Merge branch 'ijackson-all-bounds'

Author: magiclen

README.md

@@ -211,6 +211,29 @@ enum Enum<T, K> {
 
 In the above case, `T` is bound to the `Debug` trait, but `K` is not.
 
+Or, you can have `educe` replicate the behaviour of `std`'s `derive`'s,
+where a bound is produced for *every* generic parameter,
+without regard to how it's used in the structure:
+
+```rust
+#[derive(Educe)]
+#[educe(Debug(bound(*)))]
+struct Struct<T> {
+    #[educe(Debug(ignore))]
+    f: T,
+}
+```
+
+This can be useful if you don't want to make the trait implementation
+part of your permanent public API.
+In this example,
+`Struct<T>` doesn't implement `Debug` unless `T` does.
+I.e., it has a `T: Debug` bound even though that's not needed right now.
+Later we might want to display `f`; we wouldn't then need to make
+a breaking API change by adding the bound.
+
+This was the behaviour of `Trait(bound)` in educe 0.4.x and earlier.
+
 ###### Union
 
 A union will be formatted as a `u8` slice because we don't know its fields at runtime. The fields of a union cannot be ignored, renamed, or formatted with other methods. The implementation is **unsafe** because it may expose uninitialized memory.

src/common/bound.rs

@@ -1,6 +1,7 @@
 use syn::{punctuated::Punctuated, token::Comma, GenericParam, Meta, Path, Type, WherePredicate};
 
 use crate::common::where_predicates_bool::{
+    create_where_predicates_from_all_generic_parameters,
     create_where_predicates_from_generic_parameters_check_types, meta_2_where_predicates,
     WherePredicates, WherePredicatesOrBool,
 };
@@ -9,6 +10,7 @@ pub(crate) enum Bound {
     Disabled,
     Auto,
     Custom(WherePredicates),
+    All,
 }
 
 impl Bound {
@@ -27,6 +29,7 @@ impl Bound {
                     Self::Disabled
                 }
             },
+            WherePredicatesOrBool::All => Self::All,
         })
     }
 }
@@ -35,7 +38,7 @@ impl Bound {
     #[inline]
     pub(crate) fn into_where_predicates_by_generic_parameters_check_types(
         self,
-        _params: &Punctuated<GenericParam, Comma>,
+        params: &Punctuated<GenericParam, Comma>,
         bound_trait: &Path,
         types: &[&Type],
         supertraits: &[proc_macro2::TokenStream],
@@ -48,6 +51,7 @@ impl Bound {
                 supertraits,
             ),
             Self::Custom(where_predicates) => where_predicates,
+            Self::All => create_where_predicates_from_all_generic_parameters(params, bound_trait),
         }
     }
 }

src/common/where_predicates_bool.rs

@@ -14,6 +14,7 @@ pub(crate) type WherePredicates = Punctuated<WherePredicate, Token![,]>;
 pub(crate) enum WherePredicatesOrBool {
     WherePredicates(WherePredicates),
     Bool(bool),
+    All,
 }
 
 impl WherePredicatesOrBool {
@@ -42,6 +43,10 @@ impl Parse for WherePredicatesOrBool {
             return Self::from_lit(&lit);
         }
 
+        if let Ok(_star) = input.parse::<Token![*]>() {
+            return Ok(Self::All);
+        }
+
         Ok(Self::WherePredicates(input.parse_terminated(WherePredicate::parse, Token![,])?))
     }
 }
@@ -80,7 +85,6 @@ pub(crate) fn meta_2_where_predicates(meta: &Meta) -> syn::Result<WherePredicate
 }
 
 #[inline]
-#[allow(dead_code)]
 pub(crate) fn create_where_predicates_from_all_generic_parameters(
     params: &Punctuated<GenericParam, Comma>,
     bound_trait: &Path,

tests/clone_struct.rs

@@ -1,6 +1,8 @@
 #![cfg(feature = "Clone")]
 #![no_std]
 
+use core::marker::PhantomData;
+
 use educe::Educe;
 
 #[test]
@@ -169,3 +171,31 @@ fn bound_3() {
     assert_eq!(1, s.f1);
     assert_eq!(1, t.0);
 }
+
+#[test]
+fn bound_4() {
+    struct NotClone;
+
+    #[derive(Educe)]
+    // without `bound(*)` we get  E0034: multiple applicable items in scope
+    // when we call Struct<NotClone>.clone(), since .clone() is then ambiguous
+    #[educe(Clone(bound(*)))]
+    struct Struct<T> {
+        f1: PhantomData<T>,
+    }
+
+    trait ClashingFakeClone {
+        fn clone(&self) {}
+    }
+    impl ClashingFakeClone for Struct<NotClone> {}
+
+    let _: () = Struct {
+        f1: PhantomData::<NotClone>
+    }
+    .clone();
+
+    let _: Struct<_> = Struct {
+        f1: PhantomData::<()>
+    }
+    .clone();
+}