[pull] master from golang:master

src/cmd/go/internal/cfg/cfg.go

@@ -460,7 +460,7 @@ var (
 	GOROOTpkg string
 	GOROOTsrc string
 
-	GOBIN                           = Getenv("GOBIN")
+	GOBIN, GOBINChanged             = EnvOrAndChanged("GOBIN", "")
 	GOCACHEPROG, GOCACHEPROGChanged = EnvOrAndChanged("GOCACHEPROG", "")
 	GOMODCACHE, GOMODCACHEChanged   = EnvOrAndChanged("GOMODCACHE", gopathDir("pkg/mod"))
 

src/cmd/go/internal/envcmd/env.go

@@ -83,7 +83,6 @@ func MkEnv() []cfg.EnvVar {
 		{Name: "GO111MODULE", Value: cfg.Getenv("GO111MODULE")},
 		{Name: "GOARCH", Value: cfg.Goarch, Changed: cfg.Goarch != runtime.GOARCH},
 		{Name: "GOAUTH", Value: cfg.GOAUTH, Changed: cfg.GOAUTHChanged},
-		{Name: "GOBIN", Value: cfg.GOBIN},
 		{Name: "GOCACHE"},
 		{Name: "GOCACHEPROG", Value: cfg.GOCACHEPROG, Changed: cfg.GOCACHEPROGChanged},
 		{Name: "GODEBUG", Value: os.Getenv("GODEBUG")},
@@ -133,7 +132,7 @@ func MkEnv() []cfg.EnvVar {
 			if env[i].Value != "on" && env[i].Value != "" {
 				env[i].Changed = true
 			}
-		case "GOBIN", "GOEXPERIMENT", "GOFLAGS", "GOINSECURE", "GOPACKAGESDRIVER", "GOPRIVATE", "GOTMPDIR", "GOVCS":
+		case "GOEXPERIMENT", "GOFLAGS", "GOINSECURE", "GOPACKAGESDRIVER", "GOPRIVATE", "GOTMPDIR", "GOVCS":
 			if env[i].Value != "" {
 				env[i].Changed = true
 			}
@@ -210,9 +209,30 @@ func ExtraEnvVars(ld *modload.Loader) []cfg.EnvVar {
 	if cfg.Getenv("GOWORK") == "off" {
 		gowork = "off"
 	}
+	gobin := cfg.GOBIN
+	if gobin == "" && cfg.ModulesEnabled {
+		gobin = modload.BinDir(ld)
+	} else if gobin == "" {
+		// Best effort guess of where the binary will be installed.
+		// go.dev/issue/23439
+		gopaths := filepath.SplitList(cfg.BuildContext.GOPATH)
+		wd, err := os.Getwd()
+		if err == nil && len(gopaths) > 0 {
+			gopath := gopaths[0]
+			for _, p := range gopaths {
+				if strings.HasPrefix(wd, p) {
+					gopath = p
+					break
+				}
+			}
+			gobin = filepath.Join(gopath, "bin")
+		}
+	}
+
 	return []cfg.EnvVar{
 		{Name: "GOMOD", Value: gomod},
 		{Name: "GOWORK", Value: gowork},
+		{Name: "GOBIN", Value: gobin, Changed: cfg.GOBINChanged},
 	}
 }
 

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

@@ -0,0 +1,44 @@
+
+go env GOBIN
+stdout $WORK${/}gopath${/}bin
+go env -changed GOBIN
+! stdout $WORK
+
+# report explicit settings
+env GOBIN=/tmp/gobin
+go env GOBIN
+stdout /tmp/gobin
+go env -changed GOBIN
+stdout /tmp/gobin
+
+# reset
+env GOBIN=
+go env -changed GOBIN
+! stdout $WORK
+
+# In GOPATH mode
+# the default install directory depends on the GOPATH
+# technically it also depends on the install target
+# but that's not something we can report.
+env GO111MODULE=off
+env GOPATH=$WORK${/}a${:}$WORK${/}b
+
+# report GOPATH[0]/bin outside of GOPATH
+cd $WORK
+go env GOBIN
+stdout $WORK${/}a${/}bin
+
+# report the current GOPATH/bin inside of a GOPATH
+cd $WORK/a/src/example1.com
+go env GOBIN
+stdout $WORK${/}a${/}bin
+
+cd $WORK/b/src/example2.com
+go env GOBIN
+stdout $WORK${/}b${/}bin
+
+-- $WORK/a/src/example1.com/main.go --
+package main
+
+-- $WORK/b/src/example2.com/main.go --
+package main