How do I define a macro that depends on the height of an argument?

Question

I'd like to write a macro that surrounds an argument with two round parentheses which are correctly sized to the argument. Currently I'm using the following macro,

\newcommand{\inpl}[1]{{\left(\kern-.2em\left({#1} \right)\kern-.2em\right)}}

This looks fine when #1 isn't tall, but when it is there's too much whitespace between the brackets.
$\inpl{\phi,\mathbf{i}\phi}$ vs.\ $\inpl{\hat{\phi},\mathbf{i}\hat{\phi}}$
Changing the kerning amount (e.g. to -.3em) does make the larger brackets look better at the expense of making the smaller ones look too close together. I think a proper solution would be to change the amount of kerning done depending on the vertical height of #1, effectively replicating what \left does, but I don't know how to write such a macro.

Could anyone tell me how to get the vertical height of the enclosed text as a value that I can compare against, or how macros that dynamically change depending on the vertical height are usually defined?

Well actually the fundamental problem here is that you want the "two parentheses" symbol... — user202729, Aug 16 '22 at 13:10
There's spacing - Better double parenthesis notation for multiset - TeX - LaTeX Stack Exchange but doesn't look like what you want regarding the spacing I think. Neither is equations - Typesetting double brackets and double parentheses - TeX - LaTeX Stack Exchange or math mode - Paired delimiter made of several brackets - TeX - LaTeX Stack Exchange. — user202729, Aug 16 '22 at 13:11
Either way to solve the literal problem being asked -- in short • \left is a TeX primitive, it's not easy to implement that using macros & • you can make a macro that takes the content, put it in a box, measure the height of the box and do things (read TeXbook etc. for details). That may be more complex than somehow using mathrlap or something to do proper kerning though. — user202729, Aug 16 '22 at 13:16
You can also use a savebox. See `\mathsavebox' from https://tex.stackexchange.com/questions/630713/uniformly-oriented-cancelling-lines-across-math-or-texts/630755?r=SearchResults&s=1%7C22.5484#630755). Note that the baseline is not the center. — John Kormylo, Aug 16 '22 at 13:23
@user202729 : AFAIK, I'd have to use unicode-math to get the two parentheses symbol. Though even then, I still think I'd run into issues with sizing since I don't know if there are codepoints for differently sized double-parentheses. Thanks for outlining how to proceed though — Gautam Chaudhuri, Aug 16 '22 at 13:39

How do I define a macro that depends on the height of an argument?

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