Merge #3880

3880: Add support for attributes for struct fields r=matklad a=bnjjj

Hello I try to solve this example:
```rust
struct MyStruct {
    my_val: usize,
    #[cfg(feature = "foo")]
    bar: bool,
}
impl MyStruct {
    #[cfg(feature = "foo")]
    pub(crate) fn new(my_val: usize, bar: bool) -> Self {
        Self { my_val, bar }
    }
    #[cfg(not(feature = "foo"))]
    pub(crate) fn new(my_val: usize, _bar: bool) -> Self {
        Self { my_val }
    }
}
```

Here is a draft PR to try to solve this issue. In fact for now when i have this kind of example, rust-analyzer tells me that my second Self {} miss the bar field. Which is a bug.

I have some difficulties to add this features. Here in my draft I share my work about adding attributes support on struct field data. But I'm stuck when I have to fetch attributes from parent expressions. I don't really know how to do that. For the first iteration I just want to solve my issue without solving on all different expressions. And then after I will try to implement that on different kind of expression. I think I have to fetch my FunctionId and then I will be able to find attributes with myFunction.attrs() But I don't know if it's the right way.

@matklad (or anyone else) if you can help me it would be great :D 

Co-authored-by: Benjamin Coenen <5719034+bnjjj@users.noreply.github.com>

crates/ra_hir_def/src/adt.rs

@@ -54,6 +54,7 @@ pub struct StructFieldData {
 impl StructData {
     pub(crate) fn struct_data_query(db: &dyn DefDatabase, id: StructId) -> Arc<StructData> {
         let src = id.lookup(db).source(db);
+
         let name = src.value.name().map_or_else(Name::missing, |n| n.as_name());
         let variant_data = VariantData::new(db, src.map(|s| s.kind()));
         let variant_data = Arc::new(variant_data);

crates/ra_hir_def/src/data.rs

@@ -3,15 +3,18 @@
 use std::sync::Arc;
 
 use hir_expand::{
+    hygiene::Hygiene,
     name::{name, AsName, Name},
     AstId, InFile,
 };
+use ra_cfg::CfgOptions;
 use ra_prof::profile;
 use ra_syntax::ast::{
     self, AstNode, ImplItem, ModuleItemOwner, NameOwner, TypeAscriptionOwner, VisibilityOwner,
 };
 
 use crate::{
+    attr::Attrs,
     db::DefDatabase,
     path::{path, GenericArgs, Path},
     src::HasSource,
@@ -26,6 +29,7 @@ pub struct FunctionData {
     pub name: Name,
     pub params: Vec<TypeRef>,
     pub ret_type: TypeRef,
+    pub attrs: Attrs,
     /// True if the first param is `self`. This is relevant to decide whether this
     /// can be called as a method.
     pub has_self_param: bool,
@@ -63,6 +67,8 @@ impl FunctionData {
                 params.push(type_ref);
             }
         }
+        let attrs = Attrs::new(&src.value, &Hygiene::new(db.upcast(), src.file_id));
+
         let ret_type = if let Some(type_ref) = src.value.ret_type().and_then(|rt| rt.type_ref()) {
             TypeRef::from_ast(type_ref)
         } else {
@@ -81,7 +87,7 @@ impl FunctionData {
         let visibility =
             RawVisibility::from_ast_with_default(db, vis_default, src.map(|s| s.visibility()));
 
-        let sig = FunctionData { name, params, ret_type, has_self_param, visibility };
+        let sig = FunctionData { name, params, ret_type, has_self_param, visibility, attrs };
         Arc::new(sig)
     }
 }
@@ -211,6 +217,7 @@ impl ImplData {
         let module_id = impl_loc.container.module(db);
 
         let mut items = Vec::new();
+
         if let Some(item_list) = src.value.item_list() {
             items.extend(collect_impl_items(db, item_list.impl_items(), src.file_id, id));
             items.extend(collect_impl_items_in_macros(
@@ -311,6 +318,10 @@ fn collect_impl_items_in_macro(
     }
 }
 
+fn is_cfg_enabled(cfg_options: &CfgOptions, attrs: &Attrs) -> bool {
+    attrs.by_key("cfg").tt_values().all(|tt| cfg_options.is_cfg_enabled(tt) != Some(false))
+}
+
 fn collect_impl_items(
     db: &dyn DefDatabase,
     impl_items: impl Iterator<Item = ImplItem>,
@@ -318,16 +329,26 @@ fn collect_impl_items(
     id: ImplId,
 ) -> Vec<AssocItemId> {
     let items = db.ast_id_map(file_id);
+    let crate_graph = db.crate_graph();
+    let module_id = id.lookup(db).container.module(db);
 
     impl_items
-        .map(|item_node| match item_node {
+        .filter_map(|item_node| match item_node {
             ast::ImplItem::FnDef(it) => {
                 let def = FunctionLoc {
                     container: AssocContainerId::ImplId(id),
                     ast_id: AstId::new(file_id, items.ast_id(&it)),
                 }
                 .intern(db);
-                def.into()
+
+                if !is_cfg_enabled(
+                    &crate_graph[module_id.krate].cfg_options,
+                    &db.function_data(def).attrs,
+                ) {
+                    None
+                } else {
+                    Some(def.into())
+                }
             }
             ast::ImplItem::ConstDef(it) => {
                 let def = ConstLoc {
@@ -335,7 +356,7 @@ fn collect_impl_items(
                     ast_id: AstId::new(file_id, items.ast_id(&it)),
                 }
                 .intern(db);
-                def.into()
+                Some(def.into())
             }
             ast::ImplItem::TypeAliasDef(it) => {
                 let def = TypeAliasLoc {
@@ -343,7 +364,7 @@ fn collect_impl_items(
                     ast_id: AstId::new(file_id, items.ast_id(&it)),
                 }
                 .intern(db);
-                def.into()
+                Some(def.into())
             }
         })
         .collect()

crates/ra_hir_ty/src/expr.rs

@@ -4,8 +4,7 @@ use std::sync::Arc;
 
 use hir_def::{path::path, resolver::HasResolver, AdtId, FunctionId};
 use hir_expand::diagnostics::DiagnosticSink;
-use ra_syntax::ast;
-use ra_syntax::AstPtr;
+use ra_syntax::{ast, AstPtr};
 use rustc_hash::FxHashSet;
 
 use crate::{

crates/ra_hir_ty/src/tests.rs

@@ -319,3 +319,33 @@ fn no_such_field_diagnostics() {
     "###
     );
 }
+
+#[test]
+fn no_such_field_with_feature_flag_diagnostics() {
+    let diagnostics = TestDB::with_files(
+        r#"
+        //- /lib.rs crate:foo cfg:feature=foo
+        struct MyStruct {
+            my_val: usize,
+            #[cfg(feature = "foo")]
+            bar: bool,
+        }
+
+        impl MyStruct {
+            #[cfg(feature = "foo")]
+            pub(crate) fn new(my_val: usize, bar: bool) -> Self {
+                Self { my_val, bar }
+            }
+
+            #[cfg(not(feature = "foo"))]
+            pub(crate) fn new(my_val: usize, _bar: bool) -> Self {
+                Self { my_val }
+            }
+        }
+        "#,
+    )
+    .diagnostics()
+    .0;
+
+    assert_snapshot!(diagnostics, @r###""###);
+}