Fix ICE during HIR lowering of ExprWithBlock MatchExpr

When we are lowering blocks using the visitor pattern we must use the
BaseClass of ExprWithBlock to abstract away the notion that this expr
has a block such that we can handle cases like a block expr vs expressions
with a block. This makes the usage of hir lowering of match expressions to
be recursive, if we had more fine grained visitors in the AST we could fix
these types of problems with compile time enforced interfaces.

Fixes #858

Author: philberty

gcc/rust/hir/rust-ast-lower-block.h

@@ -191,6 +191,8 @@ class ASTLoweringExprWithBlock : public ASTLoweringBase
 
   void visit (AST::WhileLoopExpr &expr) override;
 
+  void visit (AST::MatchExpr &expr) override;
+
 private:
   ASTLoweringExprWithBlock ()
     : ASTLoweringBase (), translated (nullptr), terminated (false)

gcc/rust/hir/rust-ast-lower-expr.h

@@ -674,52 +674,7 @@ class ASTLoweringExpr : public ASTLoweringBase
 
   void visit (AST::MatchExpr &expr) override
   {
-    HIR::Expr *branch_value
-      = ASTLoweringExpr::translate (expr.get_scrutinee_expr ().get ());
-
-    std::vector<HIR::MatchCase> match_arms;
-    for (auto &match_case : expr.get_match_cases ())
-      {
-	HIR::Expr *kase_expr
-	  = ASTLoweringExpr::translate (match_case.get_expr ().get ());
-
-	HIR::Expr *kase_guard_expr = nullptr;
-	if (match_case.get_arm ().has_match_arm_guard ())
-	  {
-	    kase_guard_expr = ASTLoweringExpr::translate (
-	      match_case.get_arm ().get_guard_expr ().get ());
-	  }
-
-	std::vector<std::unique_ptr<HIR::Pattern> > match_arm_patterns;
-	for (auto &pattern : match_case.get_arm ().get_patterns ())
-	  {
-	    HIR::Pattern *ptrn = ASTLoweringPattern::translate (pattern.get ());
-	    match_arm_patterns.push_back (std::unique_ptr<HIR::Pattern> (ptrn));
-	  }
-
-	HIR::MatchArm arm (std::move (match_arm_patterns), expr.get_locus (),
-			   std::unique_ptr<HIR::Expr> (kase_guard_expr),
-			   match_case.get_arm ().get_outer_attrs ());
-
-	auto crate_num = mappings->get_current_crate ();
-	Analysis::NodeMapping mapping (crate_num, expr.get_node_id (),
-				       mappings->get_next_hir_id (crate_num),
-				       UNKNOWN_LOCAL_DEFID);
-
-	HIR::MatchCase kase (std::move (mapping), std::move (arm),
-			     std::unique_ptr<HIR::Expr> (kase_expr));
-	match_arms.push_back (std::move (kase));
-      }
-
-    auto crate_num = mappings->get_current_crate ();
-    Analysis::NodeMapping mapping (crate_num, expr.get_node_id (),
-				   mappings->get_next_hir_id (crate_num),
-				   UNKNOWN_LOCAL_DEFID);
-
-    translated
-      = new HIR::MatchExpr (mapping, std::unique_ptr<HIR::Expr> (branch_value),
-			    std::move (match_arms), expr.get_inner_attrs (),
-			    expr.get_outer_attrs (), expr.get_locus ());
+    translated = ASTLoweringExprWithBlock::translate (&expr, &terminated);
   }
 
   void visit (AST::RangeFromToExpr &expr) override

gcc/rust/hir/rust-ast-lower.cc

@@ -299,6 +299,57 @@ ASTLoweringExprWithBlock::visit (AST::WhileLoopExpr &expr)
 			      expr.get_outer_attrs ());
 }
 
+void
+ASTLoweringExprWithBlock::visit (AST::MatchExpr &expr)
+{
+  HIR::Expr *branch_value
+    = ASTLoweringExpr::translate (expr.get_scrutinee_expr ().get ());
+
+  std::vector<HIR::MatchCase> match_arms;
+  for (auto &match_case : expr.get_match_cases ())
+    {
+      HIR::Expr *kase_expr
+	= ASTLoweringExpr::translate (match_case.get_expr ().get ());
+
+      HIR::Expr *kase_guard_expr = nullptr;
+      if (match_case.get_arm ().has_match_arm_guard ())
+	{
+	  kase_guard_expr = ASTLoweringExpr::translate (
+	    match_case.get_arm ().get_guard_expr ().get ());
+	}
+
+      std::vector<std::unique_ptr<HIR::Pattern> > match_arm_patterns;
+      for (auto &pattern : match_case.get_arm ().get_patterns ())
+	{
+	  HIR::Pattern *ptrn = ASTLoweringPattern::translate (pattern.get ());
+	  match_arm_patterns.push_back (std::unique_ptr<HIR::Pattern> (ptrn));
+	}
+
+      HIR::MatchArm arm (std::move (match_arm_patterns), expr.get_locus (),
+			 std::unique_ptr<HIR::Expr> (kase_guard_expr),
+			 match_case.get_arm ().get_outer_attrs ());
+
+      auto crate_num = mappings->get_current_crate ();
+      Analysis::NodeMapping mapping (crate_num, expr.get_node_id (),
+				     mappings->get_next_hir_id (crate_num),
+				     UNKNOWN_LOCAL_DEFID);
+
+      HIR::MatchCase kase (std::move (mapping), std::move (arm),
+			   std::unique_ptr<HIR::Expr> (kase_expr));
+      match_arms.push_back (std::move (kase));
+    }
+
+  auto crate_num = mappings->get_current_crate ();
+  Analysis::NodeMapping mapping (crate_num, expr.get_node_id (),
+				 mappings->get_next_hir_id (crate_num),
+				 UNKNOWN_LOCAL_DEFID);
+
+  translated
+    = new HIR::MatchExpr (mapping, std::unique_ptr<HIR::Expr> (branch_value),
+			  std::move (match_arms), expr.get_inner_attrs (),
+			  expr.get_outer_attrs (), expr.get_locus ());
+}
+
 // rust-ast-lower-expr.h
 
 void

gcc/testsuite/rust/execute/torture/issue-858.rs

@@ -0,0 +1,32 @@
+/* { dg-output "Result: 123\n" } */
+extern "C" {
+    fn printf(s: *const i8, ...);
+}
+
+enum Foo<T> {
+    A,
+    B(T),
+}
+
+fn main() -> i32 {
+    let result = Foo::B(123);
+
+    match result {
+        Foo::A => unsafe {
+            let a = "A\n\0";
+            let b = a as *const str;
+            let c = b as *const i8;
+
+            printf(c);
+        },
+        Foo::B(x) => unsafe {
+            let a = "Result: %i\n\0";
+            let b = a as *const str;
+            let c = b as *const i8;
+
+            printf(c, x);
+        },
+    }
+
+    0
+}