runtime,cmd/link: include GOEXPERIMENTs in runtime.Version(), "go version X"

This adds the set of GOEXPERIMENTs to the build version if it differs
from the default set of experiments. This exposes the experiment
settings via runtime.Version() and "go version <binary>".

Change-Id: I143dbbc50f66a4cf175469199974e18848075af6
Reviewed-on: https://go-review.googlesource.com/c/go/+/307820
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/dist/buildruntime.go

@@ -19,7 +19,6 @@ import (
 //
 //	package sys
 //
-//	const TheVersion = <version>
 //	const StackGuardMultiplier = <multiplier value>
 //
 func mkzversion(dir, file string) {
@@ -28,7 +27,6 @@ func mkzversion(dir, file string) {
 	fmt.Fprintln(&buf)
 	fmt.Fprintf(&buf, "package sys\n")
 	fmt.Fprintln(&buf)
-	fmt.Fprintf(&buf, "const TheVersion = `%s`\n", findgoversion())
 	fmt.Fprintf(&buf, "const StackGuardMultiplierDefault = %d\n", stackGuardMultiplierDefault())
 
 	writefile(buf.String(), file, writeSkipSame)

src/cmd/go/testdata/script/version_goexperiment.txt

@@ -0,0 +1,16 @@
+# Test that experiments appear in "go version <binary>"
+
+# This test requires rebuilding the runtime, which takes a while.
+[short] skip
+
+env GOEXPERIMENT=fieldtrack
+go build -o main$GOEXE version.go
+go version main$GOEXE
+stdout 'X:fieldtrack$'
+exec ./main$GOEXE
+stderr 'X:fieldtrack$'
+
+-- version.go --
+package main
+import "runtime"
+func main() { println(runtime.Version()) }

src/cmd/link/internal/ld/main.go

@@ -118,6 +118,12 @@ func Main(arch *sys.Arch, theArch Arch) {
 	addstrdata1(ctxt, "runtime.defaultGOROOT="+final)
 	addstrdata1(ctxt, "cmd/internal/objabi.defaultGOROOT="+final)
 
+	buildVersion := objabi.Version
+	if goexperiment := objabi.GOEXPERIMENT(); goexperiment != "" {
+		buildVersion += " X:" + goexperiment
+	}
+	addstrdata1(ctxt, "runtime.buildVersion="+buildVersion)
+
 	// TODO(matloob): define these above and then check flag values here
 	if ctxt.Arch.Family == sys.AMD64 && objabi.GOOS == "plan9" {
 		flag.BoolVar(&flag8, "8", false, "use 64-bit addresses in symbol table")

src/internal/goexperiment/flags.go

@@ -26,6 +26,9 @@
 // In the toolchain, the set of experiments enabled for the current
 // build should be accessed via objabi.Experiment.
 //
+// The set of experiments is included in the output of runtime.Version()
+// and "go version <binary>" if it differs from the default experiments.
+//
 // For the set of experiments supported by the current toolchain, see
 // go doc internal/experiment.Flags.
 package goexperiment

src/runtime/extern.go

@@ -240,11 +240,21 @@ func GOROOT() string {
 	return defaultGOROOT
 }
 
+// buildVersion is the Go tree's version string at build time.
+//
+// If any GOEXPERIMENTs are set to non-default values, it will include
+// "X:<GOEXPERIMENT>".
+//
+// This is set by the linker.
+//
+// This is accessed by "go version <binary>".
+var buildVersion string
+
 // Version returns the Go tree's version string.
 // It is either the commit hash and date at the time of the build or,
 // when possible, a release tag like "go1.3".
 func Version() string {
-	return sys.TheVersion
+	return buildVersion
 }
 
 // GOOS is the running program's operating system target:

src/runtime/proc.go

@@ -12,8 +12,6 @@ import (
 	"unsafe"
 )
 
-var buildVersion = sys.TheVersion
-
 // set using cmd/go/internal/modload.ModInfoProg
 var modinfo string