1 files changed, 139 insertions, 0 deletions

diff --git a/crates/hir_def/src/nameres/mod_resolution.rs b/crates/hir_def/src/nameres/mod_resolution.rs
new file mode 100644
index 000000000..e8389b484
--- /dev/null
+++ b/crates/hir_def/src/nameres/mod_resolution.rs
@@ -0,0 +1,139 @@
+//! This module resolves `mod foo;` declaration to file.
+use base_db::FileId;
+use hir_expand::name::Name;
+use syntax::SmolStr;
+
+use crate::{db::DefDatabase, HirFileId};
+
+#[derive(Clone, Debug)]
+pub(super) struct ModDir {
+    /// `` for `mod.rs`, `lib.rs`
+    /// `foo/` for `foo.rs`
+    /// `foo/bar/` for `mod bar { mod x; }` nested in `foo.rs`
+    /// Invariant: path.is_empty() || path.ends_with('/')
+    dir_path: DirPath,
+    /// inside `./foo.rs`, mods with `#[path]` should *not* be relative to `./foo/`
+    root_non_dir_owner: bool,
+}
+
+impl ModDir {
+    pub(super) fn root() -> ModDir {
+        ModDir { dir_path: DirPath::empty(), root_non_dir_owner: false }
+    }
+
+    pub(super) fn descend_into_definition(
+        &self,
+        name: &Name,
+        attr_path: Option<&SmolStr>,
+    ) -> ModDir {
+        let path = match attr_path.map(|it| it.as_str()) {
+            None => {
+                let mut path = self.dir_path.clone();
+                path.push(&name.to_string());
+                path
+            }
+            Some(attr_path) => {
+                let mut path = self.dir_path.join_attr(attr_path, self.root_non_dir_owner);
+                if !(path.is_empty() || path.ends_with('/')) {
+                    path.push('/')
+                }
+                DirPath::new(path)
+            }
+        };
+        ModDir { dir_path: path, root_non_dir_owner: false }
+    }
+
+    pub(super) fn resolve_declaration(
+        &self,
+        db: &dyn DefDatabase,
+        file_id: HirFileId,
+        name: &Name,
+        attr_path: Option<&SmolStr>,
+    ) -> Result<(FileId, bool, ModDir), String> {
+        let file_id = file_id.original_file(db.upcast());
+
+        let mut candidate_files = Vec::new();
+        match attr_path {
+            Some(attr_path) => {
+                candidate_files.push(self.dir_path.join_attr(attr_path, self.root_non_dir_owner))
+            }
+            None => {
+                candidate_files.push(format!("{}{}.rs", self.dir_path.0, name));
+                candidate_files.push(format!("{}{}/mod.rs", self.dir_path.0, name));
+            }
+        };
+
+        for candidate in candidate_files.iter() {
+            if let Some(file_id) = db.resolve_path(file_id, candidate.as_str()) {
+                let is_mod_rs = candidate.ends_with("mod.rs");
+
+                let (dir_path, root_non_dir_owner) = if is_mod_rs || attr_path.is_some() {
+                    (DirPath::empty(), false)
+                } else {
+                    (DirPath::new(format!("{}/", name)), true)
+                };
+                return Ok((file_id, is_mod_rs, ModDir { dir_path, root_non_dir_owner }));
+            }
+        }
+        Err(candidate_files.remove(0))
+    }
+}
+
+#[derive(Clone, Debug)]
+struct DirPath(String);
+
+impl DirPath {
+    fn assert_invariant(&self) {
+        assert!(self.0.is_empty() || self.0.ends_with('/'));
+    }
+    fn new(repr: String) -> DirPath {
+        let res = DirPath(repr);
+        res.assert_invariant();
+        res
+    }
+    fn empty() -> DirPath {
+        DirPath::new(String::new())
+    }
+    fn push(&mut self, name: &str) {
+        self.0.push_str(name);
+        self.0.push('/');
+        self.assert_invariant();
+    }
+    fn parent(&self) -> Option<&str> {
+        if self.0.is_empty() {
+            return None;
+        };
+        let idx =
+            self.0[..self.0.len() - '/'.len_utf8()].rfind('/').map_or(0, |it| it + '/'.len_utf8());
+        Some(&self.0[..idx])
+    }
+    /// So this is the case which doesn't really work I think if we try to be
+    /// 100% platform agnostic:
+    ///
+    /// ```
+    /// mod a {
+    ///     #[path="C://sad/face"]
+    ///     mod b { mod c; }
+    /// }
+    /// ```
+    ///
+    /// Here, we need to join logical dir path to a string path from an
+    /// attribute. Ideally, we should somehow losslessly communicate the whole
+    /// construction to `FileLoader`.
+    fn join_attr(&self, mut attr: &str, relative_to_parent: bool) -> String {
+        let base = if relative_to_parent { self.parent().unwrap() } else { &self.0 };
+
+        if attr.starts_with("./") {
+            attr = &attr["./".len()..];
+        }
+        let tmp;
+        let attr = if attr.contains('\\') {
+            tmp = attr.replace('\\', "/");
+            &tmp
+        } else {
+            attr
+        };
+        let res = format!("{}{}", base, attr);
+        res
+    }
+}