warn about duplicate attributes in jsx elements

Author: evanw

internal/bundler/bundler_default_test.go

@@ -5412,14 +5412,14 @@ func TestDuplicatePropertyWarning(t *testing.T) {
 				import './outside-node-modules'
 				import 'inside-node-modules'
 			`,
-			"/outside-node-modules/index.js": `
-				console.log({ a: 1, a: 2 })
+			"/outside-node-modules/index.jsx": `
+				console.log({ a: 1, a: 2 }, <div a2 a2={3}/>)
 			`,
 			"/outside-node-modules/package.json": `
 				{ "b": 1, "b": 2 }
 			`,
-			"/node_modules/inside-node-modules/index.js": `
-				console.log({ c: 1, c: 2 })
+			"/node_modules/inside-node-modules/index.jsx": `
+				console.log({ c: 1, c: 2 }, <div c2 c2={3}/>)
 			`,
 			"/node_modules/inside-node-modules/package.json": `
 				{ "d": 1, "d": 2 }
@@ -5430,8 +5430,10 @@ func TestDuplicatePropertyWarning(t *testing.T) {
 			Mode:         config.ModeBundle,
 			AbsOutputDir: "/out",
 		},
-		expectedScanLog: `outside-node-modules/index.js: WARNING: Duplicate key "a" in object literal
-outside-node-modules/index.js: NOTE: The original key "a" is here:
+		expectedScanLog: `outside-node-modules/index.jsx: WARNING: Duplicate key "a" in object literal
+outside-node-modules/index.jsx: NOTE: The original key "a" is here:
+outside-node-modules/index.jsx: WARNING: Duplicate "a2" attribute in JSX element
+outside-node-modules/index.jsx: NOTE: The original "a2" attribute is here:
 outside-node-modules/package.json: WARNING: Duplicate key "b" in object literal
 outside-node-modules/package.json: NOTE: The original key "b" is here:
 `,

internal/bundler/snapshots/snapshots_default.txt

@@ -552,11 +552,17 @@ console.log(123);
 ================================================================================
 TestDuplicatePropertyWarning
 ---------- /out/entry.js ----------
-// outside-node-modules/index.js
-console.log({ a: 1, a: 2 });
-
-// node_modules/inside-node-modules/index.js
-console.log({ c: 1, c: 2 });
+// outside-node-modules/index.jsx
+console.log({ a: 1, a: 2 }, /* @__PURE__ */ React.createElement("div", {
+  a2: true,
+  a2: 3
+}));
+
+// node_modules/inside-node-modules/index.jsx
+console.log({ c: 1, c: 2 }, /* @__PURE__ */ React.createElement("div", {
+  c2: true,
+  c2: 3
+}));
 
 ================================================================================
 TestDynamicImportWithExpressionCJS

internal/js_parser/js_parser.go

@@ -4536,6 +4536,26 @@ func (p *parser) parseJSXElement(loc logger.Loc) js_ast.Expr {
 				break parseAttributes
 			}
 		}
+
+		// Check for and warn about duplicate attributes
+		if len(properties) > 1 && !p.suppressWarningsAboutWeirdCode {
+			keys := make(map[string]logger.Loc)
+			for _, property := range properties {
+				if property.Kind != js_ast.PropertySpread {
+					if str, ok := property.Key.Data.(*js_ast.EString); ok {
+						key := helpers.UTF16ToString(str.Value)
+						if prevLoc, ok := keys[key]; ok {
+							r := js_lexer.RangeOfIdentifier(p.source, property.Key.Loc)
+							p.log.AddIDWithNotes(logger.MsgID_JS_DuplicateObjectKey, logger.Warning, &p.tracker, r,
+								fmt.Sprintf("Duplicate %q attribute in JSX element", key),
+								[]logger.MsgData{p.tracker.MsgData(js_lexer.RangeOfIdentifier(p.source, prevLoc),
+									fmt.Sprintf("The original %q attribute is here:", key))})
+						}
+						keys[key] = property.Key.Loc
+					}
+				}
+			}
+		}
 	}
 
 	// People sometimes try to use the output of "JSON.stringify()" as a JSX