Make precision a keyword argument, improve handling of rounding mode. (…

…#29157)

* Improve handling of precision and rounding mode arguments in BigFloat constructors.

This makes a few changes to avoid unnecessarily calling `setrounding` and `setprecision`. It also changes `precision` to be a keyword argument (though does not yet deprecate the old behaviour).

NEWS.md

@@ -11,7 +11,9 @@ Language changes
 ----------------
 
   * the constructor `BigFloat(::BigFloat)` now respects the global precision setting and always
-    returns a `BigFloat` with precision equal to `precision(BigFloat)` ([#29127]).
+    returns a `BigFloat` with precision equal to `precision(BigFloat)` ([#29127]). The optional
+    `precision` argument to override the global setting is now a keyword instead of positional
+    argument ([#29157]).
   * Parser inputs ending with a comma are now consistently treated as incomplete.
     Previously they were sometimes parsed as tuples, depending on whitespace ([#28506]).
   * `Regex` now behave like a scalar when used in broadcasting ([#29913]).

base/deprecated.jl

@@ -168,4 +168,9 @@ function promote_eltype_op end
 one(::CartesianIndex{N}) where {N} = one(CartesianIndex{N})
 one(::Type{CartesianIndex{N}}) where {N} = CartesianIndex(ntuple(x -> 1, Val(N)))
 
+MPFR.BigFloat(x, prec::Int) = BigFloat(x; precision=prec)
+MPFR.BigFloat(x, prec::Int, rounding::RoundingMode) = BigFloat(x, rounding; precision=prec)
+MPFR.BigFloat(x::Real, prec::Int) = BigFloat(x; precision=prec)
+MPFR.BigFloat(x::Real, prec::Int, rounding::RoundingMode) = BigFloat(x, rounding; precision=prec)
+
 # END 1.0 deprecations

base/irrationals.jl

@@ -147,14 +147,18 @@ macro irrational(sym, val, def)
     esym = esc(sym)
     qsym = esc(Expr(:quote, sym))
     bigconvert = isa(def,Symbol) ? quote
-        function Base.BigFloat(::Irrational{$qsym})
-            c = BigFloat()
+        function Base.BigFloat(::Irrational{$qsym}, r::MPFR.MPFRRoundingMode=MPFR.ROUNDING_MODE[]; precision=precision(BigFloat))
+            c = BigFloat(;precision=precision)
             ccall(($(string("mpfr_const_", def)), :libmpfr),
-                  Cint, (Ref{BigFloat}, Int32), c, MPFR.ROUNDING_MODE[])
+                  Cint, (Ref{BigFloat}, MPFR.MPFRRoundingMode), c, r)
             return c
         end
     end : quote
-        Base.BigFloat(::Irrational{$qsym}) = $(esc(def))
+        function Base.BigFloat(::Irrational{$qsym}; precision=precision(BigFloat))
+            setprecision(BigFloat, precision) do
+                $(esc(def))
+            end
+        end
     end
     quote
         const $esym = Irrational{$qsym}()