fix(logging): report the cause of the error the line reports

Author: waleedlatif1

packages/logger/src/index.test.ts

@@ -224,6 +224,21 @@ describe('Logger', () => {
       expect(parsed.errorCode).toBe('57014')
     })
 
+    test('reports the cause of the same error the line reports when given two', () => {
+      const conflict = Object.assign(new Error('duplicate key value'), {
+        name: 'PostgresError',
+        code: '23505',
+      })
+      const second = new Error('Failed query: insert into "t" values ($1)', { cause: conflict })
+
+      createEnabledLogger().error('Retry failed', queryError('tbl_1'), second)
+
+      const parsed = JSON.parse(consoleErrorSpy.mock.calls[0][0] as string)
+      expect(parsed.error).toBe(second.message)
+      expect(parsed.errorCause).toBe('PostgresError: duplicate key value')
+      expect(parsed.errorCode).toBe('23505')
+    })
+
     test.each([
       ['an object field', (error: Error) => [{ error }]],
       ['a bare argument', (error: Error) => [error]],

packages/logger/src/index.ts

@@ -210,10 +210,15 @@ const formatObject = (obj: unknown, isDev: boolean): string => {
   }
 }
 
-/** The error a line is about: the first bare `Error` argument, else the first `{ error }` field. */
+/**
+ * The error a line is about, chosen as `mergeArgs` chooses it: the last bare
+ * `Error` argument, else the first `{ error }` field.
+ */
 const primaryError = (args: unknown[]): Error | undefined => {
-  const bare = args.find((arg) => arg instanceof Error)
-  if (bare) return bare as Error
+  for (let i = args.length - 1; i >= 0; i--) {
+    const arg = args[i]
+    if (arg instanceof Error) return arg
+  }
   for (const arg of args) {
     if (isRecordLike(arg) && arg.error instanceof Error) return arg.error
   }
@@ -238,13 +243,14 @@ const assignErrorCause = (entry: Record<string, unknown>, logged: LoggedError) =
  * cause and its code go in `errorCause` and `errorCode`.
  */
 const mergeArgs = (entry: Record<string, unknown>, args: unknown[]): Record<string, unknown> => {
+  /** The error whose stack the line carries; its cause is assigned last so a later error cannot inherit an earlier one's. */
+  let reported: LoggedError | undefined
   for (const arg of args) {
     if (arg === null || arg === undefined) continue
     if (arg instanceof Error) {
-      const logged = toLoggedError(arg)
-      entry.error = logged.message
-      entry.stack = logged.stack
-      assignErrorCause(entry, logged)
+      reported = toLoggedError(arg)
+      entry.error = reported.message
+      entry.stack = reported.stack
     } else if (typeof arg === 'object') {
       const source = arg as Record<string, unknown>
       for (const key of Object.keys(source)) {
@@ -254,7 +260,7 @@ const mergeArgs = (entry: Record<string, unknown>, args: unknown[]): Record<stri
           entry[key] = logged.message
           if (key === 'error' && entry.stack === undefined) {
             entry.stack = logged.stack
-            assignErrorCause(entry, logged)
+            reported = logged
           }
         } else {
           entry[key] = value
@@ -264,6 +270,7 @@ const mergeArgs = (entry: Record<string, unknown>, args: unknown[]): Record<stri
       entry.extra = arg
     }
   }
+  if (reported) assignErrorCause(entry, reported)
   return entry
 }