[GR-19220] Fix Method/Proc #parameters method when there are multiple _ parameters

PullRequest: truffleruby/3745

Author: andrykonchin

CHANGELOG.md

@@ -52,6 +52,7 @@ Bug fixes:
 * Fix `MatchData#[]` to support negative `length` argument (#2929, @andrykonchin).
 * Fix `IO` line reading calls when using a multi-byte delimiter (`IO#{each,gets,readline,readlines,etc.}) (#2961, @vinistock, @nirvdrum).
 * Fix the exception type raised when type coercion raises a `NoMethodError` (#2903, @paracycle, @nirvdrum).
+* Fix `Method` and `Proc` `#parameters` method to return `_` parameter name without synthetic suffix when there are multiple `_` parameters (@paracycle).
 
 Compatibility:
 

spec/ruby/core/method/parameters_spec.rb

@@ -20,6 +20,8 @@ def one_splat_one_block(*args, &block)
       local_is_not_parameter = {}
     end
 
+    def underscore_parameters(_, _, _ = 1, *_, _:, _: 2, **_, &_); end
+
     define_method(:one_optional_defined_method) {|x = 1|}
   end
 
@@ -251,6 +253,20 @@ def one_splat_one_block(*args, &block)
     m.method(:writer=).parameters.should == [[:req]]
   end
 
+  it "returns all parameters defined with the name _ as _" do
+    m = MethodSpecs::Methods.instance_method(:underscore_parameters)
+    m.parameters.should == [
+      [:req, :_],
+      [:req, :_],
+      [:opt, :_],
+      [:rest, :_],
+      [:keyreq, :_],
+      [:key, :_],
+      [:keyrest, :_],
+      [:block, :_]
+    ]
+  end
+
   it "returns [[:rest]] for core methods with variable-length argument lists" do
     # delete! takes rest args
     "foo".method(:delete!).parameters.should == [[:rest]]

spec/ruby/core/proc/parameters_spec.rb

@@ -115,4 +115,30 @@
       local_is_not_parameter = {}
     end.parameters.should == [[:rest, :args], [:block, :blk]]
   end
+
+  it "returns all parameters defined with the name _ as _" do
+    proc = proc {|_, _, _ = 1, *_, _:, _: 2, **_, &_| }
+    proc.parameters.should == [
+      [:opt, :_],
+      [:opt, :_],
+      [:opt, :_],
+      [:rest, :_],
+      [:keyreq, :_],
+      [:key, :_],
+      [:keyrest, :_],
+      [:block, :_]
+    ]
+
+    lambda = ->(_, _, _ = 1, *_, _:, _: 2, **_, &_) {}
+    lambda.parameters.should == [
+      [:req, :_],
+      [:req, :_],
+      [:opt, :_],
+      [:rest, :_],
+      [:keyreq, :_],
+      [:key, :_],
+      [:keyrest, :_],
+      [:block, :_]
+    ]
+  end
 end

src/main/java/org/truffleruby/language/arguments/ArgumentDescriptorUtils.java

@@ -47,6 +47,11 @@ private static RubyArray toArray(RubyLanguage language, RubyContext context, Arg
         if (argType.anonymous || name == null) {
             store = new Object[]{ language.getSymbol(argType.symbolicName) };
         } else {
+            // make sure to normalize parameter names to "_" if they start with "_$"
+            if (name.startsWith("_$")) {
+                name = "_";
+            }
+
             store = new Object[]{ language.getSymbol(argType.symbolicName), language.getSymbol(name) };
         }