* Make the --prebuilt-only' / -b' option work not just for queries

but installations/upgrades as well.  So `nix-env -ub \*' will
  upgrade only those packages for which a substitute is available (or
  to be precise, it will upgrade each package to the highest version
  for which a substitute is available).

doc/manual/release-notes.xml

@@ -92,7 +92,8 @@
   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>
+  source.  TODO: flag is also available in nix-env -i /
+  -u.</para></listitem>
   
 
   <listitem><para>TODO: new built-ins

src/nix-env/help.txt

@@ -63,8 +63,6 @@ Query flags:
   --out-path: print path of derivation output
   --description: print description
   --meta: print all meta attributes (only with --xml)
-  --prebuilt-only: only show derivations whose prebuilt binaries are
-      available on this machine or are downloadable
 
 Options:
 
@@ -74,3 +72,5 @@ Options:
   --keep-failed / -K: keep temporary directories of failed builds
   --preserve-installed: do not replace currently installed versions in `-i'
   --system-filter SYSTEM: only use derivations for specified platform
+  --prebuilt-only / -b: only use derivations whose prebuilt binaries are
+      available on this machine or are downloadable

src/nix-env/nix-env.cc

@@ -47,8 +47,9 @@ struct InstallSourceInfo
     Path nixExprPath; /* for srcNixExprDrvs, srcNixExprs */
     Path profile; /* for srcProfile */
     string systemFilter; /* for srcNixExprDrvs */
+    bool prebuiltOnly;
     ATermMap autoArgs;
-    InstallSourceInfo() : autoArgs() { };
+    InstallSourceInfo() : prebuiltOnly(false) { };
 };
 
 
@@ -94,6 +95,8 @@ static bool parseInstallSourceOptions(Globals & globals,
     }
     else if (arg == "--attr" || arg == "-A")
         globals.instSource.type = srcAttrPath;
+    else if (arg == "--prebuilt-only" || arg == "-b")
+        globals.instSource.prebuiltOnly = true;
     else return false;
     return true;
 }
@@ -319,9 +322,16 @@ static int comparePriorities(EvalState & state,
 }
 
 
-static DrvInfos filterBySelector(EvalState & state,
-    const DrvInfos & allElems,
-    const Strings & args, bool newestOnly)
+static bool isPrebuilt(EvalState & state, const DrvInfo & elem)
+{
+    return
+        store->isValidPath(elem.queryOutPath(state)) ||
+        store->hasSubstitutes(elem.queryOutPath(state));
+}
+
+
+static DrvInfos filterBySelector(EvalState & state, const DrvInfos & allElems,
+    const Strings & args, bool newestOnly, bool prebuiltOnly)
 {
     DrvNames selectors = drvNamesFromArgs(args);
 
@@ -340,6 +350,7 @@ static DrvInfos filterBySelector(EvalState & state,
             DrvName drvName(j->name);
             if (i->matches(drvName)) {
                 i->hits++;
+                if (!prebuiltOnly || isPrebuilt(state, *j))
                     matches.push_back(std::pair<DrvInfo, unsigned int>(*j, n));
             }
         }
@@ -429,7 +440,8 @@ static void queryInstSources(EvalState & state,
             loadDerivations(state, instSource.nixExprPath,
                 instSource.systemFilter, instSource.autoArgs, "", allElems);
 
-            elems = filterBySelector(state, allElems, args, newestOnly);
+            elems = filterBySelector(state, allElems, args,
+                newestOnly, instSource.prebuiltOnly);
     
             break;
         }
@@ -495,7 +507,7 @@ static void queryInstSources(EvalState & state,
         case srcProfile: {
             elems = filterBySelector(state,
                 queryInstalled(state, instSource.profile),
-                args, newestOnly);
+                args, newestOnly, instSource.prebuiltOnly);
             break;
         }
 
@@ -999,7 +1011,7 @@ static void opQuery(Globals & globals,
 
     DrvInfos elems = filterBySelector(globals.state,
         source == sInstalled ? installedElems : availElems,
-        remaining, false);
+        remaining, false, prebuiltOnly);
     
     DrvInfos & otherElems(source == sInstalled ? availElems : installedElems);
 
@@ -1040,12 +1052,6 @@ 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));
                 bool isInstalled = installed.find(i->queryOutPath(globals.state)) != installed.end();