From ac62b6da04c5b4d301ca46955c15c25efca81620 Mon Sep 17 00:00:00 2001
From: Yusuke Endoh <mame@ruby-lang.org>
Date: Mon, 28 Sep 2026 19:50:01 +0900
Subject: [PATCH] Analyze a pattern guard after the pattern binds its variables

IfPatternNode installed the guard before the guarded pattern, so a
variable bound by the pattern was still nil in the guard, and a common
guard like `in [x] if x.even?` reported "undefined method: nil#even?".
Ruby evaluates the guard after the pattern matches, so install the
pattern first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 lib/typeprof/core/ast/pattern.rb   |  3 ++-
 scenario/patterns/guard_binding.rb | 30 ++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 scenario/patterns/guard_binding.rb

diff --git a/lib/typeprof/core/ast/pattern.rb b/lib/typeprof/core/ast/pattern.rb
index eed2da94..3ecccb48 100644
--- a/lib/typeprof/core/ast/pattern.rb
+++ b/lib/typeprof/core/ast/pattern.rb
@@ -153,8 +153,9 @@ def initialize(raw_node, lenv)
       def subnodes = { cond:, body: }
 
       def install_pattern0(genv, subject)
-        @cond.install(genv)
+        # The guard is evaluated after the pattern binds its variables
         @body.install_pattern(genv, subject)
+        @cond.install(genv)
         subject
       end
     end
diff --git a/scenario/patterns/guard_binding.rb b/scenario/patterns/guard_binding.rb
new file mode 100644
index 00000000..70c1fc89
--- /dev/null
+++ b/scenario/patterns/guard_binding.rb
@@ -0,0 +1,30 @@
+## update: test.rb
+def cond?(x)
+  x
+end
+
+def check_if(v)
+  case v
+  in [x] if cond?(x).even?
+    x
+  end
+end
+
+def check_unless(v)
+  case v
+  in [_, y] unless cond?(y).even?
+    y
+  end
+end
+
+check_if([1])
+check_unless([:a, 1])
+
+## diagnostics
+
+## assert
+class Object
+  def cond?: (Integer) -> Integer
+  def check_if: ([Integer]) -> Integer
+  def check_unless: ([:a, Integer]) -> Integer
+end