From 131ec174b50e113bb1e26a828a868b6f04386a1b Mon Sep 17 00:00:00 2001
From: ksss <co000ri@gmail.com>
Date: Fri, 25 Sep 2026 17:14:58 +0900
Subject: [PATCH] Add implicitly-returns-nil to Kernel#caller and
 #caller_locations

They return nil only when start exceeds the stack depth, which almost
never happens in practice (even at the top level, caller(1) returns []).
Treating the result as non-nil lets common idioms such as
caller_locations(1, 1).first type-check without a nil guard, matching
Exception#backtrace.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 core/kernel.rbs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/core/kernel.rbs b/core/kernel.rbs
index fac5a887d5..be48950a6e 100644
--- a/core/kernel.rbs
+++ b/core/kernel.rbs
@@ -183,8 +183,8 @@ module Kernel : BasicObject
   #     c(5)   #=> nil
   #
   def self?.caller: () -> Array[String]
-                  | (int start, ?int? length) -> Array[String]?
-                  | (range[int] range) -> Array[String]?
+                  | %a{implicitly-returns-nil} (int start, ?int? length) -> Array[String]
+                  | %a{implicitly-returns-nil} (range[int] range) -> Array[String]
 
   # <!--
   #   rdoc-file=vm_backtrace.c
@@ -208,8 +208,8 @@ module Kernel : BasicObject
   # entries within the specified range.
   #
   def self?.caller_locations: () -> Array[Thread::Backtrace::Location]
-                            | (int start, ?int? length) -> Array[Thread::Backtrace::Location]?
-                            | (range[int] range) -> Array[Thread::Backtrace::Location]?
+                            | %a{implicitly-returns-nil} (int start, ?int? length) -> Array[Thread::Backtrace::Location]
+                            | %a{implicitly-returns-nil} (range[int] range) -> Array[Thread::Backtrace::Location]
 
   # <!--
   #   rdoc-file=vm_eval.c