Introduce method to convert to Time from TimeType

This is to satisfy the expectation
that `Time(t::Time) == t`, similar to
other subtypes of TimeType and Period.

This also resolves issues ranges of Time,
such as given by `range(Time(0), step=Hour(1), length=24)`.

Author: mtd321

stdlib/Dates/src/conversions.jl

@@ -25,7 +25,7 @@ DateTime(dt::TimeType) = convert(DateTime, dt)
 Convert a `DateTime` to a `Time`. The hour, minute, second, and millisecond parts of
 the `DateTime` are used to create the new `Time`. Microsecond and nanoseconds are zero by default.
 """
-Time(dt::DateTime) = convert(Time, dt)
+Time(dt::TimeType) = convert(Time, dt)
 
 Base.convert(::Type{DateTime}, dt::Date) = DateTime(UTM(value(dt) * 86400000))
 Base.convert(::Type{Date}, dt::DateTime) = Date(UTD(days(dt)))

stdlib/Dates/test/conversions.jl

@@ -129,4 +129,18 @@ end
     @test Dates.nanosecond(t) == 0
 end
 
+@testset "idempotency of conversion for TimeType subtypes" begin
+    for T in [DateTime, Date, Time]
+        @test T(T(0)) == T(0)
+    end
+end
+
+@testset "idempotency of conversion for Period subtypes" begin
+    for T in [Nanosecond, Millisecond,
+              Second, Minute, Hour,
+              Day, Week, Month, Quarter, Year]
+        @test T(T(0)) == T(0)
+    end
+end
+
 end

stdlib/Dates/test/ranges.jl

@@ -539,6 +539,8 @@ dr  = Dates.Time(23, 1, 1):Dates.Second(1):Dates.Time(23, 2, 1)
 dr1 = Dates.Time(23, 1, 1):Dates.Second(1):Dates.Time(23, 1, 1)
 dr2 = Dates.Time(23, 1, 1):Dates.Second(1):Dates.Time(22, 2, 1) # empty range
 dr3 = Dates.Time(23, 1, 1):Dates.Minute(-1):Dates.Time(22, 1, 1) # negative step
+dr4 = range(Dates.Time(0), step=Dates.Hour(1), length=23) # by step, length
+
 # Big ranges
 dr8 = typemin(Dates.Time):Dates.Second(1):typemax(Dates.Time)
 dr9 = typemin(Dates.Time):Dates.Nanosecond(1):typemax(Dates.Time)
@@ -555,7 +557,7 @@ dr18 = typemax(Dates.Time):Dates.Minute(-100):typemin(Dates.Time)
 dr19 = typemax(Dates.Time):Dates.Hour(-10):typemin(Dates.Time)
 dr20 = typemin(Dates.Time):Dates.Microsecond(2):typemax(Dates.Time)
 
-drs = Any[dr, dr1, dr2, dr3, dr8, dr9, dr10,
+drs = Any[dr, dr1, dr2, dr3, dr4, dr8, dr9, dr10,
           dr11, dr12, dr13, dr14, dr15, dr16, dr17, dr18, dr19, dr20]
 
 @test map(length, drs) == map(x->size(x)[1], drs)