Improve user feedback when CloudFormation reports no changes

CHANGELOG.md

@@ -12,12 +12,14 @@ The format is based on [Keep a Changelog], and this project adheres to
 
 ### Changed
 
+- Improve message when CloudFormation claims there are no changes to apply, even when a template diff is present. ([#398])
 - Display Tags diff (stack tags) in `stack_master diff` and `stack_master apply` commands. ([#397])
 - Resolve style issues identified by RuboCop. ([#396])
 
 [Unreleased]: https://github.com/envato/stack_master/compare/v2.17.1...HEAD
 [#396]: https://github.com/envato/stack_master/pull/396
 [#397]: https://github.com/envato/stack_master/pull/397
+[#398]: https://github.com/envato/stack_master/pull/398
 
 ## [2.17.1] - 2025-12-19
 

lib/stack_master/commands/apply.rb

@@ -89,7 +89,7 @@ def create_stack_by_change_set
           @change_set = ChangeSet.create(stack_options.merge(change_set_type: 'CREATE'))
           if @change_set.failed?
             ChangeSet.delete(@change_set.id)
-            halt!(@change_set.status_reason)
+            halt!(user_friendly_changeset_error(@change_set.status_reason))
           end
 
           @change_set.display(StackMaster.stdout)
@@ -123,7 +123,7 @@ def update_stack
         @change_set = ChangeSet.create(stack_options)
         if @change_set.failed?
           ChangeSet.delete(@change_set.id)
-          halt!(@change_set.status_reason)
+          halt!(user_friendly_changeset_error(@change_set.status_reason))
         end
 
         @change_set.display(StackMaster.stdout)
@@ -230,6 +230,21 @@ def set_stack_policy
         StackMaster.stdout.puts 'done.'
       end
 
+      def user_friendly_changeset_error(status_reason)
+        # CloudFormation returns various messages when there are no changes to apply
+        if status_reason =~ /didn'?t contain changes|no changes|no updates are to be performed/i
+          <<~MESSAGE.chomp
+            #{status_reason}
+
+            While there may be differences in the template file (e.g., whitespace, comments, or
+            formatting), CloudFormation has determined that no actual resource changes are needed.
+            The stack is already in the desired state.
+          MESSAGE
+        else
+          status_reason
+        end
+      end
+
       extend Forwardable
       def_delegators :@stack_definition, :stack_name, :region
     end

spec/stack_master/commands/apply_spec.rb

@@ -127,11 +127,42 @@ def apply
       before do
         allow(StackMaster::ChangeSet).to receive(:delete)
         allow(change_set).to receive(:failed?).and_return(true)
-        allow(change_set).to receive(:status_reason).and_return('reason')
       end
 
-      it 'outputs the status reason' do
-        expect { apply }.to output(/reason/).to_stdout
+      context 'with a generic error' do
+        before do
+          allow(change_set).to receive(:status_reason).and_return('reason')
+        end
+
+        it 'outputs the status reason' do
+          expect { apply }.to output(/reason/).to_stdout
+        end
+      end
+
+      context 'with a "no changes" error from CloudFormation' do
+        before do
+          allow(change_set)
+            .to receive(:status_reason)
+            .and_return("The submitted information didn't contain changes. " \
+                        'Submit different information to create a change set.')
+        end
+
+        it 'outputs a user-friendly explanation' do
+          expect { apply }.to output(/The submitted information didn't contain changes/).to_stdout
+          expect { apply }.to output(/no actual resource changes are needed/).to_stdout
+          expect { apply }.to output(/stack is already in the desired state/).to_stdout
+        end
+      end
+
+      context 'with alternative "no changes" error message' do
+        before do
+          allow(change_set).to receive(:status_reason).and_return('No updates are to be performed.')
+        end
+
+        it 'outputs a user-friendly explanation' do
+          expect { apply }.to output(/No updates are to be performed/).to_stdout
+          expect { apply }.to output(/no actual resource changes are needed/).to_stdout
+        end
       end
     end