Running builds view: show build step names

When using Hydra to build machine configurations, you'll often see
"nixosConfigurations.foo" five times, i.e. for each build step being
run. This isn't very helpful I think because in such a case, a single
build step can also be compiling the Linux kernel.

This change also fetches the `drvpath` and `type` from the `buildsteps`
relation. We're already joining it, so this doesn't make much difference
(confirmed via query logging that this doesn't cause extra SQL queries).

Unfortunately build steps don't have a human readable name, so I'm
deriving it from the drvpath by stripping away the hash (assuming that
it'll never contain a `-` and that `/nix/store/` is used as prefix). I
decided against using the Nix bindings for that to avoid too much
overhead due to store operations for each build step.

src/root/common.tt

@@ -91,6 +91,15 @@ BLOCK renderDuration;
   duration % 60 %]s[%
 END;
 
+BLOCK renderDrvInfo;
+  drvname = step.drvpath
+    .substr(11) # strip `/nix/store/`
+    .split('-').slice(1).join("-") # strip hash part
+    .substr(0, -4); # strip `.drv`
+  IF step.type == 0; action = "Build"; ELSE; action = "Substitution"; END;
+  IF drvname; %]<em> ([% action %] of [% drvname %])</em>[% END;
+END;
+
 
 BLOCK renderBuildListHeader %]
   <table class="table table-striped table-condensed clickable-rows">
@@ -131,7 +140,12 @@ BLOCK renderBuildListBody;
       [% END %]
       <td><a class="row-link" href="[% link %]">[% build.id %]</a></td>
       [% IF !hideJobName %]
-        <td><a href="[%link%]">[% IF !hideJobsetName %][%build.jobset.get_column("project")%]:[%build.jobset.get_column("name")%]:[% END %][%build.get_column("job")%]</td>
+        <td>
+          <a href="[%link%]">[% IF !hideJobsetName %][%build.jobset.get_column("project")%]:[%build.jobset.get_column("name")%]:[% END %][%build.get_column("job")%]</a>
+          [% IF showStepName %]
+            [% INCLUDE renderDrvInfo step=build.buildsteps %]
+          [% END %]
+        </td>
       [% END %]
       <td class="nowrap">[% t = showSchedulingInfo ? build.timestamp : build.stoptime; IF t; INCLUDE renderRelativeDate timestamp=(showSchedulingInfo ? build.timestamp : build.stoptime); ELSE; "-"; END %]</td>
       <td>[% !showSchedulingInfo and build.get_column('releasename') ? build.get_column('releasename') : build.nixname %]</td>

src/root/status.tt

@@ -7,7 +7,7 @@
 
 [% ELSE %]
 
-  [% INCLUDE renderBuildList builds=resource showSchedulingInfo=1 hideResultInfo=1 busy=1 %]
+  [% INCLUDE renderBuildList builds=resource showSchedulingInfo=1 hideResultInfo=1 busy=1 showStepName=1 %]
 
 [% END %]