Fix unrenamed bits in system units shipped in native packages (#144)

This is a bit of a SNAFU, because the service units are broken on fresh
systems, and on systems where EdgeDB 5.x and earlier was installed they
would work, but will initialize the data in the wrong spot
(`/var/lib/edgedb`) and owned by the wrong user (`edgedb`).  This fixes
the units and adds a check that errors out if the wrong data directory
is detected, so people who have successfully installed Gel 6.0/6.1 would
be informed to move and `chown` the data directory when upgrading to 6.2
and later.

edgedbpkg/edgedb/IDENTIFIER-SLOT.plist.in

@@ -11,17 +11,17 @@
 
     <key>ProgramArguments</key>
     <array>
-        <string>@@{bindir}/edgedb-server</string>
-        <string>--data-dir=@@{localstatedir}/lib/edgedb/@@{slot}/data/</string>
-        <string>--runstate-dir=@@{runstatedir}/edgedb/</string>
+        <string>@@{bindir}/@@{name}</string>
+        <string>--data-dir=@@{localstatedir}/lib/@@{name_for_user_and_dir}/@@{slot}/data/</string>
+        <string>--runstate-dir=@@{runstatedir}/@@{name_for_user_and_dir}/</string>
         <string>--tls-cert-mode=generate_self_signed</string>
     </array>
 
     <key>RunAtLoad</key>
     <true/>
 
     <key>UserName</key>
-    <string>edgedb</string>
+    <string>@@{name_for_user_and_dir}</string>
 
     <key>KeepAlive</key>
     <dict>

edgedbpkg/edgedb/IDENTIFIER-SLOT.service.in

@@ -7,13 +7,14 @@ After=network.target
 [Service]
 Type=notify
 
-User=edgedb
-Group=edgedb
+User=@@{name_for_user_and_dir}
+Group=@@{name_for_user_and_dir}
 
-Environment=EDGEDATA=@@{localstatedir}/lib/edgedb/@@{slot}/data/
-RuntimeDirectory=edgedb
+Environment=GELDATA=@@{localstatedir}/lib/@@{name_for_user_and_dir}/@@{slot}/data/
+RuntimeDirectory=@@{name_for_user_and_dir}
 
-ExecStart=@@{bindir}/edgedb-server --data-dir=${EDGEDATA} --runstate-dir=%t/edgedb --tls-cert-mode=generate_self_signed
+ExecStartPre=@@{pre_start_script}
+ExecStart=@@{bindir}/@@{name} --data-dir=${GELDATA} --runstate-dir=%t/@@{name_for_user_and_dir} --tls-cert-mode=generate_self_signed
 ExecReload=/bin/kill -HUP ${MAINPID}
 KillMode=mixed
 KillSignal=SIGINT

edgedbpkg/edgedb/__init__.py

@@ -308,6 +308,10 @@ def marketing_name(self) -> str:
     def marketing_slug(self) -> str:
         return "gel"
 
+    @property
+    def name_for_user_and_dir(self) -> str:
+        return self.marketing_slug
+
     def version_includes_revision(self) -> bool:
         return ".s" in self.pretty_version
 
@@ -575,6 +579,22 @@ def get_stdlib_install_script(self, build: targets.Build) -> str:
         )
         return script
 
+    def get_pre_start_script(self, build: targets.Build) -> str:
+        if self.marketing_slug == "gel" and self.slot == "6":
+            # In pre-6.2 packages we shipped broken service units files
+            # that contained non-renamed user and data directory.
+            msg = (
+                "Obsolete directory structure detected. "
+                'Please move "/var/lib/edgedb/6/data" to "/var/lib/gel/6/data"'
+                ' and run `chown -R gel:gel "/var/lib/gel/6/data"`'
+            )
+            return (
+                "/bin/sh -c 'if [ -d /var/lib/edgedb/6/data ]; then "
+                + f"echo \\'{msg}\\' >&2; exit 1; fi'"
+            )
+        else:
+            return ""
+
     def get_private_libraries(self, build: targets.Build) -> list[str]:
         # Automatic dependency introspection points to libpq.so,
         # since some Postgres' client binaries require it.  We _do_