[ruby/prism] Support `version: "nearest"`.

This clamps to supported versions based on the current Ruby version.

https://github.com/ruby/prism/commit/eb63748e8b

3 files changed, 49 insertions, 10 deletions

diff --git a/lib/prism/ffi.rb b/lib/prism/ffi.rb
index d4c9d60c9a..57d878a33f 100644
--- a/lib/prism/ffi.rb
+++ b/lib/prism/ffi.rb
@@ -423,10 +423,26 @@ module Prism
 
     # Return the value that should be dumped for the version option.
     def dump_options_version(version)
-      current = version == "current"
+      checking =
+        case version
+        when "current"
+          RUBY_VERSION
+        when "latest"
+          nil
+        when "nearest"
+          if RUBY_VERSION <= "3.3"
+            "3.3"
+          elsif RUBY_VERSION >= "4.1"
+            "4.1"
+          else
+            RUBY_VERSION
+          end
+        else
+          version
+        end
 
-      case current ? RUBY_VERSION : version
-      when nil, "latest"
+      case checking
+      when nil
         0 # Handled in pm_parser_init
       when /\A3\.3(\.\d+)?\z/
         1
@@ -437,7 +453,7 @@ module Prism
       when /\A4\.1(\.\d+)?\z/
         4
       else
-        if current
+        if version == "current"
           raise CurrentVersionError, RUBY_VERSION
         else
           raise ArgumentError, "invalid version: #{version}"
diff --git a/prism/extension.c b/prism/extension.c
index 400546a4ce..cde10bf360 100644
--- a/prism/extension.c
+++ b/prism/extension.c
@@ -201,9 +201,24 @@ build_options_i(VALUE key, VALUE value, VALUE argument) {
             const char *version = check_string(value);
 
             if (RSTRING_LEN(value) == 7 && strncmp(version, "current", 7) == 0) {
-                const char *current_version = RSTRING_PTR(rb_const_get(rb_cObject, rb_intern("RUBY_VERSION")));
-                if (!pm_options_version_set(options, current_version, 3)) {
-                    rb_exc_raise(rb_exc_new_cstr(rb_cPrismCurrentVersionError, current_version));
+                const char *ruby_version = RSTRING_PTR(rb_const_get(rb_cObject, rb_intern("RUBY_VERSION")));
+                if (!pm_options_version_set(options, ruby_version, 3)) {
+                    rb_exc_raise(rb_exc_new_cstr(rb_cPrismCurrentVersionError, ruby_version));
+                }
+            } else if (RSTRING_LEN(value) == 7 && strncmp(version, "nearest", 7) == 0) {
+                const char *ruby_version = RSTRING_PTR(rb_const_get(rb_cObject, rb_intern("RUBY_VERSION")));
+                const char *nearest_version;
+
+                if (ruby_version[0] < '3' || (ruby_version[0] == '3' && ruby_version[2] < '3')) {
+                    nearest_version = "3.3";
+                } else if (ruby_version[0] > '4' || (ruby_version[0] == '4' && ruby_version[2] > '1')) {
+                    nearest_version = "4.1";
+                } else {
+                    nearest_version = ruby_version;
+                }
+
+                if (!pm_options_version_set(options, nearest_version, 3)) {
+                    rb_raise(rb_eArgError, "invalid nearest version: %s", nearest_version);
                 }
             } else if (!pm_options_version_set(options, version, RSTRING_LEN(value))) {
                 rb_raise(rb_eArgError, "invalid version: %" PRIsVALUE, value);
@@ -894,8 +909,10 @@ parse_input(pm_string_t *input, const pm_options_t *options) {
  *       version of Ruby syntax (which you can trigger with `nil` or
  *       `"latest"`). You may also restrict the syntax to a specific version of
  *       Ruby, e.g., with `"3.3.0"`. To parse with the same syntax version that
- *       the current Ruby is running use `version: "current"`. Raises
- *       ArgumentError if the version is not currently supported by Prism.
+ *       the current Ruby is running use `version: "current"`. To parse with the
+ *       nearest version to the current Ruby that is running, use
+ *       `version: "nearest"`. Raises ArgumentError if the version is not
+ *       currently supported by Prism.
  */
 static VALUE
 parse(int argc, VALUE *argv, VALUE self) {
diff --git a/prism/options.h b/prism/options.h
index c00c7bf755..9a19a2aead 100644
--- a/prism/options.h
+++ b/prism/options.h
@@ -82,7 +82,10 @@ typedef void (*pm_options_shebang_callback_t)(struct pm_options *options, const
  * parse in the same way as a specific version of CRuby would have.
  */
 typedef enum {
-    /** If an explicit version is not provided, the current version of prism will be used. */
+    /**
+     * If an explicit version is not provided, the current version of prism will
+     * be used.
+     */
     PM_OPTIONS_VERSION_UNSET = 0,
 
     /** The vendored version of prism in CRuby 3.3.x. */
@@ -452,6 +455,9 @@ PRISM_EXPORTED_FUNCTION void pm_options_free(pm_options_t *options);
  * | ----- | ------------------------- |
  * | `0`   | use the latest version of prism |
  * | `1`   | use the version of prism that is vendored in CRuby 3.3.0 |
+ * | `2`   | use the version of prism that is vendored in CRuby 3.4.0 |
+ * | `3`   | use the version of prism that is vendored in CRuby 4.0.0 |
+ * | `4`   | use the version of prism that is vendored in CRuby 4.1.0 |
  *
  * Each scope is laid out as follows:
  *