fix(validation): catch OverlappingFieldsCanBeMergedRule violations with nested fragments (#4168) (#4199)

Author: yaacovCR

src/validation/__tests__/OverlappingFieldsCanBeMergedRule-test.ts

@@ -638,10 +638,10 @@ describe('Validate: Overlapping fields can be merged', () => {
     expectErrors(`
       {
         field {
-          ...F
+          ...I
         }
         field {
-          ...I
+          ...F
         }
       }
       fragment F on T {
@@ -661,14 +661,41 @@ describe('Validate: Overlapping fields can be merged', () => {
     `).toDeepEqual([
       {
         message:
-          'Fields "field" conflict because subfields "x" conflict because "a" and "b" are different fields and subfields "y" conflict because "c" and "d" are different fields. Use different aliases on the fields to fetch both if this was intentional.',
+          'Fields "field" conflict because subfields "y" conflict because "d" and "c" are different fields and subfields "x" conflict because "b" and "a" are different fields. Use different aliases on the fields to fetch both if this was intentional.',
         locations: [
           { line: 3, column: 9 },
-          { line: 11, column: 9 },
-          { line: 15, column: 9 },
-          { line: 6, column: 9 },
-          { line: 22, column: 9 },
           { line: 18, column: 9 },
+          { line: 22, column: 9 },
+          { line: 6, column: 9 },
+          { line: 15, column: 9 },
+          { line: 11, column: 9 },
+        ],
+      },
+    ]);
+  });
+
+  it('reports deep conflict after nested fragments', () => {
+    expectErrors(`
+      fragment F on T {
+        ...G
+      }
+      fragment G on T {
+        ...H
+      }
+      fragment H on T {
+        x: a
+      }
+      {
+        x: b
+        ...F
+      }
+    `).toDeepEqual([
+      {
+        message:
+          'Fields "x" conflict because "b" and "a" are different fields. Use different aliases on the fields to fetch both if this was intentional.',
+        locations: [
+          { line: 12, column: 9 },
+          { line: 9, column: 9 },
         ],
       },
     ]);
@@ -1265,6 +1292,33 @@ describe('Validate: Overlapping fields can be merged', () => {
     ]);
   });
 
+  it('does not infinite loop on recursive fragments separated by fields', () => {
+    expectValid(`
+      {
+        ...fragA
+        ...fragB
+      }
+
+      fragment fragA on T {
+        x {
+          ...fragA
+          x {
+            ...fragA
+          }
+        }
+      }
+
+      fragment fragB on T {
+        x {
+          ...fragB
+          x {
+            ...fragB
+          }
+        }
+      }
+    `);
+  });
+
   describe('fragment arguments must produce fields that can be merged', () => {
     it('allows conflicting spreads at different depths', () => {
       expectValid(`