Simplify wording of key warning (#14503)

I don't think "array or iterator" is adding anything, and it may well be confusing, especially since this is one of the first and most common warnings that devs see.

packages/react-dom/src/__tests__/ReactFunctionComponent-test.js

@@ -354,7 +354,7 @@ describe('ReactFunctionComponent', () => {
     }
 
     expect(() => ReactTestUtils.renderIntoDocument(<Child />)).toWarnDev(
-      'Each child in an array or iterator should have a unique "key" prop.\n\n' +
+      'Each child in a list should have a unique "key" prop.\n\n' +
         'Check the render method of `Child`.',
     );
   });

packages/react-dom/src/__tests__/ReactMultiChildText-test.js

@@ -162,8 +162,8 @@ describe('ReactMultiChildText', () => {
         ['', 'foo', <div>{true}{<div />}{1.2}{''}</div>, 'foo'], ['', 'foo', <div />, 'foo'],
       ]);
     }).toWarnDev([
-      'Warning: Each child in an array or iterator should have a unique "key" prop.',
+      'Warning: Each child in a list should have a unique "key" prop.',
-      'Warning: Each child in an array or iterator should have a unique "key" prop.',
+      'Warning: Each child in a list should have a unique "key" prop.',
     ]);
   });
 

packages/react-reconciler/src/ReactChildFiber.js

@@ -80,7 +80,7 @@ if (__DEV__) {
     child._store.validated = true;
 
     const currentComponentErrorInfo =
-      'Each child in an array or iterator should have a unique ' +
+      'Each child in a list should have a unique ' +
       '"key" prop. See https://fb.me/react-warning-keys for ' +
       'more information.' +
       getCurrentFiberStackInDev();
@@ -91,7 +91,7 @@ if (__DEV__) {
 
     warning(
       false,
-      'Each child in an array or iterator should have a unique ' +
+      'Each child in a list should have a unique ' +
         '"key" prop. See https://fb.me/react-warning-keys for ' +
         'more information.',
     );

packages/react-reconciler/src/__tests__/ReactFragment-test.js

@@ -709,7 +709,7 @@ describe('ReactFragment', () => {
 
     ReactNoop.render(<Foo condition={false} />);
     expect(ReactNoop.flush).toWarnDev(
-      'Each child in an array or iterator should have a unique "key" prop.',
+      'Each child in a list should have a unique "key" prop.',
     );
 
     expect(ops).toEqual([]);
@@ -753,12 +753,12 @@ describe('ReactFragment', () => {
 
     ReactNoop.render(<Foo condition={true} />);
     expect(ReactNoop.flush).toWarnDev(
-      'Each child in an array or iterator should have a unique "key" prop.',
+      'Each child in a list should have a unique "key" prop.',
     );
 
     ReactNoop.render(<Foo condition={false} />);
     expect(ReactNoop.flush).toWarnDev(
-      'Each child in an array or iterator should have a unique "key" prop.',
+      'Each child in a list should have a unique "key" prop.',
     );
 
     expect(ops).toEqual(['Update Stateful']);
@@ -766,7 +766,7 @@ describe('ReactFragment', () => {
 
     ReactNoop.render(<Foo condition={true} />);
     expect(ReactNoop.flush).toWarnDev(
-      'Each child in an array or iterator should have a unique "key" prop.',
+      'Each child in a list should have a unique "key" prop.',
     );
 
     expect(ops).toEqual(['Update Stateful', 'Update Stateful']);

packages/react/src/ReactElementValidator.js

@@ -126,7 +126,7 @@ function validateExplicitKey(element, parentType) {
   if (__DEV__) {
     warning(
       false,
-      'Each child in an array or iterator should have a unique "key" prop.' +
+      'Each child in a list should have a unique "key" prop.' +
         '%s%s See https://fb.me/react-warning-keys for more information.',
       currentComponentErrorInfo,
       childOwner,

packages/react/src/__tests__/ReactChildren-test.js

@@ -320,7 +320,7 @@ describe('ReactChildren', () => {
 
     let instance;
     expect(() => (instance = <div>{threeDivIterable}</div>)).toWarnDev(
-      'Warning: Each child in an array or iterator should have a unique "key" prop.',
+      'Warning: Each child in a list should have a unique "key" prop.',
     );
 
     function assertCalls() {
@@ -905,7 +905,7 @@ describe('ReactChildren', () => {
         ReactTestUtils.renderIntoDocument(<ComponentReturningArray />),
       ).toWarnDev(
         'Warning: ' +
-          'Each child in an array or iterator should have a unique "key" prop.' +
+          'Each child in a list should have a unique "key" prop.' +
           ' See https://fb.me/react-warning-keys for more information.' +
           '\n    in ComponentReturningArray (at **)',
       );
@@ -926,7 +926,7 @@ describe('ReactChildren', () => {
         ReactTestUtils.renderIntoDocument([<div />, <div />]),
       ).toWarnDev(
         'Warning: ' +
-          'Each child in an array or iterator should have a unique "key" prop.' +
+          'Each child in a list should have a unique "key" prop.' +
           ' See https://fb.me/react-warning-keys for more information.',
         {withoutStack: true}, // There's nothing on the stack
       );

packages/react/src/__tests__/ReactElementClone-test.js

@@ -259,9 +259,7 @@ describe('ReactElementClone', () => {
   it('warns for keys for arrays of elements in rest args', () => {
     expect(() =>
       React.cloneElement(<div />, null, [<div />, <div />]),
-    ).toWarnDev(
+    ).toWarnDev('Each child in a list should have a unique "key" prop.');
-      'Each child in an array or iterator should have a unique "key" prop.',
-    );
   });
 
   it('does not warns for arrays of elements with keys', () => {

packages/react/src/__tests__/ReactElementValidator-test.internal.js

@@ -42,9 +42,7 @@ describe('ReactElementValidator', () => {
 
     expect(() => {
       Component(null, [Component(), Component()]);
-    }).toWarnDev(
+    }).toWarnDev('Each child in a list should have a unique "key" prop.');
-      'Each child in an array or iterator should have a unique "key" prop.',
-    );
   });
 
   it('warns for keys for arrays of elements with owner info', () => {
@@ -67,7 +65,7 @@ describe('ReactElementValidator', () => {
     expect(() => {
       ReactTestUtils.renderIntoDocument(React.createElement(ComponentWrapper));
     }).toWarnDev(
-      'Each child in an array or iterator should have a unique "key" prop.' +
+      'Each child in a list should have a unique "key" prop.' +
         '\n\nCheck the render method of `InnerClass`. ' +
         'It was passed a child from ComponentWrapper. ',
     );
@@ -84,7 +82,7 @@ describe('ReactElementValidator', () => {
     expect(() => {
       ReactTestUtils.renderIntoDocument(<Anonymous>{divs}</Anonymous>);
     }).toWarnDev(
-      'Warning: Each child in an array or iterator should have a unique ' +
+      'Warning: Each child in a list should have a unique ' +
         '"key" prop. See https://fb.me/react-warning-keys for more information.\n' +
         '    in div (at **)',
     );
@@ -96,7 +94,7 @@ describe('ReactElementValidator', () => {
     expect(() => {
       ReactTestUtils.renderIntoDocument(<div>{divs}</div>);
     }).toWarnDev(
-      'Warning: Each child in an array or iterator should have a unique ' +
+      'Warning: Each child in a list should have a unique ' +
         '"key" prop.\n\nCheck the top-level render call using <div>. See ' +
         'https://fb.me/react-warning-keys for more information.\n' +
         '    in div (at **)',
@@ -117,7 +115,7 @@ describe('ReactElementValidator', () => {
     }
 
     expect(() => ReactTestUtils.renderIntoDocument(<GrandParent />)).toWarnDev(
-      'Warning: Each child in an array or iterator should have a unique ' +
+      'Warning: Each child in a list should have a unique ' +
         '"key" prop.\n\nCheck the render method of `Component`. See ' +
         'https://fb.me/react-warning-keys for more information.\n' +
         '    in div (at **)\n' +
@@ -161,7 +159,7 @@ describe('ReactElementValidator', () => {
     };
 
     expect(() => Component(null, iterable)).toWarnDev(
-      'Each child in an array or iterator should have a unique "key" prop.',
+      'Each child in a list should have a unique "key" prop.',
     );
   });
 

packages/react/src/__tests__/ReactJSXElementValidator-test.js

@@ -48,9 +48,7 @@ describe('ReactJSXElementValidator', () => {
       ReactTestUtils.renderIntoDocument(
         <Component>{[<Component />, <Component />]}</Component>,
       ),
-    ).toWarnDev(
+    ).toWarnDev('Each child in a list should have a unique "key" prop.');
-      'Each child in an array or iterator should have a unique "key" prop.',
-    );
   });
 
   it('warns for keys for arrays of elements with owner info', () => {
@@ -69,7 +67,7 @@ describe('ReactJSXElementValidator', () => {
     expect(() =>
       ReactTestUtils.renderIntoDocument(<ComponentWrapper />),
     ).toWarnDev(
-      'Each child in an array or iterator should have a unique "key" prop.' +
+      'Each child in a list should have a unique "key" prop.' +
         '\n\nCheck the render method of `InnerComponent`. ' +
         'It was passed a child from ComponentWrapper. ',
     );
@@ -90,9 +88,7 @@ describe('ReactJSXElementValidator', () => {
 
     expect(() =>
       ReactTestUtils.renderIntoDocument(<Component>{iterable}</Component>),
-    ).toWarnDev(
+    ).toWarnDev('Each child in a list should have a unique "key" prop.');
-      'Each child in an array or iterator should have a unique "key" prop.',
-    );
   });
 
   it('does not warn for arrays of elements with keys', () => {