update deps, add testscript.GoTool

go.mod

@@ -1,9 +1,13 @@
 module github.com/rogpeppe/go-internal
 
-go 1.23
+go 1.23.0
 
 require (
-	golang.org/x/mod v0.21.0
-	golang.org/x/sys v0.26.0
-	golang.org/x/tools v0.26.0
+	golang.org/x/mod v0.26.0
+	golang.org/x/sys v0.34.0
+	golang.org/x/tools v0.34.0
 )
+
+require golang.org/x/sync v0.15.0 // indirect
+
+tool golang.org/x/tools/cmd/stringer

go.sum

@@ -1,6 +1,10 @@
-golang.org/x/mod v0.21.0 h1:vvrHzRwRfVKSiLrG+d4FMl/Qi4ukBCE6kZlTUkDYRT0=
-golang.org/x/mod v0.21.0/go.mod h1:6SkKJ3Xj0I0BrPOZoBy3bdMptDDU9oJrpohJ3eWZ1fY=
-golang.org/x/sys v0.26.0 h1:KHjCJyddX0LoSTb3J+vWpupP9p0oznkqVk/IfjymZbo=
-golang.org/x/sys v0.26.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
-golang.org/x/tools v0.26.0 h1:v/60pFQmzmT9ExmjDv2gGIfi3OqfKoEP6I5+umXlbnQ=
-golang.org/x/tools v0.26.0/go.mod h1:TPVVj70c7JJ3WCazhD8OdXcZg/og+b9+tH/KxylGwH0=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+golang.org/x/mod v0.26.0 h1:EGMPT//Ezu+ylkCijjPc+f4Aih7sZvaAr+O3EHBxvZg=
+golang.org/x/mod v0.26.0/go.mod h1:/j6NAhSk8iQ723BGAUyoAcn7SlD7s15Dp9Nd/SfeaFQ=
+golang.org/x/sync v0.15.0 h1:KWH3jNZsfyT6xfAfKiz6MRNmd46ByHDYaZ7KSkCtdW8=
+golang.org/x/sync v0.15.0/go.mod h1:1dzgHSNfp02xaA81J2MS99Qcpr2w7fw1gpm99rleRqA=
+golang.org/x/sys v0.34.0 h1:H5Y5sJ2L2JRdyv7ROF1he/lPdvFsd0mJHFw2ThKHxLA=
+golang.org/x/sys v0.34.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+golang.org/x/tools v0.34.0 h1:qIpSLOxeCYGg9TrcJokLBG4KFA6d795g0xkBkiESGlo=
+golang.org/x/tools v0.34.0/go.mod h1:pAP9OwEaY1CAW3HOmg3hLZC5Z0CCmzjAF2UQMSqNARg=

testscript/exe.go

@@ -5,9 +5,12 @@
 package testscript
 
 import (
+	"bytes"
+	"fmt"
 	"io"
 	"log"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -58,6 +61,49 @@ func Main(m TestingM, commands map[string]func()) {
 	os.Exit(0)
 }
 
+// GoTool exposes a Go program added to the module being tested via `go get -tool`,
+// which can then be run via `go tool $name` and leverage Go's module and build caches.
+// This function must be run as part of [Main]; for example, after setting up the tool
+// via `go get -tool golang.org/x/tools/cmd/stringer`:
+//
+//	testscript.Main(m, map[string]func(){
+//		"stringer": testscript.GoTool("stringer"),
+//	})
+func GoTool(name string) func() {
+	// Since [Main] only takes a map[string]func() as a parameter, we cannot store the path
+	// to the cached tool anywhere, so we resort to setting one env var per tool.
+	// This is not ideal, but it works.
+	//
+	// We could also directly copy the cached tool binary into the $PATH that testscript sets up,
+	// to avoid an indirection via the test binary to use os/exec below.
+	// However, this again is very difficult given the current API of [Main].
+	//
+	// TODO: rethink in a future iteration of the API.
+	envName := "TESTSCRIPT_GO_TOOL_" + name
+	cachedBin := os.Getenv(envName)
+	if cachedBin == "" {
+		cmd := exec.Command("go", "tool", "-n", name)
+		out, err := cmd.CombinedOutput()
+		if err != nil {
+			log.Fatalf("failed to run %v: %v\n%s", strings.Join(cmd.Args, " "), err, out)
+		}
+		os.Setenv(envName, string(bytes.TrimSpace(out)))
+	}
+	return func() {
+		cmd := exec.Command(cachedBin, os.Args[1:]...)
+		cmd.Stdin = os.Stdin
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		if err := cmd.Run(); err != nil {
+			if err, ok := err.(*exec.ExitError); ok {
+				os.Exit(err.ExitCode())
+			}
+			fmt.Fprintln(os.Stderr, err)
+			os.Exit(1)
+		}
+	}
+}
+
 // testingMRun exists just so that we can use `defer`, given that [Main] above uses [os.Exit].
 func testingMRun(m TestingM, commands map[string]func()) int {
 	// Set up all commands in a directory, added in $PATH.

testscript/testdata/go_tool.txtar

@@ -0,0 +1,20 @@
+# We test the integration with `go tool X` with stringer, because it's contained
+# by an existing dependency of ours in the form of x/tools.
+# Moreover, it's a fairly simple tool to use, and given that it takes a relative
+# path as an argument, it will catch whether the current directory is correct.
+
+env GOCACHE=${WORK}/.gocache
+
+stringer -type Foo foo.go
+exists foo_string.go
+
+-- foo.go --
+package foo
+
+type Foo int
+
+const (
+	_ Foo = iota
+	Foo1
+	Foo2
+)

testscript/testscript.go

@@ -494,6 +494,12 @@ func (ts *TestScript) setup() string {
 			env.Vars = append(env.Vars, name+"="+val)
 		}
 	}
+	// For [GoTool] to work, we must pass its env vars through.
+	for _, kv := range os.Environ() {
+		if strings.HasPrefix(kv, "TESTSCRIPT_GO_TOOL_") {
+			env.Vars = append(env.Vars, kv)
+		}
+	}
 	// Must preserve SYSTEMROOT on Windows: https://github.com/golang/go/issues/25513 et al
 	if runtime.GOOS == "windows" {
 		env.Vars = append(env.Vars,

testscript/testscript_test.go

@@ -81,6 +81,7 @@ func TestMain(m *testing.M) {
 		"status":         exitWithStatus,
 		"signalcatcher":  signalCatcher,
 		"terminalprompt": terminalPrompt,
+		"stringer":       GoTool("stringer"),
 	})
 }