Xjyuk

Consider the following MWE:

documentclassminimal

begindocument
fboxsome text vrule more text
fboxsome text vrule more deep text
fboxsome text vrule more $int$ tall text
enddocument

In all three cases, the vrule stretches to the height of the surrounding box, but doesn't touch the edges of the fbox because of the fboxsep.

How can I make the vrule stretch by an extra fboxsep on each side? I found this question, but it only covers giving an explicit height to the vrule, while I'd like to extend it by a given amount, but otherwise let it expand and shrink as appropriate to fill the current box.

one way is to set fboxsep to zero and than instead vrule use accordingly set rule:

documentclassminimal
setlengthfboxsep0pt
newcommandVRrule[-0.4baselineskip]0.4pt1.2baselineskip 

begindocument
fbox some text VR qjf more text 
fbox some text VR more deep text 
fbox some text VR more $int$ tall text 
enddocument

You can use smashvrule, but you have to specify the height and depth.

documentclassarticle
begindocument
sbox0fboxsome text more text%
fboxsome text smashvrule heightht0 depthdp0 more text
sbox0fboxsome text more deep text%
fboxsome text smashvrule heightht0 depthdp0 more deep text
sbox0fboxsome text more $int$ tall text%
fboxsome text smashvrule heightht0 depthdp0 more $int$ tall text
enddocument

Or you could just use struts and make all your fboxes the same height.

documentclassstandalone
begindocument
fboxstrut some texthspace-fboxrulefboxstrut some text
fboxstrut some texthspace-fboxrulefboxstrut more deep text
fboxstrut some texthspace-fboxrulefboxstrut more $int$ tall text
enddocument

Looks like a tabular to me.

documentclassarticle % see https://tex.stackexchange.com/q/42114/121799
begindocument
begintabular
hline
some text & more text\
hline
endtabular

begintabular
hline
some text & more deep text\
hline
endtabular

begintabular
hline
some text & more $displaystyleint$ tall text\
hline
endtabular
enddocument

Of course you can adjust the padding.

documentclassarticle % see https://tex.stackexchange.com/q/42114/121799
% commands based on
newcommandTstrut[1]rule0pt#1 % "top" strut
newcommandBstrut[1]rule[-#1]0pt0pt % "bottom" strut
newcommandTBstrut[2]Tstrut#1Bstrut#2
begindocument
begintabular
hline
some text & more text\
hline
endtabular

begintabular
hline
TBstrut2.5ex1.5exsome text & more deep text\
hline
endtabular

begintabular
hline
TBstrut4ex3exsome text & more $displaystyleint$ tall text\[0.5ex]
hline
endtabular
enddocument