Disallow block-level const declarations without a value expression. (F…

…uelLabs#4385)

Closes FuelLabs#4218.

## Description

As the title says, disallows block-level const declarations without a
value expressions.

## Checklist

- [x] I have linked to any relevant issues.
- [x] I have commented my code, particularly in hard-to-understand
areas.
- [x] I have updated the documentation where relevant (API docs, the
reference, and the Sway book).
- [x] I have added tests that prove my fix is effective or that my
feature works.
- [x] I have added (or requested a maintainer to add) the necessary
`Breaking*` or `New Feature` labels where relevant.
- [x] I have done my best to ensure that my PR adheres to [the Fuel Labs
Code Review
Standards](https://github.com/FuelLabs/rfcs/blob/master/text/code-standards/external-contributors.md).
- [x] I have requested a review from the relevant team or maintainers.

sway-core/src/transform/to_parsed_lang/convert_parse_tree.rs

@@ -188,7 +188,7 @@ fn item_to_ast_nodes(
         )?)),
         ItemKind::Const(item_const) => decl(Declaration::ConstantDeclaration(
             item_const_to_constant_declaration(
-                context, handler, engines, item_const, attributes, is_root,
+                context, handler, engines, item_const, attributes, true,
             )?,
         )),
         ItemKind::Storage(item_storage) => decl(Declaration::StorageDeclaration(
@@ -588,10 +588,10 @@ fn item_trait_to_trait_declaration(
                     fn_signature_to_trait_fn(context, handler, engines, fn_sig, attributes)
                         .map(TraitItem::TraitFn)
                 }
-                ItemTraitItem::Const(const_decl) => {
-                    item_const_to_const_decl(context, handler, engines, const_decl, attributes)
-                        .map(TraitItem::Constant)
-                }
+                ItemTraitItem::Const(const_decl) => item_const_to_constant_declaration(
+                    context, handler, engines, const_decl, attributes, false,
+                )
+                .map(TraitItem::Constant),
             }?))
         })
         .filter_map_ok(|item| item)
@@ -656,10 +656,10 @@ fn item_impl_to_declaration(
                     item_fn_to_function_declaration(context, handler, engines, fn_item, attributes)
                         .map(ImplItem::Fn)
                 }
-                sway_ast::ItemImplItem::Const(const_item) => {
-                    item_const_to_const_decl(context, handler, engines, const_item, attributes)
-                        .map(ImplItem::Constant)
-                }
+                sway_ast::ItemImplItem::Const(const_item) => item_const_to_constant_declaration(
+                    context, handler, engines, const_item, attributes, true,
+                )
+                .map(ImplItem::Constant),
             }?))
         })
         .filter_map_ok(|item| item)
@@ -767,8 +767,8 @@ fn item_abi_to_abi_declaration(
                             )?;
                             Ok(TraitItem::TraitFn(trait_fn))
                         }
-                        ItemTraitItem::Const(const_decl) => item_const_to_const_decl(
-                            context, handler, engines, const_decl, attributes,
+                        ItemTraitItem::Const(const_decl) => item_const_to_constant_declaration(
+                            context, handler, engines, const_decl, attributes, false,
                         )
                         .map(TraitItem::Constant),
                     }?))
@@ -820,7 +820,7 @@ pub(crate) fn item_const_to_constant_declaration(
     engines: Engines<'_>,
     item_const: ItemConst,
     attributes: AttributesMap,
-    is_root: bool,
+    require_expression: bool,
 ) -> Result<ConstantDeclaration, ErrorEmitted> {
     let span = item_const.span();
 
@@ -832,7 +832,7 @@ pub(crate) fn item_const_to_constant_declaration(
     let expr = match item_const.expr_opt {
         Some(expr) => Some(expr_to_expression(context, handler, engines, expr)?),
         None => {
-            if is_root {
+            if require_expression {
                 let err = ConvertParseTreeError::ConstantRequiresExpression { span: span.clone() };
                 if let Some(errors) = emit_all(handler, vec![err]) {
                     return Err(errors);
@@ -1314,33 +1314,6 @@ fn ty_to_type_argument(
     Ok(type_argument)
 }
 
-fn item_const_to_const_decl(
-    context: &mut Context,
-    handler: &Handler,
-    engines: Engines<'_>,
-    item: ItemConst,
-    attributes: AttributesMap,
-) -> Result<ConstantDeclaration, ErrorEmitted> {
-    let span = item.name.span();
-    let value = match item.expr_opt {
-        Some(expr) => Some(expr_to_expression(context, handler, engines, expr)?),
-        None => None,
-    };
-    let type_ascription = match item.ty_opt {
-        Some((_, ty)) => ty_to_type_argument(context, handler, engines, ty)?,
-        None => engines.te().insert(engines.de(), TypeInfo::Unknown).into(),
-    };
-    Ok(ConstantDeclaration {
-        name: item.name,
-        type_ascription,
-        value,
-        visibility: Visibility::Public,
-        is_configurable: true,
-        attributes,
-        span,
-    })
-}
-
 fn fn_signature_to_trait_fn(
     context: &mut Context,
     handler: &Handler,

test/src/e2e_vm_tests/test_programs/should_fail/const_block_level_no_expr/Forc.lock

@@ -0,0 +1,3 @@
+[[package]]
+name = 'const_block_level_no_expr'
+source = 'member'

test/src/e2e_vm_tests/test_programs/should_fail/const_block_level_no_expr/Forc.toml

@@ -0,0 +1,6 @@
+[project]
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+name = "const_block_level_no_expr"
+implicit-std = false

test/src/e2e_vm_tests/test_programs/should_fail/const_block_level_no_expr/src/main.sw

@@ -0,0 +1,6 @@
+script;
+
+fn main() -> u64 {
+    const X;
+    0
+}

test/src/e2e_vm_tests/test_programs/should_fail/const_block_level_no_expr/test.toml

@@ -0,0 +1,4 @@
+category = "fail"
+
+# check: $()const X;
+# nextln: $()Constant requires expression.