[gcc/devel/rust/master] Support placeholders becoming slices

[gcc/devel/rust/master] Support placeholders becoming slices

[Thomas Schwinge]

https://gcc.gnu.org/g:f6c86fc8cdea9db5259ae67a62618b13a57ea9a1

commit f6c86fc8cdea9db5259ae67a62618b13a57ea9a1
Author: Philip Herron <philip.herron@embecosm.com>
Date:   Thu Mar 17 10:38:58 2022 +0000

    Support placeholders becoming slices
    
    When we setup trait-impls the type-alias are allowed to become any type
    this interface was missing a visitor. We also need to support constraining
    type-parameters behind slices.
    
    The get_root interface is currently unsafe, it needs a flag for allowing
    unsized and for keeping a map of adjustments along the way.
    
    Fixes #1034

Diff:
---
 gcc/rust/typecheck/rust-hir-type-check-expr.h     |  1 -
 gcc/rust/typecheck/rust-hir-type-check-implitem.h |  2 --
 gcc/rust/typecheck/rust-tyty-cmp.h                |  2 ++
 gcc/rust/typecheck/rust-tyty.cc                   | 14 ++++++++++++++
 gcc/testsuite/rust/compile/issue-1034.rs          | 16 ++++++++++++++++
 5 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/gcc/rust/typecheck/rust-hir-type-check-expr.h b/gcc/rust/typecheck/rust-hir-type-check-expr.h
index 93aa868505c..1b14693aa8d 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-expr.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-expr.h
@@ -258,7 +258,6 @@ public:
     // Get the adjusted self
     Adjuster adj (receiver_tyty);
     TyTy::BaseType *adjusted_self = adj.adjust_type (candidate.adjustments);
-    adjusted_self->debug ();
 
     // store the adjustments for code-generation to know what to do
     context->insert_autoderef_mappings (expr.get_mappings ().get_hirid (),
diff --git a/gcc/rust/typecheck/rust-hir-type-check-implitem.h b/gcc/rust/typecheck/rust-hir-type-check-implitem.h
index 1722d16e4a9..f1b5e35450e 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-implitem.h
+++ b/gcc/rust/typecheck/rust-hir-type-check-implitem.h
@@ -440,8 +440,6 @@ public:
 
   void visit (HIR::TypeAlias &type) override
   {
-    // resolved_trait_item = trait_reference.lookup_trait_item (
-    //   type.get_new_type_name (), TraitItemReference::TraitItemType::TYPE);
     trait_reference.lookup_trait_item_by_type (
       type.get_new_type_name (), TraitItemReference::TraitItemType::TYPE,
       &resolved_trait_item);
diff --git a/gcc/rust/typecheck/rust-tyty-cmp.h b/gcc/rust/typecheck/rust-tyty-cmp.h
index 436bde9a295..6504e5aee1d 100644
--- a/gcc/rust/typecheck/rust-tyty-cmp.h
+++ b/gcc/rust/typecheck/rust-tyty-cmp.h
@@ -1444,6 +1444,8 @@ public:
 
   void visit (const NeverType &) override { ok = true; }
 
+  void visit (const SliceType &) override { ok = true; }
+
   void visit (const PlaceholderType &type) override
   {
     ok = base->get_symbol ().compare (type.get_symbol ()) == 0;
diff --git a/gcc/rust/typecheck/rust-tyty.cc b/gcc/rust/typecheck/rust-tyty.cc
index c12095f26eb..1d197f5a845 100644
--- a/gcc/rust/typecheck/rust-tyty.cc
+++ b/gcc/rust/typecheck/rust-tyty.cc
@@ -201,6 +201,7 @@ BaseType::inherit_bounds (
 const BaseType *
 BaseType::get_root () const
 {
+  // FIXME this needs to be it its own visitor class with a vector adjustments
   const TyTy::BaseType *root = this;
   if (get_kind () == TyTy::REF)
     {
@@ -212,6 +213,19 @@ BaseType::get_root () const
       const PointerType *r = static_cast<const PointerType *> (root);
       root = r->get_base ()->get_root ();
     }
+
+  // these are an unsize
+  else if (get_kind () == TyTy::SLICE)
+    {
+      const SliceType *r = static_cast<const SliceType *> (root);
+      root = r->get_element_type ()->get_root ();
+    }
+  // else if (get_kind () == TyTy::ARRAY)
+  //   {
+  //     const ArrayType *r = static_cast<const ArrayType *> (root);
+  //     root = r->get_element_type ()->get_root ();
+  //   }
+
   return root;
 }
 
diff --git a/gcc/testsuite/rust/compile/issue-1034.rs b/gcc/testsuite/rust/compile/issue-1034.rs
new file mode 100644
index 00000000000..23d77005452
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-1034.rs
@@ -0,0 +1,16 @@
+trait Foo<T> {
+    type Output;
+
+    fn test(self, slice: &T) -> &Self::Output;
+}
+
+struct Bar<T>(T);
+// { dg-warning "struct is never constructed" "" { target *-*-* } .-1 }
+
+impl<T> Foo<[T]> for Bar<usize> {
+    type Output = [T];
+
+    fn test(self, slice: &[T]) -> &[T] {
+        slice
+    }
+}