Enforce @attr uses to always provide a return type (#1782)

src/Attributes.jl

@@ -274,7 +274,7 @@ end
 
 
 """
-    @attr [RetType] funcdef
+    @attr RetType funcdef
 
 This macro is applied to the definition of a unary function, and enables
 caching ("memoization") of its return values based on the argument. This
@@ -323,22 +323,11 @@ julia> myattr(obj) # second time uses the cached result
 
 ```
 """
-macro attr(ex1, exs...)
-   if length(exs) == 0
-      rettype = Any
-      expr = ex1
-   elseif length(exs) == 1
-      rettype = ex1
-      expr = exs[1]
-   else
-      throw(ArgumentError("too many macro arguments"))
-   end
+macro attr(rettype, expr::Expr)
    d = MacroTools.splitdef(expr)
    length(d[:args]) == 1 || throw(ArgumentError("Only unary functions are supported"))
    length(d[:kwargs]) == 0 || throw(ArgumentError("Keyword arguments are not supported"))
 
-# TODO: handle optional ::RetType
-
    # store the original function name
    name = d[:name]
 

src/Deprecations.jl

@@ -57,6 +57,7 @@ import .Generic: set_exponent_vector!; @deprecate set_exponent_vector!(a::Generi
 import .Generic: is_gen; @deprecate is_gen(x::Generic.MPoly{T}, ::Type{Val{ord}}) where {T <: RingElement, ord} is_gen(x, Val(ord))
 import .Generic: degree; @deprecate degree(f::Generic.MPoly{T}, i::Int, ::Type{Val{ord}}) where {T <: RingElement, ord} degree(f, i, Val(ord))
 
-# deprecated during 0.42.*
+# will become deprecated in 0.43.0
 change_base_ring(p::MPolyRingElem{T}, g, new_polynomial_ring) where {T<:RingElement} = map_coefficients(g, p, parent = new_polynomial_ring)
 mulmod(a::S, b::S, mod::Vector{S}) where {S <: MPolyRingElem} = Base.divrem(a * b, mod)[2]
+var"@attr"(__source__::LineNumberNode, __module__::Base.Module, expr::Expr) = var"@attr"(__source__, __module__, :Any, expr) # delegate `@attr functionexpression` to `@attr Any functionexpression` (macros are just functions with this weird extra syntax)

test/Attributes-test.jl

@@ -178,8 +178,8 @@ A cached attribute.
 """
 @attr Tuple{T,DataType,Vector{Any}} cached_attr(obj::T) where T = (obj,T,[])
 
-# cached attribute without return type specification
-@attr cached_attr2(obj::T) where T = (obj,T,[])
+# cached attribute with bad return type specification
+@attr Any cached_attr2(obj::T) where T = (obj,T,[])
 
 # cached attribute with return type specification depending on the input type
 my_derived_type(::Type{Tmp.Container{T}}) where T = T
@@ -201,7 +201,7 @@ my_derived_type(::Type{Tmp.Container{T}}) where T = T
     @test cached_attr(x) == y
     @test cached_attr(x) === y
 
-    # check cached without type specification is not inferring return types correctly
+    # check cached with bad type specification is not inferring return types correctly
     @test_throws ErrorException @inferred cached_attr2(x)
 
     # check when return type is derived via a function from input type
@@ -225,16 +225,16 @@ my_derived_type(::Type{Tmp.Container{T}}) where T = T
     @test functionloc(uncached_attr)[2] < functionloc(cached_attr)[2]
 end
 
-if VERSION >= v"1.7"
+@static if VERSION >= v"1.7"
     # the following tests need the improved `@macroexpand` from Julia 1.7
     @testset "@attr error handling" begin
         # wrong number of arguments
         @test_throws ArgumentError @macroexpand @attr foo() = 1
         @test_throws ArgumentError @macroexpand @attr foo(x::Int, y::Int) = 1
         @test_throws ArgumentError @macroexpand @attr Int foo() = 1
         @test_throws ArgumentError @macroexpand @attr Int foo(x::Int, y::Int) = 1
-        @test_throws ArgumentError @macroexpand @attr Int foo(x::Int) = 1 Any
-        @test_throws ArgumentError @macroexpand @attr Int Int Int
+        @test_throws MethodError @macroexpand @attr Int foo(x::Int) = 1 Any
+        @test_throws MethodError @macroexpand @attr Int Int Int
 
         # wrong kind of arguments
         #@test_throws ArgumentError @macroexpand @attr Int Int