feat(ast_tools): allow attrs on types which do not derive the trait (#…

…8874)

Generally, custom attributes relating to a trait e.g. `CloneIn` / `#[clone_in]` are only legal if the trait is derived on the type. Allow a `Derive` to choose to relax this restriction. This is necessary for #8875, #8876, and #8877.

tasks/ast_tools/src/parse/attr.rs

@@ -30,16 +30,25 @@ bitflags! {
     /// Positions in which an attribute is legal.
     #[derive(Debug, Clone, Copy, PartialEq, Eq)]
     pub struct AttrPositions: u8 {
-        /// Attribute on a struct
+        /// Attribute on a struct which derives the trait
         const Struct = 1 << 0;
-        /// Attribute on an enum
-        const Enum = 1 << 1;
+        /// Attribute on a struct which doesn't derive the trait
+        const StructNotDerived = 1 << 1;
+        /// Attribute on an enum which derives the trait
+        const Enum = 1 << 2;
+        /// Attribute on an enum which doesn't derive the trait
+        const EnumNotDerived = 1 << 3;
         /// Attribute on a struct field
-        const StructField = 1 << 2;
+        const StructField = 1 << 4;
         /// Attribute on an enum variant
-        const EnumVariant = 1 << 3;
+        const EnumVariant = 1 << 5;
         /// Part of `#[ast]` attr e.g. `visit` in `#[ast(visit)]`
-        const AstAttr = 1 << 4;
+        const AstAttr = 1 << 6;
+
+        /// Attribute on a struct which may or may not derive the trait
+        const StructMaybeDerived = Self::Struct.bits() | Self::StructNotDerived.bits();
+        /// Attribute on an enum which may or may not derive the trait
+        const EnumMaybeDerived = Self::Enum.bits() | Self::EnumNotDerived.bits();
     }
 }
 

tasks/ast_tools/src/parse/parse.rs

@@ -503,42 +503,59 @@ impl<'c> Parser<'c> {
             }
 
             if let Some((processor, positions)) = self.codegen.attr_processor(&attr_name) {
-                // Check attribute is legal in this position
-                match type_def {
+                // Check attribute is legal in this position and this type has the relevant trait
+                // `#[generate_derive]`-ed on it (unless the derive stated legal positions as
+                // `AttrPositions::StructNotDerived` or `AttrPositions::EnumNotDerived`)
+                let location = match type_def {
                     TypeDef::Struct(struct_def) => {
+                        let found_in_positions = match processor {
+                            AttrProcessor::Derive(derive_id) => {
+                                let is_derived = struct_def.generates_derive(derive_id);
+                                if is_derived {
+                                    AttrPositions::Struct
+                                } else {
+                                    AttrPositions::StructNotDerived
+                                }
+                            }
+                            AttrProcessor::Generator(_) => AttrPositions::StructMaybeDerived,
+                        };
+
                         check_attr_position(
                             positions,
-                            AttrPositions::Struct,
+                            found_in_positions,
                             struct_def.name(),
                             &attr_name,
                             "struct",
                         );
+
+                        AttrLocation::Struct(struct_def)
                     }
                     TypeDef::Enum(enum_def) => {
+                        let found_in_positions = match processor {
+                            AttrProcessor::Derive(derive_id) => {
+                                let is_derived = enum_def.generates_derive(derive_id);
+                                if is_derived {
+                                    AttrPositions::Enum
+                                } else {
+                                    AttrPositions::EnumNotDerived
+                                }
+                            }
+                            AttrProcessor::Generator(_) => AttrPositions::EnumMaybeDerived,
+                        };
+
                         check_attr_position(
                             positions,
-                            AttrPositions::Enum,
+                            found_in_positions,
                             enum_def.name(),
                             &attr_name,
                             "enum",
                         );
-                    }
-                    _ => unreachable!(),
-                }
-
-                // Check this type has the relevant trait `#[generate_derive]`-ed on it
-                check_attr_is_derived(
-                    processor,
-                    type_def.generated_derives(),
-                    type_def.name(),
-                    &attr_name,
-                );
 
-                let location = match type_def {
-                    TypeDef::Struct(struct_def) => AttrLocation::Struct(struct_def),
-                    TypeDef::Enum(enum_def) => AttrLocation::Enum(enum_def),
+                        AttrLocation::Enum(enum_def)
+                    }
                     _ => unreachable!(),
                 };
+
                 let result = process_attr(processor, &attr_name, location, &attr.meta);
                 assert!(
                     result.is_ok(),
@@ -770,13 +787,13 @@ fn check_attr_is_derived(
 /// Check attribute is in a legal position.
 fn check_attr_position(
     expected_positions: AttrPositions,
-    found_in_position: AttrPositions,
+    found_in_positions: AttrPositions,
     type_name: &str,
     attr_name: &str,
     position_debug_str: &str,
 ) {
     assert!(
-        expected_positions.contains(found_in_position),
+        expected_positions.intersects(found_in_positions),
         "`{type_name}` type has `#[{attr_name}]` attribute on a {position_debug_str}, \
         but `#[{attr_name}]` is not legal in this position."
     );