

This CL does not use this format for generated Message.String methods
as there is concerns about being inconsistent with the String methods
as implemented in other languages. Having it be a seperate package makes
it trivial to switch over to this if desired.

Change-Id: I8b3581904d1624e84bf1b1954d2f01e5774b7f87
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/223752
Reviewed-by: Damien Neil <dneil@google.com>