From 639b3d61ab124ab14e0935893abe437ed7f6ad52 Mon Sep 17 00:00:00 2001
From: Philip Herron <philip.herron@embecosm.com>
Date: Thu, 21 Apr 2022 20:14:43 +0100
Subject: [PATCH] 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
---
 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(+)
 create mode 100644 gcc/testsuite/rust/compile/issue-1129-1.rs
 create mode 100644 gcc/testsuite/rust/compile/issue-1129-2.rs

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
+    }
+}