Add "plugin" support to local backend (#2239)

and a nit to improve the clone


---
*Sponsored by Kithara Software GmbH*

docs/docs/30-administration/22-backends/20-local.md

@@ -6,11 +6,7 @@ The local backend will execute the pipelines on the local system without any iso
 
 :::note
 This backend is still pretty new and can not be treated as stable. Its
-implementation and configuration can change at any time. Binary releases of the
-agent will be available with the release of the [1.0.0
-milestone](https://github.com/woodpecker-ci/woodpecker/milestone/4), so for now
-you must compile the agent by yourself, to get the local backend functionality.
-<!-- TODO: remove the self-compile note after the release of the agent -->
+implementation and configuration can change at any time.
 :::
 
 Since the code runs directly in the same context as the agent (same user, same
@@ -92,6 +88,17 @@ steps:
       [...]
 ```
 
+### Plugins as Executable Binaries
+
+```yaml
+steps:
+  build:
+    image: /usr/bin/tree
+```
+
+If no commands are provided, we treat them as plugins in the usual manner.  
+In the context of the local backend, plugins are simply executable binaries, which can be located using their name if they are listed in `$PATH`, or through an absolute path.
+
 ### Using labels to filter tasks
 
 You can use the [agent configuration

docs/versioned_docs/version-1.0/30-administration/22-backends/20-local.md

@@ -6,11 +6,7 @@ The local backend will execute the pipelines on the local system without any iso
 
 :::note
 This backend is still pretty new and can not be treated as stable. Its
-implementation and configuration can change at any time. Binary releases of the
-agent will be available with the release of the [1.0.0
-milestone](https://github.com/woodpecker-ci/woodpecker/milestone/4), so for now
-you must compile the agent by yourself, to get the local backend functionality.
-<!-- TODO: remove the self-compile note after the release of the agent -->
+implementation and configuration can change at any time.
 :::
 
 Since the code runs directly in the same context as the agent (same user, same

pipeline/backend/local/clone.go

@@ -28,7 +28,6 @@ import (
 
 	"github.com/rs/zerolog/log"
 	"github.com/woodpecker-ci/woodpecker/pipeline/backend/types"
-	"github.com/woodpecker-ci/woodpecker/shared/constant"
 )
 
 // checkGitCloneCap check if we have the git binary on hand
@@ -64,17 +63,20 @@ func (e *local) setupClone(state *workflowState) error {
 
 // execClone executes a clone-step locally
 func (e *local) execClone(ctx context.Context, step *types.Step, state *workflowState, env []string) error {
-	if err := e.setupClone(state); err != nil {
-		return fmt.Errorf("setup clone step failed: %w", err)
+	if scm := step.Environment["CI_REPO_SCM"]; scm != "git" {
+		return fmt.Errorf("local backend can only clone from git repos, but this repo use '%s'", scm)
 	}
 
 	if err := checkGitCloneCap(); err != nil {
 		return fmt.Errorf("check for git clone capabilities failed: %w", err)
 	}
 
-	if step.Image != constant.DefaultCloneImage {
-		// TODO: write message into log
-		log.Warn().Msgf("clone step image '%s' does not match default git clone image. We ignore it assume git.", step.Image)
+	if err := e.setupClone(state); err != nil {
+		return fmt.Errorf("setup clone step failed: %w", err)
+	}
+
+	if !strings.Contains(step.Image, "plugin-git") {
+		log.Warn().Msgf("clone step image '%s' does not match default git clone image. We ignore it and use our plugin-git anyway.", step.Image)
 	}
 
 	rmCmd, err := writeNetRC(step, state)

pipeline/backend/local/local.go

@@ -120,13 +120,16 @@ func (e *local) StartStep(ctx context.Context, step *types.Step, taskUUID string
 		return e.execClone(ctx, step, state, env)
 	case types.StepTypeCommands:
 		return e.execCommands(ctx, step, state, env)
+	case types.StepTypePlugin:
+		return e.execPlugin(ctx, step, state, env)
 	default:
 		return ErrUnsupportedStepType
 	}
 }
 
+// execCommands use step.Image as shell and run the commands in it
 func (e *local) execCommands(ctx context.Context, step *types.Step, state *workflowState, env []string) error {
-	// TODO: use commands directly
+	// TODO: find a way to simulate commands to be exec as stdin user commands instead of generating a script and hope the shell understands
 	script := ""
 	for _, cmd := range step.Commands {
 		script += fmt.Sprintf("echo + %s\n%s\n", strings.TrimSpace(shellescape.Quote(cmd)), cmd)
@@ -148,6 +151,26 @@ func (e *local) execCommands(ctx context.Context, step *types.Step, state *workf
 	return cmd.Start()
 }
 
+// execPlugin use step.Image as exec binary
+func (e *local) execPlugin(ctx context.Context, step *types.Step, state *workflowState, env []string) error {
+	binary, err := exec.LookPath(step.Image)
+	if err != nil {
+		return fmt.Errorf("lookup plugin binary: %w", err)
+	}
+
+	cmd := exec.CommandContext(ctx, binary)
+	cmd.Env = env
+	cmd.Dir = state.workspaceDir
+
+	// Get output and redirect Stderr to Stdout
+	e.output, _ = cmd.StdoutPipe()
+	cmd.Stderr = cmd.Stdout
+
+	state.stepCMDs[step.Name] = cmd
+
+	return cmd.Start()
+}
+
 // WaitStep for the pipeline step to complete and returns
 // the completion results.
 func (e *local) WaitStep(_ context.Context, step *types.Step, taskUUID string) (*types.State, error) {