support comparison with zero

Author: aplavin

src/quantities.jl

@@ -274,6 +274,15 @@ for (i,j) in zip((:<, :isless), (:_lt, :_isless))
     @eval @inline ($j)(x::AbstractQuantity{T,D,U}, y::AbstractQuantity{T,D,U}) where {T,D,U} = ($i)(x.val,y.val)
     @eval @inline ($j)(x::AbstractQuantity{T,D,U1}, y::AbstractQuantity{T,D,U2}) where {T,D,U1,U2} = ($i)(promote(x,y)...)
     @eval @inline ($j)(x::AbstractQuantity{T,D1,U1}, y::AbstractQuantity{T,D2,U2}) where {T,D1,D2,U1,U2} = throw(DimensionError(x,y))
+
+    @eval @inline ($j)(x::DimensionlessQuantity{T,FreeUnits{(),NoDims,nothing}}, y::ScalarQuantity{T,D,U}) where {T,D,U} =
+        iszero(x) && !(y isa AffineQuantity) ?
+            ($i)(x.val,y.val) :
+            throw(DimensionError(x,y))
+    @eval @inline ($j)(x::ScalarQuantity{T,D,U}, y::DimensionlessQuantity{T,FreeUnits{(),NoDims,nothing}}) where {T,D,U} =
+        iszero(y) && !(x isa AffineQuantity) ?
+            ($i)(x.val,y.val) :
+            throw(DimensionError(x,y))
 end
 
 Base.rtoldefault(::Type{<:AbstractQuantity{T,D,U}}) where {T,D,U} = Base.rtoldefault(T)

test/runtests.jl

@@ -565,10 +565,13 @@ Base.:*(x::MatNum, y::MatNum) = MatNum(x.mat*y.mat)
         @test @inferred(1 > 1μm/m)
         @test @inferred(1μm/m < 1mm/m)
         @test @inferred(1mm/m > 1μm/m)
+        @test @inferred(0 < 2m)
+        @test !@inferred(2mm < 0)
         @test_throws DimensionError 1m < 1kg
         @test_throws DimensionError 1m < 1
         @test_throws DimensionError 1 < 1m
         @test_throws DimensionError 1mm/m < 1m
+        @test_throws DimensionError 0 < 100°C
         @test Base.rtoldefault(typeof(1.0u"m")) === Base.rtoldefault(typeof(1.0))
         @test Base.rtoldefault(typeof(1u"m")) === Base.rtoldefault(Int)
     end