create hook: version-name

Expose a `version-name` hook.

It is invoked *after* the traditional `RBENV_VERSION` lookup. Which means hook scripts can interrogate `$RBENV_VERSION_FILE` and/or `$RBENV_VERSION` (or use the executables).

The hooks are then run, giving plugins a chance to alter `RBENV_VERSION`. Once the hooks have run, we now have (in `$RBENV_VERSION`) the actual version we want to use (or it's empty which defaults to `system` per normal). Lastly, the same logic remains for checking if the version exists, or trimming the `ruby-` prefix.

Prime example: the ruby-bundler-ruby-version plugin can select a ruby by using the `ruby` directive from the `Gemfile` if a local `.ruby-version` doesn't exist.

libexec/rbenv-version-name

@@ -8,6 +8,13 @@ if [ -z "$RBENV_VERSION" ]; then
   RBENV_VERSION="$(rbenv-version-file-read "$RBENV_VERSION_FILE" || true)"
 fi
 
+OLDIFS="$IFS"
+IFS=$'\n' scripts=(`rbenv-hooks version-name`)
+IFS="$OLDIFS"
+for script in "${scripts[@]}"; do
+  source "$script"
+done
+
 if [ -z "$RBENV_VERSION" ] || [ "$RBENV_VERSION" = "system" ]; then
   echo "system"
   exit

test/version-name.bats

@@ -2,6 +2,13 @@
 
 load test_helper
 
+export RBENV_HOOK_PATH="${RBENV_ROOT}/rbenv.d"
+
+create_hook() {
+  mkdir -p "${RBENV_ROOT}/rbenv.d/version-name"
+  cat > "${RBENV_ROOT}/rbenv.d/version-name/$1" <<<"$2"
+}
+
 create_version() {
   mkdir -p "${RBENV_ROOT}/versions/$1"
 }
@@ -22,6 +29,18 @@ setup() {
   assert_success "system"
 }
 
+@test "RBENV_VERSION can be overridden by hook" {
+  create_version "1.8.7"
+  create_version "1.9.3"
+
+  RBENV_VERSION=1.8.7 run rbenv-version-name
+  assert_success "1.8.7"
+
+  create_hook test.bash "RBENV_VERSION=1.9.3"
+  RBENV_VERSION=1.8.7 run rbenv-version-name
+  assert_success "1.9.3"
+}
+
 @test "RBENV_VERSION has precedence over local" {
   create_version "1.8.7"
   create_version "1.9.3"