Starting from "emacs -Q -f eshell":
~ $ echo $exec-path[0]
/usr/local/sbin
~ $ echo $exec-path[${echo 0}]
/usr/local/sbin
~ $ echo $exec-path[${*echo 0}]
;; no output
This is because 'eshell-eval-indices' gets an S-expr describing code to
evaluate for the indices, and it just passes that to 'eval'. That's not
the right way to do things for Eshell: instead, we should rely on
'eshell-do-eval', which properly handles asynchronous evaluation. That's
required for working with external commands like "*echo" (which calls
the real /bin/echo).
The attached patch fixes this by changing 'eshell-eval-indices' to 'eshell-indices', which does some minimal transformations on the S-expr for the indices, and then uses it to build the final S-expr to pass to 'eshell-do-eval'.
This could possibly go in Emacs 29, since it's a bugfix to add onto a previous bugfix (see commit 990f36fa10). However, I'd lean towards just merging to master; this is a fairly obscure issue, and we can't just fix *every* bug we find on the release branch, or the branch will never stabilize. If someone else thinks it's important enough to go on the release branch though, I won't argue.
0001-Fix-evaluation-of-asynchronous-expansions-in-Eshell-.patch
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