Switch string-width to eastasianwidth (#14793)

scripts/build/transform/eastasianwidth-module.js

@@ -0,0 +1,57 @@
+import { parse } from "@babel/parser";
+import { traverseFast as traverse } from "@babel/types";
+import babelGenerator from "@babel/generator";
+
+const generate = babelGenerator.default;
+
+function transformEastAsianWidthModule(original) {
+  let eastAsianWidthFunction;
+  traverse(parse(original), (node) => {
+    // We only need `eaw.eastAsianWidth`
+    if (
+      node.type === "AssignmentExpression" &&
+      node.left.type === "MemberExpression" &&
+      !node.left.computed &&
+      !node.left.optional &&
+      node.left.object.type === "Identifier" &&
+      node.left.object.name === "eaw" &&
+      node.left.property.type === "Identifier" &&
+      node.left.property.name === "eastAsianWidth"
+    ) {
+      eastAsianWidthFunction = node.right;
+    }
+  });
+
+  const functionBody = eastAsianWidthFunction.body.body;
+
+  // We only need `IfStatement`s returns `"F"` or `"W"`
+  for (let index = functionBody.length - 1; index >= 0; index--) {
+    const node = functionBody[index];
+
+    if (
+      node.type === "IfStatement" &&
+      node.consequent.type === "BlockStatement" &&
+      node.consequent.body.length === 1 &&
+      node.consequent.body[0].type === "ReturnStatement" &&
+      node.consequent.body[0].argument.type === "StringLiteral"
+    ) {
+      const { value } = node.consequent.body[0].argument;
+      if (value !== "F" && value !== "W") {
+        functionBody.splice(index, 1);
+      }
+    }
+  }
+
+  const ast = parse("export default { eastAsianWidth() {} };", {
+    sourceType: "module",
+  });
+  Object.assign(ast.program.body[0].declaration.properties[0], {
+    params: eastAsianWidthFunction.params,
+    body: eastAsianWidthFunction.body,
+  });
+
+  const { code } = generate(ast);
+  return code;
+}
+
+export default transformEastAsianWidthModule;