internal/goexperiment: consolidate experiment-enabled constants

Currently, we have boolean and integral constants for GOEXPERIMENTs in
various places. Consolidate these into automatically generated
constants in the internal/goexperiment package.

Change-Id: I42a49aba2a3b4c722fedea23a613162cd8a67bee
Reviewed-on: https://go-review.googlesource.com/c/go/+/307818
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

20 files changed, 243 insertions, 2 deletions

diff --git a/src/internal/goexperiment/exp_fieldtrack_off.go b/src/internal/goexperiment/exp_fieldtrack_off.go
new file mode 100644
index 0000000000..e5e132660e
--- /dev/null
+++ b/src/internal/goexperiment/exp_fieldtrack_off.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.fieldtrack
+// +build !goexperiment.fieldtrack
+
+package goexperiment
+
+const FieldTrack = false
+const FieldTrackInt = 0
diff --git a/src/internal/goexperiment/exp_fieldtrack_on.go b/src/internal/goexperiment/exp_fieldtrack_on.go
new file mode 100644
index 0000000000..0d8c447246
--- /dev/null
+++ b/src/internal/goexperiment/exp_fieldtrack_on.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.fieldtrack
+// +build goexperiment.fieldtrack
+
+package goexperiment
+
+const FieldTrack = true
+const FieldTrackInt = 1
diff --git a/src/internal/goexperiment/exp_preemptibleloops_off.go b/src/internal/goexperiment/exp_preemptibleloops_off.go
new file mode 100644
index 0000000000..7a26088e80
--- /dev/null
+++ b/src/internal/goexperiment/exp_preemptibleloops_off.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.preemptibleloops
+// +build !goexperiment.preemptibleloops
+
+package goexperiment
+
+const PreemptibleLoops = false
+const PreemptibleLoopsInt = 0
diff --git a/src/internal/goexperiment/exp_preemptibleloops_on.go b/src/internal/goexperiment/exp_preemptibleloops_on.go
new file mode 100644
index 0000000000..a9ca28c57c
--- /dev/null
+++ b/src/internal/goexperiment/exp_preemptibleloops_on.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.preemptibleloops
+// +build goexperiment.preemptibleloops
+
+package goexperiment
+
+const PreemptibleLoops = true
+const PreemptibleLoopsInt = 1
diff --git a/src/internal/goexperiment/exp_regabi_off.go b/src/internal/goexperiment/exp_regabi_off.go
new file mode 100644
index 0000000000..5d8823843d
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabi_off.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabi
+// +build !goexperiment.regabi
+
+package goexperiment
+
+const Regabi = false
+const RegabiInt = 0
diff --git a/src/internal/goexperiment/exp_regabi_on.go b/src/internal/goexperiment/exp_regabi_on.go
new file mode 100644
index 0000000000..c08d58e9b2
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabi_on.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabi
+// +build goexperiment.regabi
+
+package goexperiment
+
+const Regabi = true
+const RegabiInt = 1
diff --git a/src/internal/goexperiment/exp_regabiargs_off.go b/src/internal/goexperiment/exp_regabiargs_off.go
new file mode 100644
index 0000000000..31a139bbf1
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabiargs_off.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabiargs
+// +build !goexperiment.regabiargs
+
+package goexperiment
+
+const RegabiArgs = false
+const RegabiArgsInt = 0
diff --git a/src/internal/goexperiment/exp_regabiargs_on.go b/src/internal/goexperiment/exp_regabiargs_on.go
new file mode 100644
index 0000000000..9b26f3c9cb
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabiargs_on.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabiargs
+// +build goexperiment.regabiargs
+
+package goexperiment
+
+const RegabiArgs = true
+const RegabiArgsInt = 1
diff --git a/src/internal/goexperiment/exp_regabidefer_off.go b/src/internal/goexperiment/exp_regabidefer_off.go
new file mode 100644
index 0000000000..b47c0c2cf5
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabidefer_off.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabidefer
+// +build !goexperiment.regabidefer
+
+package goexperiment
+
+const RegabiDefer = false
+const RegabiDeferInt = 0
diff --git a/src/internal/goexperiment/exp_regabidefer_on.go b/src/internal/goexperiment/exp_regabidefer_on.go
new file mode 100644
index 0000000000..bbf2f6c69b
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabidefer_on.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabidefer
+// +build goexperiment.regabidefer
+
+package goexperiment
+
+const RegabiDefer = true
+const RegabiDeferInt = 1
diff --git a/src/internal/goexperiment/exp_regabig_off.go b/src/internal/goexperiment/exp_regabig_off.go
new file mode 100644
index 0000000000..1b37d45186
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabig_off.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabig
+// +build !goexperiment.regabig
+
+package goexperiment
+
+const RegabiG = false
+const RegabiGInt = 0
diff --git a/src/internal/goexperiment/exp_regabig_on.go b/src/internal/goexperiment/exp_regabig_on.go
new file mode 100644
index 0000000000..7e5b162e0b
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabig_on.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabig
+// +build goexperiment.regabig
+
+package goexperiment
+
+const RegabiG = true
+const RegabiGInt = 1
diff --git a/src/internal/goexperiment/exp_regabireflect_off.go b/src/internal/goexperiment/exp_regabireflect_off.go
new file mode 100644
index 0000000000..515f4a53e6
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabireflect_off.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabireflect
+// +build !goexperiment.regabireflect
+
+package goexperiment
+
+const RegabiReflect = false
+const RegabiReflectInt = 0
diff --git a/src/internal/goexperiment/exp_regabireflect_on.go b/src/internal/goexperiment/exp_regabireflect_on.go
new file mode 100644
index 0000000000..e8a3e9c06a
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabireflect_on.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabireflect
+// +build goexperiment.regabireflect
+
+package goexperiment
+
+const RegabiReflect = true
+const RegabiReflectInt = 1
diff --git a/src/internal/goexperiment/exp_regabiwrappers_off.go b/src/internal/goexperiment/exp_regabiwrappers_off.go
new file mode 100644
index 0000000000..bfa0fa3779
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabiwrappers_off.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.regabiwrappers
+// +build !goexperiment.regabiwrappers
+
+package goexperiment
+
+const RegabiWrappers = false
+const RegabiWrappersInt = 0
diff --git a/src/internal/goexperiment/exp_regabiwrappers_on.go b/src/internal/goexperiment/exp_regabiwrappers_on.go
new file mode 100644
index 0000000000..11ffffbbff
--- /dev/null
+++ b/src/internal/goexperiment/exp_regabiwrappers_on.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.regabiwrappers
+// +build goexperiment.regabiwrappers
+
+package goexperiment
+
+const RegabiWrappers = true
+const RegabiWrappersInt = 1
diff --git a/src/internal/goexperiment/exp_staticlockranking_off.go b/src/internal/goexperiment/exp_staticlockranking_off.go
new file mode 100644
index 0000000000..3d546c04b4
--- /dev/null
+++ b/src/internal/goexperiment/exp_staticlockranking_off.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.staticlockranking
+// +build !goexperiment.staticlockranking
+
+package goexperiment
+
+const StaticLockRanking = false
+const StaticLockRankingInt = 0
diff --git a/src/internal/goexperiment/exp_staticlockranking_on.go b/src/internal/goexperiment/exp_staticlockranking_on.go
new file mode 100644
index 0000000000..78188fb810
--- /dev/null
+++ b/src/internal/goexperiment/exp_staticlockranking_on.go
@@ -0,0 +1,9 @@
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.staticlockranking
+// +build goexperiment.staticlockranking
+
+package goexperiment
+
+const StaticLockRanking = true
+const StaticLockRankingInt = 1
diff --git a/src/internal/goexperiment/flags.go b/src/internal/goexperiment/flags.go
index 46800b4e0f..c5e3d2c91a 100644
--- a/src/internal/goexperiment/flags.go
+++ b/src/internal/goexperiment/flags.go
@@ -17,11 +17,12 @@
 // - Build tag goexperiment.x is set if experiment x (lower case) is
 // enabled.
 //
+// - For each experiment x (in camel case), this package contains a
+// boolean constant x and an integer constant xInt.
+//
 // - In runtime assembly, the macro GOEXPERIMENT_x is defined if
 // experiment x (lower case) is enabled.
 //
-// - TODO(austin): More to come.
-//
 // In the toolchain, the set of experiments enabled for the current
 // build should be accessed via objabi.Experiment.
 //
@@ -29,11 +30,15 @@
 // go doc internal/experiment.Flags.
 package goexperiment
 
+//go:generate go run mkconsts.go
+
 // Flags is the set of experiments that can be enabled or disabled in
 // the current toolchain.
 //
 // When specified in the GOEXPERIMENT environment variable or as build
 // tags, experiments use the strings.ToLower of their field name.
+//
+// If you change this struct definition, run "go generate".
 type Flags struct {
 	FieldTrack        bool
 	PreemptibleLoops  bool
diff --git a/src/internal/goexperiment/mkconsts.go b/src/internal/goexperiment/mkconsts.go
new file mode 100644
index 0000000000..204ca9d9aa
--- /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
+}