add documentation for the local disk cache TTL config

doc/manual/command-ref/conf-file.xml

@@ -788,6 +788,30 @@ password <replaceable>my-password</replaceable>
 
   </varlistentry>
 
+  <varlistentry xml:id="conf-negative-disk-cache-ttl"><term><literal>negative-disk-cache-ttl</literal></term>
+
+    <listitem>
+
+      <para>The TTL in seconds for negative lookups. If a store path is queried from a substituer but
+      was not found, there will be a negative lookup cached in the local disk cache database for the specified
+      duration.</para>
+
+    </listitem>
+
+  </varlistentry>
+
+  <varlistentry xml:id="conf-positive-disk-cache-ttl"><term><literal>positive-disk-cache-ttl</literal></term>
+
+    <listitem>
+
+      <para>The TTL in seconds for positive lookups. If a store path is queried from a substituer, the result of
+      the query will be cached in the local disk cache database including some of the NAR metadata. Setting a TTL
+      for positive lookups can be useful in case of builds that aren't reproducible, in which case having a more
+      frequent cache invalidation would prevent hash mismatch issues.</para>
+
+    </listitem>
+
+  </varlistentry>
 
 </variablelist>
 

src/libstore/globals.hh

@@ -310,15 +310,17 @@ public:
         "Disabled substituters that may be enabled via the substituters option by untrusted users.",
         {"trusted-binary-caches"}};
 
-    Setting<int> ttlNegativeDiskCache{this, 3600, "negative-disk-cache-ttl",
-        "The TTL in seconds for negative lookups in the disk cache."};
-
-    Setting<int> ttlPositiveDiskCache{this, 30 * 24 * 3600, "positive-disk-cache-ttl",
-        "The TTL in seconds for positive lookups in the disk cache."};
-
     Setting<Strings> trustedUsers{this, {"root"}, "trusted-users",
         "Which users or groups are trusted to ask the daemon to do unsafe things."};
 
+    Setting<unsigned int> ttlNegativeDiskCache{this, 3600, "negative-disk-cache-ttl",
+        "The TTL in seconds for negative lookups in the disk cache i.e binary cache lookups that "
+        "return an invalid path result"};
+
+    Setting<unsigned int> ttlPositiveDiskCache{this, 30 * 24 * 3600, "positive-disk-cache-ttl",
+        "The TTL in seconds for positive lookups in the disk cache i.e binary cache lookups that "
+        "return a valid path result."};
+
     /* ?Who we trust to use the daemon in safe ways */
     Setting<Strings> allowedUsers{this, {"*"}, "allowed-users",
         "Which users or groups are allowed to connect to the daemon."};