Sample Elvish plugin

Elvish plugins are Elvish modules written in Go. They can be imported like modules written in Elvish.

Plugins are only supported on platforms supported by Go's plugin package.

Writing a plugin

To create an Elvish plugin, follow these steps:

Initialize a new Go module (replace github.com/elves/sample-plugin with your repo path):
```
go mod init github.com/elves/sample-plugin
```
Add Go source files to form a main package. The package should export a variable named Ns that represents an Elvish namespace.

See main.go in this repository for an example.

In general, you can reference the various builtin modules for how to build the namespace and how Go functions are exported to Elvish.
Add the latest commit of Elvish as a dependency:
```
go get src.elv.sh@master
```
This step is required for now, because the last released version of Elvish does not contain plugin support yet.
Get the go.mod and go.sum files into a buildable state:
```
go mod tidy
```

Building the plugin

With the source files ready, build the plugin with the following steps:

Build Elvish with plugin support, at exactly the same version used by the plugin:

CGO_ENABLED=1 go install src.elv.sh/cmd/elvish@$(go list -f '{{.Version}}' -m src.elv.sh)

Elvish version of the command:

E:CGO_ENABLED=1 go install src.elv.sh/cmd/elvish@(go list -f '{{.Version}}' -m src.elv.sh)

Build the plugin:
```
go build -buildmode=plugin
```
This will create a new ${name}.so in the current directory, ${name} being the same as the directory name.

Alternatively, if you have a clone of the Elvish repository, you can also use these steps:

Build Elvish with plugin support:

cd /path/to/elvish/repository
git checkout version-encoded-in-plugin-go.mod
make get ELVISH_PLUGIN_SUPPORT=1

Build the plugin:
```
go build -buildmode=plugin -trimpath
```
The -trimpath flag is needed to be consistent with the Elvish binary built in step 1.

After building the plugin, scripts may now use the .so file as a module:

elvish sample-script.elv
# Outputs "bar"

Whenever you rebuild Elvish or the plugin, you have to make sure that their versions are synchronized, and built with the same version of Go compiler.

elves/sample-plugin

Sample Elvish plugin

Writing a plugin

Building the plugin