Merge pull request #489 from jackh726/fn_def_binder

Add binders around inputs/outputs for FnDefDatum

Author: nikomatsakis

chalk-integration/src/lowering.rs

@@ -1030,10 +1030,15 @@ impl LowerFnDefn for FnDefn {
             let where_clauses = self.lower_where_clauses(env)?;
             let return_type = self.return_type.lower(env)?;
 
+            let inputs_and_output = env.in_binders(vec![], |_| {
+                Ok(rust_ir::FnDefInputsAndOutputDatum {
+                    argument_types: args?,
+                    return_type,
+                })
+            })?;
             Ok(rust_ir::FnDefDatumBound {
-                argument_types: args?,
+                inputs_and_output,
                 where_clauses,
-                return_type,
             })
         })?;
 

chalk-solve/src/rust_ir.rs

@@ -121,10 +121,10 @@ pub struct FnDefDatum<I: Interner> {
     pub binders: Binders<FnDefDatumBound<I>>,
 }
 
+/// Represents the inputs and outputs on a `FnDefDatum`. This is split
+/// from the where clauses, since these can contain bound lifetimes.
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Fold, HasInterner)]
-/// Represents the bounds on a `FnDefDatum`, including
-/// the function definition's type signature and where clauses.
-pub struct FnDefDatumBound<I: Interner> {
+pub struct FnDefInputsAndOutputDatum<I: Interner> {
     /// Types of the function's arguments
     /// ```ignore
     /// fn foo<T>(bar: i32, baz: T);
@@ -138,6 +138,26 @@ pub struct FnDefDatumBound<I: Interner> {
     ///                ^^^
     /// ```
     pub return_type: Ty<I>,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash, Fold, HasInterner)]
+/// Represents the bounds on a `FnDefDatum`, including
+/// the function definition's type signature and where clauses.
+pub struct FnDefDatumBound<I: Interner> {
+    /// Inputs and outputs defined on a function
+    /// These are needed for late-bound regions in rustc. For example the
+    /// lifetime `'a` in
+    /// ```ignore
+    /// fn foo<'a, T>(&'a T);
+    ///        ^^
+    /// ```
+    /// Rustc doesn't pass in late-bound the regions in substs, but the inputs
+    /// and outputs may use them. `where_clauses` don't need an extra set of
+    /// `Binders`, since any lifetimes found in where clauses are not late-bound.
+    ///
+    /// For more information, see [this rustc-dev-guide chapter](https://rustc-dev-guide.rust-lang.org/early-late-bound.html).
+    pub inputs_and_output: Binders<FnDefInputsAndOutputDatum<I>>,
+
     /// Where clauses defined on the function
     /// ```ignore
     /// fn foo<T>() where T: Eq;