Reimplement and simplify Hugo's template system

See #13541 for details.

Fixes #13545
Fixes #13515
Closes #7964
Closes #13365
Closes #12988
Closes #4891

Author: bep

commands/server.go

@@ -23,6 +23,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"maps"
 	"net"
 	"net/http"
 	_ "net/http/pprof"
@@ -48,6 +49,7 @@ import (
 	"github.com/fsnotify/fsnotify"
 	"github.com/gohugoio/hugo/common/herrors"
 	"github.com/gohugoio/hugo/common/hugo"
+	"github.com/gohugoio/hugo/tpl/tplimpl"
 
 	"github.com/gohugoio/hugo/common/types"
 	"github.com/gohugoio/hugo/common/urls"
@@ -57,15 +59,13 @@ import (
 	"github.com/gohugoio/hugo/hugolib"
 	"github.com/gohugoio/hugo/hugolib/filesystems"
 	"github.com/gohugoio/hugo/livereload"
-	"github.com/gohugoio/hugo/tpl"
 	"github.com/gohugoio/hugo/transform"
 	"github.com/gohugoio/hugo/transform/livereloadinject"
 	"github.com/spf13/afero"
 	"github.com/spf13/cobra"
 	"github.com/spf13/fsync"
 	"golang.org/x/sync/errgroup"
 	"golang.org/x/sync/semaphore"
-	"maps"
 )
 
 var (
@@ -897,16 +897,16 @@ func (c *serverCommand) serve() error {
 	// To allow the en user to change the error template while the server is running, we use
 	// the freshest template we can provide.
 	var (
-		errTempl     tpl.Template
-		templHandler tpl.TemplateHandler
+		errTempl     *tplimpl.TemplInfo
+		templHandler *tplimpl.TemplateStore
 	)
-	getErrorTemplateAndHandler := func(h *hugolib.HugoSites) (tpl.Template, tpl.TemplateHandler) {
+	getErrorTemplateAndHandler := func(h *hugolib.HugoSites) (*tplimpl.TemplInfo, *tplimpl.TemplateStore) {
 		if h == nil {
 			return errTempl, templHandler
 		}
-		templHandler := h.Tmpl()
-		errTempl, found := templHandler.Lookup("_server/error.html")
-		if !found {
+		templHandler := h.GetTemplateStore()
+		errTempl := templHandler.LookupByPath("/_server/error.html")
+		if errTempl == nil {
 			panic("template server/error.html not found")
 		}
 		return errTempl, templHandler

common/constants/constants.go

@@ -23,6 +23,7 @@ const (
 	WarnFrontMatterParamsOverrides = "warning-frontmatter-params-overrides"
 	WarnRenderShortcodesInHTML     = "warning-rendershortcodes-in-html"
 	WarnGoldmarkRawHTML            = "warning-goldmark-raw-html"
+	WarnPartialSuperfluousPrefix   = "warning-partial-superfluous-prefix"
 )
 
 // Field/method names with special meaning.

common/hstrings/strings.go

@@ -16,11 +16,11 @@ package hstrings
 import (
 	"fmt"
 	"regexp"
+	"slices"
 	"strings"
 	"sync"
 
 	"github.com/gohugoio/hugo/compare"
-	"slices"
 )
 
 var _ compare.Eqer = StringEqualFold("")
@@ -128,7 +128,7 @@ func ToString(v any) (string, bool) {
 	return "", false
 }
 
-type Tuple struct {
-	First  string
-	Second string
-}
+type (
+	Strings2 [2]string
+	Strings3 [3]string
+)

common/maps/cache.go

@@ -69,6 +69,14 @@ func (c *Cache[K, T]) GetOrCreate(key K, create func() (T, error)) (T, error) {
 	return v, nil
 }
 
+// Contains returns whether the given key exists in the cache.
+func (c *Cache[K, T]) Contains(key K) bool {
+	c.RLock()
+	_, found := c.m[key]
+	c.RUnlock()
+	return found
+}
+
 // InitAndGet initializes the cache if not already done and returns the value for the given key.
 // The init state will be reset on Reset or Drain.
 func (c *Cache[K, T]) InitAndGet(key K, init func(get func(key K) (T, bool), set func(key K, value T)) error) (T, error) {
@@ -108,6 +116,17 @@ func (c *Cache[K, T]) Set(key K, value T) {
 	c.Unlock()
 }
 
+// SetIfAbsent sets the given key to the given value if the key does not already exist in the cache.
+func (c *Cache[K, T]) SetIfAbsent(key K, value T) {
+	c.RLock()
+	if _, found := c.get(key); !found {
+		c.RUnlock()
+		c.Set(key, value)
+	} else {
+		c.RUnlock()
+	}
+}
+
 func (c *Cache[K, T]) set(key K, value T) {
 	c.m[key] = value
 }

common/maps/ordered.go

@@ -14,8 +14,9 @@
 package maps
 
 import (
-	"github.com/gohugoio/hugo/common/hashing"
 	"slices"
+
+	"github.com/gohugoio/hugo/common/hashing"
 )
 
 // Ordered is a map that can be iterated in the order of insertion.
@@ -57,6 +58,15 @@ func (m *Ordered[K, T]) Get(key K) (T, bool) {
 	return value, found
 }
 
+// Has returns whether the given key exists in the map.
+func (m *Ordered[K, T]) Has(key K) bool {
+	if m == nil {
+		return false
+	}
+	_, found := m.values[key]
+	return found
+}
+
 // Delete deletes the value for the given key.
 func (m *Ordered[K, T]) Delete(key K) {
 	if m == nil {