build: Allow setting the out link

Signed-off-by: Gergely Nagy <me@gergo.csillger.hu>

README.md

@@ -44,6 +44,7 @@ A thin wrapper around `nix build`, to make it slightly easier to build flakes. W
     flake: .
     package: # there's no default, Nix itself will fall back to "default"
     logs: false
+    out-link: "result"
 ```
 
 By default, it builds the default package in the flake at the root of the repository the action is used for, thus, if all you want to do is build the default package, and don't care about seeing full logs, you do not need to specify any parameters, the action will do the right thing out of the box.

build/action.yml

@@ -14,6 +14,10 @@ inputs:
     description: "Enable showing the full build logs"
     default: false
     required: false
+  out-link:
+    description: "Use this prefix for the symlinks to the build results"
+    default: "result"
+    required: true
 outputs:
   output-path:
     description: "The resulting output paths"
@@ -28,3 +32,4 @@ runs:
         INPUT_FLAKE: ${{ inputs.flake }}
         INPUT_PACKAGE: ${{ inputs.package }}
         INPUT_LOGS: ${{ inputs.logs }}
+        INPUT_OUT_LINK: ${{ inputs.out-link }}

build/bin/nix-build

@@ -8,5 +8,5 @@ case "${INPUT_LOGS}" in
         ;;
 esac
 
-nix build ${LOGS} "${INPUT_FLAKE}#${INPUT_PACKAGE}"
-echo "output-path=$(readlink result)" >>"${GITHUB_OUTPUT}"
+nix build ${LOGS} --out-link "${INPUT_OUT_LINK}" "${INPUT_FLAKE}#${INPUT_PACKAGE}"
+echo "output-path=$(readlink "${INPUT_OUT_LINK}")" >>"${GITHUB_OUTPUT}"