caddyfile: fix importGraph self-loop and stale-edge bugs (#7971)

- willCycle now reports a cycle when from == to, so addEdge rejects
  self-loops (a self-importing file was previously accepted).
- removeNode now drops the removed node's outgoing edges and any
  incoming edges pointing at it, keeping the adjacency map consistent.

Signed-off-by: Mohammed Al Sahaf <msaa1990@gmail.com>

caddyconfig/caddyfile/importgraph.go

@@ -44,6 +44,10 @@ func (i *importGraph) addNodes(names []string) {
 
 func (i *importGraph) removeNode(name string) {
 	delete(i.nodes, name)
+	delete(i.edges, name)
+	for k, targets := range i.edges {
+		i.edges[k] = slices.DeleteFunc(targets, func(t string) bool { return t == name })
+	}
 }
 
 func (i *importGraph) removeNodes(names []string) {
@@ -96,6 +100,9 @@ func (i *importGraph) areConnected(from, to string) bool {
 }
 
 func (i *importGraph) willCycle(from, to string) bool {
+	if from == to {
+		return true
+	}
 	collector := make(map[string]bool)
 
 	var visit func(string)

caddyconfig/caddyfile/importgraph_test.go

@@ -0,0 +1,45 @@
+// Copyright 2015 Matthew Holt and The Caddy Authors
+//
+// 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 caddyfile
+
+import "testing"
+
+func TestImportGraphSelfLoop(t *testing.T) {
+	g := &importGraph{}
+	g.addNode("a")
+
+	if err := g.addEdge("a", "a"); err == nil {
+		t.Error("expected error for self-loop cycle a -> a")
+	}
+}
+
+func TestImportGraphRemoveNodeCleansEdges(t *testing.T) {
+	g := &importGraph{}
+	g.addNodes([]string{"a", "b", "c"})
+	_ = g.addEdge("a", "b")
+	_ = g.addEdge("b", "c")
+
+	g.removeNode("b")
+
+	if g.exists("b") {
+		t.Error("node 'b' should not exist after removeNode")
+	}
+	if targets, ok := g.edges["b"]; ok && len(targets) > 0 {
+		t.Errorf("outgoing edges from removed node 'b' should be cleared, got %v", targets)
+	}
+	if g.areConnected("a", "b") {
+		t.Error("incoming edge 'a' -> 'b' should be removed when 'b' is removed")
+	}
+}