fix: refactor error handling around loading in tasks (#108)

## Description

Make the error more obvious if a run command is failing because the file
doesnt exist rather than there is an issue with the yaml itself.

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Other (security config, docs update, etc)

## Checklist before merging

- [x] Test, docs, adr added or updated as needed
- [x] [Contributor Guide
Steps](https://github.com/defenseunicorns/maru-runner/blob/main/CONTRIBUTING.md)
followed

---------

Co-authored-by: Wayne Starr <Racer159@users.noreply.github.com>

src/cmd/run.go

@@ -53,7 +53,7 @@ var runCmd = &cobra.Command{
 
 		err := utils.ReadYaml(config.TaskFileLocation, &tasksFile)
 		if err != nil {
-			message.Fatalf(err, "Cannot unmarshal %s", config.TaskFileLocation)
+			message.Fatalf(err, "Failed to open file: %s", err.Error())
 		}
 
 		// ensure vars are uppercase
@@ -190,7 +190,7 @@ func loadTasksFromLocalIncludes(includeFileLocation string) types.TasksFile {
 	}
 	err := utils.ReadYaml(fullPath, &includedTasksFile)
 	if err != nil {
-		message.Fatalf(err, "Cannot unmarshal %s", fullPath)
+		message.Fatalf(err, "Failed to load file: %s", err.Error())
 	}
 	return includedTasksFile
 }

src/pkg/runner/runner.go

@@ -132,7 +132,7 @@ func (r *Runner) importTasks(includes []map[string]string, dir string, setVariab
 		}
 
 		if err := utils.ReadYaml(includePath, &tasksFile); err != nil {
-			return fmt.Errorf("unable to read included file %s: %w", includePath, err)
+			return fmt.Errorf("unable to read included file: %w", err)
 		}
 
 		// prefix task names and actions with the includes key

src/pkg/utils/utils.go

@@ -82,10 +82,15 @@ func FormatEnvVar(name, value string) string {
 func ReadYaml(path string, destConfig any) error {
 	file, err := os.ReadFile(path)
 	if err != nil {
-		return err
+		return fmt.Errorf("cannot %s", err.Error())
 	}
-
-	return goyaml.Unmarshal(file, destConfig)
+	err = goyaml.Unmarshal(file, destConfig)
+	if err != nil {
+		errStr := err.Error()
+		lines := strings.SplitN(errStr, "\n", 2)
+		return fmt.Errorf("cannot unmarshal %s: %s", path, lines[0])
+	}
+	return nil
 }
 
 // MakeTempDir creates a temp directory with the maru- prefix.