1 files changed, 112 insertions, 0 deletions

diff --git a/crates/ra_hir_def/src/path/lower/lower_use.rs b/crates/ra_hir_def/src/path/lower/lower_use.rs
new file mode 100644
index 000000000..ea3fdb56c
--- /dev/null
+++ b/crates/ra_hir_def/src/path/lower/lower_use.rs
@@ -0,0 +1,112 @@
+//! Lowers a single complex use like `use foo::{bar, baz};` into a list of paths like
+//! `foo::bar`, `foo::baz`;
+
+use std::iter;
+
+use either::Either;
+use hir_expand::{
+    hygiene::Hygiene,
+    name::{AsName, Name},
+};
+use ra_syntax::ast::{self, NameOwner};
+
+use crate::path::{ModPath, PathKind};
+
+pub(crate) fn lower_use_tree(
+    prefix: Option<ModPath>,
+    tree: ast::UseTree,
+    hygiene: &Hygiene,
+    cb: &mut dyn FnMut(ModPath, &ast::UseTree, bool, Option<Name>),
+) {
+    if let Some(use_tree_list) = tree.use_tree_list() {
+        let prefix = match tree.path() {
+            // E.g. use something::{{{inner}}};
+            None => prefix,
+            // E.g. `use something::{inner}` (prefix is `None`, path is `something`)
+            // or `use something::{path::{inner::{innerer}}}` (prefix is `something::path`, path is `inner`)
+            Some(path) => match convert_path(prefix, path, hygiene) {
+                Some(it) => Some(it),
+                None => return, // FIXME: report errors somewhere
+            },
+        };
+        for child_tree in use_tree_list.use_trees() {
+            lower_use_tree(prefix.clone(), child_tree, hygiene, cb);
+        }
+    } else {
+        let alias = tree.alias().and_then(|a| a.name()).map(|a| a.as_name());
+        if let Some(ast_path) = tree.path() {
+            // Handle self in a path.
+            // E.g. `use something::{self, <...>}`
+            if ast_path.qualifier().is_none() {
+                if let Some(segment) = ast_path.segment() {
+                    if segment.kind() == Some(ast::PathSegmentKind::SelfKw) {
+                        if let Some(prefix) = prefix {
+                            cb(prefix, &tree, false, alias);
+                            return;
+                        }
+                    }
+                }
+            }
+            if let Some(path) = convert_path(prefix, ast_path, hygiene) {
+                let is_glob = tree.has_star();
+                cb(path, &tree, is_glob, alias)
+            }
+            // FIXME: report errors somewhere
+            // We get here if we do
+        }
+    }
+}
+
+fn convert_path(prefix: Option<ModPath>, path: ast::Path, hygiene: &Hygiene) -> Option<ModPath> {
+    let prefix = if let Some(qual) = path.qualifier() {
+        Some(convert_path(prefix, qual, hygiene)?)
+    } else {
+        prefix
+    };
+
+    let segment = path.segment()?;
+    let res = match segment.kind()? {
+        ast::PathSegmentKind::Name(name_ref) => {
+            match hygiene.name_ref_to_name(name_ref) {
+                Either::Left(name) => {
+                    // no type args in use
+                    let mut res = prefix.unwrap_or_else(|| ModPath {
+                        kind: PathKind::Plain,
+                        segments: Vec::with_capacity(1),
+                    });
+                    res.segments.push(name);
+                    res
+                }
+                Either::Right(crate_id) => {
+                    return Some(ModPath::from_simple_segments(
+                        PathKind::DollarCrate(crate_id),
+                        iter::empty(),
+                    ))
+                }
+            }
+        }
+        ast::PathSegmentKind::CrateKw => {
+            if prefix.is_some() {
+                return None;
+            }
+            ModPath::from_simple_segments(PathKind::Crate, iter::empty())
+        }
+        ast::PathSegmentKind::SelfKw => {
+            if prefix.is_some() {
+                return None;
+            }
+            ModPath::from_simple_segments(PathKind::Self_, iter::empty())
+        }
+        ast::PathSegmentKind::SuperKw => {
+            if prefix.is_some() {
+                return None;
+            }
+            ModPath::from_simple_segments(PathKind::Super, iter::empty())
+        }
+        ast::PathSegmentKind::Type { .. } => {
+            // not allowed in imports
+            return None;
+        }
+    };
+    Some(res)
+}