build-support: Fix error when building images with many layers

When building a docker image using `dockertools.buildLayeredImage`, the
resulting image layers are passed to `jq` through the command line. When
building an image with too many layers this would exceed the maximum
command line argument length.

Hence, we store the list of layers in the Nix store and pass them to
`jq` as a file argument using `--slurpfile`.

Fixes #140908.

pkgs/build-support/docker/default.nix

@@ -935,33 +935,34 @@ rec {
           # following lines, double-check that your code behaves properly
           # when the number of layers equals:
           #      maxLayers-1, maxLayers, and maxLayers+1, 0
-          store_layers="$(
-            paths |
-              jq -sR '
-                rtrimstr("\n") | split("\n")
-                  | (.[:$maxLayers-1] | map([.])) + [ .[$maxLayers-1:] ]
-                  | map(select(length > 0))
+          paths |
+            jq -sR '
+              rtrimstr("\n") | split("\n")
+                | (.[:$maxLayers-1] | map([.])) + [ .[$maxLayers-1:] ]
+                | map(select(length > 0))
               ' \
-                --argjson maxLayers "$availableLayers"
-          )"
+              --argjson maxLayers "$availableLayers" > store_layers.json
 
+          # The index on $store_layers is necessary because the --slurpfile
+          # automatically reads the file as an array.
           cat ${baseJson} | jq '
             . + {
               "store_dir": $store_dir,
               "from_image": $from_image,
-              "store_layers": $store_layers,
+              "store_layers": $store_layers[0],
               "customisation_layer", $customisation_layer,
               "repo_tag": $repo_tag,
               "created": $created
             }
             ' --arg store_dir "${storeDir}" \
               --argjson from_image ${if fromImage == null then "null" else "'\"${fromImage}\"'"} \
-              --argjson store_layers "$store_layers" \
+              --slurpfile store_layers store_layers.json \
               --arg customisation_layer ${customisationLayer} \
               --arg repo_tag "$imageName:$imageTag" \
               --arg created "$created" |
             tee $out
         '';
+
         result = runCommand "stream-${baseName}"
           {
             inherit (conf) imageName;