From 9d3ec06dfcdaa3ebe1c7ab6643600e0918dcaa8d Mon Sep 17 00:00:00 2001
From: Dharmik <dharmik.gangani17@gmail.com>
Date: Thu, 9 Oct 2025 21:36:52 -0300
Subject: [PATCH] support configurable

Signed-off-by: Dharmik <dharmik.gangani17@gmail.com>
---
 .changeset/easy-hands-grow.md                             | 6 ++++++
 .../src/processors/PlaceholderProcessor.ts                | 6 +++++-
 plugins/catalog-node/src/processing/parse.ts              | 8 ++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/easy-hands-grow.md

diff --git a/.changeset/easy-hands-grow.md b/.changeset/easy-hands-grow.md
new file mode 100644
index 0000000000..fc3cfd96e1
--- /dev/null
+++ b/.changeset/easy-hands-grow.md
@@ -0,0 +1,6 @@
+---
+'@backstage/plugin-catalog-backend': minor
+'@backstage/plugin-catalog-node': minor
+---
+
+Make YAML merge (<<:) support configurable in the Backstage Catalog instead of always being enabled
diff --git a/plugins/catalog-backend/src/processors/PlaceholderProcessor.ts b/plugins/catalog-backend/src/processors/PlaceholderProcessor.ts
index acc833947e..b1b5493778 100644
--- a/plugins/catalog-backend/src/processors/PlaceholderProcessor.ts
+++ b/plugins/catalog-backend/src/processors/PlaceholderProcessor.ts
@@ -138,9 +138,13 @@ export async function yamlPlaceholderResolver(
 
   params.emit(processingResult.refresh(`url:${url}`));
 
+  // YAML merge support False by default
+  const enableYamlMerge = false;
+  const parseOptions = { merge: enableYamlMerge };
+
   let documents: yaml.Document.Parsed[];
   try {
-    documents = yaml.parseAllDocuments(content, { merge: true }).filter(d => d);
+    documents = yaml.parseAllDocuments(content, parseOptions).filter(d => d);
   } catch (e) {
     throw new Error(
       `Placeholder \$${params.key} failed to parse YAML data at ${params.value}, ${e}`,
diff --git a/plugins/catalog-node/src/processing/parse.ts b/plugins/catalog-node/src/processing/parse.ts
index 2ef276d06d..4647dc8afc 100644
--- a/plugins/catalog-node/src/processing/parse.ts
+++ b/plugins/catalog-node/src/processing/parse.ts
@@ -21,6 +21,10 @@ import { LocationSpec } from '@backstage/plugin-catalog-common';
 import { CatalogProcessorResult } from '../api/processor';
 import { processingResult } from '../api/processingResult';
 
+export interface ParseEntityYamlOptions {
+  enableYamlMerge?: boolean;
+}
+
 /**
  * A helper function that parses a YAML file, properly handling multiple
  * documents in a single file.
@@ -40,12 +44,16 @@ import { processingResult } from '../api/processingResult';
 export function* parseEntityYaml(
   data: string | Buffer,
   location: LocationSpec,
+  options?: ParseEntityYamlOptions,
 ): Iterable<CatalogProcessorResult> {
+  const parseOptions = { merge: options?.enableYamlMerge ?? false };
+
   let documents: yaml.Document.Parsed[];
   try {
     documents = yaml
       .parseAllDocuments(
         typeof data === 'string' ? data : data.toString('utf8'),
+        parseOptions,
       )
       .filter(d => d);
   } catch (e) {