Test runner: when stdout is redirected, assume -pipe.

Change-Id: Ib4ecc1008ffdc40332d567fce6d6cecd6a6a6964
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/99027
Commit-Queue: Rudolf Polzer <rpolzer@google.com>
Reviewed-by: Xiangfei Ding <xfding@google.com>
Presubmit-BoringSSL-Verified: boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Benjamin <davidben@google.com>

go.mod

@@ -10,6 +10,7 @@ require (
 	github.com/hexops/gotextdiff v1.0.3
 	golang.org/x/crypto v0.52.0
 	golang.org/x/net v0.55.0
+	golang.org/x/term v0.43.0
 	google.golang.org/api v0.283.0
 )
 
@@ -50,7 +51,6 @@ require (
 	golang.org/x/oauth2 v0.36.0 // indirect
 	golang.org/x/sync v0.20.0 // indirect
 	golang.org/x/sys v0.45.0 // indirect
-	golang.org/x/term v0.43.0 // indirect
 	golang.org/x/text v0.37.0 // indirect
 	golang.org/x/time v0.15.0 // indirect
 	google.golang.org/genproto v0.0.0-20260319201613-d00831a3d3e7 // indirect

ssl/test/runner/runner.go

@@ -47,6 +47,7 @@ import (
 	"boringssl.googlesource.com/boringssl.git/util/testresult"
 	"filippo.io/mldsa"
 	"golang.org/x/crypto/cryptobyte"
+	"golang.org/x/term"
 )
 
 var (
@@ -59,7 +60,7 @@ var (
 	mallocTest         = flag.Int64("malloc-test", -1, "If non-negative, run each test with each malloc in turn failing from the given number onwards.")
 	mallocTestDebug    = flag.Bool("malloc-test-debug", false, "If true, ask bssl_shim to abort rather than fail a malloc. This can be used with a specific value for --malloc-test to identity the malloc failing that is causing problems.")
 	jsonOutput         = flag.String("json-output", "", "The file to output JSON results to.")
-	pipe               = flag.Bool("pipe", false, "If true, print status output suitable for piping into another program.")
+	pipe               = flag.Bool("pipe", !term.IsTerminal(int(os.Stdout.Fd())), "If true, print status output suitable for piping into another program.")
 	testToRun          = flag.String("test", "", "Semicolon-separated patterns of tests to run, or empty to run all tests")
 	skipTest           = flag.String("skip", "", "Semicolon-separated patterns of tests to skip")
 	allowHintMismatch  = flag.String("allow-hint-mismatch", "", "Semicolon-separated patterns of tests where hints may mismatch")