Add heredoc delimiter documentation on hover

Co-authored-by: Nick Schwaderer <Schwad@users.noreply.github.com>

lib/ruby_lsp/listeners/hover.rb

@@ -21,6 +21,7 @@ class Hover
           Prism::InstanceVariableWriteNode,
           Prism::SymbolNode,
           Prism::StringNode,
+          Prism::InterpolatedStringNode,
           Prism::SuperNode,
           Prism::ForwardingSuperNode,
         ],
@@ -68,9 +69,21 @@ def initialize(response_builder, global_state, uri, node_context, dispatcher, so
           :on_instance_variable_target_node_enter,
           :on_super_node_enter,
           :on_forwarding_super_node_enter,
+          :on_string_node_enter,
+          :on_interpolated_string_node_enter,
         )
       end
 
+      sig { params(node: Prism::StringNode).void }
+      def on_string_node_enter(node)
+        generate_heredoc_hover(node)
+      end
+
+      sig { params(node: Prism::InterpolatedStringNode).void }
+      def on_interpolated_string_node_enter(node)
+        generate_heredoc_hover(node)
+      end
+
       sig { params(node: Prism::ConstantReadNode).void }
       def on_constant_read_node_enter(node)
         return if @sorbet_level != RubyDocument::SorbetLevel::Ignore
@@ -155,6 +168,22 @@ def on_forwarding_super_node_enter(node)
 
       private
 
+      sig { params(node: T.any(Prism::InterpolatedStringNode, Prism::StringNode)).void }
+      def generate_heredoc_hover(node)
+        opening_content = node.opening_loc&.slice
+        return unless opening_content
+
+        match = /(?<=<<(-|~))(?<quote>['"`]?)(?<delimiter>\w+)\k<quote>/.match(opening_content)
+        heredoc_delimiter = match && match.named_captures["delimiter"]
+
+        if heredoc_delimiter
+          @response_builder.push(
+            "This is a heredoc definition using the `#{heredoc_delimiter}` delimiter",
+            category: :documentation,
+          )
+        end
+      end
+
       sig { void }
       def handle_super_node_hover
         # Sorbet can handle super hover on typed true or higher

test/expectations/hover/heredoc.exp.json

@@ -0,0 +1,14 @@
+{
+    "params": [
+        {
+            "line": 0,
+            "character": 2
+        }
+    ],
+    "result": {
+        "contents": {
+            "kind": "markdown",
+            "value": "This is a heredoc definition using the `HEREDOC` delimiter"
+        }
+    }
+}