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 <[email protected]>

2 files changed, 31 insertions, 2 deletions

diff --git a/crates/ra_hir_ty/src/expr.rs b/crates/ra_hir_ty/src/expr.rs
index b4592fbf5..e45e9ea14 100644
--- a/crates/ra_hir_ty/src/expr.rs
+++ b/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::{
diff --git a/crates/ra_hir_ty/src/tests.rs b/crates/ra_hir_ty/src/tests.rs
index e4a103d1b..608408d88 100644
--- a/crates/ra_hir_ty/src/tests.rs
+++ b/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###""###);
+}