Plugin RPC interface (#24)

go.mod

@@ -13,6 +13,7 @@ require (
 )
 
 require (
+	github.com/Masterminds/semver/v3 v3.2.1 // indirect
 	github.com/agext/levenshtein v1.2.1 // indirect
 	github.com/apparentlymart/go-textseg/v13 v13.0.0 // indirect
 	github.com/apparentlymart/go-textseg/v15 v15.0.0 // indirect

go.sum

@@ -1,3 +1,5 @@
+github.com/Masterminds/semver/v3 v3.2.1 h1:RN9w6+7QoMeJVGyfmbcgs28Br8cvmnucEXnY0rYXWg0=
+github.com/Masterminds/semver/v3 v3.2.1/go.mod h1:qvl/7zhW3nngYb5+80sSMF+FG2BjYrf8m9wsX0PNOMQ=
 github.com/agext/levenshtein v1.2.1 h1:QmvMAjj2aEICytGiWzmxoE0x2KZvE0fvmqMOfy2tjT8=
 github.com/agext/levenshtein v1.2.1/go.mod h1:JEDfjyjHDjOF/1e4FlBE/PkbqA9OfWu2ki2W0IB5558=
 github.com/apparentlymart/go-textseg/v13 v13.0.0 h1:Y+KvPE1NYz0xl601PVImeQfFyEy6iT90AvPUL1NNfNw=

pluginInterface/v1/plugin.go

@@ -0,0 +1,55 @@
+package plugin
+
+import (
+	"github.com/Masterminds/semver/v3"
+	"github.com/hashicorp/hcl/v2"
+	"github.com/hashicorp/hcl/v2/hcldec"
+	"github.com/zclconf/go-cty/cty"
+)
+
+// The interface exposed and used by the go-plugin (versioned as 1)
+type PluginRPC interface {
+	GetPlugins() []Plugin
+	Call(args Args) Result
+}
+
+// One go-plugin binary can provide multiple plugins and/or one plugin with multiple versions
+// Deciding if we actually will do bundling in that way or stick with one plugin - one binary
+// is a different question, but the interface wouldn't limit us either way.
+type Plugin struct {
+	// The namespace used during installation of the plugins
+	Namespace string
+	// "content" or "data" for now
+	Kind string
+	// "text", "plugin_a", etc.
+	Name string
+	// version of the plugin `Kind Name` that is provided by the current binary
+	Version semver.Version
+	// Specification of the `config` block for this plugin
+	// If nil - providing a `config Kind Name` is an error
+	ConfigSpec hcldec.Spec
+	// Specification of the invocation block's body, i.e. `content text {<spec of what's here>}`
+	InvocationSpec hcldec.Spec
+}
+
+type Args struct {
+	// Specifies which kind, name and version of plugin to execute
+	Kind    string
+	Name    string
+	Version semver.Version
+
+	// Result of decoding a config block with ConfigSpec
+	Config cty.Value
+	// Result of decoding an invocation block with InvocationSpec
+	Args cty.Value
+	// Passed to content plugins, nil for data plugins
+	Context map[string]any
+}
+
+type Result struct {
+	// `content` plugins return a markdown string
+	// `data` plugins return a map[string]any that would be put into the global config
+	// TODO: hard-code typecast based on the plugin kind while handling the result
+	result any
+	diags  hcl.Diagnostics
+}