1 files changed, 138 insertions, 13 deletions
diff --git a/tpl/internal/go_templates/testenv/exec.go b/tpl/internal/go_templates/testenv/exec.go
index 13b4c7102..88791b3b4 100644
--- a/tpl/internal/go_templates/testenv/exec.go
+++ b/tpl/internal/go_templates/testenv/exec.go
@@ -6,33 +6,78 @@ package testenv
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"os/exec"
 	"runtime"
+	"strconv"
 	"strings"
 	"sync"
 	"testing"
+	"time"
 )
 
-// HasExec reports whether the current system can start new processes
-// using os.StartProcess or (more commonly) exec.Command.
-func HasExec() bool {
-	switch runtime.GOOS {
-	case "js", "ios":
-		return false
-	}
-	return true
-}
-
 // MustHaveExec checks that the current system can start new processes
 // using os.StartProcess or (more commonly) exec.Command.
 // If not, MustHaveExec calls t.Skip with an explanation.
+//
+// On some platforms MustHaveExec checks for exec support by re-executing the
+// current executable, which must be a binary built by 'go test'.
+// We intentionally do not provide a HasExec function because of the risk of
+// inappropriate recursion in TestMain functions.
+//
+// To check for exec support outside of a test, just try to exec the command.
+// If exec is not supported, testenv.SyscallIsNotSupported will return true
+// for the resulting error.
 func MustHaveExec(t testing.TB) {
-	if !HasExec() {
-		t.Skipf("skipping test: cannot exec subprocess on %s/%s", runtime.GOOS, runtime.GOARCH)
+	tryExecOnce.Do(func() {
+		tryExecErr = tryExec()
+	})
+	if tryExecErr != nil {
+		t.Skipf("skipping test: cannot exec subprocess on %s/%s: %v", runtime.GOOS, runtime.GOARCH, tryExecErr)
 	}
 }
 
+var (
+	tryExecOnce sync.Once
+	tryExecErr  error
+)
+
+func tryExec() error {
+	switch runtime.GOOS {
+	case "wasip1", "js", "ios":
+	default:
+		// Assume that exec always works on non-mobile platforms and Android.
+		return nil
+	}
+
+	// ios has an exec syscall but on real iOS devices it might return a
+	// permission error. In an emulated environment (such as a Corellium host)
+	// it might succeed, so if we need to exec we'll just have to try it and
+	// find out.
+	//
+	// As of 2023-04-19 wasip1 and js don't have exec syscalls at all, but we
+	// may as well use the same path so that this branch can be tested without
+	// an ios environment.
+
+	/*if !testing.Testing() {
+		// This isn't a standard 'go test' binary, so we don't know how to
+		// self-exec in a way that should succeed without side effects.
+		// Just forget it.
+		return errors.New("can't probe for exec support with a non-test executable")
+	}*/
+
+	// We know that this is a test executable. We should be able to run it with a
+	// no-op flag to check for overall exec support.
+	exe, err := os.Executable()
+	if err != nil {
+		return fmt.Errorf("can't probe for exec support: %w", err)
+	}
+	cmd := exec.Command(exe, "-test.list=^$")
+	cmd.Env = origEnv
+	return cmd.Run()
+}
+
 var execPaths sync.Map // path -> error
 
 // MustHaveExecPath checks that the current system can start the named executable
@@ -82,7 +127,87 @@ func CleanCmdEnv(cmd *exec.Cmd) *exec.Cmd {
 //   - fails the test if the command does not complete before the test's deadline, and
 //   - sets a Cleanup function that verifies that the test did not leak a subprocess.
 func CommandContext(t testing.TB, ctx context.Context, name string, args ...string) *exec.Cmd {
-	panic("Not implemented, Hugo is not using this")
+	t.Helper()
+	MustHaveExec(t)
+
+	var (
+		cancelCtx   context.CancelFunc
+		gracePeriod time.Duration // unlimited unless the test has a deadline (to allow for interactive debugging)
+	)
+
+	if t, ok := t.(interface {
+		testing.TB
+		Deadline() (time.Time, bool)
+	}); ok {
+		if td, ok := t.Deadline(); ok {
+			// Start with a minimum grace period, just long enough to consume the
+			// output of a reasonable program after it terminates.
+			gracePeriod = 100 * time.Millisecond
+			if s := os.Getenv("GO_TEST_TIMEOUT_SCALE"); s != "" {
+				scale, err := strconv.Atoi(s)
+				if err != nil {
+					t.Fatalf("invalid GO_TEST_TIMEOUT_SCALE: %v", err)
+				}
+				gracePeriod *= time.Duration(scale)
+			}
+
+			// If time allows, increase the termination grace period to 5% of the
+			// test's remaining time.
+			testTimeout := time.Until(td)
+			if gp := testTimeout / 20; gp > gracePeriod {
+				gracePeriod = gp
+			}
+
+			// When we run commands that execute subprocesses, we want to reserve two
+			// grace periods to clean up: one for the delay between the first
+			// termination signal being sent (via the Cancel callback when the Context
+			// expires) and the process being forcibly terminated (via the WaitDelay
+			// field), and a second one for the delay between the process being
+			// terminated and the test logging its output for debugging.
+			//
+			// (We want to ensure that the test process itself has enough time to
+			// log the output before it is also terminated.)
+			cmdTimeout := testTimeout - 2*gracePeriod
+
+			if cd, ok := ctx.Deadline(); !ok || time.Until(cd) > cmdTimeout {
+				// Either ctx doesn't have a deadline, or its deadline would expire
+				// after (or too close before) the test has already timed out.
+				// Add a shorter timeout so that the test will produce useful output.
+				ctx, cancelCtx = context.WithTimeout(ctx, cmdTimeout)
+			}
+		}
+	}
+
+	cmd := exec.CommandContext(ctx, name, args...)
+	cmd.Cancel = func() error {
+		if cancelCtx != nil && ctx.Err() == context.DeadlineExceeded {
+			// The command timed out due to running too close to the test's deadline.
+			// There is no way the test did that intentionally — it's too close to the
+			// wire! — so mark it as a test failure. That way, if the test expects the
+			// command to fail for some other reason, it doesn't have to distinguish
+			// between that reason and a timeout.
+			t.Errorf("test timed out while running command: %v", cmd)
+		} else {
+			// The command is being terminated due to ctx being canceled, but
+			// apparently not due to an explicit test deadline that we added.
+			// Log that information in case it is useful for diagnosing a failure,
+			// but don't actually fail the test because of it.
+			t.Logf("%v: terminating command: %v", ctx.Err(), cmd)
+		}
+		return cmd.Process.Signal(Sigquit)
+	}
+	cmd.WaitDelay = gracePeriod
+
+	t.Cleanup(func() {
+		if cancelCtx != nil {
+			cancelCtx()
+		}
+		if cmd.Process != nil && cmd.ProcessState == nil {
+			t.Errorf("command was started, but test did not wait for it to complete: %v", cmd)
+		}
+	})
+
+	return cmd
 }
 
 // Command is like exec.Command, but applies the same changes as