WIP: treefile: Add package-blacklist

In FCOS we have a kola test that basically does `rpm -q python`.
It's...a bit silly to spawn a whole VM for this.  Ensuring that
some specific packages don't get included has come up in a few
cases.

I think FCOS/RHCOS at least will want to blacklist `dnf` for example.
And as noted above, FCOS could blacklist `python`.

One major benefit of doing this inside rpm-ostree is that one
gets the full "libsolv error message experience" when dependency
resolution fails, e.g. blacklisting `glibc` I get:

```
 Problem 79: conflicting requests
  - package coreos-installer-systemd-0.1.2-1.fc31.x86_64 requires coreos-installer = 0.1.2-1.fc31, but none of the providers can be installed
  - package coreos-installer-0.1.2-1.fc31.x86_64 requires rtld(GNU_HASH), but none of the providers can be installed
  - package glibc-2.30-10.fc31.x86_64 is filtered out by exclude filtering
  - package glibc-2.30-7.fc31.x86_64 is filtered out by exclude filtering
  - package glibc-2.30-8.fc31.x86_64 is filtered out by exclude filtering
  - package glibc-2.30-5.fc31.i686 is filtered out by exclude filtering
  - package glibc-2.30-5.fc31.x86_64 is filtered out by exclude filtering
  - package glibc-2.30-10.fc31.i686 is filtered out by exclude filtering
```

rust/src/treefile.rs

@@ -310,6 +310,7 @@ fn treefile_merge(dest: &mut TreeComposeConfig, src: &mut TreeComposeConfig) {
         repos,
         packages,
         bootstrap_packages,
+        blacklist_packages,
         ostree_layers,
         ostree_override_layers,
         install_langs,
@@ -656,6 +657,9 @@ struct TreeComposeConfig {
     #[serde(skip_serializing_if = "Option::is_none")]
     #[serde(rename = "ostree-override-layers")]
     ostree_override_layers: Option<Vec<String>>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    #[serde(rename = "blacklist-packages")]
+    blacklist_packages: Option<Vec<String>>,
 
     // Content installation opts
     #[serde(skip_serializing_if = "Option::is_none")]

src/app/rpmostree-composeutil.c

@@ -247,6 +247,8 @@ rpmostree_composeutil_get_treespec (RpmOstreeContext  *ctx,
 
   if (!treespec_bind_array (treedata, treespec, "packages", NULL, TRUE, error))
     return FALSE;
+  if (!treespec_bind_array (treedata, treespec, "blacklist-packages", NULL, TRUE, error))
+    return FALSE;
   if (!treespec_bind_array (treedata, treespec, "repos", NULL, TRUE, error))
     return FALSE;
   if (!treespec_bind_bool (treedata, treespec, "documentation", TRUE, error))

src/libpriv/rpmostree-core.c

@@ -257,6 +257,7 @@ rpmostree_treespec_new_from_keyfile (GKeyFile   *keyfile,
 #undef BIND_STRING
 
   add_canonicalized_string_array (&builder, "packages", NULL, keyfile);
+  add_canonicalized_string_array (&builder, "blacklist-packages", NULL, keyfile);
   add_canonicalized_string_array (&builder, "cached-packages", NULL, keyfile);
   add_canonicalized_string_array (&builder, "removed-base-packages", NULL, keyfile);
   add_canonicalized_string_array (&builder, "cached-replaced-base-packages", NULL, keyfile);
@@ -1891,8 +1892,11 @@ rpmostree_context_prepare (RpmOstreeContext *self,
 
   DnfContext *dnfctx = self->dnfctx;
   g_autofree char **pkgnames = NULL;
+  g_autofree char **blacklist_pkgnames = NULL;
   g_assert (g_variant_dict_lookup (self->spec->dict, "packages",
                                    "^a&s", &pkgnames));
+  g_variant_dict_lookup (self->spec->dict, "blacklist-packages",
+                         "^a&s", &blacklist_pkgnames);
 
   g_autofree char **cached_pkgnames = NULL;
   g_assert (g_variant_dict_lookup (self->spec->dict, "cached-packages",
@@ -2023,6 +2027,20 @@ rpmostree_context_prepare (RpmOstreeContext *self,
         }
     }
 
+  /* Process excludes */
+  for (char **iter = blacklist_pkgnames; iter && *iter; iter++)
+    {
+      const char *pkgname = *iter;
+      hy_autoquery HyQuery query = hy_query_create (sack);
+      hy_query_filter (query, HY_PKG_NAME, HY_EQ, pkgname);
+      g_autoptr(GPtrArray) pkglist = hy_query_run (query);
+      DnfPackageSet *pset = dnf_packageset_new (sack);
+      for (guint i = 0; i < pkglist->len; i++)
+        dnf_packageset_add (pset, pkglist->pdata[i]);
+      dnf_sack_add_excludes (sack, pset);
+      dnf_packageset_free (pset);
+    }
+
   /* First, handle packages to remove */
   g_autoptr(GPtrArray) removed_pkgnames = g_ptr_array_new ();
   for (char **it = removed_base_pkgnames; it && *it; it++)

tests/compose/test-misc-tweaks.sh

@@ -27,6 +27,9 @@ treefile_append "include" '["documentation.yaml", "recommends.yaml"]'
 treefile_del 'recommends'
 treefile_del 'documentation'
 
+# And test blacklists
+treefile_append "blacklist-packages" '["somenonexistent-package"]'
+
 # Note this overrides:
 # $ rpm -q systemd
 # systemd-243.4-1.fc31.x86_64