cmd/go: merge module support from x/vgo repo

This CL corresponds to CL 123361, the final manual CL in that repo,
making this the final manual sync.

All future commits will happen in this repo (the main Go repo),
and we'll update x/vgo automatically with a fixed patch+script.

Change-Id: I572243309c1809727604fd704705a23c30e85d1a
Reviewed-on: https://go-review.googlesource.com/123576
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

1 files changed, 22 insertions, 8 deletions

diff --git a/src/cmd/go/internal/envcmd/env.go b/src/cmd/go/internal/envcmd/env.go
index 1c5640f208..44fd18a015 100644
--- a/src/cmd/go/internal/envcmd/env.go
+++ b/src/cmd/go/internal/envcmd/env.go
@@ -9,6 +9,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"path/filepath"
 	"runtime"
 	"strings"
 
@@ -16,7 +17,7 @@ import (
 	"cmd/go/internal/cache"
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/load"
-	"cmd/go/internal/vgo"
+	"cmd/go/internal/modload"
 	"cmd/go/internal/work"
 )
 
@@ -112,6 +113,18 @@ func findEnv(env []cfg.EnvVar, name string) string {
 
 // ExtraEnvVars returns environment variables that should not leak into child processes.
 func ExtraEnvVars() []cfg.EnvVar {
+	gomod := ""
+	if modload.Init(); modload.ModRoot != "" {
+		gomod = filepath.Join(modload.ModRoot, "go.mod")
+	}
+	return []cfg.EnvVar{
+		{Name: "GOMOD", Value: gomod},
+	}
+}
+
+// ExtraEnvVarsCostly returns environment variables that should not leak into child processes
+// but are costly to evaluate.
+func ExtraEnvVarsCostly() []cfg.EnvVar {
 	var b work.Builder
 	b.Init()
 	cppflags, cflags, cxxflags, fflags, ldflags, err := b.CFlags(&load.Package{})
@@ -121,6 +134,7 @@ func ExtraEnvVars() []cfg.EnvVar {
 		return nil
 	}
 	cmd := b.GccCmd(".", "")
+
 	return []cfg.EnvVar{
 		// Note: Update the switch in runEnv below when adding to this list.
 		{Name: "CGO_CFLAGS", Value: strings.Join(cflags, " ")},
@@ -130,19 +144,19 @@ func ExtraEnvVars() []cfg.EnvVar {
 		{Name: "CGO_LDFLAGS", Value: strings.Join(ldflags, " ")},
 		{Name: "PKG_CONFIG", Value: b.PkgconfigCmd()},
 		{Name: "GOGCCFLAGS", Value: strings.Join(cmd[3:], " ")},
-		{Name: "VGOMODROOT", Value: vgo.ModRoot},
 	}
 }
 
 func runEnv(cmd *base.Command, args []string) {
 	env := cfg.CmdEnv
+	env = append(env, ExtraEnvVars()...)
 
-	// Do we need to call ExtraEnvVars, which is a bit expensive?
+	// Do we need to call ExtraEnvVarsCostly, which is a bit expensive?
 	// Only if we're listing all environment variables ("go env")
 	// or the variables being requested are in the extra list.
-	needExtra := true
+	needCostly := true
 	if len(args) > 0 {
-		needExtra = false
+		needCostly = false
 		for _, arg := range args {
 			switch arg {
 			case "CGO_CFLAGS",
@@ -152,12 +166,12 @@ func runEnv(cmd *base.Command, args []string) {
 				"CGO_LDFLAGS",
 				"PKG_CONFIG",
 				"GOGCCFLAGS":
-				needExtra = true
+				needCostly = true
 			}
 		}
 	}
-	if needExtra {
-		env = append(env, ExtraEnvVars()...)
+	if needCostly {
+		env = append(env, ExtraEnvVarsCostly()...)
 	}
 
 	if len(args) > 0 {