1 files changed, 83 insertions, 0 deletions
diff --git a/third_party/rust/thiserror-impl/src/generics.rs b/third_party/rust/thiserror-impl/src/generics.rs
new file mode 100644
index 0000000000..95592a7370
--- /dev/null
+++ b/third_party/rust/thiserror-impl/src/generics.rs
@@ -0,0 +1,83 @@
+use proc_macro2::TokenStream;
+use quote::ToTokens;
+use std::collections::btree_map::Entry;
+use std::collections::{BTreeMap as Map, BTreeSet as Set};
+use syn::punctuated::Punctuated;
+use syn::{parse_quote, GenericArgument, Generics, Ident, PathArguments, Token, Type, WhereClause};
+
+pub struct ParamsInScope<'a> {
+    names: Set<&'a Ident>,
+}
+
+impl<'a> ParamsInScope<'a> {
+    pub fn new(generics: &'a Generics) -> Self {
+        ParamsInScope {
+            names: generics.type_params().map(|param| &param.ident).collect(),
+        }
+    }
+
+    pub fn intersects(&self, ty: &Type) -> bool {
+        let mut found = false;
+        crawl(self, ty, &mut found);
+        found
+    }
+}
+
+fn crawl(in_scope: &ParamsInScope, ty: &Type, found: &mut bool) {
+    if let Type::Path(ty) = ty {
+        if ty.qself.is_none() {
+            if let Some(ident) = ty.path.get_ident() {
+                if in_scope.names.contains(ident) {
+                    *found = true;
+                }
+            }
+        }
+        for segment in &ty.path.segments {
+            if let PathArguments::AngleBracketed(arguments) = &segment.arguments {
+                for arg in &arguments.args {
+                    if let GenericArgument::Type(ty) = arg {
+                        crawl(in_scope, ty, found);
+                    }
+                }
+            }
+        }
+    }
+}
+
+pub struct InferredBounds {
+    bounds: Map<String, (Set<String>, Punctuated<TokenStream, Token![+]>)>,
+    order: Vec<TokenStream>,
+}
+
+impl InferredBounds {
+    pub fn new() -> Self {
+        InferredBounds {
+            bounds: Map::new(),
+            order: Vec::new(),
+        }
+    }
+
+    #[allow(clippy::type_repetition_in_bounds, clippy::trait_duplication_in_bounds)] // clippy bug: https://github.com/rust-lang/rust-clippy/issues/8771
+    pub fn insert(&mut self, ty: impl ToTokens, bound: impl ToTokens) {
+        let ty = ty.to_token_stream();
+        let bound = bound.to_token_stream();
+        let entry = self.bounds.entry(ty.to_string());
+        if let Entry::Vacant(_) = entry {
+            self.order.push(ty);
+        }
+        let (set, tokens) = entry.or_default();
+        if set.insert(bound.to_string()) {
+            tokens.push(bound);
+        }
+    }
+
+    pub fn augment_where_clause(&self, generics: &Generics) -> WhereClause {
+        let mut generics = generics.clone();
+        let where_clause = generics.make_where_clause();
+        for ty in &self.order {
+            let (_set, bounds) = &self.bounds[&ty.to_string()];
+            where_clause.predicates.push(parse_quote!(#ty: #bounds));
+        }
+        generics.where_clause.unwrap()
+    }
+}