From fb01dd28a5fbabdae6cb5f23c8493db9a377fda3 Mon Sep 17 00:00:00 2001
From: Nathan Zimmerberg <39104088+nhz2@users.noreply.github.com>
Date: Sat, 21 Oct 2023 16:20:35 -0400
Subject: [PATCH] Throw OverflowError on typemin(Int)//(-1) (#51085)

Fixes #32443

Currently `typemin(Int)//(-1) == typemin(Int)//(1)`, ignoring an
overflow.

As noted by @JeffreySarnoff in
[#32443](https://github.com/JuliaLang/julia/issues/32443#issuecomment-506816722)
This should throw an error instead of silently overflowing.

To fix this I am using `checked_neg` instead of `-` in the Rational
constructor.

With this PR `(-one(T))//typemin(T)` will now also throw an
`OverflowError` instead of an `ArgumentError`
---
 base/rational.jl |  6 ++----
 test/rational.jl | 11 ++++++++---
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/base/rational.jl b/base/rational.jl
index cfa1e257bc539..4671478f0b0d3 100644
--- a/base/rational.jl
+++ b/base/rational.jl
@@ -17,12 +17,10 @@ end
 unsafe_rational(num::T, den::T) where {T<:Integer} = unsafe_rational(T, num, den)
 unsafe_rational(num::Integer, den::Integer) = unsafe_rational(promote(num, den)...)
 
-@noinline __throw_rational_argerror_typemin(T) = throw(ArgumentError("invalid rational: denominator can't be typemin($T)"))
 function checked_den(::Type{T}, num::T, den::T) where T<:Integer
     if signbit(den)
-        den = -den
-        signbit(den) && __throw_rational_argerror_typemin(typeof(den))
-        num = -num
+        den = checked_neg(den)
+        num = checked_neg(num)
     end
     return unsafe_rational(T, num, den)
 end
diff --git a/test/rational.jl b/test/rational.jl
index 4b29618bd15e0..9efbc931650c4 100644
--- a/test/rational.jl
+++ b/test/rational.jl
@@ -28,8 +28,8 @@ using Test
     @test (1//typemax(Int)) / (1//typemax(Int)) == 1
     @test_throws OverflowError (1//2)^63
     @test inv((1+typemin(Int))//typemax(Int)) == -1
-    @test_throws ArgumentError inv(typemin(Int)//typemax(Int))
-    @test_throws ArgumentError Rational(0x1, typemin(Int32))
+    @test_throws OverflowError inv(typemin(Int)//typemax(Int))
+    @test_throws OverflowError Rational(0x1, typemin(Int32))
 
     @test @inferred(rationalize(Int, 3.0, 0.0)) === 3//1
     @test @inferred(rationalize(Int, 3.0, 0)) === 3//1
@@ -43,10 +43,15 @@ using Test
     # issue 26823
     @test_throws InexactError rationalize(Int, NaN)
     # issue 32569
-    @test_throws ArgumentError 1 // typemin(Int)
+    @test_throws OverflowError 1 // typemin(Int)
     @test_throws ArgumentError 0 // 0
     @test -2 // typemin(Int) == -1 // (typemin(Int) >> 1)
     @test 2 // typemin(Int) == 1 // (typemin(Int) >> 1)
+    # issue 32443
+    @test Int8(-128)//Int8(1) == -128
+    @test_throws OverflowError Int8(-128)//Int8(-1)
+    @test_throws OverflowError Int8(-1)//Int8(-128)
+    @test Int8(-128)//Int8(-2) == 64
 
     @test_throws InexactError Rational(UInt(1), typemin(Int32))
     @test iszero(Rational{Int}(UInt(0), 1))