[gcc/devel/rust/master] Add missing coercion rule from array to slice

[gcc/devel/rust/master] Add missing coercion rule from array to slice

[Thomas Schwinge]

https://gcc.gnu.org/g:639b3d61ab124ab14e0935893abe437ed7f6ad52

commit 639b3d61ab124ab14e0935893abe437ed7f6ad52
Author: Philip Herron <philip.herron@embecosm.com>
Date:   Thu Apr 21 20:14:43 2022 +0100

    Add missing coercion rule from array to slice
    
    Arrays are coercible into slices, this adds the missing type-resolution
    the rule which works for now. The other part of this fix is described in
    so that we reuse as much code as possible and handle complex coercion
    sites.
    
    Fixes #1129

Diff:
---
 gcc/rust/typecheck/rust-tyty-coercion.h    | 16 ++++++++++++++++
 gcc/testsuite/rust/compile/issue-1129-1.rs |  4 ++++
 gcc/testsuite/rust/compile/issue-1129-2.rs | 22 ++++++++++++++++++++++
 3 files changed, 42 insertions(+)

diff --git a/gcc/rust/typecheck/rust-tyty-coercion.h b/gcc/rust/typecheck/rust-tyty-coercion.h
index c24f17e6c94..e13c7f8d982 100644
--- a/gcc/rust/typecheck/rust-tyty-coercion.h
+++ b/gcc/rust/typecheck/rust-tyty-coercion.h
@@ -886,6 +886,22 @@ public:
 			      TyVar (base_resolved->get_ref ()));
   }
 
+  void visit (ArrayType &type) override
+  {
+    // check base type
+    auto base_resolved
+      = base->get_element_type ()->unify (type.get_element_type ());
+    if (base_resolved == nullptr)
+      {
+	BaseCoercionRules::visit (type);
+	return;
+      }
+
+    resolved = new SliceType (type.get_ref (), type.get_ty_ref (),
+			      type.get_ident ().locus,
+			      TyVar (base_resolved->get_ref ()));
+  }
+
 private:
   BaseType *get_base () override { return base; }
 
diff --git a/gcc/testsuite/rust/compile/issue-1129-1.rs b/gcc/testsuite/rust/compile/issue-1129-1.rs
new file mode 100644
index 00000000000..a15903983f0
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-1129-1.rs
@@ -0,0 +1,4 @@
+// { dg-additional-options "-w" }
+fn write_u8(i: u8) {
+    let x: &[u8] = &[i];
+}
diff --git a/gcc/testsuite/rust/compile/issue-1129-2.rs b/gcc/testsuite/rust/compile/issue-1129-2.rs
new file mode 100644
index 00000000000..25d30faf4aa
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-1129-2.rs
@@ -0,0 +1,22 @@
+// { dg-additional-options "-w" }
+pub trait Hasher {
+    fn finish(&self) -> u64;
+    fn write(&mut self, bytes: &[u8]);
+    fn write_u8(&mut self, i: u8) {
+        self.write(&[i])
+    }
+}
+
+struct SipHasher;
+
+impl Hasher for SipHasher {
+    #[inline]
+    fn write(&mut self, msg: &[u8]) {
+        loop {}
+    }
+
+    #[inline]
+    fn finish(&self) -> u64 {
+        0
+    }
+}