Make absence of perfect-derive feature on miette-derive actually disable adding trait bounds

Signed-off-by: Justus Flügel <justusfluegel@gmail.com>

Cargo.toml

@@ -50,7 +50,7 @@ strip-ansi-escapes = "0.2.0"
 [features]
 default = ["derive"]
 derive = ["dep:miette-derive"]
-perfect-derive = ["dep:miette-derive","miette-derive?/perfect-derive"]
+perfect-derive = ["derive","miette-derive?/perfect-derive"]
 no-format-args-capture = []
 fancy-base = [
     "dep:owo-colors",

miette-derive/Cargo.toml

@@ -16,4 +16,4 @@ perfect-derive = ["syn/extra-traits"]
 [dependencies]
 proc-macro2 = "1.0.83"
 quote = "1.0.35"
-syn = { version = "2.0.87", features = ["extra-traits"] }
+syn = "2.0.87"

miette-derive/src/trait_bounds/mock_store.rs

@@ -0,0 +1,24 @@
+#![allow(dead_code)]
+use syn::{punctuated::Punctuated, Generics, PredicateType, Token, WhereClause, WherePredicate};
+
+// Mock for when perfect-derive is not enabled,
+// this should be completely optimized away and enables
+// easily switching on/off the perfect-derive feature without
+// needing to modify any other code.
+pub struct TypeParamBoundStore;
+
+impl TypeParamBoundStore {
+    pub fn new(_: &Generics) -> Self {
+        Self
+    }
+
+    pub fn add_predicate(&mut self, _: PredicateType) {}
+
+    pub fn add_where_predicate(&mut self, _: WherePredicate) {}
+
+    pub fn extend_where_predicates(&mut self, _: Punctuated<WherePredicate, Token![,]>) {}
+
+    pub fn add_to_where_clause(&self, where_clause: Option<&WhereClause>) -> Option<WhereClause> {
+        where_clause.cloned()
+    }
+}

miette-derive/src/trait_bounds/mod.rs

@@ -0,0 +1,9 @@
+#[cfg(not(feature = "perfect-derive"))]
+mod mock_store;
+#[cfg(not(feature = "perfect-derive"))]
+pub use mock_store::TypeParamBoundStore;
+
+#[cfg(feature = "perfect-derive")]
+mod store;
+#[cfg(feature = "perfect-derive")]
+pub use store::TypeParamBoundStore;

miette-derive/src/trait_bounds/store.rs

@@ -12,9 +12,13 @@ use syn::{
 };
 
 // Potential improvement, although idk if this actually ends up
-// mattering is to switch this to something like FxHashMap like the rustc compiler uses internally
+// mattering (if it is a messurable improvement) is to switch this to something like FxHashMap
+// like the rustc compiler uses internally, although we should benchmark this and can always do it later
+// since it is easy enough to change.
+#[cfg(feature = "perfect-derive")]
 pub struct TypeParamBoundStore(HashMap<(Option<BoundLifetimes>, Type), HashSet<TypeParamBound>>);
 
+#[cfg(feature = "perfect-derive")]
 impl TypeParamBoundStore {
     /// Creates a new TraitBoundStore, filling it with some generics which are used to heuristically remove trivial bounds.
     ///

tests/test_derive_attr.rs

@@ -146,6 +146,7 @@ fn attr_not_required() {
     assert_eq!(err_span, expectation);
 }
 
+// Tests for the feature = "perfect-derive".
 fn assert_impl_diagnostic<T: Diagnostic>() {}
 
 #[test]