Support building with version prefix

Commonly in CI pipelines and other scripts, users may
want to install the latest from a specific series, e.g.
`3.4` or `jruby-10.0`.

```bash
$ bin/ruby-build 3.4 /tmp/3.4
...
Downloading ruby-3.4.9.tar.gz...

$ bin/ruby-build 4.0 /tmp/4.0
...
Downloading ruby-4.0.2.tar.gz...
```

Author: byroot

bin/ruby-build

@@ -1401,6 +1401,22 @@ list_maintained_versions() {
   } | extract_latest_versions | sort_versions | uniq
 }
 
+resolve_version() {
+  prefix="${1}"
+  { for DEFINITION_DIR in "${RUBY_BUILD_DEFINITIONS[@]}"; do
+      if [[ -d "$DEFINITION_DIR" ]]; then
+        pushd "$DEFINITION_DIR" > /dev/null
+        for f in "${prefix}"*; do
+          echo "${f}" | \
+          grep "^${prefix}\." | \
+          grep -v -e '-rc[0-9]*$' -e '-preview[0-9]*$' -e '-dev$'
+        done
+        popd > /dev/null
+      fi
+    done
+  } | extract_latest_versions | tail -n 1
+}
+
 extract_latest_versions() {
   # sort in this function looks redundunt but it is necessary
   # rbx-3.99 appears latest unless the sort
@@ -1543,6 +1559,16 @@ if [[ ! -f "$DEFINITION_PATH" && ! -p "$DEFINITION_PATH" ]]; then
     done
   fi
 
+  if [ ! -f "$DEFINITION_PATH" ]; then
+    fully_qualified_version=$(resolve_version "$DEFINITION_PATH")
+    for DEFINITION_DIR in "${RUBY_BUILD_DEFINITIONS[@]}"; do
+      if [ -f "${DEFINITION_DIR}/${fully_qualified_version}" ]; then
+        DEFINITION_PATH="${DEFINITION_DIR}/${fully_qualified_version}"
+        break
+      fi
+    done
+  fi
+
   if [ ! -f "$DEFINITION_PATH" ]; then
     echo "ruby-build: definition not found: ${DEFINITION_PATH}" >&2
     exit 2

test/definitions.bats

@@ -60,6 +60,20 @@ NUM_DEFINITIONS="$(ls "$BATS_TEST_DIRNAME"/../share/ruby-build | wc -l)"
   assert_success ""
 }
 
+@test "installing definition by prefix" {
+  export RUBY_BUILD_DEFINITIONS="${TMP}/definitions"
+  mkdir -p "${TMP}/definitions"
+
+  echo false > "${TMP}/definitions/1.8.6"
+  echo false > "${TMP}/definitions/1.9.3"
+  echo true  > "${TMP}/definitions/1.9.10"
+  echo false > "${TMP}/definitions/1.90.0"
+  echo false > "${TMP}/definitions/2.0.0"
+
+  run bin/ruby-build "1.9" "${TMP}/install"
+  assert_success ""
+}
+
 @test "installing nonexistent definition" {
   run ruby-build "nonexistent" "${TMP}/install"
   assert [ "$status" -eq 2 ]