Add go1.21 compat funcs

Author: nekohasekai

common/minmax.go

@@ -0,0 +1,15 @@
+//go:build go1.21
+
+package common
+
+import (
+	"cmp"
+)
+
+func Min[T cmp.Ordered](x, y T) T {
+	return min(x, y)
+}
+
+func Max[T cmp.Ordered](x, y T) T {
+	return max(x, y)
+}

common/minmax_compat.go

@@ -0,0 +1,19 @@
+//go:build go1.20 && !go1.21
+
+package common
+
+import "github.com/sagernet/sing/common/x/constraints"
+
+func Min[T constraints.Ordered](x, y T) T {
+	if x < y {
+		return x
+	}
+	return y
+}
+
+func Max[T constraints.Ordered](x, y T) T {
+	if x < y {
+		return y
+	}
+	return x
+}

common/oncefunc.go

@@ -0,0 +1,20 @@
+//go:build go1.21
+
+package common
+
+import "sync"
+
+// OnceFunc is a wrapper around sync.OnceFunc.
+func OnceFunc(f func()) func() {
+	return sync.OnceFunc(f)
+}
+
+// OnceValue is a wrapper around sync.OnceValue.
+func OnceValue[T any](f func() T) func() T {
+	return sync.OnceValue(f)
+}
+
+// OnceValues is a wrapper around sync.OnceValues.
+func OnceValues[T1, T2 any](f func() (T1, T2)) func() (T1, T2) {
+	return sync.OnceValues(f)
+}

common/oncefunc_compat.go

@@ -0,0 +1,104 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.20 && !go1.21
+
+package common
+
+import "sync"
+
+// OnceFunc returns a function that invokes f only once. The returned function
+// may be called concurrently.
+//
+// If f panics, the returned function will panic with the same value on every call.
+func OnceFunc(f func()) func() {
+	var (
+		once  sync.Once
+		valid bool
+		p     any
+	)
+	// Construct the inner closure just once to reduce costs on the fast path.
+	g := func() {
+		defer func() {
+			p = recover()
+			if !valid {
+				// Re-panic immediately so on the first call the user gets a
+				// complete stack trace into f.
+				panic(p)
+			}
+		}()
+		f()
+		f = nil      // Do not keep f alive after invoking it.
+		valid = true // Set only if f does not panic.
+	}
+	return func() {
+		once.Do(g)
+		if !valid {
+			panic(p)
+		}
+	}
+}
+
+// OnceValue returns a function that invokes f only once and returns the value
+// returned by f. The returned function may be called concurrently.
+//
+// If f panics, the returned function will panic with the same value on every call.
+func OnceValue[T any](f func() T) func() T {
+	var (
+		once   sync.Once
+		valid  bool
+		p      any
+		result T
+	)
+	g := func() {
+		defer func() {
+			p = recover()
+			if !valid {
+				panic(p)
+			}
+		}()
+		result = f()
+		f = nil
+		valid = true
+	}
+	return func() T {
+		once.Do(g)
+		if !valid {
+			panic(p)
+		}
+		return result
+	}
+}
+
+// OnceValues returns a function that invokes f only once and returns the values
+// returned by f. The returned function may be called concurrently.
+//
+// If f panics, the returned function will panic with the same value on every call.
+func OnceValues[T1, T2 any](f func() (T1, T2)) func() (T1, T2) {
+	var (
+		once  sync.Once
+		valid bool
+		p     any
+		r1    T1
+		r2    T2
+	)
+	g := func() {
+		defer func() {
+			p = recover()
+			if !valid {
+				panic(p)
+			}
+		}()
+		r1, r2 = f()
+		f = nil
+		valid = true
+	}
+	return func() (T1, T2) {
+		once.Do(g)
+		if !valid {
+			panic(p)
+		}
+		return r1, r2
+	}
+}