Extend Options with allow_erasing and allow_downgrade (#4996)

Add two new fields to the package manager Options:
  
  - `allow_erasing` (`--allowerasing`): lets DNF remove packages that
    obsolete or conflict with a requested install. Supported by DNF4 and
    DNF5.
    
- `allow_downgrade` (`--allow-downgrade`): lets DNF5 downgrade
transitive
dependencies when a requested package requires an older version. DNF4
already permits this by default, so the flag is only emitted for DNF5.

- Both options raise `PrepareError` under `YumEngine` (no equivalent
flag).
    
  Fixes #4909

---------

Co-authored-by: vaibhavdaren <vaibhavdaren@gmail.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: 3 people

tmt/package_managers/__init__.py

@@ -329,6 +329,12 @@ class Options:
     #: If set, instruct package manager to install from untrusted sources.
     allow_untrusted: bool = False
 
+    #: If set, allow erasing conflicting or obsoleting packages during install.
+    allow_erasing: bool = False
+
+    #: If set, allow downgrades of transitive dependencies during install.
+    allow_downgrade: bool = False
+
 
 class PackageManagerEngine(tmt.utils.Common):
     command: Command

tmt/package_managers/dnf.py

@@ -59,6 +59,10 @@ def _extra_dnf_options(self, options: Options, command: Optional[Command] = None
             else:
                 raise GeneralError(f"Unhandled package manager command '{command}'.")
 
+        if options.allow_erasing:
+            # Supported by DNF4 and DNF5; YumEngine raises PrepareError for this flag.
+            extra_options += Command('--allowerasing')
+
         return extra_options
 
     def _construct_presence_script(
@@ -398,6 +402,19 @@ class Dnf5Engine(DnfEngine):
     skip_missing_packages_option = '--skip-unavailable'
     skip_missing_debuginfo_option = skip_missing_packages_option
 
+    def _extra_dnf_options(self, options: Options, command: Optional[Command] = None) -> Command:
+        """
+        Collect additional options for ``dnf5`` based on given options.
+        """
+
+        extra_options = super()._extra_dnf_options(options, command)
+
+        if options.allow_downgrade:
+            # DNF4 allows transitive downgrades automatically; this flag is DNF5-specific.
+            extra_options += Command('--allow-downgrade')
+
+        return extra_options
+
 
 @provides_package_manager('dnf5')
 class Dnf5(Dnf):
@@ -415,6 +432,13 @@ class Dnf5(Dnf):
 class YumEngine(DnfEngine):
     _base_command = Command('yum')
 
+    def _extra_dnf_options(self, options: Options, command: Optional[Command] = None) -> Command:
+        if options.allow_erasing:
+            raise PrepareError("Package manager 'yum' does not support '--allowerasing'.")
+        if options.allow_downgrade:
+            raise PrepareError("Package manager 'yum' does not support '--allow-downgrade'.")
+        return super()._extra_dnf_options(options, command)
+
     def _yum_config_manager_command(self) -> Command:
         command = Command('yum-config-manager')