Add examples and specs for edge case of InlineHash

Unested symbolic or numeric keys should not be converted to strings.
These changes document that and adds specs reflecting that. Also
makes a minor change to simplify and speed perf in the InlineHash
implementation.

lib/gitlab/utils/inline_hash.rb

@@ -11,13 +11,15 @@ module Gitlab
       #
       #  {
       #    'root_param' => 'Root',
+      #    12 => 'number',
+      #    symbol: 'symbol',
       #    nested_param: {
       #      key: 'Value'
       #    },
       #    'very' => {
       #      'deep' => {
       #        'nested' => {
-      #          'param' => 'Deep nested value'
+      #          12 => 'Deep nested value'
       #        }
       #      }
       #    }
@@ -28,15 +30,17 @@ module Gitlab
       #
       #  {
       #    'root_param' => 'Root',
+      #     12 => 'number',
+      #     symbol: symbol,
       #    'nested_param.key' => 'Value',
-      #    'very.deep.nested.param' => 'Deep nested value'
+      #    'very.deep.nested.12' => 'Deep nested value'
       #  }
       #
       def merge_keys(hash, prefix: nil, connector: '.')
         result = {}
-        base_prefix = prefix ? "#{prefix}#{connector}" : ''
         pairs =
           if prefix
+            base_prefix = "#{prefix}#{connector}"
             hash.map { |key, value| ["#{base_prefix}#{key}", value] }
           else
             hash.to_a

spec/lib/gitlab/utils/inline_hash_spec.rb

@@ -6,6 +6,7 @@ describe Gitlab::Utils::InlineHash do
   describe '.merge_keys' do
     subject { described_class.merge_keys(source) }
 
+    context 'with string keys' do
       let(:source) do
         {
           nested_param: {
@@ -59,4 +60,40 @@ describe Gitlab::Utils::InlineHash do
         end
       end
     end
+
+    context 'with un-nested symbol or numeric keys' do
+      let(:unested_symbol_key_source) do
+        {
+          unnested_symbol_key: :unnested_symbol_value,
+          12 => 22,
+          nested_symbol_key: {
+            nested_symbol_key_2: :nested_symbol_value
+          }
+        }
+      end
+
+      context 'without prefix' do
+        subject { described_class.merge_keys(unested_symbol_key_source) }
+
+        it 'converts only nested keys to inline strings' do
+          is_expected.to eq(
+            :unnested_symbol_key => :unnested_symbol_value,
+            12 => 22,
+            'nested_symbol_key.nested_symbol_key_2' => :nested_symbol_value
+          )
+        end
+      end
+
+      context 'with prefix' do
+        subject { described_class.merge_keys(unested_symbol_key_source, prefix: 'options') }
+        it 'converts prefixed keys to inline strings' do
+          is_expected.to eq(
+            'options.unnested_symbol_key' => :unnested_symbol_value,
+            'options.12' => 22,
+            'options.nested_symbol_key.nested_symbol_key_2' => :nested_symbol_value
+          )
+        end
+      end
+    end
+  end
 end