GraphQL - Add extra complexity for resolvers

If a field is a resolver, its complexity is automatically
increased. By default we add extra points for sort and search
arguments (which will be common for various resolvers).

For specific resolvers we add field-specific complexity, e.g.
for Issues complexity is increased if we filter issues by `labelName`
(because then SQL query is more complex). We may want to tune these
values in future depending on real-life results.

Complexity is also dependent on the number of loaded nodes, but only
if we don't search by specific ID(s). Also added complexity is limited
(by default only twice more than child complexity) - the reason is
that although it's more complex to process more items, the complexity
increase is not linear (there is not so much difference between loading
10, 20 or 100 records from DB).

5 files changed, 64 insertions, 0 deletions

diff --git a/spec/graphql/resolvers/base_resolver_spec.rb b/spec/graphql/resolvers/base_resolver_spec.rb
index e3a34762b62..9982288e206 100644
--- a/spec/graphql/resolvers/base_resolver_spec.rb
+++ b/spec/graphql/resolvers/base_resolver_spec.rb
@@ -28,4 +28,19 @@ describe Resolvers::BaseResolver do
       expect(result).to eq(test: 1)
     end
   end
+
+  it 'increases complexity based on arguments' do
+    field = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 1)
+
+    expect(field.to_graphql.complexity.call({}, { sort: 'foo' }, 1)).to eq 3
+    expect(field.to_graphql.complexity.call({}, { search: 'foo' }, 1)).to eq 7
+  end
+
+  it 'does not increase complexity when filtering by iids' do
+    field = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 100)
+
+    expect(field.to_graphql.complexity.call({}, { sort: 'foo' }, 1)).to eq 6
+    expect(field.to_graphql.complexity.call({}, { sort: 'foo', iid: 1 }, 1)).to eq 3
+    expect(field.to_graphql.complexity.call({}, { sort: 'foo', iids: [1, 2, 3] }, 1)).to eq 3
+  end
 end
diff --git a/spec/graphql/resolvers/concerns/resolves_pipelines_spec.rb b/spec/graphql/resolvers/concerns/resolves_pipelines_spec.rb
index ea7159eacf9..3140af27af5 100644
--- a/spec/graphql/resolvers/concerns/resolves_pipelines_spec.rb
+++ b/spec/graphql/resolvers/concerns/resolves_pipelines_spec.rb
@@ -46,6 +46,14 @@ describe ResolvesPipelines do
     expect(resolve_pipelines({}, {})).to be_empty
   end
 
+  it 'increases field complexity based on arguments' do
+    field = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: resolver, null: false, max_page_size: 1)
+
+    expect(field.to_graphql.complexity.call({}, {}, 1)).to eq 2
+    expect(field.to_graphql.complexity.call({}, { sha: 'foo' }, 1)).to eq 4
+    expect(field.to_graphql.complexity.call({}, { sha: 'ref' }, 1)).to eq 4
+  end
+
   def resolve_pipelines(args = {}, context = { current_user: current_user })
     resolve(resolver, obj: project, args: args, ctx: context)
   end
diff --git a/spec/graphql/resolvers/issues_resolver_spec.rb b/spec/graphql/resolvers/issues_resolver_spec.rb
index 399a33dae75..bffcdbfe915 100644
--- a/spec/graphql/resolvers/issues_resolver_spec.rb
+++ b/spec/graphql/resolvers/issues_resolver_spec.rb
@@ -120,6 +120,13 @@ describe Resolvers::IssuesResolver do
     end
   end
 
+  it 'increases field complexity based on arguments' do
+    field = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 100)
+
+    expect(field.to_graphql.complexity.call({}, {}, 1)).to eq 4
+    expect(field.to_graphql.complexity.call({}, { labelName: 'foo' }, 1)).to eq 8
+  end
+
   def resolve_issues(args = {}, context = { current_user: current_user })
     resolve(described_class, obj: project, args: args, ctx: context)
   end
diff --git a/spec/graphql/resolvers/project_resolver_spec.rb b/spec/graphql/resolvers/project_resolver_spec.rb
index d4990c6492c..4fdbb3aa43e 100644
--- a/spec/graphql/resolvers/project_resolver_spec.rb
+++ b/spec/graphql/resolvers/project_resolver_spec.rb
@@ -26,6 +26,14 @@ describe Resolvers::ProjectResolver do
     end
   end
 
+  it 'does not increase complexity depending on number of load limits' do
+    field1 = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 100)
+    field2 = Types::BaseField.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: described_class, null: false, max_page_size: 1)
+
+    expect(field1.to_graphql.complexity.call({}, {}, 1)).to eq 2
+    expect(field2.to_graphql.complexity.call({}, {}, 1)).to eq 2
+  end
+
   def resolve_project(full_path)
     resolve(described_class, args: { full_path: full_path })
   end
diff --git a/spec/graphql/types/base_field_spec.rb b/spec/graphql/types/base_field_spec.rb
index b5697ee5245..4fe426e2447 100644
--- a/spec/graphql/types/base_field_spec.rb
+++ b/spec/graphql/types/base_field_spec.rb
@@ -4,6 +4,18 @@ require 'spec_helper'
 
 describe Types::BaseField do
   context 'when considering complexity' do
+    let(:resolver) do
+      Class.new(described_class) do
+        def self.resolver_complexity(args)
+          2 if args[:foo]
+        end
+
+        def self.complexity_multiplier(args)
+          0.01
+        end
+      end
+    end
+
     it 'defaults to 1' do
       field = described_class.new(name: 'test', type: GraphQL::STRING_TYPE, null: true)
 
@@ -15,5 +27,19 @@ describe Types::BaseField do
 
       expect(field.to_graphql.complexity).to eq 12
     end
+
+    it 'sets complexity depending on arguments for resolvers' do
+      field = described_class.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: resolver, max_page_size: 100, null: true)
+
+      expect(field.to_graphql.complexity.call({}, {}, 2)).to eq 4
+      expect(field.to_graphql.complexity.call({}, { first: 50 }, 2)).to eq 3
+    end
+
+    it 'sets complexity depending on number load limits for resolvers' do
+      field = described_class.new(name: 'test', type: GraphQL::STRING_TYPE, resolver_class: resolver, max_page_size: 100, null: true)
+
+      expect(field.to_graphql.complexity.call({}, { first: 1 }, 2)).to eq 2
+      expect(field.to_graphql.complexity.call({}, { first: 1, foo: true }, 2)).to eq 4
+    end
   end
 end