nix-env: Create ~/.nix-defexpr automatically

src/nix-env/nix-env.cc

@@ -192,12 +192,6 @@ static void loadDerivations(EvalState & state, Path nixExprPath,
 }
 
 
-static Path getDefNixExprPath()
-{
-    return getHome() + "/.nix-defexpr";
-}
-
-
 static long getPriority(EvalState & state, DrvInfo & drv)
 {
     return drv.queryMetaInt("priority", 0);
@@ -1327,9 +1321,20 @@ static int _main(int argc, char * * argv)
         Globals globals;
 
         globals.instSource.type = srcUnknown;
-        globals.instSource.nixExprPath = getDefNixExprPath();
+        globals.instSource.nixExprPath = getHome() + "/.nix-defexpr";
         globals.instSource.systemFilter = "*";
 
+        if (!pathExists(globals.instSource.nixExprPath)) {
+            createDirs(globals.instSource.nixExprPath);
+            replaceSymlink(
+                fmt("%s/profiles/per-user/%s/channels", settings.nixStateDir, getUserName()),
+                globals.instSource.nixExprPath + "/channels");
+            if (getuid() != 0)
+                replaceSymlink(
+                    fmt("%s/profiles/per-user/root/channels", settings.nixStateDir),
+                    globals.instSource.nixExprPath + "/channels_root");
+        }
+
         globals.dryRun = false;
         globals.preserveInstalled = false;
         globals.removeAll = false;