From c8a2e5df156c2af3a36197be804b08ea22174e7e Mon Sep 17 00:00:00 2001
From: Neven Sajko <s@purelymail.com>
Date: Sun, 16 Mar 2025 09:26:34 +0100
Subject: [PATCH] fix special function `::Real` fallback stack overflow

Fixes #57789
---
 base/math.jl | 2 +-
 test/math.jl | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/base/math.jl b/base/math.jl
index 0e5f9dd41bdca..beef8de09bd8b 100644
--- a/base/math.jl
+++ b/base/math.jl
@@ -1542,7 +1542,7 @@ for f in (:sin, :cos, :tan, :asin, :atan, :acos,
           :exponent, :sqrt, :cbrt, :sinpi, :cospi, :sincospi, :tanpi)
     @eval function ($f)(x::Real)
         xf = float(x)
-        x === xf && throw(MethodError($f, (x,)))
+        xf isa typeof(x) && throw(MethodError($f, (x,)))
         return ($f)(xf)
     end
     @eval $(f)(::Missing) = missing
diff --git a/test/math.jl b/test/math.jl
index 8f5ada013557c..75ee928c62e65 100644
--- a/test/math.jl
+++ b/test/math.jl
@@ -1549,6 +1549,14 @@ end
     end
 end
 
+@testset "special function `::Real` fallback shouldn't recur without bound, issue #57789" begin
+    mutable struct Issue57789 <: Real end
+    Base.float(::Issue57789) = Issue57789()
+    for f ∈ (sin, sinpi, log, exp)
+        @test_throws MethodError f(Issue57789())
+    end
+end
+
 # Test that sqrt behaves correctly and doesn't exhibit fp80 double rounding.
 # This happened on old glibc versions.
 # Test case from https://sourceware.org/bugzilla/show_bug.cgi?id=14032.