shellcheck not detecting bad substitution in dash and bash when using ${#$var}

[nihilus]

For new checks and feature suggestions

• [x] shellcheck.net (i.e. the latest commit) currently gives no useful warnings about this
• [x] I searched through https://github.com/koalaman/shellcheck/issues and didn't find anything related

Here's a snippet or screenshot that shows the problem:

#!/bin/sh
var="foo"
echo "${#$var}"

Here's what shellcheck currently says:

No issues detected!

Here's what I wanted or expected to see:

Something about 'bad substitution'.

[mmlb]

@nihilus just fyi that a tool I use along with shellcheck catches this, might want to add to the belt.

cat <<'EOF' | shfmt                                                                                                     
var="foo"
echo "${#$var}"
EOF
2:11: $ cannot be followed by a word 

[nihilus]

@mmlb nice tool, I integrated it today as part of our buildprocess.