From 76ee6c46c5e26c400289f3fbf152ba1a0bfb2bf0 Mon Sep 17 00:00:00 2001
From: Myron Marston <myron@squareup.com>
Date: Fri, 6 Dec 2024 21:20:21 -0800
Subject: [PATCH] Upgrade Steep to 1.9 and address new type check failures.

Steep 1.9 introduced support for `implicitly-returns-nil`[^1], which
causes it to treat all `hash[key]` and `array[index]` expressions as
nullable since the key or index might no be in the hash or array.
This makes the type checking stricter, yielding type checking errors
for some cases that could previously have failed at runtime due to
unexpected `nil` values.

To fix the new type check failures, I used a few different approaches:

* When doing a lookup in a hash that has a default proc, we know that
  `hash[key]` will never be `nil`. To communicate this to steep I've
  added a type assertion comment (e.g. `# : ::String`). Sometimes
  this forced me to break a single expression into multiple lines
  (so that I could put a type assertion on one part of the expression).
* Otherwise, if a value of `nil` would lead to a later runtime exception,
  I generally changed a hash lookup to use `hash.fetch(key)` instead.
  `fetch` is _not_ implicitly nil as it raises an error instead of
  returning `nil` when the key is not found. This provides a better
  error message than we would get from allowing a `nil` value.
* For other cases, I changed the code to accomodate possible `nil` values.

[^1]: https://github.com/soutaro/steep/wiki/Release-Note-1.9#implicitly-returns-nil-support
---
 .../index_definition/rollover_index_template.rb     |  2 +-
 .../graphql/aggregation/query_optimizer.rb          |  2 +-
 .../graphql/filtering/filter_args_translator.rb     |  2 +-
 .../lib/elastic_graph/graphql/http_endpoint.rb      |  2 +-
 .../elastic_graph/graphql/resolvers/query_source.rb |  2 +-
 .../sig/elastic_graph/graphql/http_endpoint.rbs     |  3 +--
 .../elastic_graph/health_check/health_checker.rb    |  3 ++-
 .../indexer/datastore_indexing_router.rb            | 12 +++++-------
 .../lib/elastic_graph/indexer/operation/factory.rb  |  2 +-
 .../lib/elastic_graph/indexer/record_preparer.rb    |  2 +-
 .../indexer_autoscaler_lambda/concurrency_scaler.rb |  3 ++-
 .../elastic_graph/json_schema/validator_factory.rb  |  2 +-
 .../elastic_graph/query_registry/query_validator.rb |  4 ++--
 .../variable_backward_incompatibility_detector.rb   |  4 ++--
 .../lib/elastic_graph/schema_artifacts/from_disk.rb |  2 +-
 .../runtime_metadata/extension_loader.rb            |  2 +-
 .../has_derived_graphql_type_customizations.rb      | 13 ++++++++-----
 .../schema_definition/mixins/has_subtypes.rb        |  5 +++--
 .../mixins/implements_interfaces.rb                 |  3 ++-
 .../lib/elastic_graph/schema_definition/results.rb  |  5 +++--
 .../schema_elements/enum_value_namer.rb             |  3 ++-
 .../lib/elastic_graph/schema_definition/state.rb    |  6 ++++--
 gemspec_helper.rb                                   |  5 ++++-
 23 files changed, 50 insertions(+), 39 deletions(-)

diff --git a/elasticgraph-datastore_core/lib/elastic_graph/datastore_core/index_definition/rollover_index_template.rb b/elasticgraph-datastore_core/lib/elastic_graph/datastore_core/index_definition/rollover_index_template.rb
index 29971a4d..9544ddbb 100644
--- a/elasticgraph-datastore_core/lib/elastic_graph/datastore_core/index_definition/rollover_index_template.rb
+++ b/elasticgraph-datastore_core/lib/elastic_graph/datastore_core/index_definition/rollover_index_template.rb
@@ -185,7 +185,7 @@ def rollover_index_suffix_for_record(record, timestamp_field_path:)
             return matching_custom_range.index_name_suffix
           end
 
-          timestamp_value.strftime(ROLLOVER_SUFFIX_FORMATS_BY_FREQUENCY[frequency])
+          timestamp_value.strftime(ROLLOVER_SUFFIX_FORMATS_BY_FREQUENCY.fetch(frequency))
         end
 
         def concrete_rollover_index_for(index_name, setting_overrides, time_set = nil)
diff --git a/elasticgraph-graphql/lib/elastic_graph/graphql/aggregation/query_optimizer.rb b/elasticgraph-graphql/lib/elastic_graph/graphql/aggregation/query_optimizer.rb
index d05ab408..6e0b72ba 100644
--- a/elasticgraph-graphql/lib/elastic_graph/graphql/aggregation/query_optimizer.rb
+++ b/elasticgraph-graphql/lib/elastic_graph/graphql/aggregation/query_optimizer.rb
@@ -154,7 +154,7 @@ def unmerge_response(response_from_merged_query, original_query)
           # If there are no aggregations, there's nothing to unmerge--just return it as is.
           return response_from_merged_query unless (aggs = response_from_merged_query["aggregations"])
 
-          prefix = @unique_prefix_by_query[original_query]
+          prefix = @unique_prefix_by_query[original_query] # : ::String
           agg_names = original_query.aggregations.keys.map { |name| "#{prefix}#{name}" }.to_set
 
           filtered_aggs = aggs
diff --git a/elasticgraph-graphql/lib/elastic_graph/graphql/filtering/filter_args_translator.rb b/elasticgraph-graphql/lib/elastic_graph/graphql/filtering/filter_args_translator.rb
index 9a483eae..8c0044f7 100644
--- a/elasticgraph-graphql/lib/elastic_graph/graphql/filtering/filter_args_translator.rb
+++ b/elasticgraph-graphql/lib/elastic_graph/graphql/filtering/filter_args_translator.rb
@@ -26,7 +26,7 @@ def initialize(schema_element_names:)
         # vs GraphQL.
         def translate_filter_args(field:, args:)
           return nil unless (filter_hash = args[filter_arg_name])
-          filter_type = field.schema.type_from(field.graphql_field.arguments[filter_arg_name].type)
+          filter_type = field.schema.type_from(field.graphql_field.arguments.fetch(filter_arg_name).type)
           convert(filter_type, filter_hash)
         end
 
diff --git a/elasticgraph-graphql/lib/elastic_graph/graphql/http_endpoint.rb b/elasticgraph-graphql/lib/elastic_graph/graphql/http_endpoint.rb
index aa18ef55..47fb1e1f 100644
--- a/elasticgraph-graphql/lib/elastic_graph/graphql/http_endpoint.rb
+++ b/elasticgraph-graphql/lib/elastic_graph/graphql/http_endpoint.rb
@@ -197,7 +197,7 @@ def normalized_headers
       end
 
       def content_type
-        @content_type ||= normalized_headers["CONTENT-TYPE"]
+        normalized_headers["CONTENT-TYPE"]
       end
 
       def self.normalize_header_name(header)
diff --git a/elasticgraph-graphql/lib/elastic_graph/graphql/resolvers/query_source.rb b/elasticgraph-graphql/lib/elastic_graph/graphql/resolvers/query_source.rb
index a95c002b..4f21c5cc 100644
--- a/elasticgraph-graphql/lib/elastic_graph/graphql/resolvers/query_source.rb
+++ b/elasticgraph-graphql/lib/elastic_graph/graphql/resolvers/query_source.rb
@@ -25,7 +25,7 @@ def initialize(datastore_router, query_tracker)
         def fetch(queries)
           responses_by_query = @datastore_router.msearch(queries, query_tracker: @query_tracker)
           @query_tracker.record_datastore_queries_for_single_request(queries)
-          queries.map { |q| responses_by_query[q] }
+          queries.map { |q| responses_by_query.fetch(q) }
         end
 
         def self.execute_many(queries, for_context:)
diff --git a/elasticgraph-graphql/sig/elastic_graph/graphql/http_endpoint.rbs b/elasticgraph-graphql/sig/elastic_graph/graphql/http_endpoint.rbs
index ca5d905a..fa083c41 100644
--- a/elasticgraph-graphql/sig/elastic_graph/graphql/http_endpoint.rbs
+++ b/elasticgraph-graphql/sig/elastic_graph/graphql/http_endpoint.rbs
@@ -84,8 +84,7 @@ module ElasticGraph
       @normalized_headers: ::Hash[::String, ::String]?
       def normalized_headers: () -> ::Hash[::String, ::String]
 
-      @content_type: ::String?
-      def content_type: () -> ::String
+      def content_type: () -> ::String?
 
       def self.normalize_header_name: (::String) -> ::String
     end
diff --git a/elasticgraph-health_check/lib/elastic_graph/health_check/health_checker.rb b/elasticgraph-health_check/lib/elastic_graph/health_check/health_checker.rb
index e1559a74..28be074d 100644
--- a/elasticgraph-health_check/lib/elastic_graph/health_check/health_checker.rb
+++ b/elasticgraph-health_check/lib/elastic_graph/health_check/health_checker.rb
@@ -169,7 +169,7 @@ def validate_and_normalize_config(config)
         #
         # So below, filter to types that have all of their datastore clusters available for querying.
         available_type_names, unavailable_type_names = valid_type_names.partition do |type_name|
-          @indexed_document_types_by_name[type_name].search_index_definitions.all? do |search_index_definition|
+          @indexed_document_types_by_name.fetch(type_name).search_index_definitions.all? do |search_index_definition|
             @datastore_clients_by_name.key?(search_index_definition.cluster_to_query.to_s)
           end
         end
@@ -190,6 +190,7 @@ def validate_and_normalize_config(config)
             .fields_by_name[check.timestamp_field]
 
           if field&.type&.unwrap_fully&.name.to_s == "DateTime"
+            # @type var field: GraphQL::Schema::Field
             # Convert the config so that we have a reference to the index field name.
             normalized_data_recency_checks[type] = check.with(timestamp_field: field.name_in_index.to_s)
           else
diff --git a/elasticgraph-indexer/lib/elastic_graph/indexer/datastore_indexing_router.rb b/elasticgraph-indexer/lib/elastic_graph/indexer/datastore_indexing_router.rb
index 91247409..c017860a 100644
--- a/elasticgraph-indexer/lib/elastic_graph/indexer/datastore_indexing_router.rb
+++ b/elasticgraph-indexer/lib/elastic_graph/indexer/datastore_indexing_router.rb
@@ -77,10 +77,8 @@ def bulk(operations, refresh: false)
         # Before writing these operations, verify their destination index mapping are consistent.
         validate_mapping_completeness_of!(:accessible_cluster_names_to_index_into, *operations.map(&:destination_index_def).uniq)
 
-        # @type var ops_by_client: ::Hash[DatastoreCore::_Client, ::Array[_Operation]]
-        ops_by_client = ::Hash.new { |h, k| h[k] = [] }
-        # @type var unsupported_ops: ::Set[_Operation]
-        unsupported_ops = ::Set.new
+        ops_by_client = ::Hash.new { |h, k| h[k] = [] } # : ::Hash[DatastoreCore::_Client, ::Array[_Operation]]
+        unsupported_ops = ::Set.new # : ::Set[_Operation]
 
         operations.reject { |op| op.to_datastore_bulk.empty? }.each do |op|
           # Note: this intentionally does not use `accessible_cluster_names_to_index_into`.
@@ -90,7 +88,8 @@ def bulk(operations, refresh: false)
 
           cluster_names.each do |cluster_name|
             if (client = @datastore_clients_by_name[cluster_name])
-              ops_by_client[client] << op
+              ops = ops_by_client[client] # : ::Array[::ElasticGraph::Indexer::_Operation]
+              ops << op
             else
               unsupported_ops << op
             end
@@ -293,8 +292,7 @@ def source_event_versions_in_index(operations)
         if failures.empty?
           client_names_and_results.each_with_object(_ = {}) do |(client_name, _success_or_failure, results), accum|
             results.each do |op, version|
-              accum[op] ||= _ = {}
-              accum[op][client_name] = version
+              (accum[op] ||= {})[client_name] = version
             end
           end
         else
diff --git a/elasticgraph-indexer/lib/elastic_graph/indexer/operation/factory.rb b/elasticgraph-indexer/lib/elastic_graph/indexer/operation/factory.rb
index a7f93515..6c027579 100644
--- a/elasticgraph-indexer/lib/elastic_graph/indexer/operation/factory.rb
+++ b/elasticgraph-indexer/lib/elastic_graph/indexer/operation/factory.rb
@@ -96,7 +96,7 @@ def select_json_schema_version(event)
         end
 
         def validator(type, selected_json_schema_version)
-          factory = validator_factories_by_version[selected_json_schema_version]
+          factory = validator_factories_by_version[selected_json_schema_version] # : JSONSchema::ValidatorFactory
           factory.validator_for(type)
         end
 
diff --git a/elasticgraph-indexer/lib/elastic_graph/indexer/record_preparer.rb b/elasticgraph-indexer/lib/elastic_graph/indexer/record_preparer.rb
index adeef348..ef5105af 100644
--- a/elasticgraph-indexer/lib/elastic_graph/indexer/record_preparer.rb
+++ b/elasticgraph-indexer/lib/elastic_graph/indexer/record_preparer.rb
@@ -31,7 +31,7 @@ def initialize(schema_artifacts)
 
         # Gets the `RecordPreparer` for the given JSON schema version.
         def for_json_schema_version(json_schema_version)
-          @preparers_by_json_schema_version[json_schema_version]
+          @preparers_by_json_schema_version[json_schema_version] # : RecordPreparer
         end
 
         # Gets the `RecordPreparer` for the latest JSON schema version. Intended primarily
diff --git a/elasticgraph-indexer_autoscaler_lambda/lib/elastic_graph/indexer_autoscaler_lambda/concurrency_scaler.rb b/elasticgraph-indexer_autoscaler_lambda/lib/elastic_graph/indexer_autoscaler_lambda/concurrency_scaler.rb
index bb8688fe..d1f4acc3 100644
--- a/elasticgraph-indexer_autoscaler_lambda/lib/elastic_graph/indexer_autoscaler_lambda/concurrency_scaler.rb
+++ b/elasticgraph-indexer_autoscaler_lambda/lib/elastic_graph/indexer_autoscaler_lambda/concurrency_scaler.rb
@@ -130,7 +130,8 @@ def get_lowest_node_free_storage_in_mb(cluster_name)
           ]
         })
 
-        metric_response.metric_data_results.first.values.first
+        results = metric_response.metric_data_results.first # : ::Aws::CloudWatch::Types::MetricDataResult
+        results.values.first.to_f
       end
 
       def get_queue_attributes(queue_urls)
diff --git a/elasticgraph-json_schema/lib/elastic_graph/json_schema/validator_factory.rb b/elasticgraph-json_schema/lib/elastic_graph/json_schema/validator_factory.rb
index 83fe31d3..6a360301 100644
--- a/elasticgraph-json_schema/lib/elastic_graph/json_schema/validator_factory.rb
+++ b/elasticgraph-json_schema/lib/elastic_graph/json_schema/validator_factory.rb
@@ -55,7 +55,7 @@ def initialize(schema:, sanitize_pii:)
       # @param type_name [String] name of an ElasticGraph type
       # @return [Validator]
       def validator_for(type_name)
-        @validators_by_type_name[type_name]
+        @validators_by_type_name[type_name] # : Validator
       end
 
       # Returns a new factory configured to disallow unknown properties. By default, JSON schema
diff --git a/elasticgraph-query_registry/lib/elastic_graph/query_registry/query_validator.rb b/elasticgraph-query_registry/lib/elastic_graph/query_registry/query_validator.rb
index 0f7f7047..aeeec60c 100644
--- a/elasticgraph-query_registry/lib/elastic_graph/query_registry/query_validator.rb
+++ b/elasticgraph-query_registry/lib/elastic_graph/query_registry/query_validator.rb
@@ -60,8 +60,8 @@ def variables_errors_for(operation_name, old_dumped_variables, new_dumped_variab
           return [{"message" => "No dumped variables for this operation exist. Correct by running: `#{rake_task}`"}]
         end
 
-        old_op_vars = old_dumped_variables[operation_name]
-        new_op_vars = new_dumped_variables[operation_name]
+        old_op_vars = old_dumped_variables.fetch(operation_name)
+        new_op_vars = new_dumped_variables.fetch(operation_name)
 
         if old_op_vars == new_op_vars
           # The previously dumped variables are up-to-date. No errors in this case.
diff --git a/elasticgraph-query_registry/lib/elastic_graph/query_registry/variable_backward_incompatibility_detector.rb b/elasticgraph-query_registry/lib/elastic_graph/query_registry/variable_backward_incompatibility_detector.rb
index cb3170ae..864eff67 100644
--- a/elasticgraph-query_registry/lib/elastic_graph/query_registry/variable_backward_incompatibility_detector.rb
+++ b/elasticgraph-query_registry/lib/elastic_graph/query_registry/variable_backward_incompatibility_detector.rb
@@ -32,12 +32,12 @@ def detect_incompatibilities(old, new, path, entry_type)
         end
 
         incompatible_commonalities = commonalities.flat_map do |name|
-          incompatibilities_for("#{path}#{name}", normalize_type_info(old[name]), normalize_type_info(new[name]))
+          incompatibilities_for("#{path}#{name}", normalize_type_info(old.fetch(name)), normalize_type_info(new.fetch(name)))
         end
 
         incompatible_additions = additions.filter_map do |name|
           # Additions are only incompatible if it's required (non-nullable).
-          _ = if normalize_type_info(new[name]).fetch("type").end_with?("!")
+          _ = if normalize_type_info(new.fetch(name)).fetch("type").end_with?("!")
             Incompatibility.new("#{path}#{name}", "new required #{entry_type}")
           end
         end
diff --git a/elasticgraph-schema_artifacts/lib/elastic_graph/schema_artifacts/from_disk.rb b/elasticgraph-schema_artifacts/lib/elastic_graph/schema_artifacts/from_disk.rb
index 4917665f..b0f5526f 100644
--- a/elasticgraph-schema_artifacts/lib/elastic_graph/schema_artifacts/from_disk.rb
+++ b/elasticgraph-schema_artifacts/lib/elastic_graph/schema_artifacts/from_disk.rb
@@ -47,7 +47,7 @@ def json_schemas_for(version)
             "Available versions: #{available_json_schema_versions.sort.join(", ")}."
         end
 
-        json_schemas_by_version[version]
+        json_schemas_by_version[version] # : ::Hash[::String, untyped]
       end
 
       def available_json_schema_versions
diff --git a/elasticgraph-schema_artifacts/lib/elastic_graph/schema_artifacts/runtime_metadata/extension_loader.rb b/elasticgraph-schema_artifacts/lib/elastic_graph/schema_artifacts/runtime_metadata/extension_loader.rb
index 39b696a0..a8a54c03 100644
--- a/elasticgraph-schema_artifacts/lib/elastic_graph/schema_artifacts/runtime_metadata/extension_loader.rb
+++ b/elasticgraph-schema_artifacts/lib/elastic_graph/schema_artifacts/runtime_metadata/extension_loader.rb
@@ -117,7 +117,7 @@ def signature_code_for(object, method_name)
           # @type var file_name: ::String?
           # @type var line_number: ::Integer?
           file_name, line_number = object.instance_method(method_name).source_location
-          ::File.read(file_name.to_s).split("\n")[line_number.to_i - 1].strip
+          ::File.read(file_name.to_s).split("\n").fetch(line_number.to_i - 1).strip
         end
       end
     end
diff --git a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/has_derived_graphql_type_customizations.rb b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/has_derived_graphql_type_customizations.rb
index 029c1877..2d85a605 100644
--- a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/has_derived_graphql_type_customizations.rb
+++ b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/has_derived_graphql_type_customizations.rb
@@ -50,7 +50,8 @@ def customize_derived_types(*type_names, &customization_block)
             derived_type_customizations_for_all_types << customization_block
           else
             type_names.each do |t|
-              derived_type_customizations_by_name[t.to_s] << customization_block
+              derived_type_customizations = derived_type_customizations_by_name[t.to_s] # : ::Array[^(::ElasticGraph::SchemaDefinition::_Type) -> void]
+              derived_type_customizations << customization_block
             end
           end
         end
@@ -75,21 +76,23 @@ def customize_derived_types(*type_names, &customization_block)
         #     end
         #   end
         def customize_derived_type_fields(type_name, *field_names, &customization_block)
-          customizations_by_field = derived_field_customizations_by_type_and_field_name[type_name]
+          customizations_by_field = derived_field_customizations_by_type_and_field_name[type_name] # : ::Hash[::String, ::Array[^(::ElasticGraph::SchemaDefinition::SchemaElements::Field) -> void]]
 
           field_names.each do |field_name|
-            customizations_by_field[field_name] << customization_block
+            customizations = customizations_by_field[field_name] # : ::Array[^(::ElasticGraph::SchemaDefinition::SchemaElements::Field) -> void]
+            customizations << customization_block
           end
         end
 
         # @private
         def derived_type_customizations_for_type(type)
-          derived_type_customizations_by_name[type.name] + derived_type_customizations_for_all_types
+          derived_type_customizations = derived_type_customizations_by_name[type.name] # : ::Array[^(::ElasticGraph::SchemaDefinition::_Type) -> void]
+          derived_type_customizations + derived_type_customizations_for_all_types
         end
 
         # @private
         def derived_field_customizations_by_name_for_type(type)
-          derived_field_customizations_by_type_and_field_name[type.name]
+          derived_field_customizations_by_type_and_field_name[type.name] # : ::Hash[::String, ::Array[^(SchemaElements::Field) -> void]]
         end
 
         # @private
diff --git a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/has_subtypes.rb b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/has_subtypes.rb
index 59bd3c2c..3019721d 100644
--- a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/has_subtypes.rb
+++ b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/has_subtypes.rb
@@ -75,8 +75,9 @@ def merge_fields_by_name_from_subtypes
             fields_by_name.merge(yield subtype) do |field_name, def1, def2|
               if (def1.name_in_index == def2.name_in_index && def1.resolve_mapping != def2.resolve_mapping) || (def1.type.unwrap_non_null != def2.type.unwrap_non_null)
                 def_strings = resolved_subtypes.each_with_object([]) do |st, defs|
-                  field = st.graphql_fields_by_name[field_name]
-                  defs << "on #{st.name}:\n#{field.to_sdl.strip} mapping: #{field.resolve_mapping.inspect}" if st.graphql_fields_by_name.key?(field_name)
+                  if (field = st.graphql_fields_by_name[field_name])
+                    defs << "on #{st.name}:\n#{field.to_sdl.strip} mapping: #{field.resolve_mapping.inspect}"
+                  end
                 end
 
                 raise Errors::SchemaError,
diff --git a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/implements_interfaces.rb b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/implements_interfaces.rb
index 0efc538b..bd5ca85b 100644
--- a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/implements_interfaces.rb
+++ b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/mixins/implements_interfaces.rb
@@ -43,7 +43,8 @@ module ImplementsInterfaces
         def implements(*interface_names)
           interface_refs = interface_names.map do |interface_name|
             schema_def_state.type_ref(interface_name).to_final_form.tap do |interface_ref|
-              schema_def_state.implementations_by_interface_ref[interface_ref] << self
+              implementations = schema_def_state.implementations_by_interface_ref[interface_ref] # : ::Set[SchemaElements::TypeWithSubfields]
+              implementations << self
             end
           end
 
diff --git a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/results.rb b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/results.rb
index f18256dc..1787d937 100644
--- a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/results.rb
+++ b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/results.rb
@@ -329,7 +329,7 @@ def check_for_circular_dependencies!
 
       def recursively_add_referenced_types_to(source_type_ref, references_cache)
         return unless (source_type = source_type_ref.as_object_type)
-        references_set = references_cache[source_type_ref.name]
+        references_set = references_cache[source_type_ref.name] # : ::Set[::String]
 
         # Recursive references are allowed only when its a relation, so skip that case.
         source_type.graphql_fields_by_name.values.reject { |f| f.relationship }.each do |field|
@@ -339,7 +339,8 @@ def recursively_add_referenced_types_to(source_type_ref, references_cache)
             recursively_add_referenced_types_to(field_type, references_cache)
           end
 
-          references_set.merge(references_cache[field_type.name])
+          field_type_references_set = references_cache[field_type.name] # : ::Set[::String]
+          references_set.merge(field_type_references_set)
         end
       end
 
diff --git a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/schema_elements/enum_value_namer.rb b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/schema_elements/enum_value_namer.rb
index 7a1d1ec6..65e0547f 100644
--- a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/schema_elements/enum_value_namer.rb
+++ b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/schema_elements/enum_value_namer.rb
@@ -29,7 +29,8 @@ def initialize(overrides_by_type_name = {})
 
         # Returns the name that should be used for the given `type_name` and `value_name`.
         def name_for(type_name, value_name)
-          @used_value_names_by_type_name[type_name] << value_name
+          used_value_names = @used_value_names_by_type_name[type_name] # : ::Array[::String]
+          used_value_names << value_name
           overrides_by_type_name.dig(type_name, value_name) || value_name
         end
 
diff --git a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/state.rb b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/state.rb
index a7868e4c..85c5aa2e 100644
--- a/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/state.rb
+++ b/elasticgraph-schema_definition/lib/elastic_graph/schema_definition/state.rb
@@ -139,7 +139,8 @@ def register_deleted_type(type_name, defined_at:, defined_via:)
       end
 
       def register_renamed_field(type_name, from:, to:, defined_at:, defined_via:)
-        renamed_fields_by_type_name_and_old_field_name[type_name][from] = factory.new_deprecated_element(
+        renamed_fields_by_old_field_name = renamed_fields_by_type_name_and_old_field_name[type_name] # : ::Hash[::String, SchemaElements::DeprecatedElement]
+        renamed_fields_by_old_field_name[from] = factory.new_deprecated_element(
           to,
           defined_at: defined_at,
           defined_via: defined_via
@@ -147,7 +148,8 @@ def register_renamed_field(type_name, from:, to:, defined_at:, defined_via:)
       end
 
       def register_deleted_field(type_name, field_name, defined_at:, defined_via:)
-        deleted_fields_by_type_name_and_old_field_name[type_name][field_name] = factory.new_deprecated_element(
+        deleted_fields_by_old_field_name = deleted_fields_by_type_name_and_old_field_name[type_name] # : ::Hash[::String, SchemaElements::DeprecatedElement]
+        deleted_fields_by_old_field_name[field_name] = factory.new_deprecated_element(
           field_name,
           defined_at: defined_at,
           defined_via: defined_via
diff --git a/gemspec_helper.rb b/gemspec_helper.rb
index 9d4cc7b8..3702df86 100644
--- a/gemspec_helper.rb
+++ b/gemspec_helper.rb
@@ -60,7 +60,10 @@ def self.define_elasticgraph_gem(gemspec_file:, category:)
 
       # Steep is our type checker. Only needed if there's a `sig` directory.
       if ::Dir.exist?(::File.join(gem_dir, "sig"))
-        spec.add_development_dependency "steep", "~> 1.8"
+        # New steep minor versions often introduce stricter type checks that we may initially fail,
+        # so we don't want to automatically upgrade when a new steep minor version is released.
+        # Therefore, we list 3 digits (in contrast to most gems).
+        spec.add_development_dependency "steep", "~> 1.9.0"
       end
 
       # If the gem has a `spec` directory then it needs our standard set of testing gems.