limit TimeType subtraction (#51743)

Disallow some type combinations that don't make sense.

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Co-authored-by: Ben Baumgold <4933671+baumgold@users.noreply.github.com>

stdlib/Dates/src/arithmetic.jl

@@ -6,8 +6,10 @@
 
 # TimeType arithmetic
 (+)(x::TimeType) = x
-(-)(x::T, y::T) where {T<:TimeType} = x.instant - y.instant
-(-)(x::TimeType, y::TimeType) = -(promote(x, y)...)
+(-)(x::Date, y::Date) = x.instant - y.instant
+(-)(x::Time, y::Time) = x.instant - y.instant
+(-)(x::DateTime, y::DateTime) = x.instant - y.instant
+(-)(x::AbstractDateTime, y::AbstractDateTime) = -(promote(x, y)...)
 
 # Date-Time arithmetic
 """

stdlib/Dates/test/arithmetic.jl

@@ -12,9 +12,7 @@ using Dates
 end
 
 @testset "TimeType arithmetic" begin
-    a = Date(2023, 5, 1)
-    b = DateTime(2023, 5, 2)
-    @test b - a == Day(1)
+    @test_throws MethodError DateTime(2023, 5, 2) - Date(2023, 5, 1)
 end
 
 @testset "Wrapping arithmetic for Months" begin