Allow user to set the crate path of num_enum (#77)

Add a `#[num_enum(crate = ..)]` attribute, which lets the user set where
the num_enum crate is located.

Author: yshui

num_enum/tests/try_build/compile_fail/custom_error_type_parsing.stderr

@@ -22,8 +22,8 @@ error: num_enum attribute must have at most one error_type
 29 | #[num_enum(error_type(name = CustomError, constructor = CustomError::new), error_type(name = CustomError, constructor = CustomError::new))]
    |                                                                            ^^^^^^^^^^
 
-error: At most one num_enum error_type attribute may be specified
-  --> tests/try_build/compile_fail/custom_error_type_parsing.rs:39:1
+error: num_enum attribute must have at most one error_type
+  --> tests/try_build/compile_fail/custom_error_type_parsing.rs:39:12
    |
 39 | #[num_enum(error_type(name = CustomError, constructor = CustomError::new))]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |            ^^^^^^^^^^

num_enum/tests/try_build/compile_fail/variants_with_fields.stderr

@@ -1,16 +1,16 @@
-error: `num_enum` only supports unit variants (with no associated data), but `Number::NonZero` was not a unit variant.
+error: `::num_enum` only supports unit variants (with no associated data), but `Number::NonZero` was not a unit variant.
  --> $DIR/variants_with_fields.rs:7:5
   |
 7 |     NonZero(u8),
   |     ^^^^^^^^^^^
 
-error: `num_enum` only supports unit variants (with no associated data), but `Colour::Red` was not a unit variant.
+error: `::num_enum` only supports unit variants (with no associated data), but `Colour::Red` was not a unit variant.
   --> $DIR/variants_with_fields.rs:13:5
    |
 13 |     Red { intensity: u8 },
    |     ^^^^^^^^^^^^^^^^^^^^^
 
-error: `num_enum` only supports unit variants (with no associated data), but `Meaningless::Beep` was not a unit variant.
+error: `::num_enum` only supports unit variants (with no associated data), but `Meaningless::Beep` was not a unit variant.
   --> $DIR/variants_with_fields.rs:19:5
    |
 19 |     Beep(),

num_enum_derive/Cargo.toml

@@ -35,7 +35,7 @@ features = ["external_doc"]
 proc-macro2 = "1.0.60"
 proc-macro-crate = { version = ">= 1, <= 3", optional = true }
 quote = "1"
-syn = { version = "2", features = ["parsing"] }
+syn = { version = "2", features = ["derive", "extra-traits", "parsing"] }
 
 [dev-dependencies]
 syn = { version = "2", features = ["extra-traits", "parsing"] }

num_enum_derive/src/enum_attributes.rs

@@ -13,20 +13,50 @@ mod kw {
 
 // Example: error_type(name = Foo, constructor = Foo::new)
 #[cfg_attr(test, derive(Debug))]
+#[derive(Default)]
 pub(crate) struct Attributes {
     pub(crate) error_type: Option<ErrorTypeAttribute>,
+    pub(crate) crate_path: Option<CrateAttribute>,
 }
 
 // Example: error_type(name = Foo, constructor = Foo::new)
 #[cfg_attr(test, derive(Debug))]
 pub(crate) enum AttributeItem {
     ErrorType(ErrorTypeAttribute),
+    CratePath(CrateAttribute),
+}
+
+impl Attributes {
+    pub(crate) fn exclusive_union(&mut self, other: Self) -> Result<()> {
+        if self.crate_path.is_some() {
+            if let Some(other) = &other.crate_path {
+                return Err(Error::new(
+                    other.span,
+                    "num_enum attribute must have at most one crate",
+                ));
+            }
+        } else {
+            self.crate_path = other.crate_path;
+        }
+        if self.error_type.is_some() {
+            if let Some(other) = &other.error_type {
+                return Err(Error::new(
+                    other.span,
+                    "num_enum attribute must have at most one error_type",
+                ));
+            }
+        } else {
+            self.error_type = other.error_type;
+        }
+        Ok(())
+    }
 }
 
 impl Parse for Attributes {
     fn parse(input: ParseStream<'_>) -> Result<Self> {
         let attribute_items = input.parse_terminated(AttributeItem::parse, syn::Token![,])?;
         let mut maybe_error_type = None;
+        let mut maybe_krate_path = None;
         for attribute_item in &attribute_items {
             match attribute_item {
                 AttributeItem::ErrorType(error_type) => {
@@ -38,10 +68,20 @@ impl Parse for Attributes {
                     }
                     maybe_error_type = Some(error_type.clone());
                 }
+                AttributeItem::CratePath(krate_path) => {
+                    if maybe_krate_path.is_some() {
+                        return Err(Error::new(
+                            krate_path.span,
+                            "num_enum attribute must have at most one crate",
+                        ));
+                    }
+                    maybe_krate_path = Some(krate_path.clone());
+                }
             }
         }
         Ok(Self {
             error_type: maybe_error_type,
+            crate_path: maybe_krate_path,
         })
     }
 }
@@ -51,6 +91,8 @@ impl Parse for AttributeItem {
         let lookahead = input.lookahead1();
         if lookahead.peek(kw::error_type) {
             input.parse().map(Self::ErrorType)
+        } else if lookahead.peek(syn::token::Crate) {
+            input.parse().map(Self::CratePath)
         } else {
             Err(lookahead.error())
         }
@@ -168,6 +210,24 @@ impl Parse for ErrorTypeConstructorAttribute {
     }
 }
 
+#[derive(Clone)]
+#[cfg_attr(test, derive(Debug))]
+pub(crate) struct CrateAttribute {
+    pub(crate) path: syn::Path,
+
+    span: Span,
+}
+
+impl Parse for CrateAttribute {
+    fn parse(input: ParseStream) -> Result<Self> {
+        let span = input.span();
+        let _: syn::token::Crate = input.parse()?;
+        let _: syn::token::Eq = input.parse()?;
+        let path = syn::Path::parse_mod_style(input)?;
+        Ok(Self { path, span })
+    }
+}
+
 #[cfg(test)]
 mod test {
     use crate::enum_attributes::Attributes;
@@ -178,11 +238,15 @@ mod test {
     fn parse_num_enum_attr() {
         let expected_name: Path = parse_quote! { Foo };
         let expected_constructor: Path = parse_quote! { ::foo::Foo::<u8>::new };
+        let expected_krate: Path = parse_quote! { ::num_enum };
 
-        let attributes: Attributes =
-            syn::parse_str("error_type(name = Foo, constructor = ::foo::Foo::<u8>::new)").unwrap();
+        let attributes: Attributes = syn::parse_str(
+            "error_type(name = Foo, constructor = ::foo::Foo::<u8>::new), crate = ::num_enum",
+        )
+        .unwrap();
         assert!(attributes.error_type.is_some());
         let error_type = attributes.error_type.unwrap();
+        let krate_path = attributes.crate_path.unwrap();
         assert_eq!(
             error_type.name.path.to_token_stream().to_string(),
             expected_name.to_token_stream().to_string()
@@ -191,6 +255,10 @@ mod test {
             error_type.constructor.path.to_token_stream().to_string(),
             expected_constructor.to_token_stream().to_string()
         );
+        assert_eq!(
+            krate_path.path.to_token_stream().to_string(),
+            expected_krate.to_token_stream().to_string()
+        );
     }
 
     #[test]

num_enum_derive/src/lib.rs

@@ -10,7 +10,7 @@ use syn::{parse_macro_input, Expr, Ident};
 
 mod enum_attributes;
 mod parsing;
-use parsing::{get_crate_name, EnumInfo};
+use parsing::{get_crate_path, EnumInfo};
 mod utils;
 mod variant_attributes;
 
@@ -90,7 +90,7 @@ pub fn derive_into_primitive(input: TokenStream) -> TokenStream {
 #[proc_macro_derive(FromPrimitive, attributes(num_enum, default, catch_all))]
 pub fn derive_from_primitive(input: TokenStream) -> TokenStream {
     let enum_info: EnumInfo = parse_macro_input!(input);
-    let krate = Ident::new(&get_crate_name(), Span::call_site());
+    let krate = get_crate_path(enum_info.crate_path.clone());
 
     let is_naturally_exhaustive = enum_info.is_naturally_exhaustive();
     let catch_all_body = match is_naturally_exhaustive {
@@ -124,7 +124,7 @@ pub fn derive_from_primitive(input: TokenStream) -> TokenStream {
     debug_assert_eq!(variant_idents.len(), variant_expressions.len());
 
     TokenStream::from(quote! {
-        impl ::#krate::FromPrimitive for #name {
+        impl #krate::FromPrimitive for #name {
             type Primitive = #repr;
 
             fn from_primitive(number: Self::Primitive) -> Self {
@@ -153,12 +153,12 @@ pub fn derive_from_primitive(input: TokenStream) -> TokenStream {
             fn from (
                 number: #repr,
             ) -> Self {
-                ::#krate::FromPrimitive::from_primitive(number)
+                #krate::FromPrimitive::from_primitive(number)
             }
         }
 
         #[doc(hidden)]
-        impl ::#krate::CannotDeriveBothFromPrimitiveAndTryFromPrimitive for #name {}
+        impl #krate::CannotDeriveBothFromPrimitiveAndTryFromPrimitive for #name {}
     })
 }
 
@@ -190,8 +190,7 @@ pub fn derive_from_primitive(input: TokenStream) -> TokenStream {
 #[proc_macro_derive(TryFromPrimitive, attributes(num_enum))]
 pub fn derive_try_from_primitive(input: TokenStream) -> TokenStream {
     let enum_info: EnumInfo = parse_macro_input!(input);
-    let krate = Ident::new(&get_crate_name(), Span::call_site());
-
+    let krate = get_crate_path(enum_info.crate_path.clone());
     let EnumInfo {
         ref name,
         ref repr,
@@ -209,7 +208,7 @@ pub fn derive_try_from_primitive(input: TokenStream) -> TokenStream {
     let error_constructor = &error_type_info.constructor;
 
     TokenStream::from(quote! {
-        impl ::#krate::TryFromPrimitive for #name {
+        impl #krate::TryFromPrimitive for #name {
             type Primitive = #repr;
             type Error = #error_type;
 
@@ -251,12 +250,12 @@ pub fn derive_try_from_primitive(input: TokenStream) -> TokenStream {
                 number: #repr,
             ) -> ::core::result::Result<Self, #error_type>
             {
-                ::#krate::TryFromPrimitive::try_from_primitive(number)
+                #krate::TryFromPrimitive::try_from_primitive(number)
             }
         }
 
         #[doc(hidden)]
-        impl ::#krate::CannotDeriveBothFromPrimitiveAndTryFromPrimitive for #name {}
+        impl #krate::CannotDeriveBothFromPrimitiveAndTryFromPrimitive for #name {}
     })
 }
 
@@ -302,14 +301,14 @@ pub fn derive_try_from_primitive(input: TokenStream) -> TokenStream {
 #[proc_macro_derive(UnsafeFromPrimitive, attributes(num_enum))]
 pub fn derive_unsafe_from_primitive(stream: TokenStream) -> TokenStream {
     let enum_info = parse_macro_input!(stream as EnumInfo);
-    let krate = Ident::new(&get_crate_name(), Span::call_site());
+    let krate = get_crate_path(enum_info.crate_path);
 
     let EnumInfo {
         ref name, ref repr, ..
     } = enum_info;
 
     TokenStream::from(quote! {
-        impl ::#krate::UnsafeFromPrimitive for #name {
+        impl #krate::UnsafeFromPrimitive for #name {
             type Primitive = #repr;
 
             unsafe fn unchecked_transmute_from(number: Self::Primitive) -> Self {