hugolib: Fix automatic section pages not replaced by sites.complements

When a home page or section page in language A is backed by a file and
language B has no content file for that section, the automatic page for
language B was not replaced by the complement from language A. This
happened because:

1. The content node shifter returned auto pages (not backed by files) as
   exact matches without trying complement fallback.
2. findContentNodeForSiteVector immediately returned auto pages as exact
   matches without considering file-backed complements.
3. getPagesInSection used Get (no fallback) for IncludeSelf, preventing
   complement resolution for home/section pages.

Fix by preferring file-backed complement pages over auto pages in the
shift and lookup mechanisms, and using fallback for self-inclusion.

Fixes #14540

Co-Authored-By: Joe Mooring <joe.mooring@veriphor.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hugolib/content_map_page.go

@@ -388,7 +388,7 @@ func (m *pageMap) getPagesInSection(q pageMapQueryPagesInSection) page.Pages {
 
 		if err == nil {
 			if q.IncludeSelf {
-				if n := m.treePages.Get(q.Path); n != nil {
+				if n := m.treePages.GetWithFallback(q.Path); n != nil {
 					if p, ok := n.(*pageState); ok && include(p) {
 						pas = append(pas, p)
 					}

hugolib/content_map_page_contentnode.go

@@ -223,6 +223,7 @@ func (h helperContentNode) findContentNodeForSiteVector(q sitesmatrix.Vector, fa
 	var (
 		best         contentNodeForSite = nil
 		bestDistance int
+		bestWeight   int
 	)
 
 	for n := range candidates {
@@ -233,27 +234,41 @@ func (h helperContentNode) findContentNodeForSiteVector(q sitesmatrix.Vector, fa
 		if m := n.(contentNodeLookupContentNodes).lookupContentNodes(q, fallback); m != nil {
 			for nn := range m {
 				vec := nn.siteVector()
-				if q == vec {
-					// Exact match.
+				var w int
+				if wp, ok := nn.(contentNodeContentWeightProvider); ok {
+					w = wp.contentWeight()
+				}
+
+				if q == vec && w > 0 {
+					// Exact match backed by a file.
 					return nn
 				}
 
 				distance := q.Distance(vec)
+				distanceAbs := absint(distance)
 
 				if best == nil {
 					best = nn
 					bestDistance = distance
+					bestWeight = w
 				} else {
-					distanceAbs := absint(distance)
 					bestDistanceAbs := absint(bestDistance)
-					if distanceAbs < bestDistanceAbs {
-						// Closer is better.
-						best = nn
-						bestDistance = distance
-					} else if distanceAbs == bestDistanceAbs && distance > 0 {
-						// Positive distance is better than negative.
+					if w > 0 && bestWeight == 0 {
+						// Prefer file-backed pages over auto pages.
 						best = nn
 						bestDistance = distance
+						bestWeight = w
+					} else if (w > 0) == (bestWeight > 0) {
+						// Both file-backed or both auto: use distance.
+						if distanceAbs < bestDistanceAbs {
+							best = nn
+							bestDistance = distance
+							bestWeight = w
+						} else if distanceAbs == bestDistanceAbs && distance > 0 {
+							best = nn
+							bestDistance = distance
+							bestWeight = w
+						}
 					}
 				}
 			}

hugolib/content_map_page_contentnodeshifter.go

@@ -152,17 +152,31 @@ func (s *contentNodeShifter) Insert(old, new contentNode) (contentNode, contentN
 }
 
 func (s *contentNodeShifter) Shift(n contentNode, siteVector sitesmatrix.Vector, fallback bool) (contentNode, bool) {
+	var exact contentNode
 	switch v := n.(type) {
 	case contentNodeLookupContentNode:
-		if vv := v.lookupContentNode(siteVector); vv != nil {
-			return vv, true
-		}
+		exact = v.lookupContentNode(siteVector)
 	default:
 		panic(fmt.Sprintf("Shift: unknown type %T for %q", n, n.Path()))
 	}
 
+	if exact != nil {
+		if !fallback {
+			return exact, true
+		}
+		// If the exact match is backed by a file, return it directly.
+		if wp, ok := exact.(contentNodeContentWeightProvider); ok && wp.contentWeight() > 0 {
+			return exact, true
+		}
+		// The exact match is an auto page (not backed by a file).
+		// Check if there's a file-backed complement that should take precedence.
+		if vvv := cnh.findContentNodeForSiteVector(siteVector, fallback, contentNodeToSeq(n)); vvv != nil {
+			return vvv, true
+		}
+		return exact, true
+	}
+
 	if !fallback {
-		// Done
 		return nil, false
 	}
 

hugolib/doctree/nodeshifttree.go

@@ -338,6 +338,22 @@ func (r *NodeShiftTree[T]) Get(s string) T {
 	return t
 }
 
+// GetWithFallback is like Get but uses the fallback/complement mechanism
+// when finding a node for the current site vector.
+func (r *NodeShiftTree[T]) GetWithFallback(s string) T {
+	s = cleanKey(s)
+	v, ok := r.tree.Get(s)
+	if !ok {
+		var t T
+		return t
+	}
+	if v, ok := r.shift(v, true); ok {
+		return v
+	}
+	var t T
+	return t
+}
+
 func (r *NodeShiftTree[T]) ForEeachInDimension(s string, dims sitesmatrix.Vector, d int, f func(T) bool) {
 	s = cleanKey(s)
 	v, ok := r.tree.Get(s)

hugolib/sitesmatrix/sitematrix_integration_test.go

@@ -1658,3 +1658,90 @@ Version: {{ .Site.Version.Name }}|
 
 	b.AssertFileContent("public/v1/index.html", "Edited version: v1|")
 }
+
+// Issue 14540
+func TestSiteComplementsOverrideAutomaticSectionPages(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['rss', 'sitemap', 'taxonomy', 'term']
+defaultContentLanguageInSubdir = true
+
+[languages.en]
+  weight = 1
+
+[languages.de]
+  weight = 2
+
+[[module.mounts]]
+  source = 'content/en'
+  target = 'content'
+  [module.mounts.sites.matrix]
+    languages = ['en']
+  [module.mounts.sites.complements]
+    languages = ['de']
+
+[[module.mounts]]
+  source = 'content/de'
+  target = 'content'
+  [module.mounts.sites.matrix]
+    languages = ['de']
+-- layouts/home.html --
+<ul>
+{{ range $k, $_ := site.Pages -}}
+  <li>[{{ $k }}] <a href="{{ .RelPermalink }}">{{ .Title }}</a></li>
+{{ end -}}
+</ul>
+-- layouts/page.html --
+{{ .Title }}|
+-- layouts/section.html --
+{{ .Title }}|
+-- content/en/_index.md --
+---
+title: home en
+---
+-- content/en/s1/_index.md --
+---
+title: s1 en
+---
+-- content/en/s1/p1.md --
+---
+title: p1 en
+---
+-- content/en/s2/_index.md --
+---
+title: s2 en
+---
+-- content/en/s2/p2.md --
+---
+title: p2 en
+---
+-- content/de/s1/p1.md --
+---
+title: p1 de
+---
+`
+
+	b := hugolib.Test(t, files)
+
+	b.AssertFileContent("public/en/index.html", `
+<ul>
+<li>[0] <a href="/en/">home en</a></li>
+<li>[1] <a href="/en/s1/p1/">p1 en</a></li>
+<li>[2] <a href="/en/s2/p2/">p2 en</a></li>
+<li>[3] <a href="/en/s1/">s1 en</a></li>
+<li>[4] <a href="/en/s2/">s2 en</a></li>
+</ul>
+	`)
+
+	b.AssertFileContent("public/de/index.html", `
+<ul>
+<li>[0] <a href="/en/">home en</a></li>
+<li>[1] <a href="/de/s1/p1/">p1 de</a></li>
+<li>[2] <a href="/en/s2/p2/">p2 en</a></li>
+<li>[3] <a href="/en/s1/">s1 en</a></li>
+<li>[4] <a href="/en/s2/">s2 en</a></li>
+</ul>
+	`)
+}