From 53f059ee8f55be99c927a5feede2f5e5b043fe0c Mon Sep 17 00:00:00 2001
From: Pete Bacon Darwin <pete@bacondarwin.com>
Date: Thu, 20 Feb 2020 21:40:56 +0100
Subject: [PATCH] fix(localize): improve placeholder mismatch error message
 (#35593)

The original error message was confusing since often it is the
translation that is at fault not the message.

PR Close #35593
---
 packages/localize/src/utils/src/translations.ts       | 3 ++-
 packages/localize/src/utils/test/translations_spec.ts | 7 +++++--
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/packages/localize/src/utils/src/translations.ts b/packages/localize/src/utils/src/translations.ts
index 2ad83cd9a0..4b5c51e346 100644
--- a/packages/localize/src/utils/src/translations.ts
+++ b/packages/localize/src/utils/src/translations.ts
@@ -68,7 +68,8 @@ export function translate(
         return message.substitutions[placeholder];
       } else {
         throw new Error(
-            `No placeholder found with name ${placeholder} in message ${describeMessage(message)}.`);
+            `There is a placeholder name mismatch with the translation provided for the message ${describeMessage(message)}.\n` +
+            `The translation contains a placeholder with name ${placeholder}, which does not exist in the message.`);
       }
     })
   ];
diff --git a/packages/localize/src/utils/test/translations_spec.ts b/packages/localize/src/utils/test/translations_spec.ts
index a4f7899659..267320534d 100644
--- a/packages/localize/src/utils/test/translations_spec.ts
+++ b/packages/localize/src/utils/test/translations_spec.ts
@@ -88,9 +88,12 @@ describe('utils', () => {
 
     it('should throw an error if the translation contains placeholders that are not in the message',
        () => {
-         expect(() => doTranslate({'abc': 'a{$PH}bc'}, parts `abc`))
+         expect(
+             () => doTranslate(
+                 {'abc{$INTERPOLATION}def': 'a{$PH}bc'}, parts `abc${1 + 2}:INTERPOLATION:def`))
              .toThrowError(
-                 'No placeholder found with name PH in message "2674653928643152084" ("abc").');
+                 `There is a placeholder name mismatch with the translation provided for the message "8986527425650846693" ("abc{$INTERPOLATION}def").\n` +
+                 `The translation contains a placeholder with name PH, which does not exist in the message.`);
        });
 
     it('(with identity translations) should render template literals as-is', () => {