Show Complex imag components directly (#53529)

Fixes #52100. 

This avoids doing math on the imaginary component — and instead just
asks if their string representation starts with a `-` to determine
whether the operator between the components should be `+` or `-`.

---------

Co-authored-by: Jameson Nash <[email protected]>
Co-authored-by: Dilum Aluthge <[email protected]>

Author: 3 people

base/complex.jl

@@ -195,16 +195,16 @@ function show(io::IO, z::Complex)
     r, i = reim(z)
     compact = get(io, :compact, false)::Bool
     show(io, r)
-    if signbit(i) && !isnan(i)
+    bufio = IOBuffer()
+    show(IOContext(bufio, io), i)
+    seekstart(bufio)
+    if peek(bufio) === UInt8('-')
+        seek(bufio, 1)
         print(io, compact ? "-" : " - ")
-        if isa(i,Signed) && !isa(i,BigInt) && i == typemin(typeof(i))
-            show(io, -widen(i))
-        else
-            show(io, -i)
-        end
+        write(io, bufio)
     else
         print(io, compact ? "+" : " + ")
-        show(io, i)
+        write(io, bufio)
     end
     if !(isa(i,Signed) || isa(i,AbstractFloat) && isfinite(i))
         print(io, "*")

test/complex.jl

@@ -24,6 +24,18 @@ for T in (Int64, Float64)
     @test complex(Complex{T}) == Complex{T}
 end
 
+@testset "show for complex" begin
+    @test sprint(show, complex(1, 0), context=:compact => true) == "1+0im"
+    @test sprint(show, complex(true, true)) == "Complex(true,true)"
+    @test sprint(show, Complex{Int8}(0, typemin(Int8))) == "0 - 128im"
+
+    @test sprint(show, prevfloat(BigFloat(-1, precision=32))im) == "-0.0 - 1.0000000005im"
+    @test sprint(show, prevfloat(BigFloat(-1, precision=512))im) == "-0.0 - 1.00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000015im"
+
+    @test sprint(show, prevfloat(BigFloat(-1, precision=32))im, context=:compact => true) == "-0.0-1.0im"
+    @test sprint(show, prevfloat(BigFloat(-1, precision=512))im, context=:compact => true) == "-0.0-1.0im"
+end
+
 @testset "show" begin
     @test sprint(show, complex(1, 0), context=:compact => true) == "1+0im"
     @test sprint(show, complex(true, true)) == "Complex(true,true)"
@@ -39,7 +51,6 @@ end
     @test sprint(show, complex(0, -Inf)) == "0.0 - Inf*im"
 end
 
-
 @testset "unary operator on complex boolean" begin
     @test +Complex(true, true) === Complex(1, 1)
     @test +Complex(true, false) === Complex(1, 0)