From f5336f07b2148c602ba74acdd964ca4f70722577 Mon Sep 17 00:00:00 2001
From: Harrison Hogg <hhogg@spotify.com>
Date: Tue, 26 Nov 2024 11:54:29 +0000
Subject: [PATCH 1/2] Fixed WinstongLogger logging fields which are not
 castable to a string

Signed-off-by: Harrison Hogg <hhogg@spotify.com>
---
 .../rootLogger/WinstonLogger.test.ts          | 24 +++++++++++++++++++
 .../entrypoints/rootLogger/WinstonLogger.ts   | 15 ++++++++----
 2 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/packages/backend-defaults/src/entrypoints/rootLogger/WinstonLogger.test.ts b/packages/backend-defaults/src/entrypoints/rootLogger/WinstonLogger.test.ts
index 0f9e079943..ec46f22759 100644
--- a/packages/backend-defaults/src/entrypoints/rootLogger/WinstonLogger.test.ts
+++ b/packages/backend-defaults/src/entrypoints/rootLogger/WinstonLogger.test.ts
@@ -93,4 +93,28 @@ describe('WinstonLogger', () => {
       expect.any(Function),
     );
   });
+
+  it('gracefully handles fields that are not castable to a string', () => {
+    const mockTransport = new Transport({
+      log: jest.fn(),
+      logv: jest.fn(),
+    });
+
+    const logger = WinstonLogger.create({
+      transports: [mockTransport],
+    });
+
+    logger.error('something went wrong', {
+      field: Object.create(null),
+    });
+
+    expect(mockTransport.log).toHaveBeenCalledWith(
+      expect.objectContaining({
+        [MESSAGE]: expect.stringContaining(
+          '[field value not castable to string]',
+        ),
+      }),
+      expect.any(Function),
+    );
+  });
 });
diff --git a/packages/backend-defaults/src/entrypoints/rootLogger/WinstonLogger.ts b/packages/backend-defaults/src/entrypoints/rootLogger/WinstonLogger.ts
index 38d05f6511..9f7532e66b 100644
--- a/packages/backend-defaults/src/entrypoints/rootLogger/WinstonLogger.ts
+++ b/packages/backend-defaults/src/entrypoints/rootLogger/WinstonLogger.ts
@@ -147,10 +147,17 @@ export class WinstonLogger implements RootLoggerService {
         const prefixColor = colorizer.colorize('prefix', prefix);
 
         const extraFields = Object.entries(fields)
-          .map(
-            ([key, value]) =>
-              `${colorizer.colorize('field', `${key}`)}=${value}`,
-          )
+          .map(([key, value]) => {
+            let stringValue = '';
+
+            try {
+              stringValue = `${value}`;
+            } catch (e) {
+              stringValue = '[field value not castable to string]';
+            }
+
+            return `${colorizer.colorize('field', `${key}`)}=${stringValue}`;
+          })
           .join(' ');
 
         return `${timestampColor} ${prefixColor} ${level} ${message} ${extraFields}`;

From cf627c6c5470e50d8bad1de16586518079c287dd Mon Sep 17 00:00:00 2001
From: Harrison Hogg <hhogg@spotify.com>
Date: Tue, 26 Nov 2024 12:06:40 +0000
Subject: [PATCH 2/2] Added changeset

Signed-off-by: Harrison Hogg <hhogg@spotify.com>
---
 .changeset/ten-keys-nail.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/ten-keys-nail.md

diff --git a/.changeset/ten-keys-nail.md b/.changeset/ten-keys-nail.md
new file mode 100644
index 0000000000..0662e4a346
--- /dev/null
+++ b/.changeset/ten-keys-nail.md
@@ -0,0 +1,5 @@
+---
+'@backstage/backend-defaults': patch
+---
+
+Fixed an issue in the WinstonLogger where Errors thrown and given to logger.error with field values that could not be cast to a string would throw a TypeError