command substitution inside parameter expansion inside "for ((;;))"

[Stephane Chazelas]

Hello,

$ bash -c 'for ((i = 0; $(echo 0); i++)); do echo x; done'

(OK)

$ bash -c 'for ((i = 0; ${x-`echo 0`}; i++)); do echo x; done'

(OK)

$ bash -c 'for ((i = 0; ${x-$(echo 0)}; i++)); do echo x; done'
bash: -c: line 0: syntax error near unexpected token `newline'
bash: -c: line 0: `for ((i = 0; ${x-$(echo 0)}; i++)); do echo x; done'

It's the same for ${x#$(echo 0)}.

I also noticed that cmd was not run in ${x#`cmd`} if x happens
to be empty (it's also the case in dash and ksh93 though only if
x is unset; zsh, mksh and yash are fine)

$ bash --version
GNU bash, version 4.4.12(1)-release (x86_64-pc-linux-gnu)

-- 
Stephane