Support result<void> to HILTI.

This allows to capture errors even if there's no actual result otherwise. Example (HILTI syntax): ``` function result<void> x(bool b) { if ( b ) return Null; # coerces to a successful result<void> else return error("trouble..."); } assert x(True); assert x(False).error() == error("trouble..."); ```
zeek · Jun 12, 2024 · ea47943 · ea47943
1 parent e0728cc
commit ea47943
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Showing 5 changed files with 36 additions and 4 deletions.
diff --git a/hilti/toolchain/src/compiler/codegen/ctors.cc b/hilti/toolchain/src/compiler/codegen/ctors.cc
@@ -157,7 +157,9 @@ struct Visitor : hilti::visitor::PreOrder {
     void operator()(ctor::Result* n) final {
         auto t = cg->compile(n->type(), codegen::TypeUsage::Storage);
 
-        if ( auto e = n->value() )
+        if ( n->value()->type()->type()->isA<type::Null>() )
+            result = fmt("::hilti::rt::Nothing{}");
+        else if ( auto e = n->value() )
             result = fmt("%s(%s)", t, cg->compile(e));
         else
             result = fmt("%s(%s)", t, cg->compile(n->error()));

diff --git a/hilti/toolchain/src/compiler/codegen/types.cc b/hilti/toolchain/src/compiler/codegen/types.cc
@@ -706,8 +706,12 @@ struct VisitorStorage : hilti::visitor::PreOrder {
     void operator()(type::Result* n) final {
         std::string t;
 
-        if ( const auto& ct = n->dereferencedType(); ! ct->isWildcard() )
-            t = fmt("::hilti::rt::Result<%s>", cg->compile(ct, codegen::TypeUsage::Storage));
+        if ( const auto& ct = n->dereferencedType(); ! ct->isWildcard() ) {
+            if ( ct->type()->isA<type::Void>() )
+                t = "::hilti::rt::Result<::hilti::rt::Nothing>";
+            else
+                t = fmt("::hilti::rt::Result<%s>", cg->compile(ct, codegen::TypeUsage::Storage));
+        }
         else
             t = "*";
 

diff --git a/hilti/toolchain/src/compiler/coercer.cc b/hilti/toolchain/src/compiler/coercer.cc
@@ -70,6 +70,11 @@ struct VisitorCtor : visitor::PreOrder {
             return;
         }
 
+        if ( auto t = dst->type()->tryAs<type::Result>(); t && t->dereferencedType()->type()->isA<type::Void>() ) {
+            result = builder->ctorResult(builder->expressionCtor(builder->ctorNull()));
+            return;
+        }
+
         if ( auto t = dst->type()->tryAs<type::StrongReference>() ) {
             result = builder->ctorStrongReference(t->dereferencedType());
             return;
@@ -462,6 +467,8 @@ struct VisitorType : visitor::PreOrder {
     void operator()(type::Null* n) final {
         if ( dst->type()->isA<type::Optional>() )
             result = dst;
+        else if ( auto t = dst->type()->tryAs<type::Result>(); t && t->dereferencedType()->type()->isA<type::Void>() )
+            result = dst;
         else if ( dst->type()->isA<type::StrongReference>() )
             result = dst;
         else if ( dst->type()->isA<type::WeakReference>() )

diff --git a/hilti/toolchain/src/compiler/validator.cc b/hilti/toolchain/src/compiler/validator.cc
@@ -643,7 +643,7 @@ struct VisitorPost : visitor::PreOrder, public validator::VisitorMixIn {
         if ( n->isWildcard() )
             return;
 
-        if ( const auto& t = n->dereferencedType(); ! t->type()->isAllocable() )
+        if ( const auto& t = n->dereferencedType(); ! t->type()->isAllocable() && ! t->type()->isA<type::Void>() )
             error(fmt("type %s cannot be used inside result", *t), n);
     }
 

diff --git a/tests/hilti/types/result/void.hlt b/tests/hilti/types/result/void.hlt
@@ -0,0 +1,19 @@
+# @TEST-EXEC: hiltic -j %INPUT >output
+#
+# @TEST-DOC: Test the special-case of `result<void>`.
+
+module Foo {
+
+import hilti;
+
+function result<void> x(bool b) {
+    if ( b )
+        return Null;
+    else
+        return error("trouble...");
+}
+
+assert x(True);
+assert x(False).error() == error("trouble...");
+
+}