How to get the spacing right with multiple underbraces within parentheses?

Question

This question is a generalization of

How to nicely lay out a parentheses-enclosed overbrace/underbrace?

Now we have parentheses with some parts of the content, of different heights, having an underbrace. Example:

\documentclass{minimal}
\begin{document}
$\left( 1 \cdot 2 \cdot \frac{3}{4} \cdot 5^2 \right)$
$\left( \underbrace{1}_{x} \cdot 2 \cdot \underbrace{\frac{3}{4}}_{\int y} \cdot 5^2 \right)$
\end{document}

produces:

which is very ugly. How can I make the underbraces ignored for the purposes of sizing the parentheses, but count for the space to the next line of text? The solution must allow me to write something like

$\magicparens{%
underbrace{1}_{x} \cdot 2 \cdot \underbrace{\frac{3}{4}}_{\int y} \cdot 5^2%
}$

and have it work. No manually specifying any sizes or lengths.

Bonus points for a second version which make all the underbraces vertically aligned.

Answer 1

Here is a version of \magicparens that sets both \left( and \right) using a \overbrace- and \underbrace-free makeup:

\documentclass{article}

\usepackage{amsmath}

\newcommand{\noubob}[1]{{
  \def\underbrace##1_##2{##1}% Remove subscript associated with \underbrace
  \def\overbrace##1^##2{##1}% Remove superscript associated with \overbrace
  #1}}
\newcommand{\magicparens}[1]{%
  \left(\vphantom{\noubob{#1}}\right.\kern-\nulldelimiterspace
  #1
  \kern-\nulldelimiterspace\left.\vphantom{\noubob{#1}}\right)
}

\begin{document}

$\left( 1 \cdot 2 \cdot \frac{3}{4} \cdot 5^2 \right)$

$\left( \underbrace{1}_{x} \cdot 2 \cdot \underbrace{\frac{3}{4}}_{\int y} \cdot 5^2 \right)$

$\magicparens{
  \underbrace{1}_{x} \cdot 2 \cdot \underbrace{\dfrac{3}{4}}_{\int y} \cdot 5^2%
}$

\end{document}

Since $\underbrace{\frac{3}{4}}_{x}$ prints the \fraction in \displaystyle while $\frac{3}{4}$ sets it in \textstyle, I've added amsmath and forced a \dfrac.

Also, the redefinition of \underbrace/\overbrace inside \magicparens requires you to necessarily use _ and ^ with the respective definitions, even though \underbrace/\overbrace can naturally be used without them. Of course, one can improve on the redefinition and peek ahead to accommodate for those situations as well.