runtime: handle GODEBUG on wasip2 (#5312)

* runtime: handle GODEBUG on wasip2
* Support env on more platforms to get GODEBUG working

src/runtime/env.go

@@ -1,4 +1,4 @@
-//go:build linux || darwin || windows || wasip1
+//go:build (linux || darwin || windows || wasip1) && !wasip2 && !baremetal && !wasm_unknown
 
 package runtime
 

src/runtime/env_nonhosted.go

@@ -0,0 +1,43 @@
+//go:build baremetal || js || wasm_unknown
+
+package runtime
+
+//go:linkname syscallSetenv syscall.runtimeSetenv
+func syscallSetenv(key, value string) {
+	entry := key + "=" + value
+	for i, e := range env {
+		if envKey(e) == key {
+			env[i] = entry
+			if key == "GODEBUG" && godebugUpdate != nil {
+				godebugUpdate(key, value)
+			}
+			return
+		}
+	}
+	env = append(env, entry)
+	if key == "GODEBUG" && godebugUpdate != nil {
+		godebugUpdate(key, value)
+	}
+}
+
+//go:linkname syscallUnsetenv syscall.runtimeUnsetenv
+func syscallUnsetenv(key string) {
+	for i, e := range env {
+		if envKey(e) == key {
+			env = append(env[:i], env[i+1:]...)
+			if key == "GODEBUG" && godebugUpdate != nil {
+				godebugUpdate(key, "")
+			}
+			return
+		}
+	}
+}
+
+func envKey(entry string) string {
+	for i := 0; i < len(entry); i++ {
+		if entry[i] == '=' {
+			return entry[:i]
+		}
+	}
+	return entry
+}

src/runtime/env_wasip2.go

@@ -0,0 +1,21 @@
+//go:build wasip2
+
+package runtime
+
+// Notify the runtime when environment variables change.
+// On wasip2, the environment is managed in Go (no C setenv), but
+// internal/godebug still needs to be notified of GODEBUG changes.
+
+//go:linkname syscallSetenv syscall.runtimeSetenv
+func syscallSetenv(key, value string) {
+	if key == "GODEBUG" && godebugUpdate != nil {
+		godebugUpdate(key, value)
+	}
+}
+
+//go:linkname syscallUnsetenv syscall.runtimeUnsetenv
+func syscallUnsetenv(key string) {
+	if key == "GODEBUG" && godebugUpdate != nil {
+		godebugUpdate(key, "")
+	}
+}