fix panic when digger is misconfigured (#1975)

* fix panic when digger is misconfigured

* add test

* handle shell error and add tests

Author: motatoes

libs/digger_config/digger_config_test.go

@@ -319,6 +319,84 @@ workflows:
 	assert.Equal(t, Step{Action: "plan", ExtraArgs: []string{"-var-file=vars/dev.tfvars"}, Shell: ""}, dg.Workflows["default"].Plan.Steps[2], "parsed struct does not match expected struct")
 }
 
+func TestProjectWithMisconfiguredRunStepThrowsError(t *testing.T) {
+	tempDir, teardown := setUp()
+	defer teardown()
+
+	diggerCfg := `
+projects:
+  - name: "dev"
+    dir: "dev"
+  - name: "staging"
+    dir: "staging"
+  - name: "prod"
+    dir: "prod"
+workflows:
+  default:
+    workflow_configuration:
+      on_pull_request_pushed: ["digger plan"]
+      on_pull_request_closed: ["digger unlock"]
+      on_commit_to_default: ["digger unlock"]
+    plan:
+      steps:
+      - init:
+          extra_args: ["-backend-config=tf_backend.tfbackend" ]
+      - run:
+          command: terragrunt plan -input=false -out=$PLANFILE
+    apply:
+      steps:
+      - init:
+          extra_args: ["-backend-config=tf_backend.tfbackend" ]
+      - apply:
+`
+	deleteFile := createFile(path.Join(tempDir, "digger.yaml"), diggerCfg)
+	defer deleteFile()
+
+	_, _, _, err := LoadDiggerConfig(tempDir, true, nil)
+	assert.Error(t, err, "expected error to be raised")
+	assert.Contains(t, err.Error(), "step.run must be a string")
+}
+
+func TestProjectWithMisconfiguredRunShellMisconfiguredThrowsError(t *testing.T) {
+	tempDir, teardown := setUp()
+	defer teardown()
+
+	diggerCfg := `
+projects:
+  - name: "dev"
+    dir: "dev"
+  - name: "staging"
+    dir: "staging"
+  - name: "prod"
+    dir: "prod"
+workflows:
+  default:
+    workflow_configuration:
+      on_pull_request_pushed: ["digger plan"]
+      on_pull_request_closed: ["digger unlock"]
+      on_commit_to_default: ["digger unlock"]
+    plan:
+      steps:
+      - init:
+          extra_args: ["-backend-config=tf_backend.tfbackend" ]
+      - run: terragrunt plan -input=false -out=$PLANFILE
+        shell:
+          - incorrect
+          - "bash"
+    apply:
+      steps:
+      - init:
+          extra_args: ["-backend-config=tf_backend.tfbackend" ]
+      - apply:
+`
+	deleteFile := createFile(path.Join(tempDir, "digger.yaml"), diggerCfg)
+	defer deleteFile()
+
+	_, _, _, err := LoadDiggerConfig(tempDir, true, nil)
+	assert.Error(t, err, "expected error to be raised")
+	assert.Contains(t, err.Error(), "step.run.shell must be a string")
+}
+
 func TestDiggerGenerateProjects(t *testing.T) {
 	tempDir, teardown := setUp()
 	defer teardown()

libs/digger_config/yaml.go

@@ -2,6 +2,7 @@ package digger_config
 
 import (
 	"errors"
+	"fmt"
 
 	"gopkg.in/yaml.v3"
 )
@@ -260,9 +261,17 @@ func (s *StepYaml) UnmarshalYAML(value *yaml.Node) error {
 
 	if _, ok := stepMap["run"]; ok {
 		s.Action = "run"
-		s.Value = stepMap["run"].(string)
+		v, ok := stepMap["run"].(string)
+		if !ok {
+			return fmt.Errorf("step.run must be a string, but got %T", stepMap["run"])
+		}
+		s.Value = v
 		if _, ok := stepMap["shell"]; ok {
-			s.Shell = stepMap["shell"].(string)
+			shell, ok := stepMap["shell"].(string)
+			if !ok {
+				return fmt.Errorf("step.run.shell must be a string, but got %T", stepMap["shell"])
+			}
+			s.Shell = shell
 		}
 		return nil
 	}