From b434bbf197b3683643d4d6b52bca687982e336b5 Mon Sep 17 00:00:00 2001
From: Richard Musiol <mail@richard-musiol.de>
Date: Sat, 23 Mar 2019 14:18:19 +0100
Subject: [PATCH] cmd/go: add GOWASM environment variable

This change adds the environment variable GOWASM, which is a comma
separated list of experimental WebAssembly features that the compiled
WebAssembly binary is allowed to use. The default is to use no
experimental features. Initially there are no features avaiable.

More information about feature proposals can be found at
https://github.com/WebAssembly/proposals

Change-Id: I4c8dc534c99ecff8bb075dded0186ca8f8decaef
Reviewed-on: https://go-review.googlesource.com/c/go/+/168881
Run-TryBot: Richard Musiol <neelance@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
---
 doc/install-source.html           | 11 +++++++++++
 src/cmd/go/internal/cfg/cfg.go    |  1 +
 src/cmd/go/internal/envcmd/env.go |  2 ++
 src/cmd/internal/objabi/util.go   | 24 ++++++++++++++++++++++++
 4 files changed, 38 insertions(+)

diff --git a/doc/install-source.html b/doc/install-source.html
index c11151be64..46dc618a9c 100644
--- a/doc/install-source.html
+++ b/doc/install-source.html
@@ -638,6 +638,17 @@ for which the compiler will target. The default is <code>power8</code>.
 </ul>
 </li>
 
+
+<li><code>$GOWASM</code> (for <code>wasm</code> only)
+	<p>
+	This variable is a comma separated list of <a href="https://github.com/WebAssembly/proposals">experimental WebAssembly features</a> that the compiled WebAssembly binary is allowed to use.
+	The default is to use no experimental features.
+	</p>
+	<ul>
+		<li>(no features yet)</li>
+	</ul>
+</li>
+
 </ul>
 
 <p>
diff --git a/src/cmd/go/internal/cfg/cfg.go b/src/cmd/go/internal/cfg/cfg.go
index 80a154b066..35f7f1a173 100644
--- a/src/cmd/go/internal/cfg/cfg.go
+++ b/src/cmd/go/internal/cfg/cfg.go
@@ -105,6 +105,7 @@ var (
 	GOMIPS   = objabi.GOMIPS
 	GOMIPS64 = objabi.GOMIPS64
 	GOPPC64  = fmt.Sprintf("%s%d", "power", objabi.GOPPC64)
+	GOWASM   = objabi.GOWASM
 )
 
 // Update build context to use our computed GOROOT.
diff --git a/src/cmd/go/internal/envcmd/env.go b/src/cmd/go/internal/envcmd/env.go
index 08291dfb14..645f83246a 100644
--- a/src/cmd/go/internal/envcmd/env.go
+++ b/src/cmd/go/internal/envcmd/env.go
@@ -83,6 +83,8 @@ func MkEnv() []cfg.EnvVar {
 		env = append(env, cfg.EnvVar{Name: "GOMIPS64", Value: cfg.GOMIPS64})
 	case "ppc64", "ppc64le":
 		env = append(env, cfg.EnvVar{Name: "GOPPC64", Value: cfg.GOPPC64})
+	case "wasm":
+		env = append(env, cfg.EnvVar{Name: "GOWASM", Value: cfg.GOWASM.String()})
 	}
 
 	cc := cfg.DefaultCC(cfg.Goos, cfg.Goarch)
diff --git a/src/cmd/internal/objabi/util.go b/src/cmd/internal/objabi/util.go
index 665c8b3be6..c007f6c475 100644
--- a/src/cmd/internal/objabi/util.go
+++ b/src/cmd/internal/objabi/util.go
@@ -29,6 +29,7 @@ var (
 	GOMIPS   = gomips()
 	GOMIPS64 = gomips64()
 	GOPPC64  = goppc64()
+	GOWASM   = gowasm()
 	GO_LDSO  = defaultGO_LDSO
 	Version  = version
 )
@@ -76,6 +77,29 @@ func goppc64() int {
 	panic("unreachable")
 }
 
+type gowasmFeatures struct {
+	// no features yet
+}
+
+func (f *gowasmFeatures) String() string {
+	var flags []string
+	// no features yet
+	return strings.Join(flags, ",")
+}
+
+func gowasm() (f gowasmFeatures) {
+	for _, opt := range strings.Split(envOr("GOWASM", ""), ",") {
+		switch opt {
+		// no features yet
+		case "":
+			// ignore
+		default:
+			log.Fatalf("Invalid GOWASM value. No such feature: " + opt)
+		}
+	}
+	return
+}
+
 func Getgoextlinkenabled() string {
 	return envOr("GO_EXTLINK_ENABLED", defaultGO_EXTLINK_ENABLED)
 }
-- 
2.51.0