Expand variables only when needed

This makes us to expand variables only when needed,
instead of requesting all variables each time.

This specifically helps in situation when explicit name
of `environment: production` is used.

1 files changed, 122 insertions, 53 deletions

diff --git a/spec/lib/expand_variables_spec.rb b/spec/lib/expand_variables_spec.rb
index 099d7b6b67c..394efa85701 100644
--- a/spec/lib/expand_variables_spec.rb
+++ b/spec/lib/expand_variables_spec.rb
@@ -4,62 +4,131 @@ require 'spec_helper'
 
 describe ExpandVariables do
   describe '#expand' do
-    subject { described_class.expand(value, variables) }
+    context 'table tests' do
+      using RSpec::Parameterized::TableSyntax
 
-    tests = [
-      { value: 'key',
-        result: 'key',
-        variables: [] },
-      { value: 'key$variable',
-        result: 'key',
-        variables: [] },
-      { value: 'key$variable',
-        result: 'keyvalue',
-        variables: [
-          { key: 'variable', value: 'value' }
-        ] },
-      { value: 'key${variable}',
-        result: 'keyvalue',
-        variables: [
-          { key: 'variable', value: 'value' }
-        ] },
-      { value: 'key$variable$variable2',
-        result: 'keyvalueresult',
-        variables: [
-          { key: 'variable', value: 'value' },
-          { key: 'variable2', value: 'result' }
-        ] },
-      { value: 'key${variable}${variable2}',
-        result: 'keyvalueresult',
-        variables: [
-          { key: 'variable', value: 'value' },
-          { key: 'variable2', value: 'result' }
-        ] },
-      { value: 'key$variable2$variable',
-        result: 'keyresultvalue',
-        variables: [
-          { key: 'variable', value: 'value' },
-          { key: 'variable2', value: 'result' }
-        ] },
-      { value: 'key${variable2}${variable}',
-        result: 'keyresultvalue',
-        variables: [
-          { key: 'variable', value: 'value' },
-          { key: 'variable2', value: 'result' }
-        ] },
-      { value: 'review/$CI_COMMIT_REF_NAME',
-        result: 'review/feature/add-review-apps',
-        variables: [
-          { key: 'CI_COMMIT_REF_NAME', value: 'feature/add-review-apps' }
-        ] }
-    ]
+      where do
+        {
+          "no expansion": {
+            value: 'key',
+            result: 'key',
+            variables: []
+          },
+          "missing variable": {
+            value: 'key$variable',
+            result: 'key',
+            variables: []
+          },
+          "simple expansion": {
+            value: 'key$variable',
+            result: 'keyvalue',
+            variables: [
+              { key: 'variable', value: 'value' }
+            ]
+          },
+          "simple with hash of variables": {
+            value: 'key$variable',
+            result: 'keyvalue',
+            variables: {
+              'variable' => 'value'
+            }
+          },
+          "complex expansion": {
+            value: 'key${variable}',
+            result: 'keyvalue',
+            variables: [
+              { key: 'variable', value: 'value' }
+            ]
+          },
+          "simple expansions": {
+            value: 'key$variable$variable2',
+            result: 'keyvalueresult',
+            variables: [
+              { key: 'variable', value: 'value' },
+              { key: 'variable2', value: 'result' }
+            ]
+          },
+          "complex expansions": {
+            value: 'key${variable}${variable2}',
+            result: 'keyvalueresult',
+            variables: [
+              { key: 'variable', value: 'value' },
+              { key: 'variable2', value: 'result' }
+            ]
+          },
+          "complex expansions with missing variable": {
+            value: 'key${variable}${variable2}',
+            result: 'keyvalue',
+            variables: [
+              { key: 'variable', value: 'value' }
+            ]
+          },
+          "out-of-order expansion": {
+            value: 'key$variable2$variable',
+            result: 'keyresultvalue',
+            variables: [
+              { key: 'variable', value: 'value' },
+              { key: 'variable2', value: 'result' }
+            ]
+          },
+          "out-of-order complex expansion": {
+            value: 'key${variable2}${variable}',
+            result: 'keyresultvalue',
+            variables: [
+              { key: 'variable', value: 'value' },
+              { key: 'variable2', value: 'result' }
+            ]
+          },
+          "review-apps expansion": {
+            value: 'review/$CI_COMMIT_REF_NAME',
+            result: 'review/feature/add-review-apps',
+            variables: [
+              { key: 'CI_COMMIT_REF_NAME', value: 'feature/add-review-apps' }
+            ]
+          },
+          "do not lazily access variables when no expansion": {
+            value: 'key',
+            result: 'key',
+            variables: -> { raise NotImplementedError }
+          },
+          "lazily access variables": {
+            value: 'key$variable',
+            result: 'keyvalue',
+            variables: -> { [{ key: 'variable', value: 'value' }] }
+          }
+        }
+      end
+
+      with_them do
+        subject { ExpandVariables.expand(value, variables) } # rubocop:disable RSpec/DescribedClass
+
+        it { is_expected.to eq(result) }
+      end
+    end
+
+    context 'lazily inits variables' do
+      let(:variables) { -> { [{ key: 'variable', value: 'result' }] } }
+
+      subject { described_class.expand(value, variables) }
+
+      context 'when expanding variable' do
+        let(:value) { 'key$variable$variable2' }
+
+        it 'calls block at most once' do
+          expect(variables).to receive(:call).once.and_call_original
+
+          is_expected.to eq('keyresult')
+        end
+      end
+
+      context 'when no expansion is needed' do
+        let(:value) { 'key' }
 
-    tests.each do |test|
-      context "#{test[:value]} resolves to #{test[:result]}" do
-        let(:value) { test[:value] }
-        let(:variables) { test[:variables] }
+        it 'does not call block' do
+          expect(variables).not_to receive(:call)
 
-        it { is_expected.to eq(test[:result]) }
+          is_expected.to eq('key')
+        end
       end
     end
   end