From b72a316f30ecb5eef15450dabb94abc928e44d39 Mon Sep 17 00:00:00 2001
From: Neven Sajko <s@purelymail.com>
Date: Tue, 24 Sep 2024 07:39:55 +0200
Subject: [PATCH 1/2] don't mutate globals when constructing Rational from
 AbstractIrrational

Relying on `ScopedValues`, set `BigFloat` precision without mutating
the global default, while constructing `Rational` from
`AbstractIrrational`.

Also helps avoid reading the global defaults for the precision and
rounding mode, together with #56095.
---
 base/irrationals.jl | 37 ++++++++++++++++++++++++++++++-------
 1 file changed, 30 insertions(+), 7 deletions(-)

diff --git a/base/irrationals.jl b/base/irrationals.jl
index 76222997865c0..963b480fbf9af 100644
--- a/base/irrationals.jl
+++ b/base/irrationals.jl
@@ -60,20 +60,43 @@ AbstractFloat(x::AbstractIrrational) = Float64(x)::Float64
 Float16(x::AbstractIrrational) = Float16(Float32(x)::Float32)
 Complex{T}(x::AbstractIrrational) where {T<:Real} = Complex{T}(T(x))
 
-function _irrational_to_rational(::Type{T}, x::AbstractIrrational) where T<:Integer
-    o = precision(BigFloat)
+function _irrational_to_rational_at_current_precision(::Type{T}, x::AbstractIrrational) where {T <: Integer}
+    bx = BigFloat(x)
+    r = rationalize(T, bx, tol = 0)
+    br = BigFloat(r, precision = precision(BigFloat) + 32)
+    if eps(bx) < abs(br - bx)
+        r
+    else
+        nothing  # Error is too small, repeat with greater precision.
+    end
+end
+function _irrational_to_rational_at_precision(::Type{T}, x::AbstractIrrational, p::Int) where {T <: Integer}
+    f = let x = x
+        () -> _irrational_to_rational_at_current_precision(T, x)
+    end
+    setprecision(f, BigFloat, p)
+end
+function _irrational_to_rational_at_current_rounding_mode(::Type{T}, x::AbstractIrrational) where {T <: Integer}
+    if T <: BigInt
+        _throw_argument_error_irrational_to_rational_bigint()  # avoid infinite loop
+    end
     p = 256
     while true
-        setprecision(BigFloat, p)
-        bx = BigFloat(x)
-        r = rationalize(T, bx, tol=0)
-        if abs(BigFloat(r) - bx) > eps(bx)
-            setprecision(BigFloat, o)
+        r = _irrational_to_rational_at_precision(T, x, p)
+        if r isa Number
             return r
         end
         p += 32
     end
 end
+function _irrational_to_rational(
+    ::Type{T}, x::AbstractIrrational,
+) where {T <: Integer}
+    f = let x = x
+        () -> _irrational_to_rational_at_current_rounding_mode(T, x)
+    end
+    setrounding(f, BigFloat, RoundNearest)
+end
 Rational{T}(x::AbstractIrrational) where {T<:Integer} = _irrational_to_rational(T, x)
 _throw_argument_error_irrational_to_rational_bigint() = throw(ArgumentError("Cannot convert an AbstractIrrational to a Rational{BigInt}: use rationalize(BigInt, x) instead"))
 Rational{BigInt}(::AbstractIrrational) = _throw_argument_error_irrational_to_rational_bigint()

From a124648b6e92b325fd8e65e85e5f0cc03f117a70 Mon Sep 17 00:00:00 2001
From: Neven Sajko <s@purelymail.com>
Date: Sat, 23 Nov 2024 09:22:41 +0100
Subject: [PATCH 2/2] less lines

---
 base/irrationals.jl | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/base/irrationals.jl b/base/irrationals.jl
index 963b480fbf9af..fc7d6eca732eb 100644
--- a/base/irrationals.jl
+++ b/base/irrationals.jl
@@ -89,9 +89,7 @@ function _irrational_to_rational_at_current_rounding_mode(::Type{T}, x::Abstract
         p += 32
     end
 end
-function _irrational_to_rational(
-    ::Type{T}, x::AbstractIrrational,
-) where {T <: Integer}
+function _irrational_to_rational(::Type{T}, x::AbstractIrrational) where {T <: Integer}
     f = let x = x
         () -> _irrational_to_rational_at_current_rounding_mode(T, x)
     end