Add a Diff Visitor for BlueprintZoneConfigs (#7336)

This visitor walks a diffus generated diff and provides callbacks for
users to hook into the parts of the diff that they care about.

To keep things minimal, we don't provide callback trait methods for
copies (when nothing changes), and we don't provide methods for most
diffus_derive generated types (the ones that start with `Edited`).

We anticipate composing these visitors to build up a full diff of a
Blueprint. They can also be used individually as demonstrated with the
included tests.

Cargo.toml

@@ -687,7 +687,7 @@ zone = { version = "0.3", default-features = false, features = ["async"] }
 # the kinds). However, uses of omicron-uuid-kinds _within omicron_ will have
 # std and the other features enabled because they'll refer to it via
 # omicron-uuid-kinds.workspace = true.
-newtype-uuid = { version = "1.1.3", default-features = false }
+newtype-uuid = { version = "1.2.1", default-features = false }
 omicron-uuid-kinds = { path = "uuid-kinds", features = ["serde", "schemars08", "uuid-v4"] }
 
 # NOTE: The test profile inherits from the dev profile, so settings under

common/src/api/external/mod.rs

@@ -751,10 +751,27 @@ impl From<ByteCount> for i64 {
     PartialEq,
     PartialOrd,
     Serialize,
-    Diffus,
 )]
 pub struct Generation(u64);
 
+// We have to manually implement `Diffable` because this is newtype with private
+// data, and we want to see the diff on the newtype not the inner data.
+impl<'a> Diffable<'a> for Generation {
+    type Diff = (&'a Generation, &'a Generation);
+
+    fn diff(&'a self, other: &'a Self) -> edit::Edit<'a, Self> {
+        if self == other {
+            edit::Edit::Copy(self)
+        } else {
+            edit::Edit::Change {
+                before: self,
+                after: other,
+                diff: (self, other),
+            }
+        }
+    }
+}
+
 impl Generation {
     pub const fn new() -> Generation {
         Generation(1)
@@ -1947,7 +1964,11 @@ impl<'a> Diffable<'a> for MacAddr {
         if self == other {
             edit::Edit::Copy(self)
         } else {
-            edit::Edit::Change((self, other))
+            edit::Edit::Change {
+                before: self,
+                after: other,
+                diff: (self, other),
+            }
         }
     }
 }

nexus/types/src/deployment.rs

@@ -54,6 +54,7 @@ use strum::IntoEnumIterator;
 mod blueprint_diff;
 mod blueprint_display;
 mod clickhouse;
+pub mod diff_visitors;
 pub mod execution;
 pub mod id_map;
 mod network_resources;
@@ -62,6 +63,7 @@ mod tri_map;
 mod zone_type;
 
 pub use clickhouse::ClickhouseClusterConfig;
+pub use diff_visitors::BpVisitorContext;
 pub use network_resources::AddNetworkResourceError;
 pub use network_resources::OmicronZoneExternalFloatingAddr;
 pub use network_resources::OmicronZoneExternalFloatingIp;

nexus/types/src/deployment/diff_visitors.rs

@@ -0,0 +1,55 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+//! An API for visiting diffs between blueprints generated via [diffus](https://github.com/oxidecomputer/diffus)
+//!
+//! Modelled after [`syn::visit`](https://docs.rs/syn/1/syn/visit).
+
+pub mod visit_blueprint_zones_config;
+
+use diffus::edit::enm;
+use omicron_uuid_kinds::{OmicronZoneUuid, SledUuid};
+
+use super::{
+    BlueprintZoneConfig, BlueprintZoneDisposition, BlueprintZoneType,
+    BlueprintZonesConfig, EditedBlueprintZoneConfig,
+};
+
+/// A context for blueprint related visitors
+#[derive(Debug, Clone, Default)]
+pub struct BpVisitorContext {
+    pub sled_id: Option<SledUuid>,
+    pub zone_id: Option<OmicronZoneUuid>,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Change<'e, T> {
+    pub before: &'e T,
+    pub after: &'e T,
+}
+
+impl<'e, T> Change<'e, T> {
+    pub fn new(before: &'e T, after: &'e T) -> Change<'e, T> {
+        Change { before, after }
+    }
+}
+
+impl<'e, T> From<(&'e T, &'e T)> for Change<'e, T> {
+    fn from(value: (&'e T, &'e T)) -> Self {
+        Change::new(value.0, value.1)
+    }
+}
+
+impl<'e, T, Diff> From<&enm::Edit<'e, T, Diff>> for Change<'e, T> {
+    fn from(value: &enm::Edit<'e, T, Diff>) -> Self {
+        match value {
+            enm::Edit::VariantChanged(before, after) => {
+                Change::new(before, after)
+            }
+            enm::Edit::AssociatedChanged { before, after, .. } => {
+                Change::new(before, after)
+            }
+        }
+    }
+}