README.maintainer.md: further improvements (#667)

README.maintainer.md

@@ -26,16 +26,16 @@ Suppose just the C++ wrappers need to be updated, without any changes to the
 Singular kernel itself.
 
 1. Commit changes to the `deps/src/` directory.
-   > ex: <https://github.com/oscar-system/Singular.jl/commit/73af1a6b0f99c11f00837c535db818ca2de7d9a2>
+   > ex: <https://github.com/oscar-system/Singular.jl/pull/661>
 
 2. After the changes are merged (and before the next `Singular.jl` release), update
    the `libsingular_julia` build script with a new version number and using the
    latest commit SHA for the `master` branch of `Singular.jl`.
-   > ex: <https://github.com/JuliaPackaging/Yggdrasil/commit/dd9d775f530b1164dd1cf6135677846dcb25fafc>
+   > ex: <https://github.com/JuliaPackaging/Yggdrasil/pull/6880>
 
 3. Wait for this to be merged into Yggdrasil, and then wait for the registry
    to pick up the new version of `libsingular_julia_jll`.
-   > ex: <https://github.com/JuliaRegistries/General/commit/00624106c204ccb28fb2c834877fb6005c653ce7>
+   > ex: <https://github.com/JuliaRegistries/General/pull/85185>
 
 4. Bump the dependence in `Singular.jl` to whatever version number was used in Step 2.
    > ex: <https://github.com/oscar-system/Singular.jl/commit/f669cea1aa4fc73082d8e8c08a1e33a7c22882ed>
@@ -53,7 +53,7 @@ in further downstream packages.
 Suppose the Singular kernel needs an update. This involves updating both build
 scripts because `libsingular_julia_jll` will need to point to the new `Singular_jll`.
 
-1. Update the Singular build script with the commit SHA of the singular sources (https://github.com/Singular/Singular)
+1. Update the Singular build script with the commit SHA of the singular sources at <https://github.com/Singular/Singular>
    > ex: <https://github.com/JuliaPackaging/Yggdrasil/commit/1996668f09e89bc8da0cc498c59d905821b150c8>
 
    In this specific commit, `FLINT_jll` was also updated, but this is not necessary to update singular.
@@ -87,3 +87,40 @@ Since updating the Singular kernel requires an update to `libsingular_julia`, th
 steps here are the same as in the previous section. Just make sure that in
 Step 3, the commit SHA used to update the `libsingular_julia` build scripts
 contains all of the desired changes to `libsingular_julia`.
+
+
+## Building a custom `Singular_jjl` locally
+
+For testing purposes one may wish to try out `Singular_jll` changes locally before
+submitting them as a PR to Yggdrasil. This can be done as shown in the following
+shell script:
+
+```shell
+# Change into a clone of the Yggdrasil repository
+git clone https://github.com/JuliaPackaging/Yggdrasil
+cd Yggdrasil
+
+# record the base path
+BASEPATH=$(pwd)
+
+# ensure building macOS binaries will work (you can omit this if you only
+# want to build for Linux)
+export BINARYBUILDER_AUTOMATIC_APPLE=true
+
+# change into the directory containing the `build_tarballs.jl` we want to build
+cd S/Singular_jll
+
+# Now `build_tarballs.jl` can be modified, e.g. to pull a different set of
+# sources, use different versions of dependencies, etc.
+
+# ensure BinaryBuilder etc. is installed in the right version
+# (ideally use the same Julia version as specified in `.ci/Manifest.toml`)
+julia --project=$BASEPATH/.ci -e 'using Pkg; Pkg.instantiate()'
+
+# get list of platforms etc.
+julia --project=$BASEPATH/.ci build_tarballs.jl --help
+
+# build and deploy the JLL locally. If you omit the comma-separated
+# list of PLATFORMS then it will build for *all* platforms
+julia --project=$BASEPATH/.ci build_tarballs.jl PLATFORMS --deploy=local
+```