Support setting shell via defaults.run (#343)

Note that we don't support the more general use of defaults, just its
run key for setting shell and working directory.

The documentation for defaults.run is here:
  https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#defaultsrun

Fixes #214.

Co-authored-by: Casey Lee <cplee@nektos.com>

pkg/runner/runner_test.go

@@ -55,6 +55,7 @@ func TestRunEvent(t *testing.T) {
 		{"commands", "push", ""},
 		{"workdir", "push", ""},
 		{"issue-228", "push", ""}, // TODO [igni]: Remove this once everything passes
+		{"defaults-run", "push", ""},
 	}
 	log.SetLevel(log.DebugLevel)
 

pkg/runner/step_context.go

@@ -111,6 +111,12 @@ func (sc *StepContext) setupShellCommand() common.Executor {
 			return err
 		}
 
+		if step.WorkingDirectory == "" {
+			step.WorkingDirectory = rc.Run.Job().Defaults.Run.WorkingDirectory
+		}
+		if step.WorkingDirectory == "" {
+			step.WorkingDirectory = rc.Run.Workflow.Defaults.Run.WorkingDirectory
+		}
 		if step.WorkingDirectory != "" {
 			_, err = script.WriteString(fmt.Sprintf("cd %s\n", step.WorkingDirectory))
 			if err != nil {
@@ -126,6 +132,13 @@ func (sc *StepContext) setupShellCommand() common.Executor {
 		scriptName := fmt.Sprintf("workflow/%s", step.ID)
 		log.Debugf("Wrote command '%s' to '%s'", run, scriptName)
 		containerPath := fmt.Sprintf("/github/%s", scriptName)
+
+		if step.Shell == "" {
+			step.Shell = rc.Run.Job().Defaults.Run.Shell
+		}
+		if step.Shell == "" {
+			step.Shell = rc.Run.Workflow.Defaults.Run.Shell
+		}
 		sc.Cmd = strings.Fields(strings.Replace(step.ShellCommand(), "{0}", containerPath, 1))
 		return rc.JobContainer.Copy("/github/", &container.FileEntry{
 			Name: scriptName,

pkg/runner/testdata/defaults-run/main.yaml

@@ -0,0 +1,29 @@
+name: defaults-run
+on:
+  - push
+defaults:
+  run:
+    shell: sh
+jobs:
+  without-defaults:
+    runs-on: ubuntu-latest
+    steps:
+    - run: echo $SHELL | grep -v bash || exit 1
+  with-defaults:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: bash
+        working-directory: /tmp
+    steps:
+    - run: |
+        echo $SHELL | grep bash || exit 1
+        [ $(pwd) = /tmp ] || exit 2
+  override-in-step:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        shell: bash
+    steps:
+    - run: echo $SHELL | grep -v bash || exit 1
+      shell: sh