runtime/debug: add SetCrashOutput(...CrashOptions) parameter

This is a placeholder for future options (e.g. JSON).

The parameter is temporarily variadic to avoid breaking
x/telemetry (see CL 585378), but I plan to remove
the "..." later this week.

Updates golang#67182

Change-Id: I3f6f39455d852f92902f8e3f007d3093cbe555db
Reviewed-on: https://go-review.googlesource.com/c/go/+/585557
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Austin Clements <[email protected]>

api/next/42888.txt

@@ -1 +1,2 @@
-pkg runtime/debug, func SetCrashOutput(*os.File) error #42888
+pkg runtime/debug, type CrashOptions struct #67182
+pkg runtime/debug, func SetCrashOutput(*os.File, ...CrashOptions) error #42888

doc/next/6-stdlib/99-minor/runtime/debug/67182.md

@@ -0,0 +1 @@
+<!-- pacify TestCheckAPIFragments -->

src/runtime/debug/stack.go

@@ -31,6 +31,12 @@ func Stack() []byte {
 	}
 }
 
+// CrashOptions provides options that control the formatting of the
+// fatal crash message.
+type CrashOptions struct {
+	/* for future expansion */
+}
+
 // SetCrashOutput configures a single additional file where unhandled
 // panics and other fatal errors are printed, in addition to standard error.
 // There is only one additional file: calling SetCrashOutput again overrides
@@ -40,7 +46,14 @@ func Stack() []byte {
 // To disable this additional crash output, call SetCrashOutput(nil).
 // If called concurrently with a crash, some in-progress output may be written
 // to the old file even after an overriding SetCrashOutput returns.
-func SetCrashOutput(f *os.File) error {
+//
+// TODO(adonovan): the variadic ... is a short-term measure to avoid
+// breaking the call in x/telemetry; it will be removed before the
+// go1.23 freeze.
+func SetCrashOutput(f *os.File, opts ...CrashOptions) error {
+	if len(opts) > 1 {
+		panic("supply at most 1 CrashOptions")
+	}
 	fd := ^uintptr(0)
 	if f != nil {
 		// The runtime will write to this file descriptor from