Pulumi Engine: plan output missing from PR comments and broken has_changes

[TheFynx]

Fixes two bugs that made the Pulumi engine non-functional with Terrateam

Bug 1: Plan output not displayed in PR comments

diff() returned None, so diff_stdout was always empty and the plan payload contained no output. Now plan() saves the pulumi preview --diff stdout to <plan_file>.diff and diff() reads it back — matching how the Terraform engine provides plan output via terraform show.

Before: (blank plan output in PR comment)

After: (attribute-level diff with GitHub syntax highlighting)

Bug 2: Missing has_changes return value

plan() returned 3 values (success, stdout, stderr) but the runner unpacks 4 (success, has_changes, stdout, stderr), causing a runtime crash on every plan. Now detects changes by checking for Pulumi's change indicators (to create, to update, to delete, to replace) in the preview output.

Additional improvements

• --diff flag added to pulumi preview for attribute-level output
• --diff flag added to pulumi up with format_diff() applied so apply output is better formatted/informative - syntax highlighting does not apply here
• Implemented diff_json(), outputs() which were stubs returning None
• format_diff() helper moves +/-/~ markers to start-of-line for GitHub ```diff coloring

How to Test

I ran through all these in my setup, but this is how to test the changes directly

• Trigger a plan — verify PR comment shows preview output with colored diff
• Trigger an apply — verify output now provides structured created/updated/destroyed list
• Verify no-op plan correctly reports has_changes=False and doesn't prompt for apply

Before

After

No Changes

Changes