Make deepcopy_internal inferrable for BigInt and BigFloat (#54496)

Co-authored-by: Lilith Orion Hafner <[email protected]>

Author: lgoettgens

base/gmp.jl

@@ -832,7 +832,7 @@ Base.add_with_overflow(a::BigInt, b::BigInt) = a + b, false
 Base.sub_with_overflow(a::BigInt, b::BigInt) = a - b, false
 Base.mul_with_overflow(a::BigInt, b::BigInt) = a * b, false
 
-Base.deepcopy_internal(x::BigInt, stackdict::IdDict) = get!(() -> MPZ.set(x), stackdict, x)
+Base.deepcopy_internal(x::BigInt, stackdict::IdDict) = get!(() -> MPZ.set(x), stackdict, x)::BigInt
 
 ## streamlined hashing for BigInt, by avoiding allocation from shifts ##
 

base/mpfr.jl

@@ -1199,7 +1199,7 @@ function Base.deepcopy_internal(x::BigFloat, stackdict::IdDict)
         y = _BigFloat(x.prec, x.sign, x.exp, d′)
         #ccall((:mpfr_custom_move,libmpfr), Cvoid, (Ref{BigFloat}, Ptr{Limb}), y, d) # unnecessary
         return y
-    end
+    end::BigFloat
 end
 
 function decompose(x::BigFloat)::Tuple{BigInt, Int, Int}

test/copy.jl

@@ -248,6 +248,11 @@ end
     @test (@inferred Base.deepcopy_internal(zeros(), IdDict())) == zeros()
 end
 
+@testset "deepcopy_internal big" begin
+    @inferred Base.deepcopy_internal(big(1), IdDict())
+    @inferred Base.deepcopy_internal(big(1.0), IdDict())
+end
+
 @testset "`copyto!`'s unaliasing" begin
     a = view([1:3;], :)
     @test copyto!(a, 2, a, 1, 2) == [1;1:2;]