eddie

Big Eddie, the Golang contract enforcer

It would be nice if we could write linters that applied only to specific elements within a program.

Current linter approaches apply rules across an entire program. These produce a wealth of useful and actionable data about how to improve the quality of a program. However, it's often the case where developers may want to apply some custom, configurable logic that isn't appropriate for a general-purpose linter.

Eddie solves the following two problems:

• Make it easy to define new contracts
• Bind those contracts to specific elements within a program

Building an enforcer

Eddie aggregates any number of types that implement the contract.Contract interface and compiles them into a stand-alone enforcer binary. For an example, see the concrete-return contract.

Here's a trivial example:

package noop

import "github.com/cockroachdb/eddie/pkg/contract"

type NoOpContract struct {}
// A specific, top-level type assertion is required. 
var _ contract.Contract = &NoOpContract{}
func (n *NoOpContract) Enforce(contract.Context) error { return nil }

The enforcer is created by running the eddie command:

$ go run github.com/cockroachdb/eddie/cmd/eddie \
  -n myenforcer \
  path/to/noop
  
wrote output to /Users/bob/eddie/myenforcer

$ ./myenforcer contracts
contract:NoOpContract
	https://godoc.org/github.com/cockroachdb/eddie/noop/#NoOpContract
	
$ ./myenforcer enforce --help
Enforce contracts defined in the given packages

Usage:
  myenforcer enforce [packages] [flags]

Flags:
      --asserted_only     only consider explicit type assertions
  -d, --dir string        override the current working directory (default ".")
  -h, --help              help for enforce
      --set_exit_status   return a non-zero exit code if errors are reported
  -t, --tests             include test sources in the analysis
  -v, --verbose           enable additional diagnostic messages

The generated myenforcer binary is a regular go binary and can be deployed in the usual manner.

Contracts that are part of the Eddie project can be included by using the --include_builtins flag.

Applying contracts

Refer to the contract package for how to bind contracts to source elements.