1 files changed, 74 insertions, 0 deletions
diff --git a/src/internal/goexperiment/mkconsts.go b/src/internal/goexperiment/mkconsts.go
new file mode 100644
index 0000000..204ca9d
--- /dev/null
+++ b/src/internal/goexperiment/mkconsts.go
@@ -0,0 +1,74 @@
+// Copyright 2021 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 ignore
+// +build ignore
+
+// mkconsts generates const definition files for each GOEXPERIMENT.
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"internal/goexperiment"
+	"log"
+	"os"
+	"reflect"
+	"strings"
+)
+
+func main() {
+	// Delete existing experiment constant files.
+	ents, err := os.ReadDir(".")
+	if err != nil {
+		log.Fatal(err)
+	}
+	for _, ent := range ents {
+		name := ent.Name()
+		if !strings.HasPrefix(name, "exp_") {
+			continue
+		}
+		// Check that this is definitely a generated file.
+		data, err := os.ReadFile(name)
+		if err != nil {
+			log.Fatalf("reading %s: %v", name, err)
+		}
+		if !bytes.Contains(data, []byte("Code generated by mkconsts")) {
+			log.Fatalf("%s: expected generated file", name)
+		}
+		if err := os.Remove(name); err != nil {
+			log.Fatal(err)
+		}
+	}
+
+	// Generate new experiment constant files.
+	rt := reflect.TypeOf(&goexperiment.Flags{}).Elem()
+	for i := 0; i < rt.NumField(); i++ {
+		f := rt.Field(i).Name
+		buildTag := "goexperiment." + strings.ToLower(f)
+		for _, val := range []bool{false, true} {
+			name := fmt.Sprintf("exp_%s_%s.go", strings.ToLower(f), pick(val, "off", "on"))
+			data := fmt.Sprintf(`// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build %s%s
+// +build %s%s
+
+package goexperiment
+
+const %s = %v
+const %sInt = %s
+`, pick(val, "!", ""), buildTag, pick(val, "!", ""), buildTag, f, val, f, pick(val, "0", "1"))
+			if err := os.WriteFile(name, []byte(data), 0666); err != nil {
+				log.Fatalf("writing %s: %v", name, err)
+			}
+		}
+	}
+}
+
+func pick(v bool, f, t string) string {
+	if v {
+		return t
+	}
+	return f
+}