cmd/go: prep for 'go env' refactoring

This CL refactors code a little to make it easier to add GOEXPERIMENT
support in the future.

Change-Id: I87903056f7863049e58be72047b2b8a60a213baf
Reviewed-on: https://go-review.googlesource.com/c/go/+/329654
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>

3 files changed, 170 insertions, 127 deletions

diff --git a/src/cmd/go/internal/envcmd/env.go b/src/cmd/go/internal/envcmd/env.go
index b30c37ab27..d88dcce5c0 100644
--- a/src/cmd/go/internal/envcmd/env.go
+++ b/src/cmd/go/internal/envcmd/env.go
@@ -10,6 +10,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"go/build"
+	"internal/buildcfg"
 	"io"
 	"os"
 	"path/filepath"
@@ -197,6 +198,21 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 	if *envU && *envW {
 		base.Fatalf("go env: cannot use -u with -w")
 	}
+
+	// Handle 'go env -w' and 'go env -u' before calling buildcfg.Check,
+	// so they can be used to recover from an invalid configuration.
+	if *envW {
+		runEnvW(args)
+		return
+	}
+
+	if *envU {
+		runEnvU(args)
+		return
+	}
+
+	buildcfg.Check()
+
 	env := cfg.CmdEnv
 	env = append(env, ExtraEnvVars()...)
 
@@ -206,14 +222,7 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 
 	// Do we need to call ExtraEnvVarsCostly, which is a bit expensive?
 	needCostly := false
-	if *envU || *envW {
-		// We're overwriting or removing default settings,
-		// so it doesn't really matter what the existing settings are.
-		//
-		// Moreover, we haven't validated the new settings yet, so it is
-		// important that we NOT perform any actions based on them,
-		// such as initializing the builder to compute other variables.
-	} else if len(args) == 0 {
+	if len(args) == 0 {
 		// We're listing all environment variables ("go env"),
 		// including the expensive ones.
 		needCostly = true
@@ -238,95 +247,6 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 		env = append(env, ExtraEnvVarsCostly()...)
 	}
 
-	if *envW {
-		// Process and sanity-check command line.
-		if len(args) == 0 {
-			base.Fatalf("go env -w: no KEY=VALUE arguments given")
-		}
-		osEnv := make(map[string]string)
-		for _, e := range cfg.OrigEnv {
-			if i := strings.Index(e, "="); i >= 0 {
-				osEnv[e[:i]] = e[i+1:]
-			}
-		}
-		add := make(map[string]string)
-		for _, arg := range args {
-			i := strings.Index(arg, "=")
-			if i < 0 {
-				base.Fatalf("go env -w: arguments must be KEY=VALUE: invalid argument: %s", arg)
-			}
-			key, val := arg[:i], arg[i+1:]
-			if err := checkEnvWrite(key, val); err != nil {
-				base.Fatalf("go env -w: %v", err)
-			}
-			if _, ok := add[key]; ok {
-				base.Fatalf("go env -w: multiple values for key: %s", key)
-			}
-			add[key] = val
-			if osVal := osEnv[key]; osVal != "" && osVal != val {
-				fmt.Fprintf(os.Stderr, "warning: go env -w %s=... does not override conflicting OS environment variable\n", key)
-			}
-		}
-
-		goos, okGOOS := add["GOOS"]
-		goarch, okGOARCH := add["GOARCH"]
-		if okGOOS || okGOARCH {
-			if !okGOOS {
-				goos = cfg.Goos
-			}
-			if !okGOARCH {
-				goarch = cfg.Goarch
-			}
-			if err := work.CheckGOOSARCHPair(goos, goarch); err != nil {
-				base.Fatalf("go env -w: %v", err)
-			}
-		}
-
-		gotmp, okGOTMP := add["GOTMPDIR"]
-		if okGOTMP {
-			if !filepath.IsAbs(gotmp) && gotmp != "" {
-				base.Fatalf("go env -w: GOTMPDIR must be an absolute path")
-			}
-		}
-
-		updateEnvFile(add, nil)
-		return
-	}
-
-	if *envU {
-		// Process and sanity-check command line.
-		if len(args) == 0 {
-			base.Fatalf("go env -u: no arguments given")
-		}
-		del := make(map[string]bool)
-		for _, arg := range args {
-			if err := checkEnvWrite(arg, ""); err != nil {
-				base.Fatalf("go env -u: %v", err)
-			}
-			del[arg] = true
-		}
-		if del["GOOS"] || del["GOARCH"] {
-			goos, goarch := cfg.Goos, cfg.Goarch
-			if del["GOOS"] {
-				goos = getOrigEnv("GOOS")
-				if goos == "" {
-					goos = build.Default.GOOS
-				}
-			}
-			if del["GOARCH"] {
-				goarch = getOrigEnv("GOARCH")
-				if goarch == "" {
-					goarch = build.Default.GOARCH
-				}
-			}
-			if err := work.CheckGOOSARCHPair(goos, goarch); err != nil {
-				base.Fatalf("go env -u: %v", err)
-			}
-		}
-		updateEnvFile(nil, del)
-		return
-	}
-
 	if len(args) > 0 {
 		if *envJson {
 			var es []cfg.EnvVar
@@ -351,6 +271,102 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 	PrintEnv(os.Stdout, env)
 }
 
+func runEnvW(args []string) {
+	// Process and sanity-check command line.
+	if len(args) == 0 {
+		base.Fatalf("go env -w: no KEY=VALUE arguments given")
+	}
+	osEnv := make(map[string]string)
+	for _, e := range cfg.OrigEnv {
+		if i := strings.Index(e, "="); i >= 0 {
+			osEnv[e[:i]] = e[i+1:]
+		}
+	}
+	add := make(map[string]string)
+	for _, arg := range args {
+		i := strings.Index(arg, "=")
+		if i < 0 {
+			base.Fatalf("go env -w: arguments must be KEY=VALUE: invalid argument: %s", arg)
+		}
+		key, val := arg[:i], arg[i+1:]
+		if err := checkEnvWrite(key, val); err != nil {
+			base.Fatalf("go env -w: %v", err)
+		}
+		if _, ok := add[key]; ok {
+			base.Fatalf("go env -w: multiple values for key: %s", key)
+		}
+		add[key] = val
+		if osVal := osEnv[key]; osVal != "" && osVal != val {
+			fmt.Fprintf(os.Stderr, "warning: go env -w %s=... does not override conflicting OS environment variable\n", key)
+		}
+	}
+
+	if err := checkBuildConfig(add, nil); err != nil {
+		base.Fatalf("go env -w: %v", err)
+	}
+
+	gotmp, okGOTMP := add["GOTMPDIR"]
+	if okGOTMP {
+		if !filepath.IsAbs(gotmp) && gotmp != "" {
+			base.Fatalf("go env -w: GOTMPDIR must be an absolute path")
+		}
+	}
+
+	updateEnvFile(add, nil)
+}
+
+func runEnvU(args []string) {
+	// Process and sanity-check command line.
+	if len(args) == 0 {
+		base.Fatalf("go env -u: no arguments given")
+	}
+	del := make(map[string]bool)
+	for _, arg := range args {
+		if err := checkEnvWrite(arg, ""); err != nil {
+			base.Fatalf("go env -u: %v", err)
+		}
+		del[arg] = true
+	}
+
+	if err := checkBuildConfig(nil, del); err != nil {
+		base.Fatalf("go env -u: %v", err)
+	}
+
+	updateEnvFile(nil, del)
+}
+
+// checkBuildConfig checks whether the build configuration is valid
+// after the specified configuration environment changes are applied.
+func checkBuildConfig(add map[string]string, del map[string]bool) error {
+	// get returns the value for key after applying add and del and
+	// reports whether it changed. cur should be the current value
+	// (i.e., before applying changes) and def should be the default
+	// value (i.e., when no environment variables are provided at all).
+	get := func(key, cur, def string) (string, bool) {
+		if val, ok := add[key]; ok {
+			return val, true
+		}
+		if del[key] {
+			val := getOrigEnv(key)
+			if val == "" {
+				val = def
+			}
+			return val, true
+		}
+		return cur, false
+	}
+
+	goos, okGOOS := get("GOOS", cfg.Goos, build.Default.GOOS)
+	goarch, okGOARCH := get("GOARCH", cfg.Goarch, build.Default.GOARCH)
+	if okGOOS || okGOARCH {
+		if err := work.CheckGOOSARCHPair(goos, goarch); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
 // PrintEnv prints the environment variables to w.
 func PrintEnv(w io.Writer, env []cfg.EnvVar) {
 	for _, e := range env {
diff --git a/src/cmd/go/main.go b/src/cmd/go/main.go
index 02174a56ff..16361e02ca 100644
--- a/src/cmd/go/main.go
+++ b/src/cmd/go/main.go
@@ -145,24 +145,6 @@ func main() {
 		os.Exit(2)
 	}
 
-	if err := buildcfg.Error; err != nil {
-		fmt.Fprintf(os.Stderr, "go: %v\n", buildcfg.Error)
-		os.Exit(2)
-	}
-
-	// Set environment (GOOS, GOARCH, etc) explicitly.
-	// In theory all the commands we invoke should have
-	// the same default computation of these as we do,
-	// but in practice there might be skew
-	// This makes sure we all agree.
-	cfg.OrigEnv = os.Environ()
-	cfg.CmdEnv = envcmd.MkEnv()
-	for _, env := range cfg.CmdEnv {
-		if os.Getenv(env.Name) != env.Value {
-			os.Setenv(env.Name, env.Value)
-		}
-	}
-
 BigCmdLoop:
 	for bigCmd := base.Go; ; {
 		for _, cmd := range bigCmd.Commands {
@@ -188,18 +170,7 @@ BigCmdLoop:
 			if !cmd.Runnable() {
 				continue
 			}
-			cmd.Flag.Usage = func() { cmd.Usage() }
-			if cmd.CustomFlags {
-				args = args[1:]
-			} else {
-				base.SetFromGOFLAGS(&cmd.Flag)
-				cmd.Flag.Parse(args[1:])
-				args = cmd.Flag.Args()
-			}
-			ctx := maybeStartTrace(context.Background())
-			ctx, span := trace.StartSpan(ctx, fmt.Sprint("Running ", cmd.Name(), " command"))
-			cmd.Run(ctx, cmd, args)
-			span.Done()
+			invoke(cmd, args)
 			base.Exit()
 			return
 		}
@@ -213,6 +184,39 @@ BigCmdLoop:
 	}
 }
 
+func invoke(cmd *base.Command, args []string) {
+	// 'go env' handles checking the build config
+	if cmd != envcmd.CmdEnv {
+		buildcfg.Check()
+	}
+
+	// Set environment (GOOS, GOARCH, etc) explicitly.
+	// In theory all the commands we invoke should have
+	// the same default computation of these as we do,
+	// but in practice there might be skew
+	// This makes sure we all agree.
+	cfg.OrigEnv = os.Environ()
+	cfg.CmdEnv = envcmd.MkEnv()
+	for _, env := range cfg.CmdEnv {
+		if os.Getenv(env.Name) != env.Value {
+			os.Setenv(env.Name, env.Value)
+		}
+	}
+
+	cmd.Flag.Usage = func() { cmd.Usage() }
+	if cmd.CustomFlags {
+		args = args[1:]
+	} else {
+		base.SetFromGOFLAGS(&cmd.Flag)
+		cmd.Flag.Parse(args[1:])
+		args = cmd.Flag.Args()
+	}
+	ctx := maybeStartTrace(context.Background())
+	ctx, span := trace.StartSpan(ctx, fmt.Sprint("Running ", cmd.Name(), " command"))
+	cmd.Run(ctx, cmd, args)
+	span.Done()
+}
+
 func init() {
 	base.Usage = mainUsage
 }
diff --git a/src/cmd/go/testdata/script/env_unset.txt b/src/cmd/go/testdata/script/env_unset.txt
new file mode 100644
index 0000000000..35fbb0a8a2
--- /dev/null
+++ b/src/cmd/go/testdata/script/env_unset.txt
@@ -0,0 +1,23 @@
+# Test that we can unset variables, even if initially invalid,
+# as long as resulting config is valid.
+
+env GOENV=badenv
+env GOOS=
+env GOARCH=
+
+! go env
+stderr '^cmd/go: unsupported GOOS/GOARCH pair bados/badarch$'
+
+! go env -u GOOS
+stderr '^go env -u: unsupported GOOS/GOARCH pair \w+/badarch$'
+
+! go env -u GOARCH
+stderr '^go env -u: unsupported GOOS/GOARCH pair bados/\w+$'
+
+go env -u GOOS GOARCH
+
+go env
+
+-- badenv --
+GOOS=bados
+GOARCH=badarch