From 65e67be4b9ff48624c71323ed7e501a6e105387f Mon Sep 17 00:00:00 2001
From: Leo Arnold <opensource@leoarnold.de>
Date: Tue, 26 May 2026 00:19:41 +0200
Subject: [PATCH] Share gems between Ruby minor versions

ASDF itself treats every install as a separate entity and does not
have a concept of sharing data between installs.

Luckily, Rubygems already provides such a concept through
[`Gem.user_dir`](https://github.com/ruby/rubygems/blob/v4.0.12/lib/rubygems/defaults.rb#L103-L109)
which holds a value like

```text
/home/johndoe/.gem/4.0.0
```

There are two features to note here:

- Since ASDF will usually install everything into the user's home
  directory (i.e. `~/.asdf/`), we can do the same with the Ruby gems
  (by using `~/.gem`) without loss of generality.
- While `RUBY_VERSION` changes with every Ruby release, the built-in
  value `RbConfig::CONFIG["ruby_version"]` stays the same for all
  versions of Ruby which are binary compatible. For example,
  all Ruby releases in the `3.4.X` series will have `3.4.0` as the
  value of `RbConfig::CONFIG["ruby_version"]`.

So, in order to have communal gem homes for binary compatible
releases of Ruby, all we need to do is to use `Gem.user_dir` as
`GEM_HOME`. We set this value at runtime using `bin/exec-env`

Fixes #119
---
 bin/exec-env       |  6 ++++++
 bin/list-bin-paths |  6 ++++--
 lib/utils.sh       | 15 +++++++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/bin/exec-env b/bin/exec-env
index 986bf4d..f2c2d07 100755
--- a/bin/exec-env
+++ b/bin/exec-env
@@ -3,9 +3,15 @@
 current_script_path="${BASH_SOURCE[0]}"
 ruby_plugin_dir="$(dirname "$(dirname "$current_script_path")")"
 
+source "$ruby_plugin_dir/lib/utils.sh"
+
 RUBYLIB=${RUBYLIB:-}
 if [ "$RUBYLIB" = "" ]; then
   export RUBYLIB="$ruby_plugin_dir/rubygems-plugin"
 else
   export RUBYLIB="$ruby_plugin_dir/rubygems-plugin:$RUBYLIB"
 fi
+
+if output=$(gem_user_dir); then
+  export GEM_HOME="$output"
+fi
diff --git a/bin/list-bin-paths b/bin/list-bin-paths
index e24bb72..66a7d0c 100755
--- a/bin/list-bin-paths
+++ b/bin/list-bin-paths
@@ -1,4 +1,6 @@
 #!/usr/bin/env bash
 
-gem_version="${ASDF_INSTALL_VERSION%.*}.0"
-echo "bin lib/ruby/gems/$gem_version/bin"
+# shellcheck source=/dev/null
+source "$(dirname "$0")/../lib/utils.sh"
+
+echo "bin lib/ruby/gems/$(ruby_minor_version)/bin"
diff --git a/lib/utils.sh b/lib/utils.sh
index 6e863bf..2608856 100644
--- a/lib/utils.sh
+++ b/lib/utils.sh
@@ -76,3 +76,18 @@ ruby_build_source_dir() {
 ruby_build_path() {
   echo "$(ruby_build_dir)/bin/ruby-build"
 }
+
+# Prevent ASDF from repeatedly invoking itself (e.g. via bin/exec-env)
+# until the host machine runs out of memory
+ruby_bypassing_asdf_callbacks() {
+  "$ASDF_INSTALL_PATH/bin/ruby" "$@"
+}
+
+ruby_minor_version() {
+  ruby_bypassing_asdf_callbacks -e 'puts RbConfig::CONFIG["ruby_version"]'
+}
+
+gem_user_dir() {
+  ruby_bypassing_asdf_callbacks -rrubygems -e 'puts Gem.user_dir'
+}
+