Rescue format errors when parsing workflows yaml

src/api/app/models/token/errors.rb

@@ -24,4 +24,8 @@ class SCMTokenInvalid < APIError
   class WorkflowsYamlNotParsable < APIError
     setup 400
   end
+
+  class WorkflowsYamlFormatError < APIError
+    setup 400
+  end
 end

src/api/app/services/workflows/yaml_to_workflows_service.rb

@@ -21,7 +21,7 @@ def call
     def create_workflows
       begin
         parsed_workflows_yaml = YAML.safe_load(parse_workflows_file(@yaml_file))
-      rescue Psych::SyntaxError => e
+      rescue Psych::SyntaxError, Token::Errors::WorkflowsYamlFormatError => e
         raise Token::Errors::WorkflowsYamlNotParsable, "Unable to parse #{@token.workflow_configuration_path}: #{e.message}"
       end
 
@@ -47,7 +47,11 @@ def parse_workflows_file(file_path)
 
       # Mapping the placeholder variables to their values from the webhook event payload
       placeholder_variables = SUPPORTED_PLACEHOLDER_VARIABLES.zip([scm_organization_name, scm_repository_name, pr_number, commit_sha]).to_h
-      format(workflows_file_content, placeholder_variables)
+      begin
+        format(workflows_file_content, placeholder_variables)
+      rescue ArgumentError => e
+        raise Token::Errors::WorkflowsYamlFormatError, e.message
+      end
     end
   end
 end

src/api/spec/services/workflows/yaml_to_workflows_service_spec.rb

@@ -83,5 +83,14 @@
         expect { subject }.to raise_error(Token::Errors::WorkflowsYamlNotParsable)
       end
     end
+
+    context 'with invalid placeholder variables' do
+      let(:workflows_yml_file) { Rails.root.join('spec/support/files/unparsable_workflows_placeholders.yml').expand_path }
+      let(:payload) { github_extractor_payload }
+
+      it 'raises a user-friendly error' do
+        expect { subject }.to raise_error(Token::Errors::WorkflowsYamlNotParsable, 'Unable to parse .obs/workflows.yml: malformed format string - %S')
+      end
+    end
   end
 end

src/api/spec/support/files/unparsable_workflows_placeholders.yml

@@ -0,0 +1,12 @@
+workflow123:
+  steps:
+    - branch_package:
+        source_project: "test-project:%SCM_ORGANIZATION_NAME"
+        source_package: "test-package:%u"
+        target_project: "test-target-project"
+  filters:
+    branches:
+      only:
+        - 'main'
+        - 'master'
+        - 'source'