shellcheck says...

[polluks]

In neatvi.sh line 52:
loc=$(sed -E -n "${lnum}s/^[A-Z]+([0-9]+(@[^ \t]+)?).*$/\1/p" <$path)
^---^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
loc=$(sed -E -n "${lnum}s/^[A-Z]+([0-9]+(@[^ \t]+)?).*$/\1/p" <"$path")

In neatvi.sh line 55:
if neatmail pg -s -b path/to/mbox -i $loc >.cur.mail 2>/dev/null; then
^--^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
if neatmail pg -s -b path/to/mbox -i "$loc" >.cur.mail 2>/dev/null; then

In neatvi.sh line 65:
loc=$(gopls definition $1:$2:$3)
^-- SC2086 (info): Double quote to prevent globbing and word splitting.
^-- SC2086 (info): Double quote to prevent globbing and word splitting.
^-- SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
loc=$(gopls definition "$1":"$2":"$3")

In neatvi.sh line 67:
echo $loc | sed -E 's/^([^:]+):([^:]+):([^:]+).*$/:e +\2 \1/'
^--^ SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
echo "$loc" | sed -E 's/^([^:]+):([^:]+):([^:]+).*$/:e +\2 \1/'

In neatvi.sh line 75:
if gopls references $1:$2:$3 >.list.ls; then
^-- SC2086 (info): Double quote to prevent globbing and word splitting.
^-- SC2086 (info): Double quote to prevent globbing and word splitting.
^-- SC2086 (info): Double quote to prevent globbing and word splitting.

Did you mean:
if gopls references "$1":"$2":"$3" >.list.ls; then

In neatvi.sh line 82:
ecmd_"$@" 2>/dev/null || echo "ec unknown command"
^-- SC2145 (error): Argument mixes string and array. Use * or separate argument.

For more information:
https://www.shellcheck.net/wiki/SC2145 -- Argument mixes string and array. ...
https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...