Unfold nested blocks when minifySyntax is enabled

[sapphi-red]

Summary

For an input like this,

function fn1 () {
  if (true) {
    let a = 'foo';
    console.log(a);
    console.log(a);
  }
}

esbuild currently outputs

function fn1() {
  {
    let a = "foo";
    console.log(a), console.log(a);
  }
}

. But this can be minified to

function fn1() {
  let a = "foo";
  console.log(a), console.log(a);
}

. This PR implements removing these braces.

Supported cases

function fn1 () {
  if (true) {
    let a = 'foo';
    console.log(a);
    console.log(a);
  }
}

const fn2 = () => {
  if (true) {
    let a = 'foo';
    console.log(a);
    console.log(a);
  }
};

const fn3 = function () {
  if (true) {
    let a = 'foo';
    console.log(a);
    console.log(a);
  }
};

const obj = {
  method2() {
    if (true) {
      let a = 'foo';
      console.log(a);
      console.log(a);
    }
  }
};

class Foo {
  static {
    if (true) {
      let a = 'foo';
      console.log(a);
      console.log(a);
    }
  }
}

current esbuild try

Other benefits

When this code is passed to Rollup,

export function fn1 () {
  {
    let a = 'foo';
    console.log(a);
    console.log(a);
  }
}

Rollup outputs

export function fn1() {
  {
    let a = "foo";
    console.log(a), console.log(a);
  }
}

(Rollup REPL).

When this output is passed to esbuild, esbuild currently outputs the braces as-is (current esbuild try).

This PR works for these cases, too.

Related information

A block inside if / for/while seems to be already supported: esbuild try

terser doesn't support this: terser/terser#1363

[ghiscoding]

@evanw any chance this could get reviewed (even if there's now conflicts)? This seems like a suboptimal output and @sapphi-red is main contributor on the Vite project. Thank you both for all these great projects :)

[hyf0]

What will happen for input?

function fn1 () {
  let a = 'foo_outer';
  if (true) {
    let a = 'foo';
    console.log(a);
    console.log(a);
  }
  console.log(a)
}

[sapphi-red]

This PR won't change the output for that case. It only affects when the block has a single block inside it.