* A flag `--keep-going / -k' to keep building goals if one fails, as

much as possible.  (This is similar to GNU Make's `-k' flag.)

* Refactoring to implement this: previously we just bombed out when
  a build failed, but now we have to clean up.  In particular this
  means that goals must be freed quickly --- they shouldn't hang
  around until the worker exits.  So the worker now maintains weak
  pointers in order not to prevent garbage collection.

* Documented the `-k' and `-j' flags.

doc/manual/opt-common-syn.xml

@@ -4,5 +4,14 @@
 <arg rep='repeat'><option>-v</option></arg>
 <arg><option>--build-output</option></arg>
 <arg><option>-B</option></arg>
+<arg>
+  <group choice='req'>
+    <arg choice='plain'><option>--max-jobs</option></arg>
+    <arg choice='plain'><option>-j</option></arg>
+  </group>
+  <replaceable>number</replaceable>
+</arg>
+<arg><option>--keep-going</option></arg>
+<arg><option>-k</option></arg>
 <arg><option>--keep-failed</option></arg>
 <arg><option>-K</option></arg>

doc/manual/opt-common.xml

@@ -108,6 +108,33 @@
 </varlistentry>
 
 
+<varlistentry>
+  <term><option>--max-jobs</option> / <option>-j</option></term>
+  <listitem>
+    <para>
+      Sets the maximum number of build jobs that Nix will perform in
+      parallel to the specified number.  The default is 1.  A higher
+      value is useful on SMP systems or to exploit I/O latency.
+    </para>
+  </listitem>
+</varlistentry>
+
+
+<varlistentry>
+  <term><option>--keep-going</option> / <option>-k</option></term>
+  <listitem>
+    <para>
+      Keep going in case of failed builds, to the greatest extent
+      possible.  That is, if building an input of some derivation
+      fails, Nix will still build the other inputs, but not the
+      derivation itself.  Without this option, Nix stops if any build
+      fails (except for builds of substitutes), possibly killing
+      builds in progress (in case of parallel or distributed builds).
+    </para>
+  </listitem>
+</varlistentry>
+
+
 <varlistentry>
   <term><option>--keep-failed</option> / <option>-K</option></term>
   <listitem>