all: Use context in lib/dialer (#6177)

* all: Use context in lib/dialer

* a bit slimmer

* https://github.com/syncthing/syncthing/pull/5753

* bot

* missed adding debug.go

* errors.Cause

* simultaneous dialing

* anti-leak

lib/connections/tcp_dial.go

@@ -7,6 +7,7 @@
 package connections
 
 import (
+	"context"
 	"crypto/tls"
 	"net/url"
 	"time"
@@ -29,10 +30,12 @@ type tcpDialer struct {
 	commonDialer
 }
 
-func (d *tcpDialer) Dial(_ protocol.DeviceID, uri *url.URL) (internalConn, error) {
+func (d *tcpDialer) Dial(ctx context.Context, _ protocol.DeviceID, uri *url.URL) (internalConn, error) {
 	uri = fixupPort(uri, config.DefaultTCPPort)
 
-	conn, err := dialer.DialTimeout(uri.Scheme, uri.Host, 10*time.Second)
+	timeoutCtx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	conn, err := dialer.DialContext(timeoutCtx, uri.Scheme, uri.Host)
 	if err != nil {
 		return internalConn{}, err
 	}