useless brackets when format the string under the template literal

input:

​```javascript
`模板字符串可以直接插入单引号'和双引号"`;
'单引号字符串可以插入反引号`';
​```

output:

​```javascript
`模板字符串可以直接插入单引号'和双引号"`;
('单引号字符串可以插入反引号`');
​```

expect: no brackets wrap the string：

'单引号字符串可以插入反引号`'

[bakkot]

This is intentional. Prettier wraps any string literal which is in statement position in parentheses because otherwise such strings would get interpreted as directives if they occurred at the top of a function or program, which can change the behavior of the program.

To illustrate:

function f() {
  'use strict';
  return this === void 0;
}

function g() {
  ('use strict');
  return this === void 0;
}

f(); // true
g(); // false

Now, it is not technically necessary to do this for strings which are not on the first line of a function or program. But doing so anyway is more consistent, and can highlight bugs. See for example this thread on twitter.

[bakkot]

The reason it wraps strings in parentheses is because it is sometimes necessary to do so to preserve the behavior of the program (and the AST), as in my example, which is one of the most important goals for prettier. Since it is sometimes necessary, for consistency it always does it, consistency being another important goal. The fact that it sometimes highlights bugs is just a bonus.