Revert "internal, log: remove code for old unsupported go-versions (#28090)"

This reverts commit 4a7485885b.

internal/debug/loudpanic.go

@@ -14,6 +14,9 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
 
+//go:build go1.6
+// +build go1.6
+
 package debug
 
 import "runtime/debug"

internal/debug/loudpanic_fallback.go

@@ -0,0 +1,25 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+//go:build !go1.6
+// +build !go1.6
+
+package debug
+
+// LoudPanic panics in a way that gets all goroutine stacks printed on stderr.
+func LoudPanic(x interface{}) {
+	panic(x)
+}

internal/debug/trace.go

@@ -14,6 +14,9 @@
 // You should have received a copy of the GNU Lesser General Public License
 // along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
 
+//go:build go1.5
+// +build go1.5
+
 package debug
 
 import (

internal/debug/trace_fallback.go

@@ -0,0 +1,32 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+//go:build !go1.5
+// +build !go1.5
+
+// no-op implementation of tracing methods for Go < 1.5.
+
+package debug
+
+import "errors"
+
+func (*HandlerT) StartGoTrace(string) error {
+	return errors.New("tracing is not supported on Go < 1.5")
+}
+
+func (*HandlerT) StopGoTrace() error {
+	return errors.New("tracing is not supported on Go < 1.5")
+}

log/handler.go

@@ -7,7 +7,6 @@ import (
 	"os"
 	"reflect"
 	"sync"
-	"sync/atomic"
 
 	"github.com/go-stack/stack"
 )
@@ -355,21 +354,3 @@ func (m muster) FileHandler(path string, fmtr Format) Handler {
 func (m muster) NetHandler(network, addr string, fmtr Format) Handler {
 	return must(NetHandler(network, addr, fmtr))
 }
-
-// swapHandler wraps another handler that may be swapped out
-// dynamically at runtime in a thread-safe fashion.
-type swapHandler struct {
-	handler atomic.Value
-}
-
-func (h *swapHandler) Log(r *Record) error {
-	return (*h.handler.Load().(*Handler)).Log(r)
-}
-
-func (h *swapHandler) Swap(newHandler Handler) {
-	h.handler.Store(&newHandler)
-}
-
-func (h *swapHandler) Get() Handler {
-	return *h.handler.Load().(*Handler)
-}

log/handler_go13.go

@@ -0,0 +1,27 @@
+//go:build !go1.4
+// +build !go1.4
+
+package log
+
+import (
+	"sync/atomic"
+	"unsafe"
+)
+
+// swapHandler wraps another handler that may be swapped out
+// dynamically at runtime in a thread-safe fashion.
+type swapHandler struct {
+	handler unsafe.Pointer
+}
+
+func (h *swapHandler) Log(r *Record) error {
+	return h.Get().Log(r)
+}
+
+func (h *swapHandler) Get() Handler {
+	return *(*Handler)(atomic.LoadPointer(&h.handler))
+}
+
+func (h *swapHandler) Swap(newHandler Handler) {
+	atomic.StorePointer(&h.handler, unsafe.Pointer(&newHandler))
+}

log/handler_go14.go

@@ -0,0 +1,24 @@
+//go:build go1.4
+// +build go1.4
+
+package log
+
+import "sync/atomic"
+
+// swapHandler wraps another handler that may be swapped out
+// dynamically at runtime in a thread-safe fashion.
+type swapHandler struct {
+	handler atomic.Value
+}
+
+func (h *swapHandler) Log(r *Record) error {
+	return (*h.handler.Load().(*Handler)).Log(r)
+}
+
+func (h *swapHandler) Swap(newHandler Handler) {
+	h.handler.Store(&newHandler)
+}
+
+func (h *swapHandler) Get() Handler {
+	return *h.handler.Load().(*Handler)
+}