Disregard case of section names when parsing

We want to make sure that we match section names regardless of case, so
[Database], [DataBase], and [database] would all be considered a single
seciton. The first case pattern that is encountered will be considered
the canonical spelling.

ee/lib/gitlab/code_owners/file.rb

@@ -3,6 +3,8 @@
 module Gitlab
   module CodeOwners
     class File
+      SECTION_HEADER_REGEX = /\[(.*?)\]/.freeze
+
       def initialize(blob, project = nil)
         @blob = blob
         @project = project
@@ -52,37 +54,51 @@ module Gitlab
 
           next if skip?(line)
 
-          extract_entry_and_populate_parsed(line, parsed)
+          extract_entry_and_populate_parsed_data(line, parsed)
         end
 
         parsed
       end
 
       def get_parsed_sectional_data
-        parsed = {}
-        section = ::Gitlab::CodeOwners::Entry::DEFAULT_SECTION
+        parsed_sectional_data = {}
+        canonical_section_name = ::Gitlab::CodeOwners::Entry::DEFAULT_SECTION
 
-        parsed[section] = {}
+        parsed_sectional_data[canonical_section_name] = {}
 
         data.lines.each do |line|
           line = line.strip
 
           next if skip?(line)
 
-          if line.starts_with?('[') && line.end_with?(']')
-            section = line[1...-1].strip
-            parsed[section] ||= {}
+          # Detect section headers, and if found, make sure data structure is
+          #   set up to hold the entries it contains, and proceed to the next
+          #   line in the file.
+          #
+          if line.match?(SECTION_HEADER_REGEX)
+            parsed_section_name = line[1...-1].strip
+            canonical_section_name = find_section_name(parsed_section_name, parsed_sectional_data)
+
+            parsed_sectional_data[canonical_section_name] ||= {}
 
             next
           end
 
-          extract_entry_and_populate_parsed(line, parsed, section)
+          extract_entry_and_populate_parsed_data(line, parsed_sectional_data, canonical_section_name)
         end
 
-        parsed
+        parsed_sectional_data
+      end
+
+      def find_section_name(section, parsed_sectional_data)
+        section_headers = parsed_sectional_data.keys
+
+        return section if section_headers.last == ::Gitlab::CodeOwners::Entry::DEFAULT_SECTION
+
+        section_headers.find { |k| k.casecmp?(section) } || section
       end
 
-      def extract_entry_and_populate_parsed(line, parsed, section = nil)
+      def extract_entry_and_populate_parsed_data(line, parsed, section = nil)
         pattern, _separator, owners = line.partition(/(?<!\\)\s+/)
 
         normalized_pattern = normalize_pattern(pattern)

ee/spec/fixtures/mixed_case_sectional_codeowners_example

+ee/ @gl-admin
+
+[Documentation]
+ee/docs    @gl-docs
+docs       @gl-docs
+
+[Database]
+README.md  @gl-database
+model/db   @gl-database
+
+[dOcUmEnTaTiOn]
+README.md  @gl-docs

ee/spec/lib/gitlab/code_owners/file_spec.rb

@@ -38,30 +38,13 @@ describe Gitlab::CodeOwners::File do
     end
 
     context "when feature flag `:sectional_codeowners` is enabled" do
+      using RSpec::Parameterized::TableSyntax
+
       before do
         stub_feature_flags(sectional_codeowners: true)
       end
 
-      it "passes the call to #get_parsed_sectional_data" do
-        expect(file).to receive(:get_parsed_sectional_data)
-
-        file.parsed_data
-      end
-
-      it "populates a hash with a single default section" do
-        data = file.parsed_data
-
-        expect(data.keys.length).to eq(1)
-        expect(data.keys).to contain_exactly(::Gitlab::CodeOwners::Entry::DEFAULT_SECTION)
-      end
-
-      context "when CODEOWNERS file contains multiple sections" do
-        using RSpec::Parameterized::TableSyntax
-
-        let(:file_content) do
-          File.read(Rails.root.join("ee", "spec", "fixtures", "sectional_codeowners_example"))
-        end
-
+      shared_examples_for "creates expected parsed results" do
         it "is a hash sorted by sections without duplicates" do
           data = file.parsed_data
 
@@ -87,6 +70,35 @@ describe Gitlab::CodeOwners::File do
           end
         end
       end
+
+      it "passes the call to #get_parsed_sectional_data" do
+        expect(file).to receive(:get_parsed_sectional_data)
+
+        file.parsed_data
+      end
+
+      it "populates a hash with a single default section" do
+        data = file.parsed_data
+
+        expect(data.keys.length).to eq(1)
+        expect(data.keys).to contain_exactly(::Gitlab::CodeOwners::Entry::DEFAULT_SECTION)
+      end
+
+      context "when CODEOWNERS file contains multiple sections" do
+        let(:file_content) do
+          File.read(Rails.root.join("ee", "spec", "fixtures", "sectional_codeowners_example"))
+        end
+
+        it_behaves_like "creates expected parsed results"
+      end
+
+      context "when CODEOWNERS file contains multiple sections with mixed-case names" do
+        let(:file_content) do
+          File.read(Rails.root.join("ee", "spec", "fixtures", "mixed_case_sectional_codeowners_example"))
+        end
+
+        it_behaves_like "creates expected parsed results"
+      end
     end
   end