From 4390f68285d00bfefd7769e209c7d70a964e095b Mon Sep 17 00:00:00 2001
From: domi <domi7777@hotmail.com>
Date: Tue, 20 Nov 2018 15:51:53 +0100
Subject: [PATCH 1/5] Add more information in conversion error

---
 src/execution/execute.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/execution/execute.js b/src/execution/execute.js
index ccf2bf3d2f..71d7cf165f 100644
--- a/src/execution/execute.js
+++ b/src/execution/execute.js
@@ -865,7 +865,7 @@ function completeValue(
       throw new Error(
         `Cannot return null for non-nullable field ${info.parentType.name}.${
           info.fieldName
-        }.`,
+        }. Value ${result} cannot be converted to ${returnType.ofType.name}`,
       );
     }
     return completed;

From 62af8b6b2ad15ec5941d62fde25a9fdd7f4e6a97 Mon Sep 17 00:00:00 2001
From: domi <domi7777@hotmail.com>
Date: Wed, 21 Nov 2018 09:07:04 +0100
Subject: [PATCH 2/5] Update execute.js

Add more information in conversion error: fix pipeline
---
 src/execution/execute.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/execution/execute.js b/src/execution/execute.js
index 71d7cf165f..16afdadba6 100644
--- a/src/execution/execute.js
+++ b/src/execution/execute.js
@@ -865,7 +865,7 @@ function completeValue(
       throw new Error(
         `Cannot return null for non-nullable field ${info.parentType.name}.${
           info.fieldName
-        }. Value ${result} cannot be converted to ${returnType.ofType.name}`,
+        }. Value ${inspect(result)} cannot be converted to ${inspect(returnType)}`,
       );
     }
     return completed;

From 3ea33bff16130246b06754d9b40e52741d48e715 Mon Sep 17 00:00:00 2001
From: Dominique Loiseau <dominique.loiseau.ext@proximus.com>
Date: Wed, 21 Nov 2018 09:15:21 +0100
Subject: [PATCH 3/5] Add more information in conversion error: lint

---
 src/execution/execute.js | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/execution/execute.js b/src/execution/execute.js
index 16afdadba6..63c451bd52 100644
--- a/src/execution/execute.js
+++ b/src/execution/execute.js
@@ -865,7 +865,9 @@ function completeValue(
       throw new Error(
         `Cannot return null for non-nullable field ${info.parentType.name}.${
           info.fieldName
-        }. Value ${inspect(result)} cannot be converted to ${inspect(returnType)}`,
+        }. Value ${inspect(result)} cannot be converted to ${inspect(
+          returnType,
+        )}`,
       );
     }
     return completed;

From b585c4c40d21f7abafb174182963bf9eb86d00c7 Mon Sep 17 00:00:00 2001
From: Dominique Loiseau <dominique.loiseau.ext@proximus.com>
Date: Wed, 21 Nov 2018 09:34:44 +0100
Subject: [PATCH 4/5] Add more information in conversion error: fix tests

---
 src/execution/__tests__/lists-test.js   | 20 ++++++++++----------
 src/execution/__tests__/nonnull-test.js | 14 +++++++-------
 2 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/src/execution/__tests__/lists-test.js b/src/execution/__tests__/lists-test.js
index feab126922..b607b66313 100644
--- a/src/execution/__tests__/lists-test.js
+++ b/src/execution/__tests__/lists-test.js
@@ -210,7 +210,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to [Int]!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test'],
             },
@@ -239,7 +239,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to [Int]!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test'],
             },
@@ -313,7 +313,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -337,7 +337,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -380,7 +380,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -424,7 +424,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -439,7 +439,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to [Int!]!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test'],
             },
@@ -461,7 +461,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -476,7 +476,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to [Int!]!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test'],
             },
@@ -514,7 +514,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test.',
+                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
diff --git a/src/execution/__tests__/nonnull-test.js b/src/execution/__tests__/nonnull-test.js
index c7795bfff7..3209a5e9b4 100644
--- a/src/execution/__tests__/nonnull-test.js
+++ b/src/execution/__tests__/nonnull-test.js
@@ -177,7 +177,7 @@ describe('Execute: handles non-nullable types', () => {
         errors: [
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull.',
+              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
             path: ['syncNest', 'syncNonNull'],
             locations: [{ line: 4, column: 11 }],
           },
@@ -216,7 +216,7 @@ describe('Execute: handles non-nullable types', () => {
         errors: [
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull.',
+              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
             path: ['promiseNest', 'syncNonNull'],
             locations: [{ line: 4, column: 11 }],
           },
@@ -409,7 +409,7 @@ describe('Execute: handles non-nullable types', () => {
         errors: [
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull.',
+              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
             path: [
               'syncNest',
               'syncNonNullNest',
@@ -422,7 +422,7 @@ describe('Execute: handles non-nullable types', () => {
           },
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull.',
+              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
             path: [
               'promiseNest',
               'syncNonNullNest',
@@ -435,7 +435,7 @@ describe('Execute: handles non-nullable types', () => {
           },
           {
             message:
-              'Cannot return null for non-nullable field DataType.promiseNonNull.',
+              'Cannot return null for non-nullable field DataType.promiseNonNull. Value null cannot be converted to String!',
             path: [
               'anotherNest',
               'syncNonNullNest',
@@ -448,7 +448,7 @@ describe('Execute: handles non-nullable types', () => {
           },
           {
             message:
-              'Cannot return null for non-nullable field DataType.promiseNonNull.',
+              'Cannot return null for non-nullable field DataType.promiseNonNull. Value null cannot be converted to String!',
             path: [
               'anotherPromiseNest',
               'syncNonNullNest',
@@ -535,7 +535,7 @@ describe('Execute: handles non-nullable types', () => {
         errors: [
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull.',
+              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
             path: ['syncNonNull'],
             locations: [{ line: 3, column: 9 }],
           },

From 8bad454757377d6bc3296a29057c70784aaacc26 Mon Sep 17 00:00:00 2001
From: Ivan Goncharov <ivan.goncharov.ua@gmail.com>
Date: Tue, 5 Feb 2019 20:20:22 +0200
Subject: [PATCH 5/5] Switch to having more granular errors

---
 src/execution/__tests__/lists-test.js   | 20 ++++++++++----------
 src/execution/__tests__/nonnull-test.js | 14 +++++++-------
 src/execution/execute.js                | 19 ++++++++++++-------
 3 files changed, 29 insertions(+), 24 deletions(-)

diff --git a/src/execution/__tests__/lists-test.js b/src/execution/__tests__/lists-test.js
index b607b66313..feab126922 100644
--- a/src/execution/__tests__/lists-test.js
+++ b/src/execution/__tests__/lists-test.js
@@ -210,7 +210,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to [Int]!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test'],
             },
@@ -239,7 +239,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to [Int]!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test'],
             },
@@ -313,7 +313,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -337,7 +337,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -380,7 +380,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -424,7 +424,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -439,7 +439,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to [Int!]!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test'],
             },
@@ -461,7 +461,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
@@ -476,7 +476,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to [Int!]!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test'],
             },
@@ -514,7 +514,7 @@ describe('Execute: Handles list nullability', () => {
           errors: [
             {
               message:
-                'Cannot return null for non-nullable field DataType.test. Value null cannot be converted to Int!',
+                'Cannot return null for non-nullable field DataType.test.',
               locations: [{ line: 1, column: 10 }],
               path: ['nest', 'test', 1],
             },
diff --git a/src/execution/__tests__/nonnull-test.js b/src/execution/__tests__/nonnull-test.js
index 3209a5e9b4..c7795bfff7 100644
--- a/src/execution/__tests__/nonnull-test.js
+++ b/src/execution/__tests__/nonnull-test.js
@@ -177,7 +177,7 @@ describe('Execute: handles non-nullable types', () => {
         errors: [
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
+              'Cannot return null for non-nullable field DataType.syncNonNull.',
             path: ['syncNest', 'syncNonNull'],
             locations: [{ line: 4, column: 11 }],
           },
@@ -216,7 +216,7 @@ describe('Execute: handles non-nullable types', () => {
         errors: [
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
+              'Cannot return null for non-nullable field DataType.syncNonNull.',
             path: ['promiseNest', 'syncNonNull'],
             locations: [{ line: 4, column: 11 }],
           },
@@ -409,7 +409,7 @@ describe('Execute: handles non-nullable types', () => {
         errors: [
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
+              'Cannot return null for non-nullable field DataType.syncNonNull.',
             path: [
               'syncNest',
               'syncNonNullNest',
@@ -422,7 +422,7 @@ describe('Execute: handles non-nullable types', () => {
           },
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
+              'Cannot return null for non-nullable field DataType.syncNonNull.',
             path: [
               'promiseNest',
               'syncNonNullNest',
@@ -435,7 +435,7 @@ describe('Execute: handles non-nullable types', () => {
           },
           {
             message:
-              'Cannot return null for non-nullable field DataType.promiseNonNull. Value null cannot be converted to String!',
+              'Cannot return null for non-nullable field DataType.promiseNonNull.',
             path: [
               'anotherNest',
               'syncNonNullNest',
@@ -448,7 +448,7 @@ describe('Execute: handles non-nullable types', () => {
           },
           {
             message:
-              'Cannot return null for non-nullable field DataType.promiseNonNull. Value null cannot be converted to String!',
+              'Cannot return null for non-nullable field DataType.promiseNonNull.',
             path: [
               'anotherPromiseNest',
               'syncNonNullNest',
@@ -535,7 +535,7 @@ describe('Execute: handles non-nullable types', () => {
         errors: [
           {
             message:
-              'Cannot return null for non-nullable field DataType.syncNonNull. Value null cannot be converted to String!',
+              'Cannot return null for non-nullable field DataType.syncNonNull.',
             path: ['syncNonNull'],
             locations: [{ line: 3, column: 9 }],
           },
diff --git a/src/execution/execute.js b/src/execution/execute.js
index 63c451bd52..08d2ff79c2 100644
--- a/src/execution/execute.js
+++ b/src/execution/execute.js
@@ -862,13 +862,18 @@ function completeValue(
       result,
     );
     if (completed === null) {
-      throw new Error(
-        `Cannot return null for non-nullable field ${info.parentType.name}.${
-          info.fieldName
-        }. Value ${inspect(result)} cannot be converted to ${inspect(
-          returnType,
-        )}`,
-      );
+      if (result == null) {
+        throw new Error(
+          `Cannot return null for non-nullable field ` +
+            `${info.parentType.name}.${info.fieldName}.`,
+        );
+      } else {
+        throw new Error(
+          `Cannot coerce '${inspect(result)}' into type ` +
+            `${inspect(returnType)} for non-nullable field ` +
+            `${info.parentType.name}.${info.fieldName}`,
+        );
+      }
     }
     return completed;
   }