Introduce guessed receiver types (#2210)

* Introduce guessed types

* Use guessed types in hover

* Use guessed types in signature help

* Use guessed types in completion

* Address PR feedback

DESIGN_AND_ROADMAP.md

@@ -218,3 +218,85 @@ Interested in contributing? Check out the issues tagged with [help-wanted] or [g
 [Explore speeding up indexing by caching the index for gems]: https://github.com/Shopify/ruby-lsp/issues/1009
 [Add range formatting support for formatters that do support it]: https://github.com/Shopify/ruby-lsp/issues/203
 [Add ERB support]: https://github.com/Shopify/ruby-lsp/issues/1055
+
+## Guessed types
+
+Guessed types is an experimental feature where the Ruby LSP attempts to identify the type of a receiver based on its
+identifier name. For example:
+
+```ruby
+# The receiver identifier here is `user` and so the Ruby LSP will assign to it the `User` type if that class exists
+user.name
+
+# Similarly, the receiver identifier here is `post` and so the LSP searches for the `Post` class
+@post.like!
+```
+
+> [!IMPORTANT] The goal of this experiment is to understand if we can get better accuracy for the code that you already
+> have. The hypothesis is that a reasonable amount of code already uses patterns like the ones in the example and, in
+> those cases, we can achieve nicer results.
+>
+> However, identifiers are not the ideal medium for proper type annotations. It would not be possible to express anything
+> complex, such as unions, intersections or generics. Additionally, it is very trivial to fool the type guessing by simply
+> naming a variable with a type name that doesn't match its actual type.
+
+```ruby
+pathname = something_that_returns_an_integer
+# This will show methods available in `Pathname`, despite the variable being an Integer
+pathname.a
+```
+
+We do not recommend renaming methods, instance variables or local variables for the sole purpose of getting better
+accuracy - readibility should always come first. For example:
+
+```ruby
+# It would not be a good idea to name every string "string" for the sake of getting better accuracy.
+# Using descriptive names will outweight the benefits of the more accurate editor experience
+
+# don't
+string = something.other_thing
+
+# do
+title = something.other_thing
+name = foo
+```
+
+That said, this feature can also be used for quickly exploring methods available in classes. Simply type the lower case
+name of the class and completion can show the methods available.
+
+```ruby
+# Any class name as an identifier
+pathname.a
+integer.a
+file.a
+```
+
+To guess types, the Ruby LSP will first try to resolve a constant based on the receiver identifier and current nesting.
+If that does not identify any valid types, then it will fallback to matching based on the first match for the
+unqualified type name. For example:
+
+```ruby
+module Admin
+  class User
+  end
+
+  # Will match to `Admin::User` because the `user` reference is inside the `Admin` namespace
+  user.a
+end
+
+module Blog
+  class User
+  end
+
+  # Will match to `Blog::User` because the `user` reference is inside the `Blog` namespace
+  user.a
+end
+
+# Will match to the first class that has the unqualified name of `User`. This may return `Admin::User` or `Blog::User`
+# randomly
+user.a
+```
+
+This is an experimental feature and can only be accessed if `initializationOptions.experimentalFeaturesEnabled` is
+`true` (the `"rubyLsp.enableExperimentalFeatures": true` setting for VS Code users). If you have feedback about this
+experiment, please let us know in a GitHub issue.

lib/ruby_indexer/lib/ruby_indexer/index.rb

@@ -84,6 +84,34 @@ def search_require_paths(query)
       @require_paths_tree.search(query)
     end
 
+    # Searches for a constant based on an unqualified name and returns the first possible match regardless of whether
+    # there are more possible matching entries
+    sig do
+      params(
+        name: String,
+      ).returns(T.nilable(T::Array[T.any(
+        Entry::Namespace,
+        Entry::Alias,
+        Entry::UnresolvedAlias,
+        Entry::Constant,
+      )]))
+    end
+    def first_unqualified_const(name)
+      _name, entries = @entries.find do |const_name, _entries|
+        const_name.end_with?(name)
+      end
+
+      T.cast(
+        entries,
+        T.nilable(T::Array[T.any(
+          Entry::Namespace,
+          Entry::Alias,
+          Entry::UnresolvedAlias,
+          Entry::Constant,
+        )]),
+      )
+    end
+
     # Searches entries in the index based on an exact prefix, intended for providing autocomplete. All possible matches
     # to the prefix are returned. The return is an array of arrays, where each entry is the array of entries for a given
     # name match. For example:

lib/ruby_indexer/test/index_test.rb

@@ -1542,6 +1542,21 @@ class Foo
       assert_empty(@index.method_completion_candidates("bar", "Foo"))
     end
 
+    def test_first_unqualified_const
+      index(<<~RUBY)
+        module Foo
+          class Bar; end
+        end
+
+        module Baz
+          class Bar; end
+        end
+      RUBY
+
+      entry = T.must(@index.first_unqualified_const("Bar")&.first)
+      assert_equal("Foo::Bar", entry.name)
+    end
+
     def test_completion_does_not_duplicate_overridden_methods
       index(<<~RUBY)
         class Foo

lib/ruby_lsp/global_state.rb

@@ -36,10 +36,10 @@ def initialize
       @test_library = T.let("minitest", String)
       @has_type_checker = T.let(true, T::Boolean)
       @index = T.let(RubyIndexer::Index.new, RubyIndexer::Index)
-      @type_inferrer = T.let(TypeInferrer.new(@index), TypeInferrer)
       @supported_formatters = T.let({}, T::Hash[String, Requests::Support::Formatter])
       @supports_watching_files = T.let(false, T::Boolean)
       @experimental_features = T.let(false, T::Boolean)
+      @type_inferrer = T.let(TypeInferrer.new(@index, @experimental_features), TypeInferrer)
     end
 
     sig { params(identifier: String, instance: Requests::Support::Formatter).void }
@@ -90,6 +90,7 @@ def apply_options(options)
       end
 
       @experimental_features = options.dig(:initializationOptions, :experimentalFeaturesEnabled) || false
+      @type_inferrer.experimental_features = @experimental_features
     end
 
     sig { returns(String) }

lib/ruby_lsp/listeners/completion.rb

@@ -262,7 +262,7 @@ def handle_instance_variable_completion(name, location)
         type = @type_inferrer.infer_receiver_type(@node_context)
         return unless type
 
-        @index.instance_variable_completion_candidates(name, type).each do |entry|
+        @index.instance_variable_completion_candidates(name, type.name).each do |entry|
           variable_name = entry.name
 
           label_details = Interface::CompletionItemLabelDetails.new(
@@ -366,8 +366,11 @@ def complete_methods(node, name)
 
         return unless range
 
-        @index.method_completion_candidates(method_name, type).each do |entry|
+        guessed_type = type.name
+
+        @index.method_completion_candidates(method_name, type.name).each do |entry|
           entry_name = entry.name
+          owner_name = entry.owner&.name
 
           label_details = Interface::CompletionItemLabelDetails.new(
             description: entry.file_name,
@@ -380,7 +383,8 @@ def complete_methods(node, name)
             text_edit: Interface::TextEdit.new(range: range, new_text: entry_name),
             kind: Constant::CompletionItemKind::METHOD,
             data: {
-              owner_name: entry.owner&.name,
+              owner_name: owner_name,
+              guessed_type: guessed_type,
             },
           )
         end

lib/ruby_lsp/listeners/definition.rb

@@ -65,7 +65,7 @@ def on_call_node_enter(node)
 
         # Until we can properly infer the receiver type in erb files (maybe with ruby-lsp-rails),
         # treating method calls' type as `nil` will allow users to get some completion support first
-        if @language_id == Document::LanguageId::ERB && inferrer_receiver_type == "Object"
+        if @language_id == Document::LanguageId::ERB && inferrer_receiver_type&.name == "Object"
           inferrer_receiver_type = nil
         end
 
@@ -176,7 +176,7 @@ def handle_instance_variable_definition(name)
         type = @type_inferrer.infer_receiver_type(@node_context)
         return unless type
 
-        entries = @index.resolve_instance_variable(name, type)
+        entries = @index.resolve_instance_variable(name, type.name)
         return unless entries
 
         entries.each do |entry|
@@ -194,10 +194,10 @@ def handle_instance_variable_definition(name)
         # If by any chance we haven't indexed the owner, then there's no way to find the right declaration
       end
 
-      sig { params(message: String, receiver_type: T.nilable(String), inherited_only: T::Boolean).void }
+      sig { params(message: String, receiver_type: T.nilable(TypeInferrer::Type), inherited_only: T::Boolean).void }
       def handle_method_definition(message, receiver_type, inherited_only: false)
         methods = if receiver_type
-          @index.resolve_method(message, receiver_type, inherited_only: inherited_only)
+          @index.resolve_method(message, receiver_type.name, inherited_only: inherited_only)
         else
           # If the method doesn't have a receiver, then we provide a few candidates to jump to
           # But we don't want to provide too many candidates, as it can be overwhelming

lib/ruby_lsp/listeners/hover.rb

@@ -171,11 +171,16 @@ def handle_method_hover(message, inherited_only: false)
         type = @type_inferrer.infer_receiver_type(@node_context)
         return unless type
 
-        methods = @index.resolve_method(message, type, inherited_only: inherited_only)
+        methods = @index.resolve_method(message, type.name, inherited_only: inherited_only)
         return unless methods
 
         title = "#{message}#{T.must(methods.first).decorated_parameters}"
 
+        if type.is_a?(TypeInferrer::GuessedType)
+          title << "\n\nGuessed receiver: #{type.name}"
+          @response_builder.push("[Learn more about guessed types](#{GUESSED_TYPES_URL})\n", category: :links)
+        end
+
         categorized_markdown_from_index_entries(title, methods).each do |category, content|
           @response_builder.push(content, category: category)
         end
@@ -190,7 +195,7 @@ def handle_instance_variable_hover(name)
         type = @type_inferrer.infer_receiver_type(@node_context)
         return unless type
 
-        entries = @index.resolve_instance_variable(name, type)
+        entries = @index.resolve_instance_variable(name, type.name)
         return unless entries
 
         categorized_markdown_from_index_entries(name, entries).each do |category, content|

lib/ruby_lsp/listeners/signature_help.rb

@@ -36,7 +36,7 @@ def on_call_node_enter(node)
         type = @type_inferrer.infer_receiver_type(@node_context)
         return unless type
 
-        methods = @index.resolve_method(message, type)
+        methods = @index.resolve_method(message, type.name)
         return unless methods
 
         target_method = methods.first
@@ -61,14 +61,21 @@ def on_call_node_enter(node)
           active_parameter += 1
         end
 
+        title = +""
+
+        extra_links = if type.is_a?(TypeInferrer::GuessedType)
+          title << "\n\nGuessed receiver: #{type.name}"
+          "[Learn more about guessed types](#{GUESSED_TYPES_URL})"
+        end
+
         signature_help = Interface::SignatureHelp.new(
           signatures: [
             Interface::SignatureInformation.new(
               label: label,
               parameters: parameters.map { |param| Interface::ParameterInformation.new(label: param.name) },
               documentation: Interface::MarkupContent.new(
                 kind: "markdown",
-                value: markdown_from_index_entries("", methods),
+                value: markdown_from_index_entries(title, methods, extra_links: extra_links),
               ),
             ),
           ],

lib/ruby_lsp/requests/completion_resolve.rb

@@ -47,7 +47,7 @@ def perform
         #
         # For example, forgetting to return the `insertText` included in the original item will make the editor use the
         # `label` for the text edit instead
-        label = @item[:label]
+        label = @item[:label].dup
         entries = @index[label] || []
 
         owner_name = @item.dig(:data, :owner_name)
@@ -62,12 +62,19 @@ def perform
         first_entry = T.must(entries.first)
 
         if first_entry.is_a?(RubyIndexer::Entry::Member)
-          label = "#{label}#{first_entry.decorated_parameters}"
+          label = +"#{label}#{first_entry.decorated_parameters}"
+        end
+
+        guessed_type = @item.dig(:data, :guessed_type)
+
+        extra_links = if guessed_type
+          label << "\n\nGuessed receiver: #{guessed_type}"
+          "[Learn more about guessed types](#{GUESSED_TYPES_URL})"
         end
 
         @item[:documentation] = Interface::MarkupContent.new(
           kind: "markdown",
-          value: markdown_from_index_entries(label, entries, MAX_DOCUMENTATION_ENTRIES),
+          value: markdown_from_index_entries(label, entries, MAX_DOCUMENTATION_ENTRIES, extra_links: extra_links),
         )
 
         @item

lib/ruby_lsp/requests/support/common.rb

@@ -130,13 +130,17 @@ def categorized_markdown_from_index_entries(title, entries, max_entries = nil)
             title: String,
             entries: T.any(T::Array[RubyIndexer::Entry], RubyIndexer::Entry),
             max_entries: T.nilable(Integer),
+            extra_links: T.nilable(String),
           ).returns(String)
         end
-        def markdown_from_index_entries(title, entries, max_entries = nil)
+        def markdown_from_index_entries(title, entries, max_entries = nil, extra_links: nil)
           categorized_markdown = categorized_markdown_from_index_entries(title, entries, max_entries)
 
+          markdown = +(categorized_markdown[:title] || "")
+          markdown << "\n\n#{extra_links}" if extra_links
+
           <<~MARKDOWN.chomp
-            #{categorized_markdown[:title]}
+            #{markdown}
 
             #{categorized_markdown[:links]}
 

lib/ruby_lsp/test_helper.rb

@@ -21,7 +21,7 @@ def with_server(source = nil, uri = Kernel.URI("file:///fake.rb"), stub_no_typec
       &block)
       server = RubyLsp::Server.new(test_mode: true)
       server.global_state.stubs(:has_type_checker).returns(false) if stub_no_typechecker
-      server.global_state.apply_options({})
+      server.global_state.apply_options({ initializationOptions: { experimentalFeaturesEnabled: true } })
       language_id = uri.to_s.end_with?(".erb") ? "erb" : "ruby"
 
       if source