tpl: Add a partial lookup cache

````
                 │ stash.bench  │          perf-v146.bench           │
                 │    sec/op    │   sec/op     vs base               │
LookupPartial-10   248.00n ± 0%   14.75n ± 2%  -94.05% (p=0.002 n=6)

                 │ stash.bench │          perf-v146.bench          │
                 │    B/op     │   B/op     vs base                │
LookupPartial-10    48.00 ± 0%   0.00 ± 0%  -100.00% (p=0.002 n=6)

                 │ stash.bench │          perf-v146.bench           │
                 │  allocs/op  │ allocs/op   vs base                │
LookupPartial-10    3.000 ± 0%   0.000 ± 0%  -100.00% (p=0.002 n=6)
```

THe speedup above assumes reuse of the same partials over and over again, which I think is not uncommon.

This commits also adds some more lookup benchmarks. The current output of these on my MacBook looks decent:

```
BenchmarkLookupPagesLayout/Single_root-10                3031562               395.5 ns/op             0 B/op          0 allocs/op
BenchmarkLookupPagesLayout/Single_sub_folder-10          2515915               480.9 ns/op             0 B/op          0 allocs/op
BenchmarkLookupPartial-10                               84808112                14.13 ns/op            0 B/op          0 allocs/op
BenchmarkLookupShortcode/toplevelpage-10                 8111779               148.2 ns/op             0 B/op          0 allocs/op
BenchmarkLookupShortcode/nestedpage-10                   8088183               148.6 ns/op             0 B/op          0 allocs/op
```

Note that in the above the partial lookups are cahced, the others not (they are harder to cache because of the page path).

Closes #13571

Author: bep

Diff for: common/maps/cache.go

@@ -160,7 +160,7 @@ func (c *Cache[K, T]) Len() int {
 
 func (c *Cache[K, T]) Reset() {
 	c.Lock()
-	c.m = make(map[K]T)
+	clear(c.m)
 	c.hasBeenInitialized = false
 	c.Unlock()
 }

Diff for: hugolib/alias.go

@@ -51,7 +51,7 @@ func (a aliasHandler) renderAlias(permalink string, p page.Page) (io.Reader, err
 	var templateDesc tplimpl.TemplateDescriptor
 	var base string = ""
 	if ps, ok := p.(*pageState); ok {
-		base, templateDesc = ps.getTemplateBasePathAndDescriptor()
+		base, templateDesc = ps.GetInternalTemplateBasePathAndDescriptor()
 	}
 	templateDesc.Layout = ""
 	templateDesc.Kind = ""

Diff for: hugolib/page.go

@@ -476,7 +476,8 @@ func (ps *pageState) initCommonProviders(pp pagePaths) error {
 	return nil
 }
 
-func (po *pageOutput) getTemplateBasePathAndDescriptor() (string, tplimpl.TemplateDescriptor) {
+// Exported so it can be used in integration tests.
+func (po *pageOutput) GetInternalTemplateBasePathAndDescriptor() (string, tplimpl.TemplateDescriptor) {
 	p := po.p
 	f := po.f
 	base := p.PathInfo().BaseReTyped(p.m.pageConfig.Type)
@@ -491,7 +492,7 @@ func (po *pageOutput) getTemplateBasePathAndDescriptor() (string, tplimpl.Templa
 }
 
 func (p *pageState) resolveTemplate(layouts ...string) (*tplimpl.TemplInfo, bool, error) {
-	dir, d := p.getTemplateBasePathAndDescriptor()
+	dir, d := p.GetInternalTemplateBasePathAndDescriptor()
 
 	if len(layouts) > 0 {
 		d.Layout = layouts[0]

Diff for: hugolib/page__common.go

@@ -97,7 +97,7 @@ type pageCommon struct {
 	pageMenus *pageMenus
 
 	// Internal use
-	page.InternalDependencies
+	page.RelatedDocsHandlerProvider
 
 	contentConverterInit sync.Once
 	contentConverter     converter.Converter

Diff for: hugolib/page__new.go

@@ -209,11 +209,11 @@ func (h *HugoSites) doNewPage(m *pageMeta) (*pageState, *paths.Path, error) {
 				ShortcodeInfoProvider:     page.NopPage,
 				LanguageProvider:          m.s,
 
-				InternalDependencies: m.s,
-				init:                 lazy.New(),
-				m:                    m,
-				s:                    m.s,
-				sWrapped:             page.WrapSite(m.s),
+				RelatedDocsHandlerProvider: m.s,
+				init:                       lazy.New(),
+				m:                          m,
+				s:                          m.s,
+				sWrapped:                   page.WrapSite(m.s),
 			},
 		}
 

Diff for: hugolib/page__per_output.go

@@ -275,7 +275,7 @@ func (pco *pageContentOutput) initRenderHooks() error {
 			// Inherit the descriptor from the page/current output format.
 			// This allows for fine-grained control of the template used for
 			// rendering of e.g. links.
-			base, layoutDescriptor := pco.po.p.getTemplateBasePathAndDescriptor()
+			base, layoutDescriptor := pco.po.p.GetInternalTemplateBasePathAndDescriptor()
 
 			switch tp {
 			case hooks.LinkRendererType:

Diff for: hugolib/shortcode.go

@@ -397,7 +397,7 @@ func doRenderShortcode(
 			ofCount[match.D.OutputFormat]++
 			return true
 		}
-		base, layoutDescriptor := po.getTemplateBasePathAndDescriptor()
+		base, layoutDescriptor := po.GetInternalTemplateBasePathAndDescriptor()
 		q := tplimpl.TemplateQuery{
 			Path:     base,
 			Name:     sc.name,

Diff for: resources/page/page.go

@@ -148,8 +148,8 @@ type InSectionPositioner interface {
 	PrevInSection() Page
 }
 
-// InternalDependencies is considered an internal interface.
-type InternalDependencies interface {
+// RelatedDocsHandlerProvider is considered an internal interface.
+type RelatedDocsHandlerProvider interface {
 	// GetInternalRelatedDocsHandler is for internal use only.
 	GetInternalRelatedDocsHandler() *RelatedDocsHandler
 }

Diff for: resources/page/pages_related.go

@@ -124,7 +124,7 @@ func (p Pages) withInvertedIndex(ctx context.Context, search func(idx *related.I
 		return nil, nil
 	}
 
-	d, ok := p[0].(InternalDependencies)
+	d, ok := p[0].(RelatedDocsHandlerProvider)
 	if !ok {
 		return nil, fmt.Errorf("invalid type %T in related search", p[0])
 	}

Diff for: tpl/tplimpl/templatestore.go

@@ -97,16 +97,16 @@ func NewStore(opts StoreOptions, siteOpts SiteOptions) (*TemplateStore, error) {
 		panic("HTML output format not found")
 	}
 	s := &TemplateStore{
-		opts:                     opts,
-		siteOpts:                 siteOpts,
-		optsOrig:                 opts,
-		siteOptsOrig:             siteOpts,
-		htmlFormat:               html,
-		storeSite:                configureSiteStorage(siteOpts, opts.Watching),
-		treeMain:                 doctree.NewSimpleTree[map[nodeKey]*TemplInfo](),
-		treeShortcodes:           doctree.NewSimpleTree[map[string]map[TemplateDescriptor]*TemplInfo](),
-		templatesByPath:          maps.NewCache[string, *TemplInfo](),
-		templateDescriptorByPath: maps.NewCache[string, PathTemplateDescriptor](),
+		opts:                opts,
+		siteOpts:            siteOpts,
+		optsOrig:            opts,
+		siteOptsOrig:        siteOpts,
+		htmlFormat:          html,
+		storeSite:           configureSiteStorage(siteOpts, opts.Watching),
+		treeMain:            doctree.NewSimpleTree[map[nodeKey]*TemplInfo](),
+		treeShortcodes:      doctree.NewSimpleTree[map[string]map[TemplateDescriptor]*TemplInfo](),
+		templatesByPath:     maps.NewCache[string, *TemplInfo](),
+		cacheLookupPartials: maps.NewCache[string, *TemplInfo](),
 
 		// Note that the funcs passed below is just for name validation.
 		tns: newTemplateNamespace(siteOpts.TemplateFuncs),
@@ -400,10 +400,9 @@ type TemplateStore struct {
 	siteOpts   SiteOptions
 	htmlFormat output.Format
 
-	treeMain                 *doctree.SimpleTree[map[nodeKey]*TemplInfo]
-	treeShortcodes           *doctree.SimpleTree[map[string]map[TemplateDescriptor]*TemplInfo]
-	templatesByPath          *maps.Cache[string, *TemplInfo]
-	templateDescriptorByPath *maps.Cache[string, PathTemplateDescriptor]
+	treeMain        *doctree.SimpleTree[map[nodeKey]*TemplInfo]
+	treeShortcodes  *doctree.SimpleTree[map[string]map[TemplateDescriptor]*TemplInfo]
+	templatesByPath *maps.Cache[string, *TemplInfo]
 
 	dh descriptorHandler
 
@@ -417,6 +416,9 @@ type TemplateStore struct {
 	// For testing benchmarking.
 	optsOrig     StoreOptions
 	siteOptsOrig SiteOptions
+
+	// caches. These need to be refreshed when the templates are refreshed.
+	cacheLookupPartials *maps.Cache[string, *TemplInfo]
 }
 
 // NewFromOpts creates a new store with the same configuration as the original.
@@ -540,15 +542,19 @@ func (s *TemplateStore) LookupPagesLayout(q TemplateQuery) *TemplInfo {
 }
 
 func (s *TemplateStore) LookupPartial(pth string) *TemplInfo {
-	d := s.templateDescriptorFromPath(pth)
-	desc := d.Desc
-	if desc.Layout != "" {
-		panic("shortcode template descriptor must not have a layout")
-	}
-	best := s.getBest()
-	defer s.putBest(best)
-	s.findBestMatchGet(s.key(path.Join(containerPartials, d.Path)), CategoryPartial, nil, desc, best)
-	return best.templ
+	ti, _ := s.cacheLookupPartials.GetOrCreate(pth, func() (*TemplInfo, error) {
+		d := s.templateDescriptorFromPath(pth)
+		desc := d.Desc
+		if desc.Layout != "" {
+			panic("shortcode template descriptor must not have a layout")
+		}
+		best := s.getBest()
+		defer s.putBest(best)
+		s.findBestMatchGet(s.key(path.Join(containerPartials, d.Path)), CategoryPartial, nil, desc, best)
+		return best.templ, nil
+	})
+
+	return ti
 }
 
 func (s *TemplateStore) LookupShortcode(q TemplateQuery) *TemplInfo {
@@ -619,8 +625,14 @@ func (s *TemplateStore) PrintDebug(prefix string, category Category, w io.Writer
 	})
 }
 
+func (s *TemplateStore) clearCaches() {
+	s.cacheLookupPartials.Reset()
+}
+
 // RefreshFiles refreshes this store for the files matching the given predicate.
 func (s *TemplateStore) RefreshFiles(include func(fi hugofs.FileMetaInfo) bool) error {
+	s.clearCaches()
+
 	if err := s.tns.createPrototypesParse(); err != nil {
 		return err
 	}
@@ -1370,43 +1382,38 @@ type PathTemplateDescriptor struct {
 // templateDescriptorFromPath returns a template descriptor from the given path.
 // This is currently used in partial lookups only.
 func (s *TemplateStore) templateDescriptorFromPath(pth string) PathTemplateDescriptor {
-	// Check cache first.
-	d, _ := s.templateDescriptorByPath.GetOrCreate(pth, func() (PathTemplateDescriptor, error) {
-		var (
-			mt media.Type
-			of output.Format
-		)
-
-		// Common cases.
-		dotCount := strings.Count(pth, ".")
-		if dotCount <= 1 {
-			if dotCount == 0 {
-				// Asume HTML.
-				of, mt = s.resolveOutputFormatAndOrMediaType("html", "")
-			} else {
-				pth = strings.TrimPrefix(pth, "/")
-				ext := path.Ext(pth)
-				pth = strings.TrimSuffix(pth, ext)
-				ext = ext[1:]
-				of, mt = s.resolveOutputFormatAndOrMediaType("", ext)
-			}
+	var (
+		mt media.Type
+		of output.Format
+	)
+
+	// Common cases.
+	dotCount := strings.Count(pth, ".")
+	if dotCount <= 1 {
+		if dotCount == 0 {
+			// Asume HTML.
+			of, mt = s.resolveOutputFormatAndOrMediaType("html", "")
 		} else {
-			path := s.opts.PathParser.Parse(files.ComponentFolderLayouts, pth)
-			pth = path.PathNoIdentifier()
-			of, mt = s.resolveOutputFormatAndOrMediaType(path.OutputFormat(), path.Ext())
-		}
-
-		return PathTemplateDescriptor{
-			Path: pth,
-			Desc: TemplateDescriptor{
-				OutputFormat: of.Name,
-				MediaType:    mt.Type,
-				IsPlainText:  of.IsPlainText,
-			},
-		}, nil
-	})
+			pth = strings.TrimPrefix(pth, "/")
+			ext := path.Ext(pth)
+			pth = strings.TrimSuffix(pth, ext)
+			ext = ext[1:]
+			of, mt = s.resolveOutputFormatAndOrMediaType("", ext)
+		}
+	} else {
+		path := s.opts.PathParser.Parse(files.ComponentFolderLayouts, pth)
+		pth = path.PathNoIdentifier()
+		of, mt = s.resolveOutputFormatAndOrMediaType(path.OutputFormat(), path.Ext())
+	}
 
-	return d
+	return PathTemplateDescriptor{
+		Path: pth,
+		Desc: TemplateDescriptor{
+			OutputFormat: of.Name,
+			MediaType:    mt.Type,
+			IsPlainText:  of.IsPlainText,
+		},
+	}
 }
 
 // resolveOutputFormatAndOrMediaType resolves the output format and/or media type

Diff for: tpl/tplimpl/templatestore_integration_test.go

@@ -8,6 +8,7 @@ import (
 	qt "github.com/frankban/quicktest"
 	"github.com/gohugoio/hugo/hugolib"
 	"github.com/gohugoio/hugo/resources/kinds"
+	"github.com/gohugoio/hugo/resources/page"
 	"github.com/gohugoio/hugo/tpl/tplimpl"
 )
 
@@ -849,7 +850,7 @@ func BenchmarkExecuteWithContext(b *testing.B) {
 disableKinds = ["taxonomy", "term", "home"]
 -- layouts/all.html --
 {{ .Title }}|
- {{ partial "p1.html" . }}
+{{ partial "p1.html" . }}
 -- layouts/_partials/p1.html --
  p1.
 {{ partial "p2.html" . }}
@@ -878,6 +879,82 @@ p3
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		err := store.ExecuteWithContext(context.Background(), ti, io.Discard, p)
-		bb.Assert(err, qt.IsNil)
+		if err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+func BenchmarkLookupPartial(b *testing.B) {
+	files := `
+-- hugo.toml --
+disableKinds = ["taxonomy", "term", "home"]
+-- layouts/all.html --
+{{ .Title }}|
+-- layouts/_partials/p1.html --
+-- layouts/_partials/p2.html --
+-- layouts/_partials/p2.json --
+-- layouts/_partials/p3.html --
+`
+	bb := hugolib.Test(b, files)
+
+	store := bb.H.TemplateStore
+
+	for i := 0; i < b.N; i++ {
+		fi := store.LookupPartial("p3.html")
+		if fi == nil {
+			b.Fatal("not found")
+		}
 	}
 }
+
+// Implemented by pageOutput.
+type getDescriptorProvider interface {
+	GetInternalTemplateBasePathAndDescriptor() (string, tplimpl.TemplateDescriptor)
+}
+
+func BenchmarkLookupShortcode(b *testing.B) {
+	files := `
+-- hugo.toml --
+disableKinds = ["taxonomy", "term", "home"]
+-- content/toplevelpage.md --
+-- content/a/b/c/nested.md --
+-- layouts/all.html --
+{{ .Title }}|
+-- layouts/_shortcodes/s.html --
+s1.
+-- layouts/_shortcodes/a/b/s.html --
+s2.
+
+`
+	bb := hugolib.Test(b, files)
+	store := bb.H.TemplateStore
+
+	runOne := func(p page.Page) {
+		pth, desc := p.(getDescriptorProvider).GetInternalTemplateBasePathAndDescriptor()
+		q := tplimpl.TemplateQuery{
+			Path:     pth,
+			Name:     "s",
+			Category: tplimpl.CategoryShortcode,
+			Desc:     desc,
+		}
+		v := store.LookupShortcode(q)
+		if v == nil {
+			b.Fatal("not found")
+		}
+	}
+
+	b.Run("toplevelpage", func(b *testing.B) {
+		toplevelpage, _ := bb.H.Sites[0].GetPage("/toplevelpage")
+		for i := 0; i < b.N; i++ {
+			runOne(toplevelpage)
+		}
+	})
+
+	b.Run("nestedpage", func(b *testing.B) {
+		toplevelpage, _ := bb.H.Sites[0].GetPage("/a/b/c/nested")
+		for i := 0; i < b.N; i++ {
+			runOne(toplevelpage)
+		}
+	})
+}