gccrs: constant evaluation like these are coercion sites

The code here was wrongly assuming the decl type from the folding of the
expression would be the type of the constant decl. This is not the case for
unsized coercions for slices, where the expression here is a reference to
an array then we require the coercion to fix the result up to the expected
type.

Fixes Rust-GCC#1525

gcc/rust/ChangeLog:

	* backend/rust-compile-base.cc: apply coercion site to result
	* backend/rust-compile-base.h: update prototype
	* backend/rust-compile-implitem.cc (CompileTraitItem::visit): send in coercion info
	* backend/rust-compile-item.cc (CompileItem::visit): likewise

gcc/testsuite/ChangeLog:

	* rust/compile/issue-1525.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

5 files changed, 50 insertions, 15 deletions

diff --git a/gcc/rust/backend/rust-compile-base.cc b/gcc/rust/backend/rust-compile-base.cc
index fb4aace..bcc7fc4 100644
--- a/gcc/rust/backend/rust-compile-base.cc
+++ b/gcc/rust/backend/rust-compile-base.cc
@@ -777,13 +777,18 @@ HIRCompileBase::compile_function (
 
 tree
 HIRCompileBase::compile_constant_item (
-  TyTy::BaseType *resolved_type, const Resolver::CanonicalPath &canonical_path,
-  HIR::Expr &const_value_expr, location_t locus)
+  HirId coercion_id, TyTy::BaseType *resolved_type,
+  TyTy::BaseType *expected_type, const Resolver::CanonicalPath &canonical_path,
+  HIR::Expr &const_value_expr, location_t locus, location_t expr_locus)
 {
   const std::string &ident = canonical_path.get ();
 
   tree type = TyTyResolveCompile::compile (ctx, resolved_type);
   tree const_type = build_qualified_type (type, TYPE_QUAL_CONST);
+
+  tree actual_type = TyTyResolveCompile::compile (ctx, expected_type);
+  tree actual_const_type = build_qualified_type (actual_type, TYPE_QUAL_CONST);
+
   bool is_block_expr
     = const_value_expr.get_expression_type () == HIR::Expr::ExprType::Block;
 
@@ -851,7 +856,11 @@ HIRCompileBase::compile_constant_item (
   tree call = build_call_array_loc (locus, const_type, fndecl, 0, NULL);
   tree folded_expr = fold_expr (call);
 
-  return named_constant_expression (const_type, ident, folded_expr, locus);
+  // coercion site
+  tree coerced = coercion_site (coercion_id, folded_expr, resolved_type,
+				expected_type, locus, expr_locus);
+
+  return named_constant_expression (actual_const_type, ident, coerced, locus);
 }
 
 tree
diff --git a/gcc/rust/backend/rust-compile-base.h b/gcc/rust/backend/rust-compile-base.h
index 5fb1d83..9328a7f 100644
--- a/gcc/rust/backend/rust-compile-base.h
+++ b/gcc/rust/backend/rust-compile-base.h
@@ -90,9 +90,11 @@ protected:
   void compile_function_body (tree fndecl, HIR::BlockExpr &function_body,
 			      TyTy::BaseType *fn_return_ty);
 
-  tree compile_constant_item (TyTy::BaseType *resolved_type,
+  tree compile_constant_item (HirId coercion_id, TyTy::BaseType *resolved_type,
+			      TyTy::BaseType *expected_type,
 			      const Resolver::CanonicalPath &canonical_path,
-			      HIR::Expr &const_value_expr, location_t locus);
+			      HIR::Expr &const_value_expr, location_t locus,
+			      location_t expr_locus);
 
   tree compile_function (const std::string &fn_name, HIR::SelfParam &self_param,
 			 std::vector<HIR::FunctionParam> &function_params,
diff --git a/gcc/rust/backend/rust-compile-implitem.cc b/gcc/rust/backend/rust-compile-implitem.cc
index 129e978..71b3e8d 100644
--- a/gcc/rust/backend/rust-compile-implitem.cc
+++ b/gcc/rust/backend/rust-compile-implitem.cc
@@ -45,9 +45,16 @@ CompileTraitItem::visit (HIR::TraitItemConst &constant)
   rust_assert (canonical_path);
 
   HIR::Expr &const_value_expr = constant.get_expr ();
+  TyTy::BaseType *expr_type = nullptr;
+  bool ok = ctx->get_tyctx ()->lookup_type (
+    const_value_expr.get_mappings ().get_hirid (), &expr_type);
+  rust_assert (ok);
+
   tree const_expr
-    = compile_constant_item (resolved_type, *canonical_path, const_value_expr,
-			     constant.get_locus ());
+    = compile_constant_item (constant.get_mappings ().get_hirid (), expr_type,
+			     resolved_type, *canonical_path, const_value_expr,
+			     constant.get_locus (),
+			     const_value_expr.get_locus ());
   ctx->push_const (const_expr);
   ctx->insert_const_decl (constant.get_mappings ().get_hirid (), const_expr);
 
diff --git a/gcc/rust/backend/rust-compile-item.cc b/gcc/rust/backend/rust-compile-item.cc
index dd37e39..52cd59f 100644
--- a/gcc/rust/backend/rust-compile-item.cc
+++ b/gcc/rust/backend/rust-compile-item.cc
@@ -35,10 +35,16 @@ CompileItem::visit (HIR::StaticItem &var)
       return;
     }
 
+  HIR::Expr &const_value_expr = var.get_expr ();
+
   TyTy::BaseType *resolved_type = nullptr;
+  TyTy::BaseType *expr_type = nullptr;
   bool ok = ctx->get_tyctx ()->lookup_type (var.get_mappings ().get_hirid (),
 					    &resolved_type);
   rust_assert (ok);
+  ok = ctx->get_tyctx ()->lookup_type (
+    const_value_expr.get_mappings ().get_hirid (), &expr_type);
+  rust_assert (ok);
 
   tree type = TyTyResolveCompile::compile (ctx, resolved_type);
 
@@ -60,10 +66,11 @@ CompileItem::visit (HIR::StaticItem &var)
 
   rust_assert (canonical_path.has_value ());
 
-  HIR::Expr &const_value_expr = var.get_expr ();
   ctx->push_const_context ();
-  tree value = compile_constant_item (resolved_type, *canonical_path,
-				      const_value_expr, var.get_locus ());
+  tree value
+    = compile_constant_item (var.get_mappings ().get_hirid (), expr_type,
+			     resolved_type, *canonical_path, const_value_expr,
+			     var.get_locus (), const_value_expr.get_locus ());
   ctx->pop_const_context ();
 
   std::string name = canonical_path->get ();
@@ -89,16 +96,21 @@ CompileItem::visit (HIR::StaticItem &var)
 void
 CompileItem::visit (HIR::ConstantItem &constant)
 {
+  HIR::Expr &const_value_expr = constant.get_expr ();
   auto &mappings = constant.get_mappings ();
 
   if (ctx->lookup_const_decl (mappings.get_hirid (), &reference))
     return;
 
   // resolve the type
-  TyTy::BaseType *resolved_type = nullptr;
+  TyTy::BaseType *constant_type = nullptr;
+  TyTy::BaseType *expr_type = nullptr;
 
   bool ok
-    = ctx->get_tyctx ()->lookup_type (mappings.get_hirid (), &resolved_type);
+    = ctx->get_tyctx ()->lookup_type (mappings.get_hirid (), &constant_type);
+  rust_assert (ok);
+  ok = ctx->get_tyctx ()->lookup_type (
+    const_value_expr.get_mappings ().get_hirid (), &expr_type);
   rust_assert (ok);
 
   // canonical path
@@ -120,11 +132,12 @@ CompileItem::visit (HIR::ConstantItem &constant)
 			 .value ();
     }
 
-  HIR::Expr &const_value_expr = constant.get_expr ();
   ctx->push_const_context ();
   tree const_expr
-    = compile_constant_item (resolved_type, canonical_path, const_value_expr,
-			     constant.get_locus ());
+    = compile_constant_item (mappings.get_hirid (), expr_type, constant_type,
+			     canonical_path, const_value_expr,
+			     constant.get_locus (),
+			     const_value_expr.get_locus ());
   ctx->pop_const_context ();
 
   ctx->push_const (const_expr);
diff --git a/gcc/testsuite/rust/compile/issue-1525.rs b/gcc/testsuite/rust/compile/issue-1525.rs
new file mode 100644
index 0000000..b2247cd
--- /dev/null
+++ b/gcc/testsuite/rust/compile/issue-1525.rs
@@ -0,0 +1,4 @@
+fn main() {
+    const slice: &[i32] = &[1, 2, 3];
+    let _slice2: &[i32] = slice;
+}