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>

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
@@ -238,7 +247,31 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 		env = append(env, ExtraEnvVarsCostly()...)
 	}
 
-	if *envW {
+	if len(args) > 0 {
+		if *envJson {
+			var es []cfg.EnvVar
+			for _, name := range args {
+				e := cfg.EnvVar{Name: name, Value: findEnv(env, name)}
+				es = append(es, e)
+			}
+			printEnvAsJSON(es)
+		} else {
+			for _, name := range args {
+				fmt.Printf("%s\n", findEnv(env, name))
+			}
+		}
+		return
+	}
+
+	if *envJson {
+		printEnvAsJSON(env)
+		return
+	}
+
+	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")
@@ -268,19 +301,9 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 		}
 	}
 
-		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 {
+	if err := checkBuildConfig(add, nil); err != nil {
 		base.Fatalf("go env -w: %v", err)
 	}
-		}
 
 	gotmp, okGOTMP := add["GOTMPDIR"]
 	if okGOTMP {
@@ -290,10 +313,9 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 	}
 
 	updateEnvFile(add, nil)
-		return
 }
 
-	if *envU {
+func runEnvU(args []string) {
 	// Process and sanity-check command line.
 	if len(args) == 0 {
 		base.Fatalf("go env -u: no arguments given")
@@ -305,50 +327,44 @@ func runEnv(ctx context.Context, cmd *base.Command, args []string) {
 		}
 		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 {
+
+	if err := checkBuildConfig(nil, del); err != nil {
 		base.Fatalf("go env -u: %v", err)
 	}
-		}
+
 	updateEnvFile(nil, del)
-		return
 }
 
-	if len(args) > 0 {
-		if *envJson {
-			var es []cfg.EnvVar
-			for _, name := range args {
-				e := cfg.EnvVar{Name: name, Value: findEnv(env, name)}
-				es = append(es, e)
+// 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
 		}
-			printEnvAsJSON(es)
-		} else {
-			for _, name := range args {
-				fmt.Printf("%s\n", findEnv(env, name))
+		if del[key] {
+			val := getOrigEnv(key)
+			if val == "" {
+				val = def
 			}
+			return val, true
 		}
-		return
+		return cur, false
 	}
 
-	if *envJson {
-		printEnvAsJSON(env)
-		return
+	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
+		}
 	}
 
-	PrintEnv(os.Stdout, env)
+	return nil
 }
 
 // PrintEnv prints the environment variables to w.

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 {
@@ -188,6 +170,39 @@ BigCmdLoop:
 			if !cmd.Runnable() {
 				continue
 			}
+			invoke(cmd, args)
+			base.Exit()
+			return
+		}
+		helpArg := ""
+		if i := strings.LastIndex(cfg.CmdName, " "); i >= 0 {
+			helpArg = " " + cfg.CmdName[:i]
+		}
+		fmt.Fprintf(os.Stderr, "go %s: unknown command\nRun 'go help%s' for usage.\n", cfg.CmdName, helpArg)
+		base.SetExitStatus(2)
+		base.Exit()
+	}
+}
+
+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:]
@@ -200,17 +215,6 @@ BigCmdLoop:
 	ctx, span := trace.StartSpan(ctx, fmt.Sprint("Running ", cmd.Name(), " command"))
 	cmd.Run(ctx, cmd, args)
 	span.Done()
-			base.Exit()
-			return
-		}
-		helpArg := ""
-		if i := strings.LastIndex(cfg.CmdName, " "); i >= 0 {
-			helpArg = " " + cfg.CmdName[:i]
-		}
-		fmt.Fprintf(os.Stderr, "go %s: unknown command\nRun 'go help%s' for usage.\n", cfg.CmdName, helpArg)
-		base.SetExitStatus(2)
-		base.Exit()
-	}
 }
 
 func init() {

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