Replace TypeInfo::SelfType with a generic type parameter (#4962)

## Description

Fixes #4877

## Tasks

- [x] Make a simple example with a trait and an impl for it compile
- [x] Fix typechecking for empty enums
- [x] Fix typechecking for trait impl methods
- [x] Fix typechecking for impl self blocks
- [x] Fix the case of non-implemented supertraits
- [x] Fix typechecking of generic traits
- [x] Fix typechecking of generic impl self blocks
- [x] Resolve ambiguity between term/path-level `Self` and the
type-level `Self` type parameter (related PR #4459):
       - [x] enums
       - [x] structs (deferred as issue #5164)
- [x] Fix `Self` for type constraints
- [x] Fix looping during insertion of trait constraints for generic
tuples (inserted `occurs_check` to prevent unification of a generic `A`
with a tuple `(A, A)`;
- [x] Fix exponential growth of the traits map (around 30 tests out of
more than 680 are failing now); related PR: #5004
- [x] Fix `Self` type for blanket implementations
- [x] Fix `Self` for associated consts
- [x] Fix name resolution issues for some tests with traits (like
`should_pass/language/eq_intrinsic`); blocking issues:
       - #5018 
       - #5036
- [x] Fix `should_fail/generic_traits` test
- [x] Fix `should_pass/language/where_clause_impls` test
- [x] Fix `should_pass/language/name_resolution_inside_intrinsics` test
- [x] Remove some commented out code in `impl_trait.rs`
- [x] Comment new code
- [x] **Disable** `should_pass/language/associated_type_container` test
- [x] **Disable** `should_pass/language/associated_type_method` test
- [x] **Disable**
`should_pass/language/associated_type_and_associated_const` test
- [x] **Disable** `should_pass/language/associated_type_iterator` test

## 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.

---------

Co-authored-by: Joshua Batty <joshpbatty@gmail.com>
Co-authored-by: IGI-111 <igi-111@protonmail.com>

forc-plugins/forc-doc/src/render/item/type_anchor.rs

@@ -119,9 +119,6 @@ pub(crate) fn render_type_anchor(
         TypeInfo::Custom { call_path, .. } => Ok(box_html! {
             : call_path.suffix.as_str();
         }),
-        TypeInfo::SelfType => Ok(box_html! {
-            : "Self";
-        }),
         TypeInfo::B256 => Ok(box_html! {
             : "b256";
         }),

sway-core/src/abi_generation/evm_abi.rs

@@ -102,7 +102,6 @@ pub fn abi_str(type_info: &TypeInfo, type_engine: &TypeEngine, decl_engine: &Dec
                 .collect::<Vec<String>>();
             format!("({})", field_strs.join(", "))
         }
-        SelfType => "Self".into(),
         B256 => "uint256".into(),
         Numeric => "u64".into(), // u64 is the default
         Contract => "contract".into(),

sway-core/src/abi_generation/fuel_abi.rs

@@ -807,7 +807,6 @@ impl TypeInfo {
                     .collect::<Vec<String>>();
                 format!("({})", field_strs.join(", "))
             }
-            SelfType => "Self".into(),
             B256 => "b256".into(),
             Numeric => "u64".into(), // u64 is the default
             Contract => "contract".into(),

sway-core/src/control_flow_analysis/dead_code_analysis.rs

@@ -922,10 +922,10 @@ fn connect_typed_fn_decl<'eng: 'cfg, 'cfg>(
     for fn_param in fn_decl.parameters.iter() {
         let fn_param_node = graph.add_node(ControlFlowGraphNode::FunctionParameter {
             param_name: fn_param.name.clone(),
-            is_self: matches!(
-                type_engine.get(fn_param.type_argument.initial_type_id),
-                TypeInfo::SelfType
-            ),
+            is_self: engines
+                .te()
+                .get(fn_param.type_argument.initial_type_id)
+                .is_self_type(),
         });
         graph.add_edge(entry_node, fn_param_node, "".into());
 

sway-core/src/decl_engine/id.rs

@@ -134,6 +134,7 @@ impl SubstTypes for DeclId<TyTypeAliasDecl> {
         decl_engine.replace(*self, decl);
     }
 }
+
 impl SubstTypes for DeclId<TyTraitType> {
     fn subst_inner(&mut self, type_mapping: &TypeSubstMap, engines: &Engines) {
         let decl_engine = engines.de();
@@ -142,68 +143,3 @@ impl SubstTypes for DeclId<TyTraitType> {
         decl_engine.replace(*self, decl);
     }
 }
-
-impl ReplaceSelfType for DeclId<TyFunctionDecl> {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(self);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.replace(*self, decl);
-    }
-}
-impl ReplaceSelfType for DeclId<TyTraitDecl> {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(self);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.replace(*self, decl);
-    }
-}
-impl ReplaceSelfType for DeclId<TyTraitFn> {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(self);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.replace(*self, decl);
-    }
-}
-impl ReplaceSelfType for DeclId<TyImplTrait> {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(self);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.replace(*self, decl);
-    }
-}
-impl ReplaceSelfType for DeclId<TyStructDecl> {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(self);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.replace(*self, decl);
-    }
-}
-impl ReplaceSelfType for DeclId<TyEnumDecl> {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(self);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.replace(*self, decl);
-    }
-}
-impl ReplaceSelfType for DeclId<TyTypeAliasDecl> {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(self);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.replace(*self, decl);
-    }
-}
-impl ReplaceSelfType for DeclId<TyTraitType> {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(self);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.replace(*self, decl);
-    }
-}

sway-core/src/decl_engine/mapping.rs

@@ -56,6 +56,16 @@ impl fmt::Debug for DeclMapping {
 }
 
 impl DeclMapping {
+    pub(crate) fn new() -> Self {
+        Self {
+            mapping: Vec::new(),
+        }
+    }
+
+    pub(crate) fn insert(&mut self, k: SourceDecl, v: DestinationDecl) {
+        self.mapping.push((k, v))
+    }
+
     pub(crate) fn is_empty(&self) -> bool {
         self.mapping.is_empty()
     }

sway-core/src/decl_engine/ref.rs

@@ -119,22 +119,6 @@ where
         decl_engine.insert(decl)
     }
 }
-impl<T> DeclRef<DeclId<T>>
-where
-    DeclEngine: DeclEngineIndex<T>,
-    T: Named + Spanned + ReplaceSelfType,
-{
-    pub(crate) fn replace_self_type_and_insert_new(
-        &self,
-        engines: &Engines,
-        self_type: TypeId,
-    ) -> Self {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(&self.id);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.insert(decl)
-    }
-}
 
 impl<T> DeclRef<DeclId<T>>
 where
@@ -170,30 +154,12 @@ where
             .with_parent(decl_engine, self.id.into())
     }
 }
+
 impl<T> DeclRef<DeclId<T>>
 where
     AssociatedItemDeclId: From<DeclId<T>>,
     DeclEngine: DeclEngineIndex<T>,
-    T: Named + Spanned + ReplaceSelfType,
-{
-    pub(crate) fn replace_self_type_and_insert_new_with_parent(
-        &self,
-        engines: &Engines,
-        self_type: TypeId,
-    ) -> Self {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(&self.id);
-        decl.replace_self_type(engines, self_type);
-        decl_engine
-            .insert(decl)
-            .with_parent(decl_engine, self.id.into())
-    }
-}
-impl<T> DeclRef<DeclId<T>>
-where
-    AssociatedItemDeclId: From<DeclId<T>>,
-    DeclEngine: DeclEngineIndex<T>,
-    T: Named + Spanned + ReplaceDecls,
+    T: Named + Spanned + ReplaceDecls + std::fmt::Debug,
 {
     pub(crate) fn replace_decls_and_insert_new_with_parent(
         &self,
@@ -324,19 +290,6 @@ where
     }
 }
 
-impl<T> ReplaceSelfType for DeclRef<DeclId<T>>
-where
-    DeclEngine: DeclEngineIndex<T>,
-    T: Named + Spanned + ReplaceSelfType,
-{
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        let decl_engine = engines.de();
-        let mut decl = decl_engine.get(&self.id);
-        decl.replace_self_type(engines, self_type);
-        decl_engine.replace(self.id, decl);
-    }
-}
-
 impl ReplaceDecls for DeclRefFunction {
     fn replace_decls_inner(
         &mut self,

sway-core/src/ir_generation/convert.rs

@@ -158,7 +158,6 @@ fn convert_resolved_type(
         // Unsupported types which shouldn't exist in the AST after type checking and
         // monomorphisation.
         TypeInfo::Custom { .. } => reject_type!("Custom"),
-        TypeInfo::SelfType { .. } => reject_type!("Self"),
         TypeInfo::Contract => reject_type!("Contract"),
         TypeInfo::ContractCaller { .. } => reject_type!("ContractCaller"),
         TypeInfo::Unknown => reject_type!("Unknown"),

sway-core/src/language/ty/ast_node.rs

@@ -72,24 +72,6 @@ impl SubstTypes for TyAstNode {
     }
 }
 
-impl ReplaceSelfType for TyAstNode {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        match self.content {
-            TyAstNodeContent::ImplicitReturnExpression(ref mut exp) => {
-                exp.replace_self_type(engines, self_type)
-            }
-            TyAstNodeContent::Declaration(ref mut decl) => {
-                decl.replace_self_type(engines, self_type)
-            }
-            TyAstNodeContent::Expression(ref mut expr) => {
-                expr.replace_self_type(engines, self_type)
-            }
-            TyAstNodeContent::SideEffect(_) => (),
-            TyAstNodeContent::Error(_, _) => (),
-        }
-    }
-}
-
 impl ReplaceDecls for TyAstNode {
     fn replace_decls_inner(
         &mut self,

sway-core/src/language/ty/code_block.rs

@@ -34,14 +34,6 @@ impl SubstTypes for TyCodeBlock {
     }
 }
 
-impl ReplaceSelfType for TyCodeBlock {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        self.contents
-            .iter_mut()
-            .for_each(|x| x.replace_self_type(engines, self_type));
-    }
-}
-
 impl ReplaceDecls for TyCodeBlock {
     fn replace_decls_inner(
         &mut self,

sway-core/src/language/ty/declaration/constant.rs

@@ -94,16 +94,6 @@ impl SubstTypes for TyConstantDecl {
     }
 }
 
-impl ReplaceSelfType for TyConstantDecl {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        self.return_type.replace_self_type(engines, self_type);
-        self.type_ascription.replace_self_type(engines, self_type);
-        if let Some(expr) = &mut self.value {
-            expr.replace_self_type(engines, self_type);
-        }
-    }
-}
-
 impl ReplaceDecls for TyConstantDecl {
     fn replace_decls_inner(
         &mut self,

sway-core/src/language/ty/declaration/declaration.rs

@@ -349,46 +349,6 @@ impl SubstTypes for TyDecl {
     }
 }
 
-impl ReplaceSelfType for TyDecl {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        match self {
-            TyDecl::VariableDecl(ref mut var_decl) => {
-                var_decl.replace_self_type(engines, self_type)
-            }
-            TyDecl::FunctionDecl(FunctionDecl {
-                ref mut decl_id, ..
-            }) => decl_id.replace_self_type(engines, self_type),
-            TyDecl::TraitDecl(TraitDecl {
-                ref mut decl_id, ..
-            }) => decl_id.replace_self_type(engines, self_type),
-            TyDecl::StructDecl(StructDecl {
-                ref mut decl_id, ..
-            }) => decl_id.replace_self_type(engines, self_type),
-            TyDecl::EnumDecl(EnumDecl {
-                ref mut decl_id, ..
-            }) => decl_id.replace_self_type(engines, self_type),
-            TyDecl::EnumVariantDecl(EnumVariantDecl {
-                ref mut enum_ref, ..
-            }) => enum_ref.replace_self_type(engines, self_type),
-            TyDecl::ImplTrait(ImplTrait {
-                ref mut decl_id, ..
-            }) => decl_id.replace_self_type(engines, self_type),
-            TyDecl::TypeAliasDecl(TypeAliasDecl {
-                ref mut decl_id, ..
-            }) => decl_id.replace_self_type(engines, self_type),
-            TyDecl::TraitTypeDecl(TraitTypeDecl {
-                ref mut decl_id, ..
-            }) => decl_id.replace_self_type(engines, self_type),
-            // generics in an ABI is unsupported by design
-            TyDecl::AbiDecl(_)
-            | TyDecl::ConstantDecl(_)
-            | TyDecl::StorageDecl(_)
-            | TyDecl::GenericTypeForFunctionScope(_)
-            | TyDecl::ErrorRecovery(..) => (),
-        }
-    }
-}
-
 impl TyDecl {
     pub fn get_fun_decl_ref(&self) -> Option<DeclRefFunction> {
         if let TyDecl::FunctionDecl(FunctionDecl {
@@ -613,6 +573,16 @@ impl TyDecl {
                     .get(ty.type_id)
                     .expect_enum(handler, engines, "", &span)
             }
+            // `Self` type parameter might resolve to an Enum
+            TyDecl::GenericTypeForFunctionScope(GenericTypeForFunctionScope {
+                type_id, ..
+            }) => match engines.te().get(*type_id) {
+                TypeInfo::Enum(r) => Ok(r),
+                _ => Err(handler.emit_err(CompileError::DeclIsNotAnEnum {
+                    actually: self.friendly_type_name().to_string(),
+                    span: self.span(),
+                })),
+            },
             TyDecl::ErrorRecovery(_, err) => Err(*err),
             decl => Err(handler.emit_err(CompileError::DeclIsNotAnEnum {
                 actually: decl.friendly_type_name().to_string(),

sway-core/src/language/ty/declaration/enum.rs

@@ -73,17 +73,6 @@ impl SubstTypes for TyEnumDecl {
     }
 }
 
-impl ReplaceSelfType for TyEnumDecl {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        self.variants
-            .iter_mut()
-            .for_each(|x| x.replace_self_type(engines, self_type));
-        self.type_parameters
-            .iter_mut()
-            .for_each(|x| x.replace_self_type(engines, self_type));
-    }
-}
-
 impl Spanned for TyEnumDecl {
     fn span(&self) -> Span {
         self.span.clone()
@@ -98,6 +87,10 @@ impl MonomorphizeHelper for TyEnumDecl {
     fn name(&self) -> &Ident {
         &self.call_path.suffix
     }
+
+    fn has_self_type_param(&self) -> bool {
+        false
+    }
 }
 
 impl TyEnumDecl {
@@ -184,9 +177,3 @@ impl SubstTypes for TyEnumVariant {
         self.type_argument.subst_inner(type_mapping, engines);
     }
 }
-
-impl ReplaceSelfType for TyEnumVariant {
-    fn replace_self_type(&mut self, engines: &Engines, self_type: TypeId) {
-        self.type_argument.replace_self_type(engines, self_type);
-    }
-}