Fix sprint

Author: ScottPJones

src/io.jl

@@ -213,16 +213,15 @@ print(io::IO, str::MaybeSub{<:Str{<:CSE}}) = (_write(UTF8CSE, io, str) ; nothing
 print(io::IO, str::MaybeSub{T}) where {T<:Str{<:Union{Binary_CSEs,ASCIICSE,UTF8_CSEs}}} =
     (_fastwrite(io, str); nothing)
 
-function Base.sprint(f::Function, ::Type{T}, args...;
-                context=nothing, sizehint::Integer=0) where {T<:Union{String, Str}}
+function Base.sprint(f::Function, ::T, args...; context=nothing, sizehint::Integer=0
+                     ) where {C<:Union{Binary_CSEs,ASCIICSE,UTF8_CSEs},T<:Str{C}}
     s = IOBuffer(sizehint=sizehint)
-    if context !== nothing
-        f(IOContext(s, context), args...)
-        S = get(context, :type, T)
-        S(resize!(s.data, s.size))
+    if context != nothing
+        f(context isa Tuple ? IOContext(s, context...) : IOContext(s, context), args...)
+        Str(get(s.dict, :type, C), resize!(s.data, s.size))
     else
         f(s, args...)
-        T(resize!(s.data, s.size))
+        String(_unsafe_take!(s))
     end
 end
 

test/basic.jl

@@ -962,7 +962,7 @@ end
     @test Meta.lower(Main, sym) === sym
     res = string(Meta.parse(string(Char(0xdcdb)," = 1"),1,raise=false)[1])
     @static if VERSION ≥ v"1.5.0-DEV.460"
-        @test res == "\$(Expr(:error, \"invalid UTF-8 sequence\"))"
+        @test contains(res, "invalid UTF-8 sequence")
     else
         @test startswith(res, "\$(Expr(:error, \"invalid character \\\"\\udcdb\\\"")
         @test endswith(res,   "\"))")