Add descriptive error to name collision

Project.toml

@@ -1,7 +1,7 @@
 name = "IrrationalConstants"
 uuid = "92d709cd-6900-40b7-9082-c6be49f344b6"
 authors = ["JuliaMath"]
-version = "0.2.5"
+version = "0.2.6"
 
 [compat]
 julia = "1.10"

src/macro.jl

@@ -47,6 +47,9 @@ julia> IrrationalConstants.@irrational twoπ 2*big(π)
 julia> twoπ
 twoπ = 6.2831853071795...
 
+julia> typeof(twoπ)
+Twoπ
+
 julia> IrrationalConstants.@irrational sqrt2 1.4142135623730950488 √big(2)
 
 julia> sqrt2
@@ -65,12 +68,18 @@ ERROR: AssertionError: Float64($(Expr(:escape, :sqrt5))) == Float64(big($(Expr(:
 ```
 """
 macro irrational(sym::Symbol, val::Float64, def::Union{Symbol,Expr}, T::Symbol=Symbol(uppercasefirst(string(sym))))
-    irrational(sym, val, def, T)
+    irrational(__module__, sym, val, def, T)
 end
 macro irrational(sym::Symbol, def::Union{Symbol,Expr}, T::Symbol=Symbol(uppercasefirst(string(sym))))
-    irrational(sym, :(big($(esc(sym)))), def, T)
+    irrational(__module__, sym, :(big($(esc(sym)))), def, T)
 end
-function irrational(sym::Symbol, val::Union{Float64,Expr}, def::Union{Symbol,Expr}, T::Symbol)
+function irrational(mod::Module, sym::Symbol, val::Union{Float64,Expr}, def::Union{Symbol,Expr}, T::Symbol)
+    if isdefined(mod, T)
+        throw(ArgumentError(LazyString("Type `", T, "` of irrational constant `", sym, "` is already defined in module `", mod, "`.")))
+    end
+    if sym == T
+        throw(ArgumentError(LazyString("The name of the irrational constant (", sym, ") and its type (", T, ") cannot be the same. Please choose a different name for the constant or specify a different type name as the last argument to the macro.")))
+    end
     esym = esc(sym)
     qsym = esc(Expr(:quote, sym))
     eT = esc(T)

test/runtests.jl

@@ -257,3 +257,27 @@ end
 @testset "slow comparisons" begin
     @test iszero(@allocated(3.0 <= invsqrt2))
 end
+
+# issues #43
+@testset "macro error" begin
+    msg = "The name of the irrational constant (Myπ) and its type (Myπ) cannot be the same. Please choose a different name for the constant or specify a different type name as the last argument to the macro."
+    @test_throws ArgumentError(msg) @macroexpand(IrrationalConstants.@irrational Myπ big(π))
+    @test_throws ArgumentError(msg) @macroexpand(IrrationalConstants.@irrational Myπ 1.0 big(π))
+    @test_throws ArgumentError(msg) @macroexpand(IrrationalConstants.@irrational Myπ big(π) Myπ)
+    @test_throws ArgumentError(msg) @macroexpand(IrrationalConstants.@irrational Myπ 1.0 big(π) Myπ)
+end
+
+# test that defining a type that already exists throws an error
+module TestTypeCollision
+    using IrrationalConstants
+    using Test
+    struct MyExistingType end
+
+    @testset "type collision" begin
+        msg1 = "Type `MyExistingType` of irrational constant `myExistingType` is already defined in module `Main.TestTypeCollision`."
+        @test_throws ArgumentError(msg1) @macroexpand(IrrationalConstants.@irrational myExistingType big(π))
+        msg2 = "Type `MyExistingType` of irrational constant `myconst` is already defined in module `Main.TestTypeCollision`."
+        @test_throws ArgumentError(msg2) @macroexpand(IrrationalConstants.@irrational myconst big(π) MyExistingType)
+        @test_throws ArgumentError(msg2) @macroexpand(IrrationalConstants.@irrational myconst 1.0 big(π) MyExistingType)
+    end
+end