make auto plugin building work in dev builds

2 files changed, 37 insertions, 5 deletions

diff --git a/doc/plugins.md b/doc/plugins.md
index d943ea0..2e9b2d2 100644
--- a/doc/plugins.md
+++ b/doc/plugins.md
@@ -38,8 +38,6 @@ To use this, clone the plugin repository, cd into it and run:
 mt-build-plugin
 ```
 
-This tool won't work in development builds.
-
 ## Developing plugins
 A plugin is simply a main package without a main function. Use the init
 functions instead. Plugins can import
@@ -84,6 +82,9 @@ and copy everything excluding the `require `. Then append a new line:
 `replace github.com/HimbeerserverDE/mt-multiserver-proxy SOMEVERSION => ../path/to/proxy/repo/`.
 Now rebuild and install the plugin and it should be loaded.
 
-As of now there is no way to automate this, though the go toolchain
-provides everything needed to implement it.
-Expect this feature to be added soon.
+### Automatic development version management
+The `mt-build-plugin` tool as well as the proxy itself are capable of
+handling development versions, but the former only works if it's located
+in the same directory as the proxy executable. See
+[Automatic version management](https://github.com/HimbeerserverDE/mt-multiserver-proxy/blob/main/doc/plugins.md#automatic-version-management)
+for details.
diff --git a/plugin.go b/plugin.go
index f399a8f..aeb9b8d 100644
--- a/plugin.go
+++ b/plugin.go
@@ -16,6 +16,14 @@ func BuildPlugin() error {
 		return err
 	}
 
+	if version == "(devel)" {
+		return buildPluginDev(version)
+	}
+
+	return buildPlugin(version)
+}
+
+func buildPlugin(version string) error {
 	pathVer := "github.com/HimbeerserverDE/mt-multiserver-proxy@" + version
 
 	if err := goCmd("get", pathVer); err != nil {
@@ -33,6 +41,29 @@ func BuildPlugin() error {
 	return nil
 }
 
+func buildPluginDev(version string) error {
+	replace := "-replace=github.com/HimbeerserverDE/mt-multiserver-proxy=" + Path()
+	const dropReplace = "-dropreplace=github.com/HimbeerserverDE/mt-multiserver-proxy"
+
+	if err := goCmd("mod", "edit", replace); err != nil {
+		return err
+	}
+
+	if err := goCmd("mod", "tidy"); err != nil {
+		return err
+	}
+
+	if err := goCmd("build", "-buildmode=plugin"); err != nil {
+		return err
+	}
+
+	if err := goCmd("mod", "edit", dropReplace); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func loadPlugins() {
 	pluginsOnce.Do(openPlugins)
 }