nix flake update: Imply --refresh

src/nix/flake.cc

@@ -119,6 +119,9 @@ struct CmdFlakeUpdate : FlakeCommand
 
     void run(nix::ref<nix::Store> store) override
     {
+        /* Use --refresh by default for 'nix flake update'. */
+        settings.tarballTtl = 0;
+
         lockFlake();
     }
 };

tests/flakes.sh

@@ -589,8 +589,7 @@ nix flake info --json hg+file://$flake5Dir
 nix build -o $TEST_ROOT/result hg+file://$flake5Dir --no-registries --no-allow-dirty
 
 # Test tarball flakes
-rm -rf $flake5Dir/.hg
-tar cfz $TEST_ROOT/flake.tar.gz -C $TEST_ROOT flake5
+tar cfz $TEST_ROOT/flake.tar.gz -C $TEST_ROOT --exclude .hg flake5
 
 nix build -o $TEST_ROOT/result file://$TEST_ROOT/flake.tar.gz