Auto merge of #15350 - max-heller:issue-11756, r=Veykril

Handle `#[cfg]`s on generic parameters

Records attributes on generic parameters in the item tree and filters out generic parameters disabled by `#[cfg]`s in `generic_params_query`.

Closes #11756

6 files changed, 142 insertions, 24 deletions

diff --git a/crates/hir-def/src/generics.rs b/crates/hir-def/src/generics.rs
index d7d44e41388..540fa115a00 100644
--- a/crates/hir-def/src/generics.rs
+++ b/crates/hir-def/src/generics.rs
@@ -21,6 +21,7 @@ use crate::{
     db::DefDatabase,
     dyn_map::{keys, DynMap},
     expander::Expander,
+    item_tree::{AttrOwner, ItemTree},
     lower::LowerCtx,
     nameres::{DefMap, MacroSubNs},
     src::{HasChildSource, HasSource},
@@ -154,12 +155,58 @@ impl GenericParams {
         def: GenericDefId,
     ) -> Interned<GenericParams> {
         let _p = profile::span("generic_params_query");
+
+        let krate = def.module(db).krate;
+        let cfg_options = db.crate_graph();
+        let cfg_options = &cfg_options[krate].cfg_options;
+
+        // Returns the generic parameters that are enabled under the current `#[cfg]` options
+        let enabled_params = |params: &Interned<GenericParams>, item_tree: &ItemTree| {
+            let enabled = |param| item_tree.attrs(db, krate, param).is_cfg_enabled(cfg_options);
+
+            // In the common case, no parameters will by disabled by `#[cfg]` attributes.
+            // Therefore, make a first pass to check if all parameters are enabled and, if so,
+            // clone the `Interned<GenericParams>` instead of recreating an identical copy.
+            let all_type_or_consts_enabled =
+                params.type_or_consts.iter().all(|(idx, _)| enabled(idx.into()));
+            let all_lifetimes_enabled = params.lifetimes.iter().all(|(idx, _)| enabled(idx.into()));
+
+            if all_type_or_consts_enabled && all_lifetimes_enabled {
+                params.clone()
+            } else {
+                Interned::new(GenericParams {
+                    type_or_consts: all_type_or_consts_enabled
+                        .then(|| params.type_or_consts.clone())
+                        .unwrap_or_else(|| {
+                            params
+                                .type_or_consts
+                                .iter()
+                                .filter_map(|(idx, param)| {
+                                    enabled(idx.into()).then(|| param.clone())
+                                })
+                                .collect()
+                        }),
+                    lifetimes: all_lifetimes_enabled
+                        .then(|| params.lifetimes.clone())
+                        .unwrap_or_else(|| {
+                            params
+                                .lifetimes
+                                .iter()
+                                .filter_map(|(idx, param)| {
+                                    enabled(idx.into()).then(|| param.clone())
+                                })
+                                .collect()
+                        }),
+                    where_predicates: params.where_predicates.clone(),
+                })
+            }
+        };
         macro_rules! id_to_generics {
             ($id:ident) => {{
                 let id = $id.lookup(db).id;
                 let tree = id.item_tree(db);
                 let item = &tree[id.value];
-                item.generic_params.clone()
+                enabled_params(&item.generic_params, &tree)
             }};
         }
 
@@ -169,7 +216,8 @@ impl GenericParams {
                 let tree = loc.id.item_tree(db);
                 let item = &tree[loc.id.value];
 
-                let mut generic_params = GenericParams::clone(&item.explicit_generic_params);
+                let enabled_params = enabled_params(&item.explicit_generic_params, &tree);
+                let mut generic_params = GenericParams::clone(&enabled_params);
 
                 let module = loc.container.module(db);
                 let func_data = db.function_data(id);
@@ -198,9 +246,14 @@ impl GenericParams {
         }
     }
 
-    pub(crate) fn fill(&mut self, lower_ctx: &LowerCtx<'_>, node: &dyn HasGenericParams) {
+    pub(crate) fn fill(
+        &mut self,
+        lower_ctx: &LowerCtx<'_>,
+        node: &dyn HasGenericParams,
+        add_param_attrs: impl FnMut(AttrOwner, ast::GenericParam),
+    ) {
         if let Some(params) = node.generic_param_list() {
-            self.fill_params(lower_ctx, params)
+            self.fill_params(lower_ctx, params, add_param_attrs)
         }
         if let Some(where_clause) = node.where_clause() {
             self.fill_where_predicates(lower_ctx, where_clause);
@@ -218,7 +271,12 @@ impl GenericParams {
         }
     }
 
-    fn fill_params(&mut self, lower_ctx: &LowerCtx<'_>, params: ast::GenericParamList) {
+    fn fill_params(
+        &mut self,
+        lower_ctx: &LowerCtx<'_>,
+        params: ast::GenericParamList,
+        mut add_param_attrs: impl FnMut(AttrOwner, ast::GenericParam),
+    ) {
         for type_or_const_param in params.type_or_const_params() {
             match type_or_const_param {
                 ast::TypeOrConstParam::Type(type_param) => {
@@ -232,13 +290,14 @@ impl GenericParams {
                         default,
                         provenance: TypeParamProvenance::TypeParamList,
                     };
-                    self.type_or_consts.alloc(param.into());
+                    let idx = self.type_or_consts.alloc(param.into());
                     let type_ref = TypeRef::Path(name.into());
                     self.fill_bounds(
                         lower_ctx,
                         type_param.type_bound_list(),
                         Either::Left(type_ref),
                     );
+                    add_param_attrs(idx.into(), ast::GenericParam::TypeParam(type_param));
                 }
                 ast::TypeOrConstParam::Const(const_param) => {
                     let name = const_param.name().map_or_else(Name::missing, |it| it.as_name());
@@ -250,7 +309,8 @@ impl GenericParams {
                         ty: Interned::new(ty),
                         has_default: const_param.default_val().is_some(),
                     };
-                    self.type_or_consts.alloc(param.into());
+                    let idx = self.type_or_consts.alloc(param.into());
+                    add_param_attrs(idx.into(), ast::GenericParam::ConstParam(const_param));
                 }
             }
         }
@@ -258,13 +318,14 @@ impl GenericParams {
             let name =
                 lifetime_param.lifetime().map_or_else(Name::missing, |lt| Name::new_lifetime(&lt));
             let param = LifetimeParamData { name: name.clone() };
-            self.lifetimes.alloc(param);
+            let idx = self.lifetimes.alloc(param);
             let lifetime_ref = LifetimeRef::new_name(name);
             self.fill_bounds(
                 lower_ctx,
                 lifetime_param.type_bound_list(),
                 Either::Right(lifetime_ref),
             );
+            add_param_attrs(idx.into(), ast::GenericParam::LifetimeParam(lifetime_param));
         }
     }
 
diff --git a/crates/hir-def/src/item_tree.rs b/crates/hir-def/src/item_tree.rs
index c9b0f75f1a8..701fee40ab2 100644
--- a/crates/hir-def/src/item_tree.rs
+++ b/crates/hir-def/src/item_tree.rs
@@ -64,7 +64,7 @@ use triomphe::Arc;
 use crate::{
     attr::Attrs,
     db::DefDatabase,
-    generics::GenericParams,
+    generics::{GenericParams, LifetimeParamData, TypeOrConstParamData},
     path::{path, AssociatedTypeBinding, GenericArgs, ImportAlias, ModPath, Path, PathKind},
     type_ref::{Mutability, TraitRef, TypeBound, TypeRef},
     visibility::RawVisibility,
@@ -296,10 +296,12 @@ pub enum AttrOwner {
     Variant(Idx<Variant>),
     Field(Idx<Field>),
     Param(Idx<Param>),
+    TypeOrConstParamData(Idx<TypeOrConstParamData>),
+    LifetimeParamData(Idx<LifetimeParamData>),
 }
 
 macro_rules! from_attrs {
-    ( $( $var:ident($t:ty) ),+ ) => {
+    ( $( $var:ident($t:ty) ),+ $(,)? ) => {
         $(
             impl From<$t> for AttrOwner {
                 fn from(t: $t) -> AttrOwner {
@@ -310,7 +312,14 @@ macro_rules! from_attrs {
     };
 }
 
-from_attrs!(ModItem(ModItem), Variant(Idx<Variant>), Field(Idx<Field>), Param(Idx<Param>));
+from_attrs!(
+    ModItem(ModItem),
+    Variant(Idx<Variant>),
+    Field(Idx<Field>),
+    Param(Idx<Param>),
+    TypeOrConstParamData(Idx<TypeOrConstParamData>),
+    LifetimeParamData(Idx<LifetimeParamData>),
+);
 
 /// Trait implemented by all item nodes in the item tree.
 pub trait ItemTreeNode: Clone {
diff --git a/crates/hir-def/src/item_tree/lower.rs b/crates/hir-def/src/item_tree/lower.rs
index 7b898e62dba..e719f9291bd 100644
--- a/crates/hir-def/src/item_tree/lower.rs
+++ b/crates/hir-def/src/item_tree/lower.rs
@@ -602,7 +602,21 @@ impl<'a> Ctx<'a> {
             generics.fill_bounds(&self.body_ctx, bounds, Either::Left(self_param));
         }
 
-        generics.fill(&self.body_ctx, node);
+        let add_param_attrs = |item, param| {
+            let attrs = RawAttrs::new(self.db.upcast(), &param, self.body_ctx.hygiene());
+            // This is identical to the body of `Ctx::add_attrs()` but we can't call that here
+            // because it requires `&mut self` and the call to `generics.fill()` below also
+            // references `self`.
+            match self.tree.attrs.entry(item) {
+                Entry::Occupied(mut entry) => {
+                    *entry.get_mut() = entry.get().merge(attrs);
+                }
+                Entry::Vacant(entry) => {
+                    entry.insert(attrs);
+                }
+            }
+        };
+        generics.fill(&self.body_ctx, node, add_param_attrs);
 
         generics.shrink_to_fit();
         Interned::new(generics)
diff --git a/crates/hir-def/src/item_tree/pretty.rs b/crates/hir-def/src/item_tree/pretty.rs
index da30830fe45..4b852dd613e 100644
--- a/crates/hir-def/src/item_tree/pretty.rs
+++ b/crates/hir-def/src/item_tree/pretty.rs
@@ -16,7 +16,7 @@ pub(super) fn print_item_tree(db: &dyn ExpandDatabase, tree: &ItemTree) -> Strin
     let mut p = Printer { db, tree, buf: String::new(), indent_level: 0, needs_indent: true };
 
     if let Some(attrs) = tree.attrs.get(&AttrOwner::TopLevel) {
-        p.print_attrs(attrs, true);
+        p.print_attrs(attrs, true, "\n");
     }
     p.blank();
 
@@ -84,22 +84,23 @@ impl Printer<'_> {
         }
     }
 
-    fn print_attrs(&mut self, attrs: &RawAttrs, inner: bool) {
+    fn print_attrs(&mut self, attrs: &RawAttrs, inner: bool, separated_by: &str) {
         let inner = if inner { "!" } else { "" };
         for attr in &**attrs {
-            wln!(
+            w!(
                 self,
-                "#{}[{}{}]",
+                "#{}[{}{}]{}",
                 inner,
                 attr.path.display(self.db),
                 attr.input.as_ref().map(|it| it.to_string()).unwrap_or_default(),
+                separated_by,
             );
         }
     }
 
-    fn print_attrs_of(&mut self, of: impl Into<AttrOwner>) {
+    fn print_attrs_of(&mut self, of: impl Into<AttrOwner>, separated_by: &str) {
         if let Some(attrs) = self.tree.attrs.get(&of.into()) {
-            self.print_attrs(attrs, false);
+            self.print_attrs(attrs, false, separated_by);
         }
     }
 
@@ -118,7 +119,7 @@ impl Printer<'_> {
                 self.indented(|this| {
                     for field in fields.clone() {
                         let Field { visibility, name, type_ref, ast_id: _ } = &this.tree[field];
-                        this.print_attrs_of(field);
+                        this.print_attrs_of(field, "\n");
                         this.print_visibility(*visibility);
                         w!(this, "{}: ", name.display(self.db));
                         this.print_type_ref(type_ref);
@@ -132,7 +133,7 @@ impl Printer<'_> {
                 self.indented(|this| {
                     for field in fields.clone() {
                         let Field { visibility, name, type_ref, ast_id: _ } = &this.tree[field];
-                        this.print_attrs_of(field);
+                        this.print_attrs_of(field, "\n");
                         this.print_visibility(*visibility);
                         w!(this, "{}: ", name.display(self.db));
                         this.print_type_ref(type_ref);
@@ -195,7 +196,7 @@ impl Printer<'_> {
     }
 
     fn print_mod_item(&mut self, item: ModItem) {
-        self.print_attrs_of(item);
+        self.print_attrs_of(item, "\n");
 
         match item {
             ModItem::Use(it) => {
@@ -261,7 +262,7 @@ impl Printer<'_> {
                 if !params.is_empty() {
                     self.indented(|this| {
                         for param in params.clone() {
-                            this.print_attrs_of(param);
+                            this.print_attrs_of(param, "\n");
                             match &this.tree[param] {
                                 Param::Normal(ty) => {
                                     if flags.contains(FnFlags::HAS_SELF_PARAM) {
@@ -319,7 +320,7 @@ impl Printer<'_> {
                 self.indented(|this| {
                     for variant in variants.clone() {
                         let Variant { name, fields, ast_id: _ } = &this.tree[variant];
-                        this.print_attrs_of(variant);
+                        this.print_attrs_of(variant, "\n");
                         w!(this, "{}", name.display(self.db));
                         this.print_fields(fields);
                         wln!(this, ",");
@@ -484,11 +485,12 @@ impl Printer<'_> {
 
         w!(self, "<");
         let mut first = true;
-        for (_, lt) in params.lifetimes.iter() {
+        for (idx, lt) in params.lifetimes.iter() {
             if !first {
                 w!(self, ", ");
             }
             first = false;
+            self.print_attrs_of(idx, " ");
             w!(self, "{}", lt.name.display(self.db));
         }
         for (idx, x) in params.type_or_consts.iter() {
@@ -496,6 +498,7 @@ impl Printer<'_> {
                 w!(self, ", ");
             }
             first = false;
+            self.print_attrs_of(idx, " ");
             match x {
                 TypeOrConstParamData::TypeParamData(ty) => match &ty.name {
                     Some(name) => w!(self, "{}", name.display(self.db)),
diff --git a/crates/hir-def/src/item_tree/tests.rs b/crates/hir-def/src/item_tree/tests.rs
index 5ded4b6b273..4180f817209 100644
--- a/crates/hir-def/src/item_tree/tests.rs
+++ b/crates/hir-def/src/item_tree/tests.rs
@@ -358,3 +358,15 @@ trait Tr<'a, T: 'a>: Super where Self: for<'a> Tr<'a, T> {}
         "#]],
     )
 }
+
+#[test]
+fn generics_with_attributes() {
+    check(
+        r#"
+struct S<#[cfg(never)] T>;
+        "#,
+        expect![[r#"
+            pub(self) struct S<#[cfg(never)] T>;
+        "#]],
+    )
+}
diff --git a/crates/ide/src/hover/tests.rs b/crates/ide/src/hover/tests.rs
index ddc71dffa8a..133a488e1de 100644
--- a/crates/ide/src/hover/tests.rs
+++ b/crates/ide/src/hover/tests.rs
@@ -6469,3 +6469,22 @@ fn test() {
         "#]],
     );
 }
+
+#[test]
+fn generic_params_disabled_by_cfg() {
+    check(
+        r#"
+struct S<#[cfg(never)] T>;
+fn test() {
+    let s$0: S = S;
+}
+"#,
+        expect![[r#"
+            *s*
+
+            ```rust
+            let s: S // size = 0, align = 1
+            ```
+        "#]],
+    );
+}