mirror of https://github.com/digital-asset/daml.git synced 2024-11-10 10:46:11 +03:00

Bazel: Factor out logic around Protobuf JARs. [KVL-714] (#8084 )

* kvutils: Use ScalaPB to generate a Scala JAR for daml_kvutils.proto.

* Bazel: Delete the unused `da_java_binary` rule, and inline `_wrap_rule`.

* Bazel: Factor out Java/Scala protobuf class generation into a helper.

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* daml-lf/archive: Use `proto_jars`.

* Bazel: Remove the visibility modifier from `proto_jars`.

It's too confusing. Just make everything public.

* daml-lf/archive: Push protobuf source tarballs into `proto_jars`.

* Bazel: Add comments to the various parts of `proto_jars`.

* daml-assistant: Do unpleasant things with `location` in Bazel.

2020-11-27 08:34:53 +00:00

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DAML-LF archive

This component contains the .proto definitions specifying the format in which DAML-LF packages are stored -- the DAML-LF archive. All the proto definitions are kept in the directory src/protobuf/com/daml/daml_lf_dev/

The entry point definition is Archive in src/protobuf/com/daml/daml_lf_dev/daml_lf.proto. Archive contains some metadata about the actual archive (currently the hashing function and the hash), and then a binary blob containing the archive. The binary blob must be an ArchivePayload -- we keep it in binary form to facilitate hashing, signing, etc. The encoding and decoding of the payload is handled by Haskell and Java libraries in daml-core-package, so that consumers and producers do not really need to worry about it.

ArchivePayload is a sum type containing the various DAML-LF versions supported by the DAML-LF archive. Currently we have two major versions:

DAML-LF-0, which is the deprecated legacy DAML core;
DAML-LF-1, which is the first version of DAML-LF as specified by https://github.com/digital-asset/daml/blob/master/daml-lf/spec/daml-lf-1.rst.

Snapshot versions

The component contains also an arbitrary number of snapshots of the protobuf definitions as they were as the time a particular version of DAML-LF was frozen. For versions <= 1.8, those snapshots are kept in the directories src/protobuf/com/digitalasset/daml_lf_x_y/, where x.y is a already frozen DAML-LF version. For newer versions, the directory is src/protobuf/com/daml/daml_lf_x_y/. A snapshot for version x.y can be used to read any DAML-LF version from 1.0 to x.y without suffering breaking changes (at the generated code level) often introduced in the current version.

Building

It produces several libraries containing code to encode / decode such definition, a Haskell one, and several Java ones:

$ bazel build //daml-lf/archive:daml_lf_archive_haskell_proto
$ bazel build //daml-lf/archive:daml_lf_dev_archive_proto_java
$ bazel build //daml-lf/archive:daml_lf_1_6_archive_proto_java

Editing the `.proto` definitions

When editing the proto definitions, you must make sure to not change them in a backwards-incompatible way. To make sure this doesn't happen:

DO NOT delete message fields;
DO NOT change the number of a message field or an enum value;
DO NOT change the type of a message field;

Note that "fields" include oneof fields. Also note that the "don't delete fields" rule is there not because they introduce a backwards incompatible change, but rather because after a field has been deleted another commiter might redefine it with a different type without realizing.

What is OK is renaming message fields while keeping the number and semantics unchanged. For example, if you have

message Foo {
  bytes blah = 1;
}

it's OK to change it to

message Foo {
  // this field is deprecated -- use baz instead!
  bytes blah_deprecated = 1;
  string baz = 2;
}

Conversion from the `.proto` to AST

The .proto definitions contain the serialized format for DAML-LF packages, however the code to convert from the .proto definitions to the actual AST lives elsewhere.

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