nixos/mysql: drop services.mysql.pidDir

mysql already has its socket path hardcoded to to
/run/mysqld/mysqld.sock.
There's not much value in making the pidDir configurable, which also
points to /run/mysqld by default.

We only seem to use `services.mysql.pidDir` in the wordpress startup
script, to wait for mysql to boot up, but we can also simply wait on the
(hardcoded) socket location too.

A much nicer way to accomplish that would be to properly describe a
dependency on mysqld.service. This however is not easily doable, due to
how the apache-httpd module was designed.

nixos/doc/manual/release-notes/rl-1909.xml

@@ -93,6 +93,14 @@
       the module for some time and so was removed as cleanup.
     </para>
    </listitem>
+   <listitem>
+    <para>
+      The <option>services.mysql.pidDir</option> option was removed, as it was only used by the wordpress
+      apache-httpd service to wait for mysql to have started up.
+      This can be accomplished by either describing a dependency on mysql.service (preferred)
+      or waiting for the (hardcoded) <filename>/run/mysqld/mysql.sock</filename> file to appear.
+    </para>
+   </listitem>
    <listitem>
     <para>
       The <option>services.emby.enable</option> module has been removed, see

nixos/modules/rename.nix

@@ -212,6 +212,7 @@ with lib;
     (mkRemovedOptionModule [ "services" "logstash" "enableWeb" ] "The web interface was removed from logstash")
     (mkRemovedOptionModule [ "boot" "zfs" "enableLegacyCrypto" ] "The corresponding package was removed from nixpkgs.")
     (mkRemovedOptionModule [ "services" "winstone" ] "The corresponding package was removed from nixpkgs.")
+    (mkRemovedOptionModule [ "services" "mysql" "pidDir" ] "Don't wait for pidfiles, describe dependencies through systemd")
 
     # ZSH
     (mkRenamedOptionModule [ "programs" "zsh" "enableSyntaxHighlighting" ] [ "programs" "zsh" "syntaxHighlighting" "enable" ])

nixos/modules/services/databases/mysql.nix

@@ -18,16 +18,12 @@ let
     in (pName mysql == pName pkgs.mysql57)
        && ((builtins.compareVersions mysql.version "5.7") >= 0);
 
-  pidFile = "${cfg.pidDir}/mysqld.pid";
-
-  mysqldAndInstallOptions =
-    "--user=${cfg.user} --datadir=${cfg.dataDir} --basedir=${mysql}";
   mysqldOptions =
-    "${mysqldAndInstallOptions} --pid-file=${pidFile}";
+    "--user=${cfg.user} --datadir=${cfg.dataDir} --basedir=${mysql}";
   # For MySQL 5.7+, --insecure creates the root user without password
   # (earlier versions and MariaDB do this by default).
   installOptions =
-    "${mysqldAndInstallOptions} ${lib.optionalString isMysqlAtLeast57 "--insecure"}";
+    "${mysqldOptions} ${lib.optionalString isMysqlAtLeast57 "--insecure"}";
 
 in
 
@@ -80,11 +76,6 @@ in
         description = "Location where MySQL stores its table files";
       };
 
-      pidDir = mkOption {
-        default = "/run/mysqld";
-        description = "Location of the file which stores the PID of the MySQL server";
-      };
-
       extraOptions = mkOption {
         type = types.lines;
         default = "";
@@ -298,7 +289,6 @@ in
 
     systemd.tmpfiles.rules = [
       "d '${cfg.dataDir}' 0700 ${cfg.user} mysql -"
-      "d '${cfg.pidDir}' 0755 ${cfg.user} mysql -"
     ];
 
     systemd.services.mysql = let
@@ -329,7 +319,6 @@ in
           User = cfg.user;
           Group = "mysql";
           Type = if hasNotify then "notify" else "simple";
-          # /run/mysqld needs to be created in addition to pidDir, as they could point to different locations
           RuntimeDirectory = "mysqld";
           RuntimeDirectoryMode = "0755";
           # The last two environment variables are used for starting Galera clusters

nixos/modules/services/web-servers/apache-httpd/wordpress.nix

@@ -273,7 +273,7 @@ in
     if [ ! -d ${serverInfo.fullConfig.services.mysql.dataDir}/${config.dbName} ]; then
       echo "Need to create the database '${config.dbName}' and grant permissions to user named '${config.dbUser}'."
       # Wait until MySQL is up
-      while [ ! -e ${serverInfo.fullConfig.services.mysql.pidDir}/mysqld.pid ]; do
+      while [ ! -S /run/mysqld/mysqld.sock ]; do
         sleep 1
       done
       ${pkgs.mysql}/bin/mysql -e 'CREATE DATABASE ${config.dbName};'