8 files changed, 232 insertions, 89 deletions

diff --git a/crates/hir_def/src/attr.rs b/crates/hir_def/src/attr.rs
index 9cd0b72aa..042e119b1 100644
--- a/crates/hir_def/src/attr.rs
+++ b/crates/hir_def/src/attr.rs
@@ -5,20 +5,21 @@ use std::{ops, sync::Arc};
 use base_db::CrateId;
 use cfg::{CfgExpr, CfgOptions};
 use either::Either;
-use hir_expand::{hygiene::Hygiene, AstId, InFile};
+use hir_expand::{hygiene::Hygiene, name::AsName, AstId, InFile};
 use itertools::Itertools;
 use mbe::ast_to_token_tree;
 use syntax::{
     ast::{self, AstNode, AttrsOwner},
     match_ast, AstToken, SmolStr, SyntaxNode,
 };
+use test_utils::mark;
 use tt::Subtree;
 
 use crate::{
     db::DefDatabase,
     item_tree::{ItemTreeId, ItemTreeNode},
     nameres::ModuleSource,
-    path::ModPath,
+    path::{ModPath, PathKind},
     src::HasChildSource,
     AdtId, AttrDefId, Lookup,
 };
@@ -41,7 +42,7 @@ impl From<Documentation> for String {
 
 /// Syntactical attributes, without filtering of `cfg_attr`s.
 #[derive(Default, Debug, Clone, PartialEq, Eq)]
-pub struct RawAttrs {
+pub(crate) struct RawAttrs {
     entries: Option<Arc<[Attr]>>,
 }
 
@@ -71,35 +72,34 @@ impl ops::Deref for Attrs {
 }
 
 impl RawAttrs {
-    pub const EMPTY: Self = Self { entries: None };
+    pub(crate) const EMPTY: Self = Self { entries: None };
 
     pub(crate) fn new(owner: &dyn AttrsOwner, hygiene: &Hygiene) -> Self {
-        let (inner_attrs, inner_docs) = inner_attributes(owner.syntax())
-            .map_or((None, None), |(attrs, docs)| ((Some(attrs), Some(docs))));
-
-        let outer_attrs = owner.attrs().filter(|attr| attr.excl_token().is_none());
-        let attrs = outer_attrs
-            .chain(inner_attrs.into_iter().flatten())
-            .map(|attr| (attr.syntax().text_range().start(), Attr::from_src(attr, hygiene)));
-
-        let outer_docs =
-            ast::CommentIter::from_syntax_node(owner.syntax()).filter(ast::Comment::is_outer);
-        let docs = outer_docs.chain(inner_docs.into_iter().flatten()).map(|docs_text| {
-            (
-                docs_text.syntax().text_range().start(),
-                docs_text.doc_comment().map(|doc| Attr {
-                    input: Some(AttrInput::Literal(SmolStr::new(doc))),
-                    path: ModPath::from(hir_expand::name!(doc)),
-                }),
-            )
-        });
-        // sort here by syntax node offset because the source can have doc attributes and doc strings be interleaved
-        let attrs: Vec<_> = docs.chain(attrs).sorted_by_key(|&(offset, _)| offset).collect();
+        let attrs: Vec<_> = collect_attrs(owner).collect();
         let entries = if attrs.is_empty() {
             // Avoid heap allocation
             None
         } else {
-            Some(attrs.into_iter().flat_map(|(_, attr)| attr).collect())
+            Some(
+                attrs
+                    .into_iter()
+                    .enumerate()
+                    .flat_map(|(i, attr)| match attr {
+                        Either::Left(attr) => Attr::from_src(attr, hygiene).map(|attr| (i, attr)),
+                        Either::Right(comment) => comment.doc_comment().map(|doc| {
+                            (
+                                i,
+                                Attr {
+                                    index: 0,
+                                    input: Some(AttrInput::Literal(SmolStr::new(doc))),
+                                    path: ModPath::from(hir_expand::name!(doc)),
+                                },
+                            )
+                        }),
+                    })
+                    .map(|(i, attr)| Attr { index: i as u32, ..attr })
+                    .collect(),
+            )
         };
         Self { entries }
     }
@@ -122,9 +122,69 @@ impl RawAttrs {
     }
 
     /// Processes `cfg_attr`s, returning the resulting semantic `Attrs`.
-    pub(crate) fn filter(self, _db: &dyn DefDatabase, _krate: CrateId) -> Attrs {
-        // FIXME actually implement this
-        Attrs(self)
+    pub(crate) fn filter(self, db: &dyn DefDatabase, krate: CrateId) -> Attrs {
+        let has_cfg_attrs = self.iter().any(|attr| {
+            attr.path.as_ident().map_or(false, |name| *name == hir_expand::name![cfg_attr])
+        });
+        if !has_cfg_attrs {
+            return Attrs(self);
+        }
+
+        let crate_graph = db.crate_graph();
+        let new_attrs = self
+            .iter()
+            .filter_map(|attr| {
+                let attr = attr.clone();
+                let is_cfg_attr =
+                    attr.path.as_ident().map_or(false, |name| *name == hir_expand::name![cfg_attr]);
+                if !is_cfg_attr {
+                    return Some(attr);
+                }
+
+                let subtree = match &attr.input {
+                    Some(AttrInput::TokenTree(it)) => it,
+                    _ => return Some(attr),
+                };
+
+                // Input subtree is: `(cfg, attr)`
+                // Split it up into a `cfg` and an `attr` subtree.
+                // FIXME: There should be a common API for this.
+                let mut saw_comma = false;
+                let (mut cfg, attr): (Vec<_>, Vec<_>) =
+                    subtree.clone().token_trees.into_iter().partition(|tree| {
+                        if saw_comma {
+                            return false;
+                        }
+
+                        match tree {
+                            tt::TokenTree::Leaf(tt::Leaf::Punct(p)) if p.char == ',' => {
+                                saw_comma = true;
+                            }
+                            _ => {}
+                        }
+
+                        true
+                    });
+                cfg.pop(); // `,` ends up in here
+
+                let attr = Subtree { delimiter: None, token_trees: attr };
+                let cfg = Subtree { delimiter: subtree.delimiter, token_trees: cfg };
+                let cfg = CfgExpr::parse(&cfg);
+
+                let cfg_options = &crate_graph[krate].cfg_options;
+                if cfg_options.check(&cfg) == Some(false) {
+                    None
+                } else {
+                    mark::hit!(cfg_attr_active);
+
+                    let attr = ast::Attr::parse(&format!("#[{}]", attr)).ok()?;
+                    let hygiene = Hygiene::new_unhygienic(); // FIXME
+                    Attr::from_src(attr, &hygiene)
+                }
+            })
+            .collect();
+
+        Attrs(RawAttrs { entries: Some(new_attrs) })
     }
 }
 
@@ -180,24 +240,11 @@ impl Attrs {
         raw_attrs.filter(db, def.krate(db))
     }
 
-    pub fn merge(&self, other: Attrs) -> Attrs {
-        match (&self.0.entries, &other.0.entries) {
-            (None, None) => Attrs::EMPTY,
-            (Some(entries), None) | (None, Some(entries)) => {
-                Attrs(RawAttrs { entries: Some(entries.clone()) })
-            }
-            (Some(a), Some(b)) => {
-                Attrs(RawAttrs { entries: Some(a.iter().chain(b.iter()).cloned().collect()) })
-            }
-        }
-    }
-
     pub fn by_key(&self, key: &'static str) -> AttrQuery<'_> {
         AttrQuery { attrs: self, key }
     }
 
     pub fn cfg(&self) -> Option<CfgExpr> {
-        // FIXME: handle cfg_attr :-)
         let mut cfgs = self.by_key("cfg").tt_values().map(CfgExpr::parse).collect::<Vec<_>>();
         match cfgs.len() {
             0 => None,
@@ -268,6 +315,7 @@ fn inner_attributes(
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Attr {
+    index: u32,
     pub(crate) path: ModPath,
     pub(crate) input: Option<AttrInput>,
 }
@@ -294,7 +342,59 @@ impl Attr {
         } else {
             None
         };
-        Some(Attr { path, input })
+        Some(Attr { index: 0, path, input })
+    }
+
+    /// Maps this lowered `Attr` back to its original syntax node.
+    ///
+    /// `owner` must be the original owner of the attribute.
+    ///
+    /// Note that the returned syntax node might be a `#[cfg_attr]`, or a doc comment, instead of
+    /// the attribute represented by `Attr`.
+    pub fn to_src(&self, owner: &dyn AttrsOwner) -> Either<ast::Attr, ast::Comment> {
+        collect_attrs(owner).nth(self.index as usize).unwrap_or_else(|| {
+            panic!("cannot find `Attr` at index {} in {}", self.index, owner.syntax())
+        })
+    }
+
+    /// Parses this attribute as a `#[derive]`, returns an iterator that yields all contained paths
+    /// to derive macros.
+    ///
+    /// Returns `None` when the attribute is not a well-formed `#[derive]` attribute.
+    pub(crate) fn parse_derive(&self) -> Option<impl Iterator<Item = ModPath>> {
+        if self.path.as_ident() != Some(&hir_expand::name![derive]) {
+            return None;
+        }
+
+        match &self.input {
+            Some(AttrInput::TokenTree(args)) => {
+                let mut counter = 0;
+                let paths = args
+                    .token_trees
+                    .iter()
+                    .group_by(move |tt| {
+                        match tt {
+                            tt::TokenTree::Leaf(tt::Leaf::Punct(p)) if p.char == ',' => {
+                                counter += 1;
+                            }
+                            _ => {}
+                        }
+                        counter
+                    })
+                    .into_iter()
+                    .map(|(_, tts)| {
+                        let segments = tts.filter_map(|tt| match tt {
+                            tt::TokenTree::Leaf(tt::Leaf::Ident(id)) => Some(id.as_name()),
+                            _ => None,
+                        });
+                        ModPath::from_segments(PathKind::Plain, segments)
+                    })
+                    .collect::<Vec<_>>();
+
+                Some(paths.into_iter())
+            }
+            _ => None,
+        }
     }
 }
 
@@ -323,7 +423,7 @@ impl<'a> AttrQuery<'a> {
         self.attrs().next().is_some()
     }
 
-    fn attrs(self) -> impl Iterator<Item = &'a Attr> {
+    pub(crate) fn attrs(self) -> impl Iterator<Item = &'a Attr> {
         let key = self.key;
         self.attrs
             .iter()
@@ -344,3 +444,23 @@ fn attrs_from_item_tree<N: ItemTreeNode>(id: ItemTreeId<N>, db: &dyn DefDatabase
     let mod_item = N::id_to_mod_item(id.value);
     tree.raw_attrs(mod_item.into()).clone()
 }
+
+fn collect_attrs(owner: &dyn AttrsOwner) -> impl Iterator<Item = Either<ast::Attr, ast::Comment>> {
+    let (inner_attrs, inner_docs) = inner_attributes(owner.syntax())
+        .map_or((None, None), |(attrs, docs)| ((Some(attrs), Some(docs))));
+
+    let outer_attrs = owner.attrs().filter(|attr| attr.excl_token().is_none());
+    let attrs = outer_attrs
+        .chain(inner_attrs.into_iter().flatten())
+        .map(|attr| (attr.syntax().text_range().start(), Either::Left(attr)));
+
+    let outer_docs =
+        ast::CommentIter::from_syntax_node(owner.syntax()).filter(ast::Comment::is_outer);
+    let docs = outer_docs
+        .chain(inner_docs.into_iter().flatten())
+        .map(|docs_text| (docs_text.syntax().text_range().start(), Either::Right(docs_text)));
+    // sort here by syntax node offset because the source can have doc attributes and doc strings be interleaved
+    let attrs: Vec<_> = docs.chain(attrs).sorted_by_key(|&(offset, _)| offset).collect();
+
+    attrs.into_iter().map(|(_, attr)| attr)
+}
diff --git a/crates/hir_def/src/item_tree.rs b/crates/hir_def/src/item_tree.rs
index 5eb7cae7f..100dbf5d6 100644
--- a/crates/hir_def/src/item_tree.rs
+++ b/crates/hir_def/src/item_tree.rs
@@ -12,7 +12,7 @@ use std::{
 };
 
 use arena::{Arena, Idx, RawId};
-use ast::{AstNode, AttrsOwner, NameOwner, StructKind};
+use ast::{AstNode, NameOwner, StructKind};
 use base_db::CrateId;
 use either::Either;
 use hir_expand::{
@@ -495,7 +495,6 @@ pub struct Import {
     pub alias: Option<ImportAlias>,
     pub visibility: RawVisibilityId,
     pub is_glob: bool,
-    pub is_prelude: bool,
     /// AST ID of the `use` or `extern crate` item this import was derived from. Note that many
     /// `Import`s can map to the same `use` item.
     pub ast_id: FileAstId<ast::Use>,
@@ -511,8 +510,6 @@ pub struct ExternCrate {
     pub name: Name,
     pub alias: Option<ImportAlias>,
     pub visibility: RawVisibilityId,
-    /// Whether this is a `#[macro_use] extern crate ...`.
-    pub is_macro_use: bool,
     pub ast_id: FileAstId<ast::ExternCrate>,
 }
 
diff --git a/crates/hir_def/src/item_tree/lower.rs b/crates/hir_def/src/item_tree/lower.rs
index c8f090c22..3b206ef85 100644
--- a/crates/hir_def/src/item_tree/lower.rs
+++ b/crates/hir_def/src/item_tree/lower.rs
@@ -485,8 +485,6 @@ impl Ctx {
     }
 
     fn lower_use(&mut self, use_item: &ast::Use) -> Vec<FileItemTreeId<Import>> {
-        // FIXME: cfg_attr
-        let is_prelude = use_item.has_atom_attr("prelude_import");
         let visibility = self.lower_visibility(use_item);
         let ast_id = self.source_ast_id_map.ast_id(use_item);
 
@@ -502,7 +500,6 @@ impl Ctx {
                     alias,
                     visibility,
                     is_glob,
-                    is_prelude,
                     ast_id,
                     index: imports.len(),
                 })));
@@ -522,10 +519,8 @@ impl Ctx {
         });
         let visibility = self.lower_visibility(extern_crate);
         let ast_id = self.source_ast_id_map.ast_id(extern_crate);
-        // FIXME: cfg_attr
-        let is_macro_use = extern_crate.has_atom_attr("macro_use");
 
-        let res = ExternCrate { name, alias, visibility, is_macro_use, ast_id };
+        let res = ExternCrate { name, alias, visibility, ast_id };
         Some(id(self.data().extern_crates.alloc(res)))
     }
 
diff --git a/crates/hir_def/src/nameres/collector.rs b/crates/hir_def/src/nameres/collector.rs
index b114a6fe4..a636ec77d 100644
--- a/crates/hir_def/src/nameres/collector.rs
+++ b/crates/hir_def/src/nameres/collector.rs
@@ -136,23 +136,35 @@ struct Import {
 }
 
 impl Import {
-    fn from_use(tree: &ItemTree, id: ItemTreeId<item_tree::Import>) -> Self {
+    fn from_use(
+        db: &dyn DefDatabase,
+        krate: CrateId,
+        tree: &ItemTree,
+        id: ItemTreeId<item_tree::Import>,
+    ) -> Self {
         let it = &tree[id.value];
+        let attrs = &tree.attrs(db, krate, ModItem::from(id.value).into());
         let visibility = &tree[it.visibility];
         Self {
             path: it.path.clone(),
             alias: it.alias.clone(),
             visibility: visibility.clone(),
             is_glob: it.is_glob,
-            is_prelude: it.is_prelude,
+            is_prelude: attrs.by_key("prelude_import").exists(),
             is_extern_crate: false,
             is_macro_use: false,
             source: ImportSource::Import(id),
         }
     }
 
-    fn from_extern_crate(tree: &ItemTree, id: ItemTreeId<item_tree::ExternCrate>) -> Self {
+    fn from_extern_crate(
+        db: &dyn DefDatabase,
+        krate: CrateId,
+        tree: &ItemTree,
+        id: ItemTreeId<item_tree::ExternCrate>,
+    ) -> Self {
         let it = &tree[id.value];
+        let attrs = &tree.attrs(db, krate, ModItem::from(id.value).into());
         let visibility = &tree[it.visibility];
         Self {
             path: ModPath::from_segments(PathKind::Plain, iter::once(it.name.clone())),
@@ -161,7 +173,7 @@ impl Import {
             is_glob: false,
             is_prelude: false,
             is_extern_crate: true,
-            is_macro_use: it.is_macro_use,
+            is_macro_use: attrs.by_key("macro_use").exists(),
             source: ImportSource::ExternCrate(id),
         }
     }
@@ -930,7 +942,12 @@ impl ModCollector<'_, '_> {
             if attrs.cfg().map_or(true, |cfg| self.is_cfg_enabled(&cfg)) {
                 if let ModItem::ExternCrate(id) = item {
                     let import = self.item_tree[*id].clone();
-                    if import.is_macro_use {
+                    let attrs = self.item_tree.attrs(
+                        self.def_collector.db,
+                        krate,
+                        ModItem::from(*id).into(),
+                    );
+                    if attrs.by_key("macro_use").exists() {
                         self.def_collector.import_macros_from_extern_crate(self.module_id, &import);
                     }
                 }
@@ -956,6 +973,8 @@ impl ModCollector<'_, '_> {
                     self.def_collector.unresolved_imports.push(ImportDirective {
                         module_id: self.module_id,
                         import: Import::from_use(
+                            self.def_collector.db,
+                            krate,
                             &self.item_tree,
                             InFile::new(self.file_id, import_id),
                         ),
@@ -966,6 +985,8 @@ impl ModCollector<'_, '_> {
                     self.def_collector.unresolved_imports.push(ImportDirective {
                         module_id: self.module_id,
                         import: Import::from_extern_crate(
+                            self.def_collector.db,
+                            krate,
                             &self.item_tree,
                             InFile::new(self.file_id, import_id),
                         ),
@@ -1268,20 +1289,20 @@ impl ModCollector<'_, '_> {
     }
 
     fn collect_derives(&mut self, attrs: &Attrs, ast_id: FileAstId<ast::Item>) {
-        for derive_subtree in attrs.by_key("derive").tt_values() {
-            // for #[derive(Copy, Clone)], `derive_subtree` is the `(Copy, Clone)` subtree
-            for tt in &derive_subtree.token_trees {
-                let ident = match &tt {
-                    tt::TokenTree::Leaf(tt::Leaf::Ident(ident)) => ident,
-                    tt::TokenTree::Leaf(tt::Leaf::Punct(_)) => continue, // , is ok
-                    _ => continue, // anything else would be an error (which we currently ignore)
-                };
-                let path = ModPath::from_tt_ident(ident);
-
-                let ast_id = AstIdWithPath::new(self.file_id, ast_id, path);
-                self.def_collector
-                    .unexpanded_attribute_macros
-                    .push(DeriveDirective { module_id: self.module_id, ast_id });
+        for derive in attrs.by_key("derive").attrs() {
+            match derive.parse_derive() {
+                Some(derive_macros) => {
+                    for path in derive_macros {
+                        let ast_id = AstIdWithPath::new(self.file_id, ast_id, path);
+                        self.def_collector
+                            .unexpanded_attribute_macros
+                            .push(DeriveDirective { module_id: self.module_id, ast_id });
+                    }
+                }
+                None => {
+                    // FIXME: diagnose
+                    log::debug!("malformed derive: {:?}", derive);
+                }
             }
         }
     }
diff --git a/crates/hir_def/src/nameres/tests.rs b/crates/hir_def/src/nameres/tests.rs
index a4d1fb8f3..c459fa66d 100644
--- a/crates/hir_def/src/nameres/tests.rs
+++ b/crates/hir_def/src/nameres/tests.rs
@@ -13,8 +13,8 @@ use test_utils::mark;
 
 use crate::{db::DefDatabase, nameres::*, test_db::TestDB};
 
-fn compute_crate_def_map(fixture: &str) -> Arc<CrateDefMap> {
-    let db = TestDB::with_files(fixture);
+fn compute_crate_def_map(ra_fixture: &str) -> Arc<CrateDefMap> {
+    let db = TestDB::with_files(ra_fixture);
     let krate = db.crate_graph().iter().next().unwrap();
     db.crate_def_map(krate)
 }
diff --git a/crates/hir_def/src/nameres/tests/diagnostics.rs b/crates/hir_def/src/nameres/tests/diagnostics.rs
index 1a7b98831..58d69d3c6 100644
--- a/crates/hir_def/src/nameres/tests/diagnostics.rs
+++ b/crates/hir_def/src/nameres/tests/diagnostics.rs
@@ -1,4 +1,5 @@
 use base_db::fixture::WithFixture;
+use test_utils::mark;
 
 use crate::test_db::TestDB;
 
@@ -119,3 +120,20 @@ fn inactive_item() {
         "#,
     );
 }
+
+/// Tests that `cfg` attributes behind `cfg_attr` is handled properly.
+#[test]
+fn inactive_via_cfg_attr() {
+    mark::check!(cfg_attr_active);
+    check_diagnostics(
+        r#"
+        //- /lib.rs
+          #[cfg_attr(not(never), cfg(no))] fn f() {}
+        //^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ code is inactive due to #[cfg] directives: no is disabled
+
+          #[cfg_attr(not(never), cfg(not(no)))] fn f() {}
+
+          #[cfg_attr(never, cfg(no))] fn g() {}
+        "#,
+    );
+}
diff --git a/crates/hir_def/src/nameres/tests/macros.rs b/crates/hir_def/src/nameres/tests/macros.rs
index 6fe2ee78a..f9bf5bc72 100644
--- a/crates/hir_def/src/nameres/tests/macros.rs
+++ b/crates/hir_def/src/nameres/tests/macros.rs
@@ -632,11 +632,11 @@ pub struct bar;
 #[test]
 fn expand_derive() {
     let map = compute_crate_def_map(
-        "
+        r#"
         //- /main.rs crate:main deps:core
-        use core::*;
+        use core::Copy;
 
-        #[derive(Copy, Clone)]
+        #[derive(Copy, core::Clone)]
         struct Foo;
 
         //- /core.rs crate:core
@@ -645,7 +645,7 @@ fn expand_derive() {
 
         #[rustc_builtin_macro]
         pub macro Clone {}
-        ",
+        "#,
     );
     assert_eq!(map.modules[map.root].scope.impls().len(), 2);
 }
diff --git a/crates/hir_def/src/path.rs b/crates/hir_def/src/path.rs
index 00a69a8a6..e2bf85bbc 100644
--- a/crates/hir_def/src/path.rs
+++ b/crates/hir_def/src/path.rs
@@ -9,11 +9,8 @@ use std::{
 
 use crate::{body::LowerCtx, type_ref::LifetimeRef};
 use base_db::CrateId;
-use hir_expand::{
-    hygiene::Hygiene,
-    name::{AsName, Name},
-};
-use syntax::ast::{self};
+use hir_expand::{hygiene::Hygiene, name::Name};
+use syntax::ast;
 
 use crate::{
     type_ref::{TypeBound, TypeRef},
@@ -56,11 +53,6 @@ impl ModPath {
         ModPath { kind, segments }
     }
 
-    /// Converts an `tt::Ident` into a single-identifier `Path`.
-    pub(crate) fn from_tt_ident(ident: &tt::Ident) -> ModPath {
-        ident.as_name().into()
-    }
-
     /// Calls `cb` with all paths, represented by this use item.
     pub(crate) fn expand_use_item(
         item_src: InFile<ast::Use>,