[go] text/template: avoid reflect.Value.Call for common builtins
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Zhandos Zhandarbek (Gerrit)
Sep 24, 2026, 12:42:37 AM (10 days ago) Sep 24
to Alan Donovan, goph...@pubsubhelper.golang.org, golang-co...@googlegroups.com
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Commit message
text/template: avoid reflect.Value.Call for common builtins
CL 835445 added a fast path in safeCall for func(...any) string. The
other builtins still go through reflect.Value.Call: eq, ne, lt, le, gt,
ge, index, slice, len, not and printf. Comparisons and index appear in
almost every real template, typically as {{if eq .X "y"}}.
Check for the signatures of these builtins in safeCall and call the
function directly. Arguments of type reflect.Value are unwrapped with
reflect.TypeAssert, which does not allocate. User-defined functions
with the same signatures take the same path. The checks sit inside the
existing recover, so a panic is still reported as an error. Functions
with other signatures are unaffected (userFunc below).
Old and new binaries run alternately, 10 runs each, on an Apple M4 Pro:
pkg: text/template
│ old.txt │ new.txt │
│ sec/op │ sec/op vs base │
ExecuteBuiltins/eq-12 548.2n ± 2% 286.4n ± 2% -47.77% (p=0.000 n=10)
ExecuteBuiltins/eqMulti-12 666.2n ± 2% 391.0n ± 4% -41.32% (p=0.000 n=10)
ExecuteBuiltins/lt-12 476.1n ± 2% 262.4n ± 3% -44.88% (p=0.000 n=10)
ExecuteBuiltins/not-12 362.1n ± 2% 210.0n ± 2% -42.00% (p=0.000 n=10)
ExecuteBuiltins/len-12 434.8n ± 3% 245.6n ± 3% -43.53% (p=0.000 n=10)
ExecuteBuiltins/index-12 617.6n ± 3% 356.4n ± 5% -42.31% (p=0.000 n=10)
ExecuteBuiltins/printf-12 655.4n ± 3% 439.9n ± 4% -32.88% (p=0.000 n=10)
│ old.txt │ new.txt │
│ allocs/op │ allocs/op vs base │
ExecuteBuiltins/eq-12 14.000 ± 0% 9.000 ± 0% -35.71% (p=0.000 n=10)
ExecuteBuiltins/eqMulti-12 18.00 ± 0% 13.00 ± 0% -27.78% (p=0.000 n=10)
ExecuteBuiltins/lt-12 10.000 ± 0% 7.000 ± 0% -30.00% (p=0.000 n=10)
ExecuteBuiltins/not-12 7.000 ± 0% 5.000 ± 0% -28.57% (p=0.000 n=10)
ExecuteBuiltins/len-12 8.000 ± 0% 5.000 ± 0% -37.50% (p=0.000 n=10)
ExecuteBuiltins/index-12 15.00 ± 0% 11.00 ± 0% -26.67% (p=0.000 n=10)
ExecuteBuiltins/printf-12 14.00 ± 0% 11.00 ± 0% -21.43% (p=0.000 n=10)
pkg: text/template
│ old.txt │ new.txt │
│ sec/op │ sec/op vs base │
ExecuteBuiltins/userFunc-12 372.7n ± 2% 371.6n ± 3% ~ (p=0.955 n=10)
Updates #81610
Change-Id: Ic0cbe2fb8b5770699083321e90113e07f35a3c68
Change diff
diff --git a/src/text/template/exec_test.go b/src/text/template/exec_test.go
index 48895db..53359c6 100644
--- a/src/text/template/exec_test.go
+++ b/src/text/template/exec_test.go
@@ -1782,6 +1782,12 @@
"doPanicVariadic": func(...any) string {
panic("custom panic string")
},
+ "doPanicCompare": func(reflect.Value, reflect.Value) (bool, error) {
+ panic("custom panic string")
+ },
+ "doPanicFormat": func(string, ...any) string {
+ panic("custom panic string")
+ },
}
tests := []struct {
name string
@@ -1810,6 +1816,16 @@
`template: t:1:6: executing "t" at <doPanicVariadic>: error calling doPanicVariadic: custom panic string`,
},
{
+ "compare-like func call panics",
+ "{{doPanicCompare 1 2}}", (*T)(nil),
+ `template: t:1:2: executing "t" at <doPanicCompare 1 2>: error calling doPanicCompare: custom panic string`,
+ },
+ {
+ "printf-like func call panics",
+ `{{2 | doPanicFormat "%d"}}`, (*T)(nil),
+ `template: t:1:6: executing "t" at <doPanicFormat "%d">: error calling doPanicFormat: custom panic string`,
+ },
+ {
"direct method call panics",
"{{.GetU}}", (*T)(nil),
`template: t:1:2: executing "t" at <.GetU>: error calling GetU: runtime error: invalid memory address or nil pointer dereference`,
@@ -2043,3 +2059,90 @@
}
}
}
+
+func BenchmarkExecuteBuiltins(b *testing.B) {
+ data := map[string]any{
+ "S": "active",
+ "N": 3,
+ "L": []int{1, 2, 3},
+ "M": map[string]string{"k": "v"},
+ }
+ tmpls := []struct{ name, text string }{
+ {"eq", `{{if eq .S "active"}}y{{end}}`},
+ {"eqMulti", `{{if eq .S "a" "b" "active"}}y{{end}}`},
+ {"lt", `{{if lt .N 5}}y{{end}}`},
+ {"not", `{{if not .S}}y{{end}}`},
+ {"len", `{{len .L}}`},
+ {"index", `{{index .M "k"}}`},
+ {"printf", `{{printf "%s-%d" .S .N}}`},
+ {"userFunc", `{{double .N}}`},
+ }
+ for _, tt := range tmpls {
+ tmpl := Must(New("t").Funcs(FuncMap{"double": func(n int) int { return 2 * n }}).Parse(tt.text))
+ b.Run(tt.name, func(b *testing.B) {
+ b.ReportAllocs()
+ for b.Loop() {
+ if err := tmpl.Execute(io.Discard, data); err != nil {
+ b.Fatal(err)
+ }
+ }
+ })
+ }
+}
+
+func TestExecuteBuiltinSignatureFuncs(t *testing.T) {
+ funcs := FuncMap{
+ "same": func(a, b reflect.Value) (bool, error) {
+ if a.Kind() != b.Kind() {
+ return false, fmt.Errorf("kinds differ: %s, %s", a.Kind(), b.Kind())
+ }
+ return a.Interface() == b.Interface(), nil
+ },
+ "anyOf": func(x reflect.Value, ys ...reflect.Value) (bool, error) {
+ for _, y := range ys {
+ if x.Interface() == y.Interface() {
+ return true, nil
+ }
+ }
+ return false, nil
+ },
+ "first": func(x reflect.Value, _ ...reflect.Value) (reflect.Value, error) {
+ return x.Index(0), nil
+ },
+ "size": func(x reflect.Value) (int, error) { return x.Len(), nil },
+ "isStr": func(x reflect.Value) bool { return x.Kind() == reflect.String },
+ "fmt": func(format string, args ...any) string { return fmt.Sprintf(format, args...) },
+ }
+ tests := []struct {
+ input, want, wantErr string
+ }{
+ {`{{same 1 1}} {{same "a" "b"}} {{1 | same 1}}`, "true false true", ""},
+ {`{{same 1 "a"}}`, "", "error calling same: kinds differ: int, string"},
+ {`{{anyOf 3 1 2 3}} {{anyOf 3}} {{3 | anyOf 1 2}}`, "true false false", ""},
+ {`{{first .L}} {{.L | first}}`, "x x", ""},
+ {`{{size .L}} {{.L | size}}`, "2 2", ""},
+ {`{{isStr "a"}} {{isStr 1}} {{"a" | isStr}}`, "true false true", ""},
+ {`{{same .RV "s"}} {{isStr .RV}} {{size .RV}}`, "true true 1", ""},
+ {`{{eq nil nil}} {{not nil}}`, "true true", ""},
+ {`{{fmt "%s=%d" "a" 1}} {{1 | fmt "%d"}} {{"%%" | fmt}}`, "a=1 1 %", ""},
+ }
+ for _, tt := range tests {
+ tmpl := Must(New("t").Funcs(funcs).Parse(tt.input))
+ var b strings.Builder
+ err := tmpl.Execute(&b, struct {
+ L []string
+ RV reflect.Value
+ }{[]string{"x", "y"}, reflect.ValueOf("s")})
+ if tt.wantErr != "" {
+ if err == nil || !strings.Contains(err.Error(), tt.wantErr) {
+ t.Errorf("%s: got error %v, want %q", tt.input, err, tt.wantErr)
+ }
+ continue
+ }
+ if err != nil {
+ t.Errorf("%s: unexpected error: %v", tt.input, err)
+ } else if b.String() != tt.want {
+ t.Errorf("%s: got %q, want %q", tt.input, b.String(), tt.want)
+ }
+ }
+}
diff --git a/src/text/template/funcs.go b/src/text/template/funcs.go
index 9985eab..9e2fb71 100644
--- a/src/text/template/funcs.go
+++ b/src/text/template/funcs.go
@@ -373,6 +373,33 @@
}
return reflect.ValueOf(f(anyArgs...)), nil
}
+ // Fast paths for the signatures of the other builtins.
+ if f, ok := reflect.TypeAssert[func(reflect.Value, reflect.Value) (bool, error)](fun); ok {
+ r, err := f(unwrapArg(args[0]), unwrapArg(args[1]))
+ return reflect.ValueOf(r), err
+ }
+ if f, ok := reflect.TypeAssert[func(reflect.Value, ...reflect.Value) (bool, error)](fun); ok {
+ r, err := f(unwrapArg(args[0]), unwrapArgs(args[1:])...)
+ return reflect.ValueOf(r), err
+ }
+ if f, ok := reflect.TypeAssert[func(reflect.Value, ...reflect.Value) (reflect.Value, error)](fun); ok {
+ r, err := f(unwrapArg(args[0]), unwrapArgs(args[1:])...)
+ return reflect.ValueOf(r), err
+ }
+ if f, ok := reflect.TypeAssert[func(reflect.Value) (int, error)](fun); ok {
+ r, err := f(unwrapArg(args[0]))
+ return reflect.ValueOf(r), err
+ }
+ if f, ok := reflect.TypeAssert[func(reflect.Value) bool](fun); ok {
+ return reflect.ValueOf(f(unwrapArg(args[0]))), nil
+ }
+ if f, ok := reflect.TypeAssert[func(string, ...any) string](fun); ok {
+ anyArgs := make([]any, len(args)-1)
+ for i, arg := range args[1:] {
+ anyArgs[i] = arg.Interface()
+ }
+ return reflect.ValueOf(f(args[0].String(), anyArgs...)), nil
+ }
ret := fun.Call(args)
if len(ret) == 2 && !ret[1].IsNil() {
return ret[0], ret[1].Interface().(error)
@@ -380,6 +407,24 @@
return ret[0], nil
}
+// unwrapArg returns the reflect.Value that evalCall wraps in another
+// reflect.Value for parameters of type reflect.Value.
+func unwrapArg(arg reflect.Value) reflect.Value {
+ v, ok := reflect.TypeAssert[reflect.Value](arg)
+ if !ok {
+ panic("text/template: argument is not a wrapped reflect.Value")
+ }
+ return v
+}
+
+func unwrapArgs(args []reflect.Value) []reflect.Value {
+ vs := make([]reflect.Value, len(args))
+ for i, arg := range args {
+ vs[i] = unwrapArg(arg)
+ }
+ return vs
+}
+
// Boolean logic.
func truth(arg reflect.Value) bool {
Change information
Files:
- M src/text/template/exec_test.go
- M src/text/template/funcs.go
Change size: M
Delta: 2 files changed, 148 insertions(+), 0 deletions(-)
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Gopher Robot (Gerrit)
Sep 24, 2026, 12:45:59 AM (10 days ago) Sep 24
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Sep 24, 2026, 1:08:31 AM (10 days ago) Sep 24
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Zhandos Zhandarbek (Gerrit)
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Patchset-level comments
File-level comment, Patchset 2 (Latest):
Zhandos Zhandarbek . resolved
PS2: added an html/template page benchmark (-37% time, -38% allocs) and switched to a type switch so functions with other signatures are not slowed down. PS1 was measured against the wrong baseline and missed a ~3% overhead there.
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Alan Donovan (Gerrit)
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Alan Donovan . resolved
Are all of these needed? I would guess most builtins are pretty rarely used in production and not worth optimizing.
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Sep 25, 2026, 3:47:25 AM (9 days ago) Sep 25
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Alan Donovan . resolved
Are all of these needed? I would guess most builtins are pretty rarely used in production and not worth optimizing.
Zhandos Zhandarbek
Fair enough. I grepped bitnami/charts (~3300 templates, plain
text/template + sprig) to see what's actually used:
printf 2.5%, not 2.4%, eq 2.2%, ne 0.5% of all actions
index 0.1%, len/lt/le/gt/ge/slice under 0.1%
and/or are already handled separately in evalCall.
So I dropped index, slice and len in PS3. The page benchmark is still
-38%
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Change information
Commit message:
text/template: call eq, not, printf and comparisons directly
CL 835445 added a fast path in safeCall for func(...any) string.
eq, ne, lt, le, gt, ge, not and printf still go through
reflect.Value.Call. In bitnami/charts, printf, not, eq and ne make up
about 7.6% of all template actions; the other builtins are rare.
Switch on the function type in safeCall and call these signatures
directly. Functions with other signatures pay one type comparison
(userFunc below). The call is still inside the existing recover.
Old and new binaries run alternately on an Apple M4 Pro:
pkg: html/template
│ old │ new │
│ sec/op │ sec/op vs base │
EscapedExecuteBuiltinsPage-12 35.53µ ± 2% 21.95µ ± 2% -38.24% (p=0.000 n=15)
│ old │ new │
│ allocs/op │ allocs/op vs base │
EscapedExecuteBuiltinsPage-12 564.0 ± 0% 364.0 ± 0% -35.46% (p=0.000 n=15)
pkg: text/template
│ old │ new │
│ sec/op │ sec/op vs base │
ExecuteBuiltins/eq-12 548.6n ± 2% 275.9n ± 4% -49.71% (p=0.000 n=15)
ExecuteBuiltins/eqMulti-12 672.5n ± 3% 373.0n ± 2% -44.54% (p=0.000 n=15)
ExecuteBuiltins/lt-12 476.1n ± 3% 265.4n ± 3% -44.26% (p=0.000 n=15)
ExecuteBuiltins/not-12 362.3n ± 1% 198.2n ± 2% -45.29% (p=0.000 n=15)
ExecuteBuiltins/printf-12 651.2n ± 2% 418.8n ± 3% -35.69% (p=0.000 n=15)
ExecuteBuiltins/userFunc-12 361.7n ± 3% 356.6n ± 3% ~ (p=0.721 n=15)
geomean 496.5n 305.2n -38.53%
│ old │ new │
│ allocs/op │ allocs/op vs base │
ExecuteBuiltins/eq-12 14.000 ± 0% 9.000 ± 0% -35.71% (p=0.000 n=15)
ExecuteBuiltins/eqMulti-12 18.00 ± 0% 13.00 ± 0% -27.78% (p=0.000 n=15)
ExecuteBuiltins/lt-12 10.000 ± 0% 7.000 ± 0% -30.00% (p=0.000 n=15)
ExecuteBuiltins/not-12 7.000 ± 0% 5.000 ± 0% -28.57% (p=0.000 n=15)
ExecuteBuiltins/printf-12 14.00 ± 0% 11.00 ± 0% -21.43% (p=0.000 n=15)
ExecuteBuiltins/userFunc-12 6.000 ± 0% 6.000 ± 0% ~ (p=1.000 n=15)
Updates #81610
Change-Id: Ic0cbe2fb8b5770699083321e90113e07f35a3c68
Reviewed-on: https://go-review.googlesource.com/c/go/+/837945
Reviewed-by: Sean Liao <se...@liao.dev>
LUCI-TryBot-Result: golang...@luci-project-accounts.iam.gserviceaccount.com <golang...@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adon...@google.com>
Reviewed-by: Michael Pratt <mpr...@google.com>
Auto-Submit: Sean Liao <se...@liao.dev>
Files:
- M src/html/template/escape_test.go
- M src/text/template/exec_test.go
- M src/text/template/funcs.go
Change size: M
Delta: 3 files changed, 160 insertions(+), 0 deletions(-)
Branch: refs/heads/master
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