Add --update-input flag to update a specific flake input

Typical usage:

  $ nix flake update ~/Misc/eelco-configurations/hagbard --update-input nixpkgs

to update the 'nixpkgs' input of a flake while leaving every other
input unchanged.

The argument is an input path, so you can do e.g. '--update-input
dwarffs/nixpkgs' to update an input of an input.

Fixes #2928.

1 files changed, 8 insertions, 0 deletions

diff --git a/src/nix/installables.cc b/src/nix/installables.cc
index 24eb739f5..77a43ef2a 100644
--- a/src/nix/installables.cc
+++ b/src/nix/installables.cc
@@ -40,6 +40,14 @@ MixFlakeOptions::MixFlakeOptions()
         .set(&lockFlags.useRegistries, false);
 
     mkFlag()
+        .longName("update-input")
+        .description("update a specific flake input")
+        .label("input-path")
+        .handler([&](std::vector<std::string> ss) {
+            lockFlags.inputUpdates.insert(flake::parseInputPath(ss[0]));
+        });
+
+    mkFlag()
         .longName("override-input")
         .description("override a specific flake input (e.g. 'dwarffs/nixpkgs')")
         .arity(2)