* nix-env -q now has a flag --prebuilt-only (-b<) that causes nix-env

to show only those derivations whose output is already in the Nix
  store or that can be substituted (i.e., downloaded from somewhere).
  In other words, it shows the packages that can be installed “quickly”,
  i.e., don’t need to be built from source.

doc/manual/release-notes.xml

@@ -74,6 +74,15 @@
   <option>--set-flag</option>.</para></listitem>
   
 
+  <listitem><para><command>nix-env -q</command> now has a flag
+  <option>--prebuilt-only</option> (<option>-b</option>) that causes
+  <command>nix-env</command> to show only those derivations whose
+  output is already in the Nix store or that can be substituted (i.e.,
+  downloaded from somewhere).  In other words, it shows the packages
+  that can be installed “quickly”, i.e., don’t need to be built from
+  source.</para></listitem>
+  
+
   <listitem><para>TODO: new built-ins
   <function>builtins.attrNames</function>,
   <function>builtins.filterSource</function>,

src/nix-env/help.txt

@@ -45,7 +45,12 @@ Upgrade flags:
   --eq: "upgrade" if the current version is equal
   --always: upgrade regardless of current version
 
-Query types:
+Query sources:
+
+  --installed: use installed derivations (default)
+  --available / -a: use derivations available in Nix expression
+
+Query flags:
 
   --status / -s: print installed/present status
   --no-name: hide derivation names
@@ -55,11 +60,8 @@ Query types:
   --compare-versions / -c: compare version to available or installed
   --drv-path: print path of derivation
   --out-path: print path of derivation output
-
+  --prebuilt-only: only show derivations whose prebuilt binaries are
-Query sources:
+      available on this machine or are downloadable
-
-  --installed: use installed derivations (default)
-  --available / -a: use derivations available in Nix expression
 
 Options:
 

src/nix-env/nix-env.cc

@@ -831,6 +831,7 @@ static void opQuery(Globals & globals,
     bool printDrvPath = false;
     bool printOutPath = false;
     bool printDescription = false;
+    bool prebuiltOnly = false;
     bool compareVersions = false;
     bool xmlOutput = false;
 
@@ -849,6 +850,7 @@ static void opQuery(Globals & globals,
         else if (*i == "--out-path") printOutPath = true;
         else if (*i == "--installed") source = sInstalled;
         else if (*i == "--available" || *i == "-a") source = sAvailable;
+        else if (*i == "--prebuilt-only" || *i == "-b") prebuiltOnly = true;
         else if (*i == "--xml") xmlOutput = true;
         else throw UsageError(format("unknown flag `%1%'") % *i);
 
@@ -914,6 +916,12 @@ static void opQuery(Globals & globals,
 
             /* For XML output. */
             XMLAttrs attrs;
+
+            if (prebuiltOnly) {
+                if (!store->isValidPath(i->queryOutPath(globals.state)) &&
+                    !store->hasSubstitutes(i->queryOutPath(globals.state)))
+                    continue;
+            }
         
             if (printStatus) {
                 bool hasSubs = store->hasSubstitutes(i->queryOutPath(globals.state));