1 files changed, 148 insertions, 0 deletions

diff --git a/crates/ra_hir/src/path.rs b/crates/ra_hir/src/path.rs
new file mode 100644
index 000000000..8279daf4b
--- /dev/null
+++ b/crates/ra_hir/src/path.rs
@@ -0,0 +1,148 @@
+use ra_syntax::{SmolStr, ast, AstNode, TextRange};
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) struct Path {
+    pub(crate) kind: PathKind,
+    pub(crate) segments: Vec<SmolStr>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum PathKind {
+    Plain,
+    Self_,
+    Super,
+    Crate,
+}
+
+impl Path {
+    /// Calls `cb` with all paths, represented by this use item.
+    pub(crate) fn expand_use_item(item: ast::UseItem, mut cb: impl FnMut(Path, Option<TextRange>)) {
+        if let Some(tree) = item.use_tree() {
+            expand_use_tree(None, tree, &mut cb);
+        }
+    }
+
+    /// Converts an `ast::Path` to `Path`. Works with use trees.
+    pub(crate) fn from_ast(mut path: ast::Path) -> Option<Path> {
+        let mut kind = PathKind::Plain;
+        let mut segments = Vec::new();
+        loop {
+            let segment = path.segment()?;
+            match segment.kind()? {
+                ast::PathSegmentKind::Name(name) => segments.push(name.text()),
+                ast::PathSegmentKind::CrateKw => {
+                    kind = PathKind::Crate;
+                    break;
+                }
+                ast::PathSegmentKind::SelfKw => {
+                    kind = PathKind::Self_;
+                    break;
+                }
+                ast::PathSegmentKind::SuperKw => {
+                    kind = PathKind::Super;
+                    break;
+                }
+            }
+            path = match qualifier(path) {
+                Some(it) => it,
+                None => break,
+            };
+        }
+        segments.reverse();
+        return Some(Path { kind, segments });
+
+        fn qualifier(path: ast::Path) -> Option<ast::Path> {
+            if let Some(q) = path.qualifier() {
+                return Some(q);
+            }
+            // TODO: this bottom up traversal is not too precise.
+            // Should we handle do a top-down analysiss, recording results?
+            let use_tree_list = path.syntax().ancestors().find_map(ast::UseTreeList::cast)?;
+            let use_tree = use_tree_list.parent_use_tree();
+            use_tree.path()
+        }
+    }
+
+    /// `true` is this path is a single identifier, like `foo`
+    pub(crate) fn is_ident(&self) -> bool {
+        self.kind == PathKind::Plain && self.segments.len() == 1
+    }
+}
+
+fn expand_use_tree(
+    prefix: Option<Path>,
+    tree: ast::UseTree,
+    cb: &mut impl FnMut(Path, Option<TextRange>),
+) {
+    if let Some(use_tree_list) = tree.use_tree_list() {
+        let prefix = match tree.path() {
+            None => prefix,
+            Some(path) => match convert_path(prefix, path) {
+                Some(it) => Some(it),
+                None => return, // TODO: report errors somewhere
+            },
+        };
+        for tree in use_tree_list.use_trees() {
+            expand_use_tree(prefix.clone(), tree, cb);
+        }
+    } else {
+        if let Some(ast_path) = tree.path() {
+            if let Some(path) = convert_path(prefix, ast_path) {
+                let range = if tree.has_star() {
+                    None
+                } else {
+                    let range = ast_path.segment().unwrap().syntax().range();
+                    Some(range)
+                };
+                cb(path, range)
+            }
+        }
+    }
+}
+
+fn convert_path(prefix: Option<Path>, path: ast::Path) -> Option<Path> {
+    let prefix = if let Some(qual) = path.qualifier() {
+        Some(convert_path(prefix, qual)?)
+    } else {
+        None
+    };
+    let segment = path.segment()?;
+    let res = match segment.kind()? {
+        ast::PathSegmentKind::Name(name) => {
+            let mut res = prefix.unwrap_or_else(|| Path {
+                kind: PathKind::Plain,
+                segments: Vec::with_capacity(1),
+            });
+            res.segments.push(name.text());
+            res
+        }
+        ast::PathSegmentKind::CrateKw => {
+            if prefix.is_some() {
+                return None;
+            }
+            Path {
+                kind: PathKind::Crate,
+                segments: Vec::new(),
+            }
+        }
+        ast::PathSegmentKind::SelfKw => {
+            if prefix.is_some() {
+                return None;
+            }
+            Path {
+                kind: PathKind::Self_,
+                segments: Vec::new(),
+            }
+        }
+        ast::PathSegmentKind::SuperKw => {
+            if prefix.is_some() {
+                return None;
+            }
+            Path {
+                kind: PathKind::Super,
+                segments: Vec::new(),
+            }
+        }
+    };
+    Some(res)
+}