Introduce the ! type (named "never")

Author: lrh2000

gcc/rust/backend/rust-compile-context.h

@@ -503,6 +503,11 @@ class TyTyResolveCompile : public TyTy::TyVisitor
     translated = compiled_type;
   }
 
+  void visit (TyTy::NeverType &) override
+  {
+    translated = ctx->get_backend ()->void_type ();
+  }
+
 private:
   TyTyResolveCompile (Context *ctx) : ctx (ctx), translated (nullptr) {}
 

gcc/rust/backend/rust-compile-tyty.h

@@ -222,6 +222,11 @@ class TyTyCompile : public TyTy::TyVisitor
       = backend->named_type ("str", raw_str, Linemap::predeclared_location ());
   }
 
+  void visit (TyTy::NeverType &) override
+  {
+    translated = backend->void_type ();
+  }
+
 private:
   TyTyCompile (::Backend *backend)
     : backend (backend), translated (nullptr),

gcc/rust/typecheck/rust-hir-type-check-expr.h

@@ -146,7 +146,7 @@ class TypeCheckExpr : public TypeCheckBase
   {
     if (!expr.has_return_expr ())
       {
-	infered = new TyTy::TupleType (expr.get_mappings ().get_hirid ());
+	infered = new TyTy::NeverType (expr.get_mappings ().get_hirid ());
 	return;
       }
 
@@ -165,6 +165,8 @@ class TypeCheckExpr : public TypeCheckBase
     fn_return_tyty->append_reference (expr_ty->get_ref ());
     for (auto &ref : infered->get_combined_refs ())
       fn_return_tyty->append_reference (ref);
+
+    infered = new TyTy::NeverType (expr.get_mappings ().get_hirid ());
   }
 
   void visit (HIR::CallExpr &expr) override
@@ -904,7 +906,7 @@ class TypeCheckExpr : public TypeCheckBase
 	context->swap_head_loop_context (unified_ty);
       }
 
-    infered = new TyTy::TupleType (expr.get_mappings ().get_hirid ());
+    infered = new TyTy::NeverType (expr.get_mappings ().get_hirid ());
   }
 
   void visit (HIR::ContinueExpr &expr) override
@@ -916,7 +918,7 @@ class TypeCheckExpr : public TypeCheckBase
 	return;
       }
 
-    infered = new TyTy::TupleType (expr.get_mappings ().get_hirid ());
+    infered = new TyTy::NeverType (expr.get_mappings ().get_hirid ());
   }
 
   void visit (HIR::BorrowExpr &expr) override

gcc/rust/typecheck/rust-hir-type-check-stmt.h

@@ -42,6 +42,12 @@ class TypeCheckStmt : public TypeCheckBase
   void visit (HIR::ExprStmtWithBlock &stmt) override
   {
     infered = TypeCheckExpr::Resolve (stmt.get_expr (), inside_loop);
+
+    if (stmt.is_unit_check_needed ())
+      {
+	auto unit = new TyTy::TupleType (stmt.get_mappings ().get_hirid ());
+	infered = unit->unify (infered);
+      }
   }
 
   void visit (HIR::ExprStmtWithoutBlock &stmt) override

gcc/rust/typecheck/rust-hir-type-check.cc

@@ -82,44 +82,27 @@ TypeResolution::Resolve (HIR::Crate &crate)
 void
 TypeCheckExpr::visit (HIR::BlockExpr &expr)
 {
-  TyTy::BaseType *block_tyty
-    = new TyTy::TupleType (expr.get_mappings ().get_hirid ());
-
   expr.iterate_stmts ([&] (HIR::Stmt *s) mutable -> bool {
-    bool is_final_stmt = expr.is_final_stmt (s);
-    bool has_final_expr = expr.has_expr () && expr.tail_expr_reachable ();
-    bool stmt_is_final_expr = is_final_stmt && !has_final_expr;
-
     auto resolved = TypeCheckStmt::Resolve (s, inside_loop);
     if (resolved == nullptr)
       {
 	rust_error_at (s->get_locus_slow (), "failure to resolve type");
 	return false;
       }
 
-    if (stmt_is_final_expr)
-      {
-	delete block_tyty;
-	block_tyty = resolved;
-      }
-    else if (!resolved->is_unit ())
-      {
-	rust_error_at (s->get_locus_slow (), "expected () got %s",
-		       resolved->as_string ().c_str ());
-      }
-
     return true;
   });
 
   if (expr.has_expr ())
-    {
-      delete block_tyty;
-
-      block_tyty
-	= TypeCheckExpr::Resolve (expr.get_final_expr ().get (), inside_loop);
-    }
-
-  infered = block_tyty->clone ();
+      infered = TypeCheckExpr::Resolve (
+	  expr.get_final_expr ().get (),
+	  inside_loop)->clone ();
+  else if (expr.is_tail_reachable ())
+      infered = new TyTy::TupleType (
+	  expr.get_mappings ().get_hirid ());
+  else
+      infered = new TyTy::NeverType (
+	  expr.get_mappings ().get_hirid ());
 }
 
 // RUST_HIR_TYPE_CHECK_STRUCT_FIELD

gcc/rust/typecheck/rust-substitution-mapper.h

@@ -94,6 +94,7 @@ class SubstMapper : public TyTy::TyVisitor
   void visit (TyTy::ReferenceType &) override { gcc_unreachable (); }
   void visit (TyTy::ParamType &) override { gcc_unreachable (); }
   void visit (TyTy::StrType &) override { gcc_unreachable (); }
+  void visit (TyTy::NeverType &) override { gcc_unreachable (); }
 
 private:
   SubstMapper (HirId ref, HIR::GenericArgs *generics, Location locus)
@@ -152,6 +153,7 @@ class SubstMapperInternal : public TyTy::TyVisitor
   void visit (TyTy::ReferenceType &) override { gcc_unreachable (); }
   void visit (TyTy::ParamType &) override { gcc_unreachable (); }
   void visit (TyTy::StrType &) override { gcc_unreachable (); }
+  void visit (TyTy::NeverType &) override { gcc_unreachable (); }
 
 private:
   SubstMapperInternal (HirId ref, TyTy::SubstitutionArgumentMappings &mappings)
@@ -206,6 +208,7 @@ class SubstMapperFromExisting : public TyTy::TyVisitor
   void visit (TyTy::ReferenceType &) override { gcc_unreachable (); }
   void visit (TyTy::ParamType &) override { gcc_unreachable (); }
   void visit (TyTy::StrType &) override { gcc_unreachable (); }
+  void visit (TyTy::NeverType &) override { gcc_unreachable (); }
 
 private:
   SubstMapperFromExisting (TyTy::BaseType *concrete, TyTy::BaseType *receiver)

gcc/rust/typecheck/rust-tycheck-dump.h

@@ -107,7 +107,7 @@ class TypeResolverDump : public TypeCheckBase
       return true;
     });
 
-    if (expr.has_expr () && expr.tail_expr_reachable ())
+    if (expr.has_expr ())
       {
 	dump += indent ();
 	expr.expr->accept_vis (*this);

gcc/rust/typecheck/rust-tyty-call.h

@@ -53,6 +53,7 @@ class TypeCheckCallExpr : private TyVisitor
   void visit (ReferenceType &type) override { gcc_unreachable (); }
   void visit (ParamType &) override { gcc_unreachable (); }
   void visit (StrType &) override { gcc_unreachable (); }
+  void visit (NeverType &) override { gcc_unreachable (); }
 
   // tuple-structs
   void visit (ADTType &type) override;
@@ -100,6 +101,7 @@ class TypeCheckMethodCallExpr : private TyVisitor
   void visit (ReferenceType &type) override { gcc_unreachable (); }
   void visit (ParamType &) override { gcc_unreachable (); }
   void visit (StrType &) override { gcc_unreachable (); }
+  void visit (NeverType &) override { gcc_unreachable (); }
 
   // FIXME
   void visit (FnPtr &type) override { gcc_unreachable (); }