Upgrade MySQL version to 8.0

This reverts commit f5231a33955e62adecd8ed2e43ab7b1ee7c5c600.

env/cpp.nix

@@ -1,5 +0,0 @@
-{ pkgs ? import <nixpkgs> { } }:
-
-with pkgs;
-
-mkShell { buildInputs = [ ccls cmake ]; }

env/mysql.nix

@@ -2,19 +2,24 @@
 
 with pkgs;
 
-mkShell {
-  buildInputs = [ mysql57 ];
+let
+  sql_file = "database/db.sql";
+  data_dir = "$(pwd)/.mysql";
+  socket = "${data_dir}/mysql.sock";
+
+in mkShell {
+  buildInputs = [ mysql80 ];
 
   shellHook = ''
-    pkill mysql
-    rm -rf .mysql && mkdir .mysql
+    trap "kill 0" EXIT
+    [ -d ${data_dir} ] || mkdir ${data_dir}
 
-    mysqld --datadir="$(pwd)/.mysql" --socket="$(pwd)/.mysql/mysql.sock" --initialize-insecure
-    mysqld --datadir="$(pwd)/.mysql" --socket="$(pwd)/.mysql/mysql.sock" --skip-networking &
+    mysqld --datadir="${data_dir}" --socket="${socket}" --initialize-insecure
+    mysqld --datadir="${data_dir}" --socket="${socket}" --skip-networking --skip-mysqlx &
     sleep 1
 
-    mysql --socket="$(pwd)/.mysql/mysql.sock" -u root < $(pwd)/database/db.sql
+    mysql --socket="${socket}" -u root < ${sql_file}
 
-    alias mysql='mysql --socket="$(pwd)/.mysql/mysql.sock" -u root'
+    alias mysql='mysql --socket="${socket}" -u root'
   '';
 }