Improve the error message for bad type bounds

We emit one error for all unsatisfied bounds such as:

test.rs:26:31: error: bounds not satisfied for Test ‘Bar, Baz’ is not satisfied
   21 | fn type_bound_test<T: Foo + Bar + Baz>() -> i32 {
      |                             ~     ~
......
   26 |     let a = type_bound_test::<Test>();
      |                               ^

4 files changed, 60 insertions, 29 deletions

diff --git a/gcc/rust/typecheck/rust-hir-type-check-type.h b/gcc/rust/typecheck/rust-hir-type-check-type.h
index ef1510e..fff86be 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-type.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-type.h
@@ -283,7 +283,7 @@ public:
 
 		  TraitReference *trait = resolve_trait_path (b->get_path ());
 		  TyTy::TypeBoundPredicate predicate (
-		    trait->get_mappings ().get_defid ());
+		    trait->get_mappings ().get_defid (), b->get_locus ());
 
 		  specified_bounds.push_back (std::move (predicate));
 		}
diff --git a/gcc/rust/typecheck/rust-tyty-bounds.cc b/gcc/rust/typecheck/rust-tyty-bounds.cc
index 3562e85..008dc19 100644
--- a/gcc/rust/typecheck/rust-tyty-bounds.cc
+++ b/gcc/rust/typecheck/rust-tyty-bounds.cc
@@ -83,5 +83,11 @@ TypeBoundPredicate::get () const
   return ref;
 }
 
+std::string
+TypeBoundPredicate::get_name () const
+{
+  return get ()->get_name ();
+}
+
 } // namespace TyTy
 } // namespace Rust
diff --git a/gcc/rust/typecheck/rust-tyty.cc b/gcc/rust/typecheck/rust-tyty.cc
index 88b6c35..2d165c3 100644
--- a/gcc/rust/typecheck/rust-tyty.cc
+++ b/gcc/rust/typecheck/rust-tyty.cc
@@ -62,6 +62,49 @@ BaseType::satisfies_bound (const TypeBoundPredicate &predicate) const
   return false;
 }
 
+bool
+BaseType::bounds_compatible (const BaseType &other, Location locus) const
+{
+  std::vector<std::reference_wrapper<const TypeBoundPredicate>>
+    unsatisfied_bounds;
+  for (auto &bound : get_specified_bounds ())
+    {
+      if (!other.satisfies_bound (bound))
+	unsatisfied_bounds.push_back (bound);
+    }
+
+  // lets emit a single error for this
+  if (unsatisfied_bounds.size () > 0)
+    {
+      RichLocation r (locus);
+      std::string missing_preds;
+      for (size_t i = 0; i < unsatisfied_bounds.size (); i++)
+	{
+	  const TypeBoundPredicate &pred = unsatisfied_bounds.at (i);
+	  r.add_range (pred.get_locus ());
+	  missing_preds += pred.get_name ();
+
+	  bool have_next = (i + 1) < unsatisfied_bounds.size ();
+	  if (have_next)
+	    missing_preds += ", ";
+	}
+
+      rust_error_at (r, "bounds not satisfied for %s %<%s%> is not satisfied",
+		     other.get_name ().c_str (), missing_preds.c_str ());
+    }
+
+  return unsatisfied_bounds.size () == 0;
+}
+
+void
+BaseType::inherit_bounds (const BaseType &other)
+{
+  for (auto &bound : other.get_specified_bounds ())
+    {
+      add_bound (bound);
+    }
+}
+
 TyVar::TyVar (HirId ref) : ref (ref)
 {
   // ensure this reference is defined within the context
diff --git a/gcc/rust/typecheck/rust-tyty.h b/gcc/rust/typecheck/rust-tyty.h
index f6f9579..c1afa14 100644
--- a/gcc/rust/typecheck/rust-tyty.h
+++ b/gcc/rust/typecheck/rust-tyty.h
@@ -132,14 +132,21 @@ public:
 class TypeBoundPredicate
 {
 public:
-  TypeBoundPredicate (DefId reference) : reference (reference) {}
+  TypeBoundPredicate (DefId reference, Location locus)
+    : reference (reference), locus (locus)
+  {}
 
   std::string as_string () const;
 
   const Resolver::TraitReference *get () const;
 
+  Location get_locus () const { return locus; }
+
+  std::string get_name () const;
+
 private:
   DefId reference;
+  Location locus;
 };
 
 class TypeBoundsMappings
@@ -241,34 +248,9 @@ public:
 
   bool satisfies_bound (const TypeBoundPredicate &predicate) const;
 
-  bool bounds_compatible (const BaseType &other, Location locus) const
-  {
-    std::vector<std::reference_wrapper<const TypeBoundPredicate>>
-      unsatisfied_bounds;
-    for (auto &bound : get_specified_bounds ())
-      {
-	if (!other.satisfies_bound (bound))
-	  unsatisfied_bounds.push_back (bound);
-      }
-
-    if (unsatisfied_bounds.size () > 0)
-      {
-	RichLocation r (locus);
-	rust_error_at (r, "bounds not satisfied for %s",
-		       other.as_string ().c_str ());
-	return false;
-      }
-
-    return unsatisfied_bounds.size () == 0;
-  }
+  bool bounds_compatible (const BaseType &other, Location locus) const;
 
-  void inherit_bounds (const BaseType &other)
-  {
-    for (auto &bound : other.get_specified_bounds ())
-      {
-	add_bound (bound);
-      }
-  }
+  void inherit_bounds (const BaseType &other);
 
   virtual bool is_unit () const { return false; }