refactor(web/cgit-tvl): Move cgit config back out of module

It occured to me yesterday that with the config inside of the module
it is kind of difficult to test cgit locally.

This moves it back to a separate location (//web/cgit-tvl) and makes
the most important things configurable via overrides.

Change-Id: I9b0f4c60b75c31441e1718e63b5b55aba3100aae
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5893
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

ops/machines/whitby/default.nix

@@ -10,7 +10,7 @@ in
 {
   imports = [
     (mod "atward.nix")
-    (mod "cgit/default.nix")
+    (mod "cgit.nix")
     (mod "clbot.nix")
     (mod "gerrit-queue.nix")
     (mod "irccat.nix")

ops/modules/cgit.nix

@@ -0,0 +1,39 @@
+# Configuration for running the TVL cgit instance using thttpd.
+{ config, depot, lib, pkgs, ... }:
+
+let
+  cfg = config.services.depot.cgit;
+in
+{
+  options.services.depot.cgit = with lib; {
+    enable = mkEnableOption "Run cgit web interface for depot";
+
+    port = mkOption {
+      description = "Port on which cgit should listen";
+      type = types.int;
+      default = 2448;
+    };
+
+    repo = mkOption {
+      description = "Path to depot's .git folder on the machine";
+      type = types.str;
+      default = "/var/lib/gerrit/git/depot.git/";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    systemd.services.cgit = {
+      wantedBy = [ "multi-user.target" ];
+
+      serviceConfig = {
+        Restart = "on-failure";
+        User = "git";
+        Group = "git";
+
+        ExecStart = depot.web.cgit-tvl.override {
+          inherit (cfg) port repo;
+        };
+      };
+    };
+  };
+}

web/cgit-tvl/default.nix

@@ -1,12 +1,12 @@
-# Configuration for running the TVL cgit instance using thttpd.
-{ config, depot, lib, pkgs, ... }:
+# Wrapper for running cgit through thttpd with TVL-specific
+# configuration.
+#
+# In practice this is only used for //ops/modules/cgit, but exposing
+# it here makes it easy to experiment with cgit locally.
+{ depot, lib, pkgs, ... }:
 
 let
-  inherit (pkgs) writeText;
-
-  cfg = config.services.depot.cgit;
-
-  cgitConfig = writeText "cgitrc" ''
+  cgitConfig = repo: pkgs.writeText "cgitrc" ''
     # Global configuration
     virtual-root=/
     enable-http-clone=0
@@ -22,14 +22,14 @@ let
 
     # Repository configuration
     repo.url=depot
-    repo.path=/var/lib/gerrit/git/depot.git/
+    repo.path=${repo}
     repo.desc=monorepo for the virus lounge
     repo.owner=The Virus Lounge
     repo.clone-url=https://code.tvl.fyi/depot.git
   '';
 
-  thttpdConfig = writeText "thttpd.conf" ''
-    port=${toString cfg.port}
+  thttpdConfig = port: pkgs.writeText "thttpd.conf" ''
+    port=${toString port}
     dir=${depot.third_party.cgit}/cgit
     nochroot
     novhost
@@ -42,7 +42,7 @@ let
   #
   # Things are done this way because recompilation of thttpd is much
   # faster than cgit.
-  thttpdConfigPatch = writeText "thttpd_cgit_conf.patch" ''
+  thttpdConfigPatch = repo: pkgs.writeText "thttpd_cgit_conf.patch" ''
     diff --git a/libhttpd.c b/libhttpd.c
     index c6b1622..eef4b73 100644
     --- a/libhttpd.c
@@ -51,42 +51,23 @@ let
 
          envn = 0;
     +    // force cgit to load the correct configuration
-    +    envp[envn++] = "CGIT_CONFIG=${cgitConfig}";
+    +    envp[envn++] = "CGIT_CONFIG=${cgitConfig repo}";
          envp[envn++] = build_env( "PATH=%s", CGI_PATH );
      #ifdef CGI_LD_LIBRARY_PATH
   '';
 
-  thttpdCgit = pkgs.thttpd.overrideAttrs (old: {
+  thttpdCgit = repo: pkgs.thttpd.overrideAttrs (old: {
     patches = [
       ./thttpd_cgi_idx.patch
-      thttpdConfigPatch
+      (thttpdConfigPatch repo)
     ];
   });
+
 in
-{
-  options.services.depot.cgit = with lib; {
-    enable = mkEnableOption "Run cgit web interface for depot";
-
-    port = mkOption {
-      description = "Port on which cgit should listen";
-      type = types.int;
-      default = 2448;
-    };
-  };
-
-  config = lib.mkIf cfg.enable {
-    systemd.services.cgit = {
-      wantedBy = [ "multi-user.target" ];
-
-      serviceConfig = {
-        Restart = "on-failure";
-        User = "git";
-        Group = "git";
-
-        ExecStart = pkgs.writeShellScript "cgit-launch" ''
-          exec ${thttpdCgit}/bin/thttpd -D -C ${thttpdConfig}
-        '';
-      };
-    };
-  };
-}
+lib.makeOverridable
+  ({ port ? 2448
+   , repo ? "/var/lib/gerrit/git/depot.git/"
+   }: pkgs.writeShellScript "cgit-launch" ''
+    exec ${thttpdCgit repo}/bin/thttpd -D -C ${thttpdConfig port}
+  '')
+{ }