Extract struct from enum variant filters generics

Extracting a struct from an enum variant now filters out only the
generic parameters necessary for the new struct.
Bounds will be copied to the new struct, but unneeded ones are not
filtered out.
Extracting bounds in a where clause are still not implemented.

crates/ide_assists/src/handlers/extract_struct_from_enum_variant.rs

@@ -16,7 +16,7 @@ use rustc_hash::FxHashSet;
 use syntax::{
     ast::{
         self, edit::IndentLevel, edit_in_place::Indent, make, AstNode, HasAttrs, HasGenericParams,
-        HasName, HasTypeBounds, HasVisibility,
+        HasName, HasVisibility,
     },
     match_ast,
     ted::{self, Position},
@@ -106,7 +106,26 @@ pub(crate) fn extract_struct_from_enum_variant(
             }
 
             let indent = enum_ast.indent_level();
-            let def = create_struct_def(variant_name.clone(), &variant, &field_list, &enum_ast);
+            let generic_params = enum_ast
+                .generic_param_list()
+                .map(|known_generics| extract_generic_params(&known_generics, &field_list));
+            let generics =
+                generic_params.as_ref().filter(|generics| !generics.all_empty()).map(|generics| {
+                    make::generic_param_list(
+                        generics
+                            .lifetimes
+                            .iter()
+                            .cloned()
+                            .map(ast::GenericParam::LifetimeParam)
+                            .chain(generics.types.iter().cloned().map(ast::GenericParam::TypeParam))
+                            .chain(
+                                generics.consts.iter().cloned().map(ast::GenericParam::ConstParam),
+                            ),
+                    )
+                    .clone_for_update()
+                });
+            let def =
+                create_struct_def(variant_name.clone(), &variant, &field_list, generics, &enum_ast);
             def.reindent_to(indent);
 
             let start_offset = &variant.parent_enum().syntax().clone();
@@ -118,7 +137,7 @@ pub(crate) fn extract_struct_from_enum_variant(
                 ],
             );
 
-            update_variant(&variant, enum_ast.generic_param_list());
+            update_variant(&variant, generic_params);
         },
     )
 }
@@ -159,10 +178,95 @@ fn existing_definition(db: &RootDatabase, variant_name: &ast::Name, variant: &Va
         .any(|(name, _)| name.to_string() == variant_name.to_string())
 }
 
+struct ExtractedGenerics {
+    lifetimes: Vec<ast::LifetimeParam>,
+    types: Vec<ast::TypeParam>,
+    consts: Vec<ast::ConstParam>,
+}
+
+impl ExtractedGenerics {
+    fn all_empty(&self) -> bool {
+        self.lifetimes.is_empty() && self.types.is_empty() && self.consts.is_empty()
+    }
+}
+
+fn extract_generic_params(
+    known_generics: &ast::GenericParamList,
+    field_list: &Either<ast::RecordFieldList, ast::TupleFieldList>,
+) -> ExtractedGenerics {
+    let mut lifetimes = known_generics.lifetime_params().map(|x| (x, false)).collect_vec();
+    let mut types = known_generics.type_params().map(|x| (x, false)).collect_vec();
+    let mut consts = known_generics.const_params().map(|x| (x, false)).collect_vec();
+
+    match field_list {
+        Either::Left(field_list) => field_list
+            .fields()
+            .filter_map(|f| f.ty())
+            .for_each(|ty| tag_generics_in_variant(&ty, &mut lifetimes, &mut types, &mut consts)),
+        Either::Right(field_list) => field_list
+            .fields()
+            .filter_map(|f| f.ty())
+            .for_each(|ty| tag_generics_in_variant(&ty, &mut lifetimes, &mut types, &mut consts)),
+    }
+
+    let lifetimes = lifetimes.into_iter().filter_map(|(x, present)| present.then(|| x)).collect();
+    let types = types.into_iter().filter_map(|(x, present)| present.then(|| x)).collect();
+    let consts = consts.into_iter().filter_map(|(x, present)| present.then(|| x)).collect();
+
+    ExtractedGenerics { lifetimes, types, consts }
+}
+
+fn tag_generics_in_variant(
+    ty: &ast::Type,
+    lifetimes: &mut [(ast::LifetimeParam, bool)],
+    types: &mut [(ast::TypeParam, bool)],
+    consts: &mut [(ast::ConstParam, bool)],
+) {
+    for token in
+        ty.syntax().preorder_with_tokens().filter_map(|node_or_token| match node_or_token {
+            syntax::WalkEvent::Enter(syntax::NodeOrToken::Token(token)) => Some(token),
+            _ => None,
+        })
+    {
+        match token.kind() {
+            T![lifetime_ident] => {
+                for (lt, present) in lifetimes.iter_mut() {
+                    if let Some(lt) = lt.lifetime() {
+                        if lt.text().as_str() == token.text() {
+                            *present = true;
+                            break;
+                        }
+                    }
+                }
+            }
+            T![ident] => {
+                for (ty, present) in types.iter_mut() {
+                    if let Some(name) = ty.name() {
+                        if name.text().as_str() == token.text() {
+                            *present = true;
+                            break;
+                        }
+                    }
+                }
+                for (cnst, present) in consts.iter_mut() {
+                    if let Some(name) = cnst.name() {
+                        if name.text().as_str() == token.text() {
+                            *present = true;
+                            break;
+                        }
+                    }
+                }
+            }
+            _ => (),
+        }
+    }
+}
+
 fn create_struct_def(
     variant_name: ast::Name,
     variant: &ast::Variant,
     field_list: &Either<ast::RecordFieldList, ast::TupleFieldList>,
+    generics: Option<ast::GenericParamList>,
     enum_: &ast::Enum,
 ) -> ast::Struct {
     let enum_vis = enum_.visibility();
@@ -204,9 +308,7 @@ fn create_struct_def(
 
     field_list.reindent_to(IndentLevel::single());
 
-    // FIXME: This uses all the generic params of the enum, but the variant might not use all of them.
-    let strukt = make::struct_(enum_vis, variant_name, enum_.generic_param_list(), field_list)
-        .clone_for_update();
+    let strukt = make::struct_(enum_vis, variant_name, generics, field_list).clone_for_update();
 
     // FIXME: Consider making this an actual function somewhere (like in `AttrsOwnerEdit`) after some deliberation
     let attrs_and_docs = |node: &SyntaxNode| {
@@ -243,26 +345,24 @@ fn create_struct_def(
     strukt
 }
 
-fn update_variant(variant: &ast::Variant, generic: Option<ast::GenericParamList>) -> Option<()> {
+fn update_variant(variant: &ast::Variant, generics: Option<ExtractedGenerics>) -> Option<()> {
     let name = variant.name()?;
-    let ty = match generic {
-        // FIXME: This uses all the generic params of the enum, but the variant might not use all of them.
-        Some(gpl) => {
-            let gpl = gpl.clone_for_update();
-            gpl.generic_params().for_each(|gp| {
-                let tbl = match gp {
-                    ast::GenericParam::LifetimeParam(it) => it.type_bound_list(),
-                    ast::GenericParam::TypeParam(it) => it.type_bound_list(),
-                    ast::GenericParam::ConstParam(_) => return,
-                };
-                if let Some(tbl) = tbl {
-                    tbl.remove();
-                }
-            });
-            make::ty(&format!("{}<{}>", name.text(), gpl.generic_params().join(", ")))
-        }
-        None => make::ty(&name.text()),
-    };
+    let ty = generics
+        .filter(|generics| !generics.all_empty())
+        .map(|generics| {
+            let generics_str = [
+                generics.lifetimes.iter().filter_map(|lt| lt.lifetime()).join(", "),
+                generics.types.iter().filter_map(|ty| ty.name()).join(", "),
+                generics.consts.iter().filter_map(|cnst| cnst.name()).join(", "),
+            ]
+            .iter()
+            .filter(|s| !s.is_empty())
+            .join(", ");
+
+            make::ty(&format!("{}<{}>", &name.text(), &generics_str))
+        })
+        .unwrap_or_else(|| make::ty(&name.text()));
+
     let tuple_field = make::tuple_field(None, ty);
     let replacement = make::variant(
         name,
@@ -902,4 +1002,92 @@ enum A { $0One(u8, u32) }
     fn test_extract_not_applicable_no_field_named() {
         check_assist_not_applicable(extract_struct_from_enum_variant, r"enum A { $0None {} }");
     }
+
+    #[test]
+    fn test_extract_struct_only_copies_needed_generics() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            r#"
+enum X<'a, 'b, 'x> {
+    $0A { a: &'a &'x mut () },
+    B { b: &'b () },
+    C { c: () },
+}
+"#,
+            r#"
+struct A<'a, 'x>{ a: &'a &'x mut () }
+
+enum X<'a, 'b, 'x> {
+    A(A<'a, 'x>),
+    B { b: &'b () },
+    C { c: () },
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_struct_with_liftime_type_const() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            r#"
+enum X<'b, T, V, const C: usize> {
+    $0A { a: T, b: X<'b>, c: [u8; C] },
+    D { d: V },
+}
+"#,
+            r#"
+struct A<'b, T, const C: usize>{ a: T, b: X<'b>, c: [u8; C] }
+
+enum X<'b, T, V, const C: usize> {
+    A(A<'b, T, C>),
+    D { d: V },
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_struct_without_generics() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            r#"
+enum X<'a, 'b> {
+    A { a: &'a () },
+    B { b: &'b () },
+    $0C { c: () },
+}
+"#,
+            r#"
+struct C{ c: () }
+
+enum X<'a, 'b> {
+    A { a: &'a () },
+    B { b: &'b () },
+    C(C),
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_extract_struct_keeps_trait_bounds() {
+        check_assist(
+            extract_struct_from_enum_variant,
+            r#"
+enum En<T: TraitT, V: TraitV> {
+    $0A { a: T },
+    B { b: V },
+}
+"#,
+            r#"
+struct A<T: TraitT>{ a: T }
+
+enum En<T: TraitT, V: TraitV> {
+    A(A<T>),
+    B { b: V },
+}
+"#,
+        );
+    }
 }