Cache reflect.MethodByName

The isolated benchmark for the function is obviously much faster:

```bash
name                old time/op    new time/op    delta
GetMethodByName-10    1.21µs ± 7%    0.23µs ± 5%   -81.42%  (p=0.029 n=4+4)

name                old alloc/op   new alloc/op   delta
GetMethodByName-10      680B ± 0%        0B       -100.00%  (p=0.029 n=4+4)

name                old allocs/op  new allocs/op  delta
GetMethodByName-10      20.0 ± 0%       0.0       -100.00%  (p=0.029 n=4+4)
```

But more pleasing is the overall performance looking at the site benchmarks:

```bash
name                                      old time/op    new time/op    delta
SiteNew/Regular_Bundle_with_image-10        6.25ms ± 2%    6.10ms ± 2%     ~     (p=0.057 n=4+4)
SiteNew/Regular_Bundle_with_JSON_file-10    6.30ms ± 2%    5.66ms ±11%     ~     (p=0.057 n=4+4)
SiteNew/Regular_Tags_and_categories-10      22.2ms ± 2%    17.4ms ± 1%  -21.88%  (p=0.029 n=4+4)
SiteNew/Regular_Canonify_URLs-10             108ms ± 0%     107ms ± 0%   -1.20%  (p=0.029 n=4+4)
SiteNew/Regular_Deep_content_tree-10        36.1ms ± 1%    33.8ms ± 1%   -6.44%  (p=0.029 n=4+4)
SiteNew/Regular_TOML_front_matter-10        24.9ms ± 1%    22.6ms ± 1%   -9.30%  (p=0.029 n=4+4)
SiteNew/Regular_Many_HTML_templates-10      17.9ms ± 1%    16.7ms ± 1%   -6.43%  (p=0.029 n=4+4)
SiteNew/Regular_Page_collections-10         23.3ms ± 1%    22.0ms ± 0%   -5.58%  (p=0.029 n=4+4)
SiteNew/Regular_List_terms-10               8.00ms ± 1%    7.63ms ± 0%   -4.62%  (p=0.029 n=4+4)

name                                      old alloc/op   new alloc/op   delta
SiteNew/Regular_Bundle_with_image-10        2.10MB ± 0%    2.07MB ± 0%   -1.46%  (p=0.029 n=4+4)
SiteNew/Regular_Bundle_with_JSON_file-10    1.88MB ± 0%    1.85MB ± 0%   -1.76%  (p=0.029 n=4+4)
SiteNew/Regular_Tags_and_categories-10      13.5MB ± 0%    11.6MB ± 0%  -13.99%  (p=0.029 n=4+4)
SiteNew/Regular_Canonify_URLs-10            96.1MB ± 0%    95.8MB ± 0%   -0.40%  (p=0.029 n=4+4)
SiteNew/Regular_Deep_content_tree-10        28.4MB ± 0%    27.3MB ± 0%   -3.83%  (p=0.029 n=4+4)
SiteNew/Regular_TOML_front_matter-10        16.9MB ± 0%    15.1MB ± 0%  -10.58%  (p=0.029 n=4+4)
SiteNew/Regular_Many_HTML_templates-10      8.98MB ± 0%    8.44MB ± 0%   -6.04%  (p=0.029 n=4+4)
SiteNew/Regular_Page_collections-10         17.1MB ± 0%    16.5MB ± 0%   -3.91%  (p=0.029 n=4+4)
SiteNew/Regular_List_terms-10               3.92MB ± 0%    3.72MB ± 0%   -5.03%  (p=0.029 n=4+4)

name                                      old allocs/op  new allocs/op  delta
SiteNew/Regular_Bundle_with_image-10         25.8k ± 0%     24.9k ± 0%   -3.49%  (p=0.029 n=4+4)
SiteNew/Regular_Bundle_with_JSON_file-10     25.8k ± 0%     24.9k ± 0%   -3.49%  (p=0.029 n=4+4)
SiteNew/Regular_Tags_and_categories-10        288k ± 0%      233k ± 0%  -18.90%  (p=0.029 n=4+4)
SiteNew/Regular_Canonify_URLs-10              375k ± 0%      364k ± 0%   -2.80%  (p=0.029 n=4+4)
SiteNew/Regular_Deep_content_tree-10          314k ± 0%      283k ± 0%   -9.77%  (p=0.029 n=4+4)
SiteNew/Regular_TOML_front_matter-10          302k ± 0%      252k ± 0%  -16.55%  (p=0.029 n=4+4)
SiteNew/Regular_Many_HTML_templates-10        133k ± 0%      117k ± 0%  -11.81%  (p=0.029 n=4+4)
SiteNew/Regular_Page_collections-10           202k ± 0%      183k ± 0%   -9.55%  (p=0.029 n=4+4)
SiteNew/Regular_List_terms-10                55.6k ± 0%     49.8k ± 0%  -10.40%  (p=0.029 n=4+4)
```

Thanks to @quasilyte for the suggestion.

Fixes 9386

common/hreflect/helpers.go

@@ -19,6 +19,7 @@ package hreflect
 import (
 	"context"
 	"reflect"
+	"sync"
 
 	"github.com/gohugoio/hugo/common/types"
 )
@@ -115,6 +116,58 @@ func IsTruthfulValue(val reflect.Value) (truth bool) {
 	return
 }
 
+type methodKey struct {
+	typ  reflect.Type
+	name string
+}
+
+type methods struct {
+	sync.RWMutex
+	cache map[methodKey]int
+}
+
+var methodCache = &methods{cache: make(map[methodKey]int)}
+
+// GetMethodByName is the samve as reflect.Value.MethodByName, but it caches the
+// type lookup.
+func GetMethodByName(v reflect.Value, name string) reflect.Value {
+	index := GetMethodIndexByName(v.Type(), name)
+
+	if index == -1 {
+		return reflect.Value{}
+	}
+
+	return v.Method(index)
+}
+
+// GetMethodIndexByName returns the index of the method with the given name, or
+// -1 if no such method exists.
+func GetMethodIndexByName(tp reflect.Type, name string) int {
+	k := methodKey{tp, name}
+	methodCache.RLock()
+	index, found := methodCache.cache[k]
+	methodCache.RUnlock()
+	if found {
+		return index
+	}
+
+	methodCache.Lock()
+	defer methodCache.Unlock()
+
+	m, ok := tp.MethodByName(name)
+	index = m.Index
+	if !ok {
+		index = -1
+	}
+	methodCache.cache[k] = index
+
+	if !ok {
+		return -1
+	}
+
+	return m.Index
+}
+
 // Based on: https://github.com/golang/go/blob/178a2c42254166cffed1b25fb1d3c7a5727cada6/src/text/template/exec.go#L931
 func indirectInterface(v reflect.Value) reflect.Value {
 	if v.Kind() != reflect.Interface {

common/hreflect/helpers_test.go

@@ -30,6 +30,16 @@ func TestIsTruthful(t *testing.T) {
 	c.Assert(IsTruthful(time.Time{}), qt.Equals, false)
 }
 
+func TestGetMethodByName(t *testing.T) {
+	c := qt.New(t)
+	v := reflect.ValueOf(&testStruct{})
+	tp := v.Type()
+
+	c.Assert(GetMethodIndexByName(tp, "Method1"), qt.Equals, 0)
+	c.Assert(GetMethodIndexByName(tp, "Method3"), qt.Equals, 2)
+	c.Assert(GetMethodIndexByName(tp, "Foo"), qt.Equals, -1)
+}
+
 func BenchmarkIsTruthFul(b *testing.B) {
 	v := reflect.ValueOf("Hugo")
 
@@ -40,3 +50,37 @@ func BenchmarkIsTruthFul(b *testing.B) {
 		}
 	}
 }
+
+type testStruct struct{}
+
+func (t *testStruct) Method1() string {
+	return "Hugo"
+}
+
+func (t *testStruct) Method2() string {
+	return "Hugo"
+}
+
+func (t *testStruct) Method3() string {
+	return "Hugo"
+}
+
+func (t *testStruct) Method4() string {
+	return "Hugo"
+}
+
+func (t *testStruct) Method5() string {
+	return "Hugo"
+}
+
+func BenchmarkGetMethodByName(b *testing.B) {
+	v := reflect.ValueOf(&testStruct{})
+	methods := []string{"Method1", "Method2", "Method3", "Method4", "Method5"}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for _, method := range methods {
+			_ = GetMethodByName(v, method)
+		}
+	}
+}

langs/i18n/i18n.go

@@ -160,7 +160,7 @@ func getPluralCount(v interface{}) interface{} {
 			if f.IsValid() {
 				return toPluralCountValue(f.Interface())
 			}
-			m := vv.MethodByName(countFieldName)
+			m := hreflect.GetMethodByName(vv, countFieldName)
 			if m.IsValid() && m.Type().NumIn() == 0 && m.Type().NumOut() == 1 {
 				c := m.Call(nil)
 				return toPluralCountValue(c[0].Interface())
@@ -169,7 +169,6 @@ func getPluralCount(v interface{}) interface{} {
 	}
 
 	return toPluralCountValue(v)
-
 }
 
 // go-i18n expects floats to be represented by string.

resources/page/pagegroup.go

@@ -24,6 +24,7 @@ import (
 	"github.com/spf13/cast"
 
 	"github.com/gohugoio/hugo/common/collections"
+	"github.com/gohugoio/hugo/common/hreflect"
 	"github.com/gohugoio/hugo/compare"
 
 	"github.com/gohugoio/hugo/resources/resource"
@@ -112,8 +113,9 @@ func (p Pages) GroupBy(key string, order ...string) (PagesGroup, error) {
 	}
 
 	var ft interface{}
-	m, ok := pagePtrType.MethodByName(key)
+	index := hreflect.GetMethodIndexByName(pagePtrType, key)
-	if ok {
+	if index != -1 {
+		m := pagePtrType.Method(index)
 		if m.Type.NumOut() == 0 || m.Type.NumOut() > 2 {
 			return nil, errors.New(key + " is a Page method but you can't use it with GroupBy")
 		}
@@ -125,6 +127,7 @@ func (p Pages) GroupBy(key string, order ...string) (PagesGroup, error) {
 		}
 		ft = m
 	} else {
+		var ok bool
 		ft, ok = pagePtrType.Elem().FieldByName(key)
 		if !ok {
 			return nil, errors.New(key + " is neither a field nor a method of Page")
@@ -146,7 +149,7 @@ func (p Pages) GroupBy(key string, order ...string) (PagesGroup, error) {
 		case reflect.StructField:
 			fv = ppv.Elem().FieldByName(key)
 		case reflect.Method:
-			fv = ppv.MethodByName(key).Call([]reflect.Value{})[0]
+			fv = hreflect.GetMethodByName(ppv, key).Call([]reflect.Value{})[0]
 		}
 		if !fv.IsValid() {
 			continue

resources/postpub/postpub.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/spf13/cast"
 
+	"github.com/gohugoio/hugo/common/hreflect"
 	"github.com/gohugoio/hugo/common/maps"
 	"github.com/gohugoio/hugo/media"
 	"github.com/gohugoio/hugo/resources/resource"
@@ -125,7 +126,7 @@ func (r *PostPublishResource) fieldToString(receiver interface{}, path string) s
 	default:
 		v := receiverv.FieldByName(fieldname)
 		if !v.IsValid() {
-			method := receiverv.MethodByName(fieldname)
+			method := hreflect.GetMethodByName(receiverv, fieldname)
 			if method.IsValid() {
 				vals := method.Call(nil)
 				if len(vals) > 0 {

tpl/collections/apply.go

@@ -131,7 +131,7 @@ func (ns *Namespace) lookupFunc(fname string) (reflect.Value, bool) {
 	nv = reflect.ValueOf(v)
 
 	// method
-	m := nv.MethodByName(ss[1])
+	m := hreflect.GetMethodByName(nv, ss[1])
 
 	if m.Kind() == reflect.Invalid {
 		return reflect.Value{}, false

tpl/collections/where.go

@@ -19,6 +19,7 @@ import (
 	"reflect"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/hreflect"
 	"github.com/gohugoio/hugo/common/maps"
 )
 
@@ -300,8 +301,9 @@ func evaluateSubElem(obj reflect.Value, elemName string) (reflect.Value, error)
 		objPtr = objPtr.Addr()
 	}
 
-	mt, ok := objPtr.Type().MethodByName(elemName)
+	index := hreflect.GetMethodIndexByName(objPtr.Type(), elemName)
-	if ok {
+	if index != -1 {
+		mt := objPtr.Type().Method(index)
 		switch {
 		case mt.PkgPath != "":
 			return zero, fmt.Errorf("%s is an unexported method of type %s", elemName, typ)
@@ -513,5 +515,5 @@ func toTimeUnix(v reflect.Value) int64 {
 	if v.Type() != timeType {
 		panic("coding error: argument must be time.Time type reflect Value")
 	}
-	return v.MethodByName("Unix").Call([]reflect.Value{})[0].Int()
+	return hreflect.GetMethodByName(v, "Unix").Call([]reflect.Value{})[0].Int()
 }

tpl/internal/go_templates/texttemplate/hugo_template_test.go

@@ -21,6 +21,7 @@ import (
 	"testing"
 
 	qt "github.com/frankban/quicktest"
+	"github.com/gohugoio/hugo/common/hreflect"
 )
 
 type TestStruct struct {
@@ -59,7 +60,7 @@ func (e *execHelper) GetMethod(ctx context.Context, tmpl Preparer, receiver refl
 	if name != "Hello1" {
 		return zero, zero
 	}
-	m := receiver.MethodByName("Hello2")
+	m := hreflect.GetMethodByName(receiver, "Hello2")
 	return m, reflect.ValueOf("v2")
 }
 

tpl/tplimpl/template_funcs.go

@@ -20,9 +20,9 @@ import (
 	"reflect"
 	"strings"
 
-	"github.com/gohugoio/hugo/tpl"
+	"github.com/gohugoio/hugo/common/hreflect"
-
 	"github.com/gohugoio/hugo/common/maps"
+	"github.com/gohugoio/hugo/tpl"
 
 	template "github.com/gohugoio/hugo/tpl/internal/go_templates/htmltemplate"
 	texttemplate "github.com/gohugoio/hugo/tpl/internal/go_templates/texttemplate"
@@ -111,9 +111,6 @@ func (t *templateExecHelper) GetMapValue(ctx context.Context, tmpl texttemplate.
 
 func (t *templateExecHelper) GetMethod(ctx context.Context, tmpl texttemplate.Preparer, receiver reflect.Value, name string) (method reflect.Value, firstArg reflect.Value) {
 	if t.running {
-		// This is a hot path and receiver.MethodByName really shows up in the benchmarks,
-		// so we maintain a list of method names with that signature.
-		// TODO(bep) I have a branch that makes this construct superflous.
 		switch name {
 		case "GetPage", "Render":
 			if info, ok := tmpl.(tpl.Info); ok {
@@ -124,7 +121,7 @@ func (t *templateExecHelper) GetMethod(ctx context.Context, tmpl texttemplate.Pr
 		}
 	}
 
-	fn := receiver.MethodByName(name)
+	fn := hreflect.GetMethodByName(receiver, name)
 	if !fn.IsValid() {
 		return zero, zero
 	}