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ADR 053: Go Module Refactoring

Changelog​

  • 2022-04-27: First Draft

Status​

PROPOSED

Abstract​

The current SDK is built as a single monolithic go module. This ADR describes how we refactor the SDK into smaller independently versioned go modules for ease of maintenance.

Context​

Go modules impose certain requirements on software projects with respect to stable version numbers (anything above 0.x) in that any API breaking changes necessitate a major version increase which technically creates a new go module (with a v2, v3, etc. suffix).

Keeping modules API compatible in this way requires a fair amount of fair thought and discipline.

The Cosmos SDK is a fairly large project which originated before go modules came into existence and has always been under a v0.x release even though it has been used in production for years now, not because it isn't production quality software, but rather because the API compatibility guarantees required by go modules are fairly complex to adhere to with such a large project. Up to now, it has generally been deemed more important to be able to break the API if needed rather than require all users update all package import paths to accommodate breaking changes causing v2, v3, etc. releases. This is in addition to the other complexities related to protobuf generated code that will be addressed in a separate ADR.

Nevertheless, the desire for semantic versioning has been strong in the community and the single go module release process has made it very hard to release small changes to isolated features in a timely manner. Release cycles often exceed six months which means small improvements done in a day or two get bottle-necked by everything else in the monolithic release cycle.

Decision​

To improve the current situation, the SDK is being refactored into multiple go modules within the current repository. There has been a fair amount of debate as to how to do this, with some developers arguing for larger vs smaller module scopes. There are pros and cons to both approaches (which will be discussed below in the Consequences section), but the approach being adopted is the following:

  • a go module should generally be scoped to a specific coherent set of functionality (such as math, errors, store, etc.)
  • when code is removed from the core SDK and moved to a new module path, every effort should be made to avoid API breaking changes in the existing code using aliases and wrapper types (as done in https://github.com/cosmos/cosmos-sdk/pull/10779 and https://github.com/cosmos/cosmos-sdk/pull/11788)
  • new go modules should be moved to a standalone domain (cosmossdk.io) before being tagged as v1.0.0 to accommodate the possibility that they may be better served by a standalone repository in the future
  • all go modules should follow the guidelines in https://go.dev/blog/module-compatibility before v1.0.0 is tagged and should make use of internal packages to limit the exposed API surface
  • the new go module's API may deviate from the existing code where there are clear improvements to be made or to remove legacy dependencies (for instance on amino or gogo proto), as long the old package attempts to avoid API breakage with aliases and wrappers
  • care should be taken when simply trying to turn an existing package into a new go module: https://github.com/golang/go/wiki/Modules#is-it-possible-to-add-a-module-to-a-multi-module-repository. In general, it seems safer to just create a new module path (appending v2, v3, etc. if necessary), rather than trying to make an old package a new module.

Consequences​

Backwards Compatibility​

If the above guidelines are followed to use aliases or wrapper types pointing in existing APIs that point back to the new go modules, there should be no or very limited breaking changes to existing APIs.

Positive​

  • standalone pieces of software will reach v1.0.0 sooner
  • new features to specific functionality will be released sooner

Negative​

  • there will be more go module versions to update in the SDK itself and per-project, although most of these will hopefully be indirect

Neutral​

Further Discussions​

Further discussions are occurring in primarily in https://github.com/cosmos/cosmos-sdk/discussions/10582 and within the Cosmos SDK Framework Working Group.

References​