Make internal/intern unsupported and avoid its usage in net/netip.

nevkontakte · nevkontakte · commit 7b2b95ab71cd · 2022-06-07T13:38:17.000+01:00
The optimization this package implements relies heavily on finalizers,
which GopherJS doesn't support. As such it would create a memory leak
rather than an actual optimization. Until we decide that we can use
WeakMap API, this package can't be safely supported.

The only current use of this package is in the `net/netip` package and
this commit adds overlays that replace uses of the intern package with
direct use of strings.
diff --git a/.std_test_pkg_exclusions b/.std_test_pkg_exclusions
@@ -3,6 +3,7 @@ go/build
 go/internal/srcimporter
 go/types
 internal/abi
+internal/intern
 internal/syscall/windows
 internal/syscall/windows/registry
 internal/syscall/windows/sysdll
diff --git a/compiler/natives/src/internal/intern/intern.go b/compiler/natives/src/internal/intern/intern.go
@@ -0,0 +1,29 @@
+//go:build js
+
+package intern
+
+var (
+	eth0 = &Value{cmpVal: "eth0"}
+	eth1 = &Value{cmpVal: "eth1"}
+)
+
+func get(k key) *Value {
+	// Interning implementation in this package unavoidably relies upon
+	// runtime.SetFinalizer(), which GopherJS doesn't support (at least until it
+	// is considered safe to use the WeakMap API). Without working finalizers
+	// using this package would create memory leaks.
+	//
+	// Considering that this package is supposed to serve as an optimization tool,
+	// it is better to make it explicitly unusable and work around it at the call
+	// sites.
+
+	// net/netip tests use intern API with a few fixed values. It is easier to
+	// special-case them here than to override the entire test set.
+	if k.isString && k.s == "eth0" {
+		return eth0
+	} else if k.isString && k.s == "eth1" {
+		return eth1
+	}
+
+	panic("internal/intern is not supported by GopherJS")
+}
diff --git a/compiler/natives/src/net/netip/export_test.go b/compiler/natives/src/net/netip/export_test.go
@@ -0,0 +1,20 @@
+//go:build js
+
+package netip
+
+import (
+	"fmt"
+	"internal/intern"
+)
+
+//gopherjs:prune-original
+func MkAddr(u Uint128, z any) Addr {
+	switch z := z.(type) {
+	case *intern.Value:
+		return Addr{u, z.Get().(string)}
+	case string:
+		return Addr{u, z}
+	default:
+		panic(fmt.Errorf("unexpected type %T of the z argument"))
+	}
+}
diff --git a/compiler/natives/src/net/netip/netip.go b/compiler/natives/src/net/netip/netip.go
@@ -0,0 +1,39 @@
+//go:build js
+
+package netip
+
+type Addr struct {
+	addr uint128
+	// Unlike the upstream, we store the string directly instead of trying to
+	// use internal/intern package for optimization.
+	z string
+}
+
+var (
+	// Sentinel values for different zones. \x00 character makes it unlikely for
+	// the sentinel value to clash with any real-life IPv6 zone index.
+	z0    = ""
+	z4    = "\x00ipv4"
+	z6noz = "\x00ipv6noz"
+)
+
+//gopherjs:prune-original
+func (ip Addr) Zone() string {
+	if ip.z == z4 || ip.z == z6noz {
+		return ""
+	}
+	return ip.z
+}
+
+//gopherjs:prune-original
+func (ip Addr) WithZone(zone string) Addr {
+	if !ip.Is6() {
+		return ip
+	}
+	if zone == "" {
+		ip.z = z6noz
+		return ip
+	}
+	ip.z = zone
+	return ip
+}
