[ruby/error_highlight] Identify which node in Foo::Bar::Baz causes a NameError

In Ruby 3.2 or later, a nested constant access like `Foo::Bar::Baz` is
compiled to one instruction by the optimization https://github.com/ruby/ruby/pull/6187

We try to spot which sub-node caues a NameError in question based on the
constant name. We will give up if the same constant name is accessed in
a nested access (`Foo::Foo`).

Fixes https://github.com/ruby/error_highlight/pull/31

https://github.com/ruby/error_highlight/commit/0a4db7da0a

lib/error_highlight/base.rb

@@ -98,9 +98,40 @@ module ErrorHighlight
       end
     end
 
+    OPT_GETCONSTANT_PATH = (RUBY_VERSION.split(".").map {|s| s.to_i } <=> [3, 2]) >= 0
+    private_constant :OPT_GETCONSTANT_PATH
+
     def spot
       return nil unless @node
 
+      if OPT_GETCONSTANT_PATH && @node.type == :COLON2
+        # In Ruby 3.2 or later, a nested constant access (like `Foo::Bar::Baz`)
+        # is compiled to one instruction (opt_getconstant_path).
+        # @node points to the node of the whole `Foo::Bar::Baz` even if `Foo`
+        # or `Foo::Bar` causes NameError.
+        # So we try to spot the sub-node that causes the NameError by using
+        # `NameError#name`.
+        subnodes = []
+        node = @node
+        while node.type == :COLON2
+          node2, const = node.children
+          subnodes << node if const == @name
+          node = node2
+        end
+        if node.type == :CONST || node.type == :COLON3
+          if node.children.first == @name
+            subnodes << node
+          end
+
+          # If we found only one sub-node whose name is equal to @name, use it
+          return nil if subnodes.size != 1
+          @node = subnodes.first
+        else
+          # Do nothing; opt_getconstant_path is used only when the const base is
+          # NODE_CONST (`Foo`) or NODE_COLON3 (`::Foo`)
+        end
+      end
+
       case @node.type
 
       when :CALL, :QCALL

test/error_highlight/test_error_highlight.rb

@@ -818,6 +818,54 @@ uninitialized constant ErrorHighlightTest::NotDefined
     end
   end
 
+  def test_COLON2_3
+    assert_error_message(NameError, <<~END) do
+uninitialized constant ErrorHighlightTest::NotDefined
+
+      ErrorHighlightTest::NotDefined::Foo
+                        ^^^^^^^^^^^^
+    END
+
+      ErrorHighlightTest::NotDefined::Foo
+    end
+  end
+
+  def test_COLON2_4
+    assert_error_message(NameError, <<~END) do
+uninitialized constant ErrorHighlightTest::NotDefined
+
+      ::ErrorHighlightTest::NotDefined::Foo
+                          ^^^^^^^^^^^^
+    END
+
+      ::ErrorHighlightTest::NotDefined::Foo
+    end
+  end
+
+  if ErrorHighlight.const_get(:Spotter).const_get(:OPT_GETCONSTANT_PATH)
+    def test_COLON2_5
+      # Unfortunately, we cannot identify which `NotDefined` caused the NameError
+      assert_error_message(NameError, <<~END) do
+uninitialized constant ErrorHighlightTest::NotDefined
+      END
+
+        ErrorHighlightTest::NotDefined::NotDefined
+      end
+    end
+  else
+    def test_COLON2_5
+      assert_error_message(NameError, <<~END) do
+uninitialized constant ErrorHighlightTest::NotDefined
+
+        ErrorHighlightTest::NotDefined::NotDefined
+                          ^^^^^^^^^^^^
+      END
+
+        ErrorHighlightTest::NotDefined::NotDefined
+      end
+    end
+  end
+
   def test_COLON3
     assert_error_message(NameError, <<~END) do
 uninitialized constant NotDefined