Fix panic on server rebuilds when using both base templates and template.Defer

Fixes #12963

5 files changed, 110 insertions, 65 deletions

diff --git a/common/types/evictingqueue.go b/common/types/evictingqueue.go
index 88add59d5..5ab715aa8 100644
--- a/common/types/evictingqueue.go
+++ b/common/types/evictingqueue.go
@@ -65,6 +65,9 @@ func (q *EvictingStringQueue) Len() int {
 
 // Contains returns whether the queue contains v.
 func (q *EvictingStringQueue) Contains(v string) bool {
+	if q == nil {
+		return false
+	}
 	q.mu.Lock()
 	defer q.mu.Unlock()
 	return q.set[v]
diff --git a/hugolib/integrationtest_builder.go b/hugolib/integrationtest_builder.go
index b593cd965..7a6c040b1 100644
--- a/hugolib/integrationtest_builder.go
+++ b/hugolib/integrationtest_builder.go
@@ -25,6 +25,7 @@ import (
 	"github.com/gohugoio/hugo/common/hexec"
 	"github.com/gohugoio/hugo/common/loggers"
 	"github.com/gohugoio/hugo/common/maps"
+	"github.com/gohugoio/hugo/common/types"
 	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/config/allconfig"
 	"github.com/gohugoio/hugo/config/security"
@@ -466,6 +467,28 @@ func (s *IntegrationTestBuilder) Build() *IntegrationTestBuilder {
 	return s
 }
 
+func (s *IntegrationTestBuilder) BuildPartial(urls ...string) *IntegrationTestBuilder {
+	if _, err := s.BuildPartialE(urls...); err != nil {
+		s.Fatal(err)
+	}
+	return s
+}
+
+func (s *IntegrationTestBuilder) BuildPartialE(urls ...string) (*IntegrationTestBuilder, error) {
+	if s.buildCount == 0 {
+		panic("BuildPartial can only be used after a full build")
+	}
+	if !s.Cfg.Running {
+		panic("BuildPartial can only be used in server mode")
+	}
+	visited := types.NewEvictingStringQueue(len(urls))
+	for _, url := range urls {
+		visited.Add(url)
+	}
+	buildCfg := BuildCfg{RecentlyVisited: visited, PartialReRender: true}
+	return s, s.build(buildCfg)
+}
+
 func (s *IntegrationTestBuilder) Close() {
 	s.Helper()
 	s.Assert(s.H.Close(), qt.IsNil)
@@ -747,10 +770,6 @@ func (s *IntegrationTestBuilder) build(cfg BuildCfg) error {
 	s.counters = &buildCounters{}
 	cfg.testCounters = s.counters
 
-	if s.buildCount > 0 && (len(changeEvents) == 0) {
-		return nil
-	}
-
 	s.buildCount++
 
 	err := s.H.Build(cfg, changeEvents...)
diff --git a/internal/js/esbuild/batch_integration_test.go b/internal/js/esbuild/batch_integration_test.go
index 55528bdf0..b4a2454ac 100644
--- a/internal/js/esbuild/batch_integration_test.go
+++ b/internal/js/esbuild/batch_integration_test.go
@@ -721,43 +721,3 @@ console.log("config.params.id", id3);
 	b.EditFileReplaceAll("assets/other/bar.css", ".bar-edit {", ".bar-edit2 {").Build()
 	b.AssertFileContent("public/mybundle/reactbatch.css", ".bar-edit2 {")
 }
-
-func TestEditBaseofManyTimes(t *testing.T) {
-	files := `
--- hugo.toml --
-baseURL = "https://example.com"
-disableLiveReload = true
-disableKinds = ["taxonomy", "term"]
--- layouts/_default/baseof.html --
-Baseof.
-{{ block "main" . }}{{ end }}
-{{ with (templates.Defer (dict "key" "global")) }}
-Now. {{ now }}
-{{ end }}
--- layouts/_default/single.html --
-{{ define "main" }}
-Single.
-{{ end }}
---
--- layouts/_default/list.html --
-{{ define "main" }}
-List.
-{{ end }}
--- content/mybundle/index.md --
----
-title: "My Bundle"
----
--- content/_index.md --
----
-title: "Home"
----
-`
-
-	b := hugolib.TestRunning(t, files)
-	b.AssertFileContent("public/index.html", "Baseof.")
-
-	for i := 0; i < 100; i++ {
-		b.EditFileReplaceAll("layouts/_default/baseof.html", "Now", "Now.").Build()
-		b.AssertFileContent("public/index.html", "Now..")
-	}
-}
diff --git a/tpl/tplimpl/template.go b/tpl/tplimpl/template.go
index 9e2af046d..0a593593b 100644
--- a/tpl/tplimpl/template.go
+++ b/tpl/tplimpl/template.go
@@ -30,6 +30,7 @@ import (
 	"unicode"
 	"unicode/utf8"
 
+	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/common/types"
 	"github.com/gohugoio/hugo/output/layouts"
 
@@ -191,8 +192,10 @@ func newTemplateHandlers(d *deps.Deps) (*tpl.TemplateHandlers, error) {
 
 func newTemplateNamespace(funcs map[string]any) *templateNamespace {
 	return &templateNamespace{
-		prototypeHTML: htmltemplate.New("").Funcs(funcs),
-		prototypeText: texttemplate.New("").Funcs(funcs),
+		prototypeHTML:           htmltemplate.New("").Funcs(funcs),
+		prototypeText:           texttemplate.New("").Funcs(funcs),
+		prototypeHTMLCloneCache: maps.NewCache[prototypeCloneID, *htmltemplate.Template](),
+		prototypeTextCloneCache: maps.NewCache[prototypeCloneID, *texttemplate.Template](),
 		templateStateMap: &templateStateMap{
 			templates: make(map[string]*templateState),
 		},
@@ -688,7 +691,7 @@ func (t *templateHandler) addTemplateTo(info templateInfo, to *templateNamespace
 func (t *templateHandler) applyBaseTemplate(overlay, base templateInfo) (tpl.Template, error) {
 	if overlay.isText {
 		var (
-			templ = t.main.prototypeTextClone.New(overlay.name)
+			templ = t.main.getPrototypeText(prototypeCloneIDBaseof).New(overlay.name)
 			err   error
 		)
 
@@ -713,7 +716,7 @@ func (t *templateHandler) applyBaseTemplate(overlay, base templateInfo) (tpl.Tem
 	}
 
 	var (
-		templ = t.main.prototypeHTMLClone.New(overlay.name)
+		templ = t.main.getPrototypeHTML(prototypeCloneIDBaseof).New(overlay.name)
 		err   error
 	)
 
@@ -953,27 +956,37 @@ func (t *templateHandler) postTransform() error {
 	return nil
 }
 
+type prototypeCloneID uint16
+
+const (
+	prototypeCloneIDBaseof prototypeCloneID = iota + 1
+	prototypeCloneIDDefer
+)
+
 type templateNamespace struct {
-	prototypeText      *texttemplate.Template
-	prototypeHTML      *htmltemplate.Template
-	prototypeTextClone *texttemplate.Template
-	prototypeHTMLClone *htmltemplate.Template
+	prototypeText *texttemplate.Template
+	prototypeHTML *htmltemplate.Template
+
+	prototypeHTMLCloneCache *maps.Cache[prototypeCloneID, *htmltemplate.Template]
+	prototypeTextCloneCache *maps.Cache[prototypeCloneID, *texttemplate.Template]
 
 	*templateStateMap
 }
 
-func (t *templateNamespace) getPrototypeText() *texttemplate.Template {
-	if t.prototypeTextClone != nil {
-		return t.prototypeTextClone
+func (t *templateNamespace) getPrototypeText(id prototypeCloneID) *texttemplate.Template {
+	v, ok := t.prototypeTextCloneCache.Get(id)
+	if !ok {
+		return t.prototypeText
 	}
-	return t.prototypeText
+	return v
 }
 
-func (t *templateNamespace) getPrototypeHTML() *htmltemplate.Template {
-	if t.prototypeHTMLClone != nil {
-		return t.prototypeHTMLClone
+func (t *templateNamespace) getPrototypeHTML(id prototypeCloneID) *htmltemplate.Template {
+	v, ok := t.prototypeHTMLCloneCache.Get(id)
+	if !ok {
+		return t.prototypeHTML
 	}
-	return t.prototypeHTML
+	return v
 }
 
 func (t *templateNamespace) Lookup(name string) (tpl.Template, bool) {
@@ -989,9 +1002,10 @@ func (t *templateNamespace) Lookup(name string) (tpl.Template, bool) {
 }
 
 func (t *templateNamespace) createPrototypes() error {
-	t.prototypeTextClone = texttemplate.Must(t.prototypeText.Clone())
-	t.prototypeHTMLClone = htmltemplate.Must(t.prototypeHTML.Clone())
-
+	for _, id := range []prototypeCloneID{prototypeCloneIDBaseof, prototypeCloneIDDefer} {
+		t.prototypeHTMLCloneCache.Set(id, htmltemplate.Must(t.prototypeHTML.Clone()))
+		t.prototypeTextCloneCache.Set(id, texttemplate.Must(t.prototypeText.Clone()))
+	}
 	return nil
 }
 
@@ -1021,7 +1035,7 @@ func (t *templateNamespace) addDeferredTemplate(owner *templateState, name strin
 	var templ tpl.Template
 
 	if owner.isText() {
-		prototype := t.getPrototypeText()
+		prototype := t.getPrototypeText(prototypeCloneIDDefer)
 		tt, err := prototype.New(name).Parse("")
 		if err != nil {
 			return fmt.Errorf("failed to parse empty text template %q: %w", name, err)
@@ -1029,7 +1043,7 @@ func (t *templateNamespace) addDeferredTemplate(owner *templateState, name strin
 		tt.Tree.Root = n
 		templ = tt
 	} else {
-		prototype := t.getPrototypeHTML()
+		prototype := t.getPrototypeHTML(prototypeCloneIDDefer)
 		tt, err := prototype.New(name).Parse("")
 		if err != nil {
 			return fmt.Errorf("failed to parse empty HTML template %q: %w", name, err)
diff --git a/tpl/tplimpl/tplimpl_integration_test.go b/tpl/tplimpl/tplimpl_integration_test.go
index 1e7aa3111..dbadece4e 100644
--- a/tpl/tplimpl/tplimpl_integration_test.go
+++ b/tpl/tplimpl/tplimpl_integration_test.go
@@ -649,3 +649,52 @@ E: An _emphasized_ word.
 		"<details>\n  <summary>Details</summary>\n  <p>D: An <em>emphasized</em> word.</p>\n</details>",
 	)
 }
+
+// Issue 12963
+func TestEditBaseofParseAfterExecute(t *testing.T) {
+	files := `
+-- hugo.toml --
+baseURL = "https://example.com"
+disableLiveReload = true
+disableKinds = ["taxonomy", "term", "rss", "404", "sitemap"]
+[internal]
+fastRenderMode = true
+-- layouts/_default/baseof.html --
+Baseof!
+{{ block "main" . }}default{{ end }}
+{{ with (templates.Defer (dict "key" "global")) }}
+Now. {{ now }}
+{{ end }}
+-- layouts/_default/single.html --
+{{ define "main" }}
+Single.
+{{ end }}
+-- layouts/_default/list.html --
+{{ define "main" }}
+List.
+{{ .Content }}
+{{ range .Pages }}{{ .Title }}{{ end }}|
+{{ end }}
+-- content/mybundle1/index.md --
+---
+title: "My Bundle 1"
+---
+-- content/mybundle2/index.md --
+---
+title: "My Bundle 2"
+---
+-- content/_index.md --
+---
+title: "Home"
+---
+Home!
+`
+
+	b := hugolib.TestRunning(t, files)
+	b.AssertFileContent("public/index.html", "Home!")
+	b.EditFileReplaceAll("layouts/_default/baseof.html", "Baseof", "Baseof!").Build()
+	b.BuildPartial("/")
+	b.AssertFileContent("public/index.html", "Baseof!!")
+	b.BuildPartial("/mybundle1/")
+	b.AssertFileContent("public/mybundle1/index.html", "Baseof!!")
+}