Add DryRunner interface and DryRun capability for dry-run support detection

Co-authored-by: taigrr <8261498+taigrr@users.noreply.github.com>

apk/capabilities.go

@@ -11,8 +11,12 @@ var (
 	_ snack.VersionQuerier = (*Apk)(nil)
 	_ snack.Cleaner        = (*Apk)(nil)
 	_ snack.FileOwner      = (*Apk)(nil)
+	_ snack.DryRunner      = (*Apk)(nil)
 )
 
+// SupportsDryRun reports that apk honors [snack.WithDryRun] via --simulate.
+func (a *Apk) SupportsDryRun() bool { return true }
+
 // LatestVersion returns the latest available version from configured repositories.
 func (a *Apk) LatestVersion(ctx context.Context, pkg string) (string, error) {
 	return latestVersion(ctx, pkg)

apt/apt.go

@@ -196,6 +196,9 @@ func (a *Apt) ParseArch(name string) (string, string) {
 	return parseArch(name)
 }
 
+// SupportsDryRun reports that apt honors [snack.WithDryRun] via --dry-run.
+func (a *Apt) SupportsDryRun() bool { return true }
+
 // Compile-time interface checks.
 var (
 	_ snack.Manager        = (*Apt)(nil)
@@ -206,4 +209,5 @@ var (
 	_ snack.RepoManager    = (*Apt)(nil)
 	_ snack.KeyManager     = (*Apt)(nil)
 	_ snack.NameNormalizer = (*Apt)(nil)
+	_ snack.DryRunner      = (*Apt)(nil)
 )

capabilities.go

@@ -12,6 +12,7 @@ type Capabilities struct {
 	KeyManagement  bool
 	Groups         bool
 	NameNormalize  bool
+	DryRun         bool
 }
 
 // GetCapabilities probes a Manager for all optional interface support.
@@ -24,6 +25,7 @@ func GetCapabilities(m Manager) Capabilities {
 	_, km := m.(KeyManager)
 	_, g := m.(Grouper)
 	_, nn := m.(NameNormalizer)
+	_, dr := m.(DryRunner)
 	return Capabilities{
 		VersionQuery:   vq,
 		Hold:           h,
@@ -33,5 +35,6 @@ func GetCapabilities(m Manager) Capabilities {
 		KeyManagement:  km,
 		Groups:         g,
 		NameNormalize:  nn,
+		DryRun:         dr,
 	}
 }

dnf/capabilities.go

@@ -16,8 +16,12 @@ var (
 	_ snack.KeyManager     = (*DNF)(nil)
 	_ snack.Grouper        = (*DNF)(nil)
 	_ snack.NameNormalizer = (*DNF)(nil)
+	_ snack.DryRunner      = (*DNF)(nil)
 )
 
+// SupportsDryRun reports that dnf honors [snack.WithDryRun] via --setopt=tsflags=test.
+func (d *DNF) SupportsDryRun() bool { return true }
+
 // LatestVersion returns the latest available version from configured repositories.
 func (d *DNF) LatestVersion(ctx context.Context, pkg string) (string, error) {
 	return latestVersion(ctx, pkg, d.v5)

pacman/capabilities.go

@@ -12,12 +12,16 @@ var (
 	_ snack.Cleaner        = (*Pacman)(nil)
 	_ snack.FileOwner      = (*Pacman)(nil)
 	_ snack.Grouper        = (*Pacman)(nil)
+	_ snack.DryRunner      = (*Pacman)(nil)
 )
 
 // NOTE: snack.Holder is not implemented for pacman. While pacman supports
 // IgnorePkg in /etc/pacman.conf, there is no clean CLI command to hold/unhold
 // packages. pacman-contrib provides some tooling but it's not standard.
 
+// SupportsDryRun reports that pacman honors [snack.WithDryRun] via --print.
+func (p *Pacman) SupportsDryRun() bool { return true }
+
 // LatestVersion returns the latest available version from configured repositories.
 func (p *Pacman) LatestVersion(ctx context.Context, pkg string) (string, error) {
 	return latestVersion(ctx, pkg)

snack.go

@@ -199,3 +199,18 @@ type NameNormalizer interface {
 	// Returns the name without arch and the arch string.
 	ParseArch(name string) (string, string)
 }
+
+// DryRunner reports whether a Manager backend natively supports dry-run mode.
+// Backends that implement this interface honor [WithDryRun] in Install, Remove,
+// Purge, and Upgrade and pass the appropriate flag to the underlying CLI
+// (e.g. apt-get --dry-run, apk --simulate, dnf --setopt=tsflags=test,
+// pacman --print).
+//
+// Backends that do NOT implement this interface (snap, flatpak, rpm, ports)
+// silently ignore [WithDryRun].
+//
+// Supported by: apt, apk, dnf, pacman.
+type DryRunner interface {
+	// SupportsDryRun reports whether this backend honors [WithDryRun].
+	SupportsDryRun() bool
+}

snack_test.go

@@ -91,6 +91,7 @@ func TestGetCapabilities_NilSafe(t *testing.T) {
 	assert.False(t, caps.KeyManagement)
 	assert.False(t, caps.Groups)
 	assert.False(t, caps.NameNormalize)
+	assert.False(t, caps.DryRun)
 }
 
 func TestErrors(t *testing.T) {