Generate better builder names for JSX* and TS* (#6967)

e.g. JSXIdentifier -> jsxIdentifier.
The jSXIdentifier alias isn't removed, so this commit doesn't introduce breaking changes.

packages/babel-types/scripts/generators/generateBuilders.js

@@ -1,5 +1,6 @@
 "use strict";
 const definitions = require("../../lib/definitions");
+const formatBuilderName = require("../utils/formatBuilderName");
 const lowerFirst = require("../utils/lowerFirst");
 
 module.exports = function generateBuilders() {
@@ -12,7 +13,14 @@ import builder from "../builder";\n\n`;
 
   Object.keys(definitions.BUILDER_KEYS).forEach(type => {
     output += `export function ${type}(...args: Array<any>): Object { return builder("${type}", ...args); }
-export { ${type} as ${lowerFirst(type)} };\n`;
+export { ${type} as ${formatBuilderName(type)} };\n`;
+
+    // This is needed for backwards compatibility.
+    // It should be removed in the next major version.
+    // JSXIdentifier -> jSXIdentifier
+    if (/^[A-Z]{2}/.test(type)) {
+      output += `export { ${type} as ${lowerFirst(type)} }\n`;
+    }
   });
 
   Object.keys(definitions.DEPRECATED_KEYS).forEach(type => {
@@ -21,7 +29,14 @@ export { ${type} as ${lowerFirst(type)} };\n`;
   console.trace("The node type ${type} has been renamed to ${newType}");
   return ${type}("${type}", ...args);
 }
-export { ${type} as ${lowerFirst(type)} };\n`;
+export { ${type} as ${formatBuilderName(type)} };\n`;
+
+    // This is needed for backwards compatibility.
+    // It should be removed in the next major version.
+    // JSXIdentifier -> jSXIdentifier
+    if (/^[A-Z]{2}/.test(type)) {
+      output += `export { ${type} as ${lowerFirst(type)} }\n`;
+    }
   });
 
   return output;

packages/babel-types/scripts/utils/formatBuilderName.js

@@ -0,0 +1,9 @@
+"use strict";
+
+const toLowerCase = Function.call.bind("".toLowerCase);
+
+module.exports = function formatBuilderName(type) {
+  // FunctionExpression -> functionExpression
+  // JSXIdentifier -> jsxIdentifier
+  return type.replace(/^([A-Z](?=[a-z])|[A-Z]+(?=[A-Z]))/, toLowerCase);
+};