I have been trying to connect to a localdb instance with the latest version (at this time) of heidisql to no avail.
I have followed the instructions from this answer her
As of heidisql.exe Revision 9.3.0.5108 you could also:
"C:\Program Files\Microsoft SQL Server\120\Tools\Binn\SqlLocalDB.exe" start "MSSQLLocalDB"
"C:\Program Files\Microsoft SQL Server\120\Tools\Binn\SqlLocalDB.exe" info "MSSQLLocalDB"
(e.g., \\.\pipe\LOCALDB#1B9DCF1E\tsql\query
"C:\Program Files\HeidiSQL\heidisql.exe --nettype=3 --host="\\.\pipe\LOCALDB#1B9DCF1E\tsql\query" --winauth=1"
I use a Bash script that automates all that, and it goes roughly like this:
shopt -s expand_aliases
alias __sqllocaldb='/c/Program\ Files/Microsoft\ SQL\ Server/120/Tools/Binn/SqlLocalDB.exe'
alias __heidisql='/c/Program\ Files/HeidiSQL/heidisql.exe'
__sqllocaldb start "Development"
hostname=$(__sqllocaldb info "Development" | tail -1 | sed 's/\(Instance pipe name: np:\)//')
__heidisql --nettype=3 --host="$hostname" --winauth=1