feat: 迁移 Database Instance 领域基线

internal/database/domain/instance/extensions.go

@@ -0,0 +1,84 @@
+/*
+Copyright 2026.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package instance
+
+import "slices"
+
+// ExtensionSet is an immutable set of exact names. Zero represents the empty set.
+// It does not impose identifier syntax or claim that a server supports any name.
+type ExtensionSet struct {
+	names []string
+}
+
+func NewExtensionSet(names []string) ExtensionSet {
+	copied := slices.Clone(names)
+	slices.Sort(copied)
+	return ExtensionSet{names: slices.Compact(copied)}
+}
+
+// Names returns a sorted, deduplicated copy.
+func (s ExtensionSet) Names() []string { return slices.Clone(s.names) }
+
+type ExtensionDecision string
+
+const (
+	ExtensionsAccepted         ExtensionDecision = "Accepted"
+	ExtensionsUnsupported      ExtensionDecision = "ExtensionsUnsupported"
+	ExtensionSupportUnobserved ExtensionDecision = "ExtensionSupportUnobserved"
+)
+
+// ExtensionCheck reports support only, not readiness or permission to install.
+// Unsupported is a detached, sorted list and is populated only for known support.
+type ExtensionCheck struct {
+	Decision    ExtensionDecision
+	Unsupported []string
+}
+
+// ExtensionSupport is the extension-list component of an Instance observation.
+// Zero means unobserved, not an observed empty list. Target/revision binding and
+// invalidation belong to the containing Instance observation, not this set value.
+type ExtensionSupport struct {
+	observed  bool
+	available ExtensionSet
+}
+
+// ObserveExtensionSupport records a successfully read list, including an empty one.
+// A failed query must not call this constructor with an empty list: the application
+// must propagate the dependency failure and leave support unobserved.
+func ObserveExtensionSupport(available []string) ExtensionSupport {
+	return ExtensionSupport{observed: true, available: NewExtensionSet(available)}
+}
+
+// Check performs no IO and cannot install or remove extensions.
+func (s ExtensionSupport) Check(requested ExtensionSet) ExtensionCheck {
+	if len(requested.names) == 0 {
+		return ExtensionCheck{Decision: ExtensionsAccepted}
+	}
+	if !s.observed {
+		return ExtensionCheck{Decision: ExtensionSupportUnobserved}
+	}
+	var unsupported []string
+	for _, name := range requested.names {
+		if _, found := slices.BinarySearch(s.available.names, name); !found {
+			unsupported = append(unsupported, name)
+		}
+	}
+	if len(unsupported) != 0 {
+		return ExtensionCheck{Decision: ExtensionsUnsupported, Unsupported: unsupported}
+	}
+	return ExtensionCheck{Decision: ExtensionsAccepted}
+}