Why bash-minimal is part of sbcl package

[Pan Xie]

Hello

I find this interesting thing but I don't have an explanation. When 
query the "references" of my Gnu Store item "sbcl", it shows that sbcl 
references bash-mininal, as the following output shows:

# guix gc --references /gnu/store/sbbp9nvslqcf3bmcnz5wgxf2qpsi757
/gnu/store/6ncav55lbk5kqvwwflrzcr41hp5jbq0c-gcc-11.3.0-lib
/gnu/store/ln6hxqjvz6m9gdd9s97pivlqck7hzs99-glibc-2.35
/gnu/store/mzx7j93w5szyzrgnql8dqhqdgjh6si02-mpfr-4.2.0
/gnu/store/nl194qnq5lhjxpfwcs15xqihnfqif335-zstd-1.5.2-lib
/gnu/store/sbbp9nvslqcf3bmcnz5wgxf2qpsi757i-sbcl-2.3.7
/gnu/store/v9p25q9l5nnaixkhpap5rnymmwbhf9rp-bash-minimal-5.1.16
/gnu/store/ybadavwz1z9kmxanqy3siw38lnkwnkrp-gmp-6.2.1

However when I look into sbcl's package definition, there is no 
bash-minimal as its input. I can use guix graph find a path from sbcl to 
bash-minimal:

# guix graph --path sbcl bash-minimal
sbcl@2.3.7
texlive-updmap.cfg@66594
texlive-scheme-basic@66594
texlive-collection-basic@66594
texlive-bin@20230313
cairo@1.16.0
bash-minimal@5.1.16

bash-minimal is indeed one of cairo's package input. However cairo also 
has inputs like ghostscript and libspectre, which sbcl does not reference.

"guix size sbcl" also reports bash-minimal is part of sbcl package, and 
"guix pack sbcl" will include bash-minimal in its final tarball.

So the question is, which part of sbcl's package definition tells Guix 
it need to add bash-minimal as part of sbcl? Is there a practical method 
to figure that out?