Automatically look for built-in definitions

bin/ruby-build

@@ -2,6 +2,20 @@
 
 set -e
 
+abs_dirname() {
+  local cwd="$(pwd)"
+  local path="$1"
+
+  while [ -n "$path" ]; do
+    cd "${path%/*}"
+    local name="${path##*/}"
+    path="$(readlink "$name" || true)"
+  done
+
+  pwd
+  cd "$cwd"
+}
+
 install_package() {
   local cwd="$(pwd)"
   local package_name="$1"
@@ -96,12 +110,19 @@ usage() {
 }
 
 
+RUBY_BUILD_ROOT="$(abs_dirname "$0")/.."
+
 DEFINITION_PATH="$1"
 if [ -z "$DEFINITION_PATH" ]; then
   usage
 elif [ ! -e "$DEFINITION_PATH" ]; then
-  echo "ruby-build: definition not found: ${DEFINITION_PATH}" >&2
-  exit 1
+  BUILTIN_DEFINITION_PATH="${RUBY_BUILD_ROOT}/share/ruby-build/${DEFINITION_PATH}"
+  if [ -e "$BUILTIN_DEFINITION_PATH" ]; then
+    DEFINITION_PATH="$BUILTIN_DEFINITION_PATH"
+  else
+    echo "ruby-build: definition not found: ${DEFINITION_PATH}" >&2
+    exit 1
+  fi
 fi
 
 PREFIX_PATH="$2"