From ff32d81cb0e67e10ff3b780bdf79cb9c9bc2a7da Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Justus=20Fl=C3=BCgel?= <justusfluegel@gmail.com>
Date: Mon, 10 Mar 2025 21:36:11 +0100
Subject: [PATCH] Simplify the trait bound store and just register where
 clauses directly
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Signed-off-by: Justus Flügel <justusfluegel@gmail.com>
---
 miette-derive/src/diagnostic.rs        |  18 +-
 miette-derive/src/diagnostic_source.rs |  11 +-
 miette-derive/src/forward.rs           |  12 +-
 miette-derive/src/label.rs             |  34 +-
 miette-derive/src/related.rs           |  18 +-
 miette-derive/src/source_code.rs       |  20 +-
 miette-derive/src/trait_bounds.rs      | 412 ++++++-------------------
 miette-derive/src/utils.rs             |  35 ++-
 8 files changed, 200 insertions(+), 360 deletions(-)

diff --git a/miette-derive/src/diagnostic.rs b/miette-derive/src/diagnostic.rs
index 629051e..df963f0 100644
--- a/miette-derive/src/diagnostic.rs
+++ b/miette-derive/src/diagnostic.rs
@@ -11,7 +11,7 @@ use crate::label::Labels;
 use crate::related::Related;
 use crate::severity::Severity;
 use crate::source_code::SourceCode;
-use crate::trait_bounds::TraitBoundStore;
+use crate::trait_bounds::TypeParamBoundStore;
 use crate::url::Url;
 
 pub enum Diagnostic {
@@ -20,13 +20,13 @@ pub enum Diagnostic {
         ident: syn::Ident,
         fields: syn::Fields,
         args: DiagnosticDefArgs,
-        bound_store: TraitBoundStore,
+        bound_store: TypeParamBoundStore,
     },
     Enum {
         ident: syn::Ident,
         generics: syn::Generics,
         variants: Vec<DiagnosticDef>,
-        bound_store: TraitBoundStore,
+        bound_store: TypeParamBoundStore,
     },
 }
 
@@ -76,7 +76,7 @@ pub struct DiagnosticConcreteArgs {
 impl DiagnosticConcreteArgs {
     fn for_fields(
         fields: &syn::Fields,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> Result<Self, syn::Error> {
         let labels = Labels::from_fields(fields, bounds_store)?;
         let source_code = SourceCode::from_fields(fields, bounds_store)?;
@@ -162,7 +162,7 @@ impl DiagnosticDefArgs {
         _ident: &syn::Ident,
         fields: &syn::Fields,
         attrs: &[&syn::Attribute],
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
         allow_transparent: bool,
     ) -> syn::Result<Self> {
         let mut errors = Vec::new();
@@ -233,7 +233,7 @@ impl Diagnostic {
             .collect::<Vec<&syn::Attribute>>();
         Ok(match input.data {
             syn::Data::Struct(data_struct) => {
-                let mut bounds_store = TraitBoundStore::new(&input.generics);
+                let mut bounds_store = TypeParamBoundStore::new(&input.generics);
 
                 let args = DiagnosticDefArgs::parse(
                     &input.ident,
@@ -253,7 +253,7 @@ impl Diagnostic {
             }
             syn::Data::Enum(syn::DataEnum { variants, .. }) => {
                 let mut vars = Vec::new();
-                let mut bound_store = TraitBoundStore::new(&input.generics);
+                let mut bound_store = TypeParamBoundStore::new(&input.generics);
                 for var in variants {
                     let mut variant_attrs = input_attrs.clone();
                     variant_attrs
@@ -297,7 +297,7 @@ impl Diagnostic {
                 bound_store,
             } => {
                 let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
-                let where_clause = bound_store.merge_with(where_clause);
+                let where_clause = bound_store.add_to_where_clause(where_clause);
 
                 match args {
                     DiagnosticDefArgs::Transparent(forward) => {
@@ -397,7 +397,7 @@ impl Diagnostic {
                 bound_store,
             } => {
                 let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
-                let where_clause = bound_store.merge_with(where_clause);
+                let where_clause = bound_store.add_to_where_clause(where_clause);
 
                 let code_body = Code::gen_enum(variants);
                 let help_body = Help::gen_enum(variants);
diff --git a/miette-derive/src/diagnostic_source.rs b/miette-derive/src/diagnostic_source.rs
index 8e66e29..4fc9c28 100644
--- a/miette-derive/src/diagnostic_source.rs
+++ b/miette-derive/src/diagnostic_source.rs
@@ -3,7 +3,7 @@ use quote::quote;
 use syn::spanned::Spanned;
 
 use crate::forward::WhichFn;
-use crate::trait_bounds::TraitBoundStore;
+use crate::trait_bounds::TypeParamBoundStore;
 use crate::{
     diagnostic::{DiagnosticConcreteArgs, DiagnosticDef},
     utils::{display_pat_members, gen_all_variants_with},
@@ -14,7 +14,7 @@ pub struct DiagnosticSource(syn::Member);
 impl DiagnosticSource {
     pub(crate) fn from_fields(
         fields: &syn::Fields,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> syn::Result<Option<Self>> {
         match fields {
             syn::Fields::Named(named) => {
@@ -29,7 +29,7 @@ impl DiagnosticSource {
 
     fn from_fields_vec(
         fields: Vec<&syn::Field>,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> syn::Result<Option<Self>> {
         for (i, field) in fields.iter().enumerate() {
             for attr in &field.attrs {
@@ -43,7 +43,10 @@ impl DiagnosticSource {
                         })
                     };
 
-                    bounds_store.register_source_usage(&field.ty);
+                    let ty = &field.ty;
+                    bounds_store.add_where_predicate(
+                        syn::parse_quote!(#ty: ::miette::Diagnostic + 'static),
+                    );
 
                     return Ok(Some(DiagnosticSource(diagnostic_source)));
                 }
diff --git a/miette-derive/src/forward.rs b/miette-derive/src/forward.rs
index 11cb3bb..33d87c2 100644
--- a/miette-derive/src/forward.rs
+++ b/miette-derive/src/forward.rs
@@ -6,7 +6,7 @@ use syn::{
     spanned::Spanned,
 };
 
-use crate::trait_bounds::TraitBoundStore;
+use crate::trait_bounds::TypeParamBoundStore;
 
 pub enum Forward {
     Unnamed(usize),
@@ -98,7 +98,7 @@ impl WhichFn {
 impl Forward {
     pub fn for_transparent_field(
         fields: &syn::Fields,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> syn::Result<Self> {
         let make_err = || {
             syn::Error::new(
@@ -118,7 +118,9 @@ impl Forward {
                     .clone()
                     .unwrap_or_else(|| format_ident!("unnamed"));
 
-                bounds_store.register_transparent_usage(&field.ty);
+                let ty = &field.ty;
+                bounds_store
+                    .add_where_predicate(syn::parse_quote! {#ty: ::miette::Diagnostic + 'static});
                 Ok(Self::Named(field_name))
             }
             syn::Fields::Unnamed(unnamed) => {
@@ -128,7 +130,9 @@ impl Forward {
                     return Err(make_err());
                 }
 
-                bounds_store.register_transparent_usage(&field.ty);
+                let ty = &field.ty;
+                bounds_store
+                    .add_where_predicate(syn::parse_quote! {#ty: ::miette::Diagnostic + 'static});
                 Ok(Self::Unnamed(0))
             }
             _ => Err(syn::Error::new(
diff --git a/miette-derive/src/label.rs b/miette-derive/src/label.rs
index 191b7b3..3cc071b 100644
--- a/miette-derive/src/label.rs
+++ b/miette-derive/src/label.rs
@@ -4,15 +4,15 @@ use syn::{
     parenthesized,
     parse::{Parse, ParseStream},
     spanned::Spanned,
-    Token,
+    Lifetime, Token,
 };
 
 use crate::{
     diagnostic::{DiagnosticConcreteArgs, DiagnosticDef},
     fmt::{self, Display},
     forward::WhichFn,
-    trait_bounds::TraitBoundStore,
-    utils::{display_pat_members, gen_all_variants_with},
+    trait_bounds::TypeParamBoundStore,
+    utils::{display_pat_members, extract_option, gen_all_variants_with},
 };
 
 pub struct Labels(Vec<Label>);
@@ -110,7 +110,7 @@ impl Parse for LabelAttr {
 impl Labels {
     pub fn from_fields(
         fields: &syn::Fields,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> syn::Result<Option<Self>> {
         match fields {
             syn::Fields::Named(named) => {
@@ -125,7 +125,7 @@ impl Labels {
 
     fn from_fields_vec(
         fields: Vec<&syn::Field>,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> syn::Result<Option<Self>> {
         let mut labels = Vec::new();
         for (i, field) in fields.iter().enumerate() {
@@ -156,11 +156,31 @@ impl Labels {
 
                     match lbl_ty {
                         LabelType::Default | LabelType::Primary => {
-                            bounds_store.register_label_usage(&field.ty);
+                            let option_ty = extract_option(&field.ty).unwrap_or(&field.ty);
+                            bounds_store.extend_where_predicates(syn::parse_quote!{
+                                #option_ty: ::std::borrow::ToOwned,
+                                <#option_ty as ::std::borrow::ToOwned>::Owned: ::std::convert::Into<::miette::SourceSpan>
+                            });
                         }
 
                         LabelType::Collection => {
-                            bounds_store.register_label_collection_usage(&field.ty);
+                            let ty = &field.ty;
+                            let lt: Lifetime = syn::parse_quote!('__miette_internal_lt);
+                            bounds_store.extend_where_predicates(syn::parse_quote!{
+                                for<#lt> &#lt #ty: ::std::iter::IntoIterator,
+                                for<#lt> <&#lt #ty as ::std::iter::IntoIterator>::Item: ::std::ops::Deref,
+                                for<#lt> <
+                                    <&#lt #ty as ::std::iter::IntoIterator>::Item
+                                    as ::std::ops::Deref
+                                >::Target : ::std::borrow::ToOwned,
+                                for<#lt> <
+                                    <
+                                        <&#lt #ty as ::std::iter::IntoIterator>::Item
+                                        as ::std::ops::Deref
+                                    >::Target
+                                    as ::std::borrow::ToOwned
+                                >::Owned: ::std::convert::Into<::miette::SourceSpan>
+                            });
                         }
                     }
 
diff --git a/miette-derive/src/related.rs b/miette-derive/src/related.rs
index cd87899..4cb8881 100644
--- a/miette-derive/src/related.rs
+++ b/miette-derive/src/related.rs
@@ -5,7 +5,7 @@ use syn::spanned::Spanned;
 use crate::{
     diagnostic::{DiagnosticConcreteArgs, DiagnosticDef},
     forward::WhichFn,
-    trait_bounds::TraitBoundStore,
+    trait_bounds::TypeParamBoundStore,
     utils::{display_pat_members, gen_all_variants_with},
 };
 
@@ -14,7 +14,7 @@ pub struct Related(syn::Member);
 impl Related {
     pub(crate) fn from_fields(
         fields: &syn::Fields,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> syn::Result<Option<Self>> {
         match fields {
             syn::Fields::Named(named) => {
@@ -29,7 +29,7 @@ impl Related {
 
     fn from_fields_vec(
         fields: Vec<&syn::Field>,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> syn::Result<Option<Self>> {
         for (i, field) in fields.iter().enumerate() {
             for attr in &field.attrs {
@@ -42,7 +42,17 @@ impl Related {
                             span: field.span(),
                         })
                     };
-                    bounds_store.register_related_usage(&field.ty);
+                    // this is somewhat hacky and only supports concrete types for the #[related] type
+                    // ittself but supports generics for the arguments, i.e. Vec<T> where T is generic.
+                    //
+                    // I think that this is a current limitation of the design of the Diagnostic trait,
+                    // since we'd need bounds on the method and we can't do that (to refer to the lifetime)
+                    //
+                    // Someone smarter than me might be able to figure out a better solution (?)
+                    let ty = &field.ty;
+                    bounds_store.add_where_predicate(syn::parse_quote!(
+                        <#ty as ::std::iter::IntoIterator>::Item: ::miette::Diagnostic + 'static
+                    ));
                     return Ok(Some(Related(related)));
                 }
             }
diff --git a/miette-derive/src/source_code.rs b/miette-derive/src/source_code.rs
index 493d3a5..b1a179f 100644
--- a/miette-derive/src/source_code.rs
+++ b/miette-derive/src/source_code.rs
@@ -1,12 +1,12 @@
 use proc_macro2::TokenStream;
 use quote::{format_ident, quote};
-use syn::{spanned::Spanned, AngleBracketedGenericArguments, GenericArgument, PathArguments};
+use syn::spanned::Spanned;
 
 use crate::{
     diagnostic::{DiagnosticConcreteArgs, DiagnosticDef},
     forward::WhichFn,
-    trait_bounds::TraitBoundStore,
-    utils::{display_pat_members, gen_all_variants_with},
+    trait_bounds::TypeParamBoundStore,
+    utils::{display_pat_members, extract_option, gen_all_variants_with},
 };
 
 pub struct SourceCode {
@@ -17,7 +17,7 @@ pub struct SourceCode {
 impl SourceCode {
     pub fn from_fields(
         fields: &syn::Fields,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> syn::Result<Option<Self>> {
         match fields {
             syn::Fields::Named(named) => {
@@ -32,18 +32,16 @@ impl SourceCode {
 
     fn from_fields_vec(
         fields: Vec<&syn::Field>,
-        bounds_store: &mut TraitBoundStore,
+        bounds_store: &mut TypeParamBoundStore,
     ) -> syn::Result<Option<Self>> {
         for (i, field) in fields.iter().enumerate() {
             for attr in &field.attrs {
                 if attr.path().is_ident("source_code") {
-                    let is_option = TraitBoundStore::extract_option(&field.ty);
+                    let is_option = extract_option(&field.ty);
 
-                    if let Some(option_ty) = is_option {
-                        bounds_store.register_source_code_usage(option_ty);
-                    } else {
-                        bounds_store.register_source_code_usage(&field.ty);
-                    }
+                    let code_ty = is_option.unwrap_or(&field.ty);
+                    bounds_store
+                        .add_where_predicate(syn::parse_quote!(#code_ty: ::miette::SourceCode));
 
                     let source_code = if let Some(ident) = field.ident.clone() {
                         syn::Member::Named(ident)
diff --git a/miette-derive/src/trait_bounds.rs b/miette-derive/src/trait_bounds.rs
index e69d3c1..8894f3b 100644
--- a/miette-derive/src/trait_bounds.rs
+++ b/miette-derive/src/trait_bounds.rs
@@ -1,176 +1,51 @@
 use std::{
-    collections::{HashMap, VecDeque},
-    iter::{once, FromIterator},
+    collections::{HashMap, HashSet, VecDeque},
+    iter::once,
 };
 
 use proc_macro2::Span;
 use syn::{
-    punctuated::Punctuated, token::Plus, AngleBracketedGenericArguments, AssocType, BoundLifetimes,
-    GenericArgument, GenericParam, Generics, ParenthesizedGenericArguments, Path, PathArguments,
-    PathSegment, PredicateType, ReturnType, Token, TraitBound, Type, TypeArray, TypeGroup,
-    TypeParamBound, TypeParen, TypePath, TypePtr, TypeReference, TypeSlice, TypeTuple, WhereClause,
-    WherePredicate,
+    punctuated::Punctuated, AngleBracketedGenericArguments, AssocType, BoundLifetimes,
+    GenericArgument, GenericParam, Generics, ParenthesizedGenericArguments, PathArguments,
+    PredicateType, ReturnType, Token, Type, TypeArray, TypeGroup, TypeParamBound, TypeParen,
+    TypePath, TypePtr, TypeReference, TypeSlice, TypeTuple, WhereClause, WherePredicate,
 };
 
-#[derive(Default)]
-pub struct RequiredTraitBound {
-    r#static: bool,
-    std_error: bool,
-    miette_diagnostic: bool,
-    source_code: bool,
-    into_source_span: bool,
-    std_into_iter: bool,
-    std_deref: bool,
-    std_to_owned: bool,
-}
+// Potential improvement, although idk if this actually ends up
+// mattering is to switch this to something like FxHashMap like the rustc compiler uses internally
+pub struct TypeParamBoundStore(HashMap<(Option<BoundLifetimes>, Type), HashSet<TypeParamBound>>);
 
-impl RequiredTraitBound {
-    fn to_bounds(&self) -> Punctuated<TypeParamBound, Plus> {
-        let mut bounds = Punctuated::new();
-        if self.std_error && !self.miette_diagnostic {
-            bounds.push(TypeParamBound::Trait(syn::parse_quote!(
-                ::std::error::Error
-            )));
-        }
-
-        if self.miette_diagnostic {
-            bounds.push(TypeParamBound::Trait(syn::parse_quote!(
-                ::miette::Diagnostic
-            )))
-        }
-
-        if self.source_code {
-            bounds.push(TypeParamBound::Trait(syn::parse_quote!(
-                ::miette::SourceCode
-            )))
-        }
-
-        if self.into_source_span {
-            bounds.push(TypeParamBound::Trait(syn::parse_quote!(
-                ::std::convert::Into<::miette::SourceSpan>
-            )))
-        }
-
-        if self.std_into_iter {
-            bounds.push(TypeParamBound::Trait(syn::parse_quote!(
-                ::std::iter::IntoIterator
-            )))
-        }
-
-        if self.std_deref {
-            bounds.push(TypeParamBound::Trait(syn::parse_quote!(::std::ops::Deref)))
-        }
-
-        if self.std_to_owned {
-            bounds.push(TypeParamBound::Trait(syn::parse_quote!(
-                ::std::borrow::ToOwned
-            )))
-        }
-
-        if self.r#static {
-            bounds.push(TypeParamBound::Lifetime(syn::parse_quote!('static)))
-        }
-
-        bounds
-    }
-
-    fn register_transparent_usage(&mut self) {
-        self.r#static = true;
-        self.miette_diagnostic = true;
-    }
-
-    fn register_source_code_usage(&mut self) {
-        self.source_code = true;
-    }
-
-    fn register_label_usage(&mut self) {
-        self.into_source_span = true;
-    }
-
-    fn register_collection_usage(&mut self) {
-        self.std_into_iter = true;
-    }
-    fn register_related_item_usage(&mut self) {
-        self.miette_diagnostic = true;
-        self.r#static = true;
-    }
-
-    fn register_source_usage(&mut self) {
-        self.miette_diagnostic = true;
-        self.r#static = true;
-    }
-
-    fn register_deref_usage(&mut self) {
-        self.std_deref = true;
-    }
-
-    fn register_to_owned_usage(&mut self) {
-        self.std_to_owned = true;
-    }
-}
-
-pub struct TraitBoundStore(HashMap<(Option<BoundLifetimes>, Type), RequiredTraitBound>);
-
-impl TraitBoundStore {
+impl TypeParamBoundStore {
+    /// Creates a new TraitBoundStore, filling it with some generics which are used to heuristically remove trivial bounds.
+    ///
+    /// Note that it is essential that all relevant generics are actually passed here, since if they aren't bounds which are required might be heuristically removed.
     pub fn new(generics: &Generics) -> Self {
         let hash_map = generics
             .params
             .iter()
-            .filter_map(|param| {
-                if let GenericParam::Type(ty) = param {
-                    Some(ty)
-                } else {
-                    None
-                }
+            .filter_map(|param| match param {
+                GenericParam::Type(ty) => Some(ty),
+                _ => None,
             })
             .map(|param| {
-                Type::Path(TypePath {
-                    qself: None,
-                    path: Path {
-                        leading_colon: None,
-                        segments: Punctuated::from_iter(once(PathSegment {
-                            ident: param.ident.clone(),
-                            arguments: PathArguments::None,
-                        })),
-                    },
-                })
+                let ident = &param.ident;
+                Type::Path(syn::parse_quote!(#ident))
             })
-            .map(|v| ((None, v), RequiredTraitBound::default()))
+            .map(|ty| ((None, ty), Default::default()))
             .collect::<HashMap<_, _>>();
 
         Self(hash_map)
     }
 
-    pub fn extract_option(r#type: &Type) -> Option<&Type> {
-        if let syn::Type::Path(syn::TypePath {
-            path: syn::Path { segments, .. },
-            ..
-        }) = r#type
-        {
-            segments
-                .last()
-                .filter(|seg| seg.ident == "Option")
-                .and_then(|seg| match &seg.arguments {
-                    PathArguments::AngleBracketed(AngleBracketedGenericArguments {
-                        args, ..
-                    }) => {
-                        let mut iter = args.iter();
-
-                        let ty = iter.next();
-                        iter.next().xor(ty)
-                    }
-                    _ => None,
-                })
-                .and_then(|arg| match arg {
-                    GenericArgument::Type(ty) => Some(ty),
-                    _ => None,
-                })
-        } else {
-            None
-        }
-    }
-
-    fn check_generic_usage<'ty>(&self, mut r#type: &'ty Type) -> Option<&'ty Type> {
+    /// Checks heuristically if `type` is using any generic type inside it.
+    ///
+    /// This is guaranteed to never false-negative but might
+    /// false-positive if checking exhaustively would be expensive or
+    /// an unexpected case is encountered which this can't handle.
+    ///
+    /// # Returns
+    /// Option with a simplified type if determined to be dependant, none otherwise
+    fn generic_usage_heuristics(&self, mut r#type: Type) -> Option<Type> {
         // in theory we could skip all this logic and just allow trivial bounds but that would add redundant trait bounds
         // to the derived impl - would be another choice to make. I choose to filter as much as possible so that we don't
         // introduce unneccessary bounds.
@@ -178,8 +53,8 @@ impl TraitBoundStore {
         // this reduces the type down as much as possible to remove unneeded groups.
         let original_type = loop {
             match r#type {
-                Type::Paren(TypeParen { elem, .. }) => r#type = &**elem,
-                Type::Group(TypeGroup { elem, .. }) => r#type = &**elem,
+                Type::Paren(TypeParen { elem, .. }) => r#type = *elem,
+                Type::Group(TypeGroup { elem, .. }) => r#type = *elem,
                 x => break x,
             }
         };
@@ -193,7 +68,7 @@ impl TraitBoundStore {
         let max_depth = 8;
 
         let mut to_check_queue: VecDeque<(&Type, usize)> = VecDeque::new();
-        to_check_queue.push_back((original_type, 0));
+        to_check_queue.push_back((&original_type, 0));
 
         while !depends_on_generic {
             // this needs to be like this cuz if-let-chains aren't supported yet
@@ -299,173 +174,70 @@ impl TraitBoundStore {
         depends_on_generic.then_some(original_type)
     }
 
-    pub fn merge_with(&self, where_clause: Option<&WhereClause>) -> Option<WhereClause> {
-        let mut where_clause = where_clause.cloned().unwrap_or_else(|| WhereClause {
-            where_token: Token![where](Span::mixed_site()),
-            predicates: Punctuated::new(),
-        });
+    pub fn add_predicate(
+        &mut self,
+        PredicateType {
+            lifetimes,
+            bounded_ty,
+            colon_token: _,
+            bounds,
+        }: PredicateType,
+    ) {
+        let Some(bounded_ty) = self.generic_usage_heuristics(bounded_ty) else {
+            return;
+        };
 
-        where_clause
-            .predicates
-            .extend(self.0.iter().filter_map(|(ty, bounds)| {
-                let bounds = bounds.to_bounds();
-                (!bounds.is_empty()).then(|| {
-                    WherePredicate::Type(PredicateType {
-                        lifetimes: ty.0.clone(),
-                        bounded_ty: ty.1.clone(),
-                        colon_token: Token![:](Span::mixed_site()),
-                        bounds,
-                    })
+        self.0
+            .entry((lifetimes, bounded_ty))
+            .or_default()
+            .extend(bounds);
+    }
+
+    // Since syn for some reason doesn't implement `Parse` for `PredicateType`
+    // this method is meant for ease of use with `syn::parse_quote!`.
+    pub fn add_where_predicate(&mut self, predicate: WherePredicate) {
+        let WherePredicate::Type(ty) = predicate else {
+            unimplemented!("Only type predicates are supported");
+        };
+
+        self.add_predicate(ty);
+    }
+
+    pub fn extend_where_predicates(&mut self, predicates: Punctuated<WherePredicate, Token![,]>) {
+        for predicate in predicates {
+            self.add_where_predicate(predicate);
+        }
+    }
+
+    pub fn add_to_where_clause(&self, where_clause: Option<&WhereClause>) -> Option<WhereClause> {
+        let predicates = self
+            .0
+            .iter()
+            .filter(|(_, bounds)| !bounds.is_empty())
+            .map(|(a, b)| (a.clone(), b.clone()))
+            .map(|((lifetimes, bounded_ty), bounds)| {
+                WherePredicate::Type(PredicateType {
+                    lifetimes,
+                    bounded_ty,
+                    colon_token: Token![:](Span::mixed_site()),
+                    bounds: bounds.into_iter().collect(),
                 })
-            }));
+            })
+            .peekable();
 
-        where_clause
-            .predicates
-            .push(WherePredicate::Type(PredicateType {
-                lifetimes: None,
-                bounded_ty: Type::Path(TypePath {
-                    qself: None,
-                    path: Path {
-                        leading_colon: None,
-                        segments: Punctuated::from_iter(once(PathSegment {
-                            ident: syn::Ident::new("Self", Span::mixed_site()),
-                            arguments: PathArguments::None,
-                        })),
-                    },
-                }),
-                colon_token: syn::Token![:](Span::mixed_site()),
-                bounds: Punctuated::from_iter(once(TypeParamBound::Trait(TraitBound {
-                    paren_token: None,
-                    modifier: syn::TraitBoundModifier::None,
-                    lifetimes: None,
-                    path: syn::parse_quote!(::std::error::Error),
-                }))),
-            }));
+        // de-duplicate elements newly added and within existing where clause
+        let predicates = predicates
+            .chain(
+                where_clause
+                    .into_iter()
+                    .flat_map(|where_clause| where_clause.predicates.clone()),
+            )
+            .chain(once(syn::parse_quote!(Self: ::std::error::Error)))
+            .collect::<HashSet<_>>();
 
-        Some(where_clause)
-    }
-
-    pub fn register_transparent_usage(&mut self, r#type: &Type) {
-        let Some(r#type) = self.check_generic_usage(r#type) else {
-            return;
-        };
-
-        let type_opts = self.0.entry((None, r#type.clone())).or_default();
-        type_opts.register_transparent_usage()
-    }
-
-    pub fn register_source_code_usage(&mut self, r#type: &Type) {
-        let Some(r#type) = self.check_generic_usage(r#type) else {
-            return;
-        };
-
-        let type_opts = self.0.entry((None, r#type.clone())).or_default();
-        type_opts.register_source_code_usage()
-    }
-
-    pub fn register_label_usage(&mut self, r#type: &Type) {
-        let r#type = Self::extract_option(r#type).unwrap_or(r#type);
-
-        let Some(ty) = self.check_generic_usage(r#type) else {
-            return;
-        };
-
-        let type_opts = self.0.entry((None, ty.clone())).or_default();
-
-        type_opts.register_to_owned_usage();
-
-        let type_opts_to_owned = self
-            .0
-            .entry((
-                None,
-                syn::parse_quote!(<#ty as ::std::borrow::ToOwned>::Owned),
-            ))
-            .or_default();
-        type_opts_to_owned.register_label_usage();
-    }
-
-    pub fn register_label_collection_usage(&mut self, r#type: &Type) {
-        let Some(ty) = self.check_generic_usage(r#type) else {
-            return;
-        };
-
-        let ty: syn::Type = syn::parse_quote!(&'__miette_internal_lt #ty);
-
-        let type_opts = self
-            .0
-            .entry((
-                Some(syn::parse_quote!(for<'__miette_internal_lt>)),
-                ty.clone(),
-            ))
-            .or_default();
-        type_opts.register_collection_usage();
-
-        let type_opts_item = self
-            .0
-            .entry((
-                Some(syn::parse_quote!(for<'__miette_internal_lt>)),
-                syn::parse_quote!(<#ty as ::std::iter::IntoIterator>::Item),
-            ))
-            .or_default();
-        type_opts_item.register_deref_usage();
-
-        let type_opts_deref_item = self
-            .0
-            .entry((
-                Some(syn::parse_quote! {for<'__miette_internal_lt>}),
-                syn::parse_quote! {
-                    <<#ty as ::std::iter::IntoIterator>::Item as ::std::ops::Deref>::Target
-                },
-            ))
-            .or_default();
-        type_opts_deref_item.register_to_owned_usage();
-
-        let type_opts_deref_to_owned_item = self
-            .0
-            .entry((
-                Some(syn::parse_quote! {for<'__miette_internal_lt>}),
-                syn::parse_quote! {
-                    <
-                        <
-                            <#ty as ::std::iter::IntoIterator>::Item
-                            as ::std::ops::Deref
-                        >::Target
-                        as ::std::borrow::ToOwned
-                    >::Owned
-                },
-            ))
-            .or_default();
-        type_opts_deref_to_owned_item.register_label_usage();
-    }
-
-    pub fn register_related_usage(&mut self, r#type: &Type) {
-        let Some(ty) = self.check_generic_usage(r#type) else {
-            return;
-        };
-
-        // this is somewhat hacky and only supports concrete types for the #[related] type
-        // ittself but supports generics for the arguments, i.e. Vec<T> where T is generic.
-        //
-        // I think that this is a current limitation of the design of the Diagnostic trait,
-        // since we'd need bounds on the method and we can't do that (to refer to the lifetime)
-        //
-        // Someone smarter than me might be able to figure out a better solution (?)
-        let type_opts_item = self
-            .0
-            .entry((
-                None,
-                syn::parse_quote!(<#ty as ::std::iter::IntoIterator>::Item),
-            ))
-            .or_default();
-        type_opts_item.register_related_item_usage();
-    }
-
-    pub fn register_source_usage(&mut self, r#type: &Type) {
-        let Some(ty) = self.check_generic_usage(r#type) else {
-            return;
-        };
-
-        let type_opts = self.0.entry((None, ty.clone())).or_default();
-        type_opts.register_source_usage();
+        Some(WhereClause {
+            where_token: Token![where](Span::mixed_site()),
+            predicates: predicates.into_iter().collect(),
+        })
     }
 }
diff --git a/miette-derive/src/utils.rs b/miette-derive/src/utils.rs
index 2d58444..cbacdff 100644
--- a/miette-derive/src/utils.rs
+++ b/miette-derive/src/utils.rs
@@ -1,6 +1,6 @@
 use proc_macro2::TokenStream;
 use quote::{format_ident, quote};
-use syn::spanned::Spanned;
+use syn::{spanned::Spanned, AngleBracketedGenericArguments, GenericArgument, PathArguments, Type};
 
 use crate::{
     diagnostic::{DiagnosticConcreteArgs, DiagnosticDef},
@@ -104,3 +104,36 @@ impl Display {
         (fmt, args)
     }
 }
+
+/// Tries to extract the type of a (presumed) option type, returning the extracted type if it suceeded.
+pub fn extract_option(r#type: &Type) -> Option<&Type> {
+    let syn::Type::Path(syn::TypePath {
+        path: syn::Path { segments, .. },
+        ..
+    }) = r#type
+    else {
+        return None;
+    };
+
+    let last_segment = segments.last()?;
+
+    if last_segment.ident != "Option" {
+        return None;
+    }
+
+    let PathArguments::AngleBracketed(AngleBracketedGenericArguments { args, .. }) =
+        &last_segment.arguments
+    else {
+        return None;
+    };
+
+    if args.len() != 1 {
+        return None;
+    }
+
+    let Some(GenericArgument::Type(ty)) = args.first() else {
+        return None;
+    };
+
+    Some(ty)
+}