Introduce ModuleId

Previously, module was synonym with a file, and so a module could have
had several parents. This commit introduces a separate module concept,
such that each module has only one parent, but a single file can
correspond to different modules.

crates/ra_analysis/src/descriptors/module/mod.rs

@@ -0,0 +1,176 @@
+mod imp;
+
+use std::sync::Arc;
+
+use relative_path::RelativePathBuf;
+use ra_syntax::{ast::{self, NameOwner, AstNode}, SmolStr, SyntaxNode};
+
+use crate::{
+    FileId, Cancelable,
+    db::SyntaxDatabase,
+};
+
+salsa::query_group! {
+    pub(crate) trait ModulesDatabase: SyntaxDatabase {
+        fn module_tree() -> Cancelable<Arc<ModuleTree>> {
+            type ModuleTreeQuery;
+            use fn imp::module_tree;
+        }
+        fn submodules(file_id: FileId) -> Cancelable<Arc<Vec<SmolStr>>> {
+            type SubmodulesQuery;
+            use fn imp::submodules;
+        }
+    }
+}
+
+
+#[derive(Debug, PartialEq, Eq, Hash)]
+pub(crate) struct ModuleTree {
+    mods: Vec<ModuleData>,
+    links: Vec<LinkData>,
+}
+
+impl ModuleTree {
+    pub(crate) fn modules_for_file(&self, file_id: FileId) -> Vec<ModuleId> {
+        self.mods.iter()
+            .enumerate()
+            .filter(|(_idx, it)| it.file_id == file_id).map(|(idx, _)| ModuleId(idx as u32))
+            .collect()
+    }
+
+    pub(crate) fn any_module_for_file(&self, file_id: FileId) -> Option<ModuleId> {
+        self.modules_for_file(file_id).pop()
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Debug)]
+pub(crate) struct ModuleId(u32);
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+pub(crate) struct LinkId(u32);
+
+#[derive(Clone, Debug, Hash, PartialEq, Eq)]
+pub enum Problem {
+    UnresolvedModule {
+        candidate: RelativePathBuf,
+    },
+    NotDirOwner {
+        move_to: RelativePathBuf,
+        candidate: RelativePathBuf,
+    },
+}
+
+impl ModuleId {
+    pub(crate) fn file_id(self, tree: &ModuleTree) -> FileId {
+        tree.module(self).file_id
+    }
+    pub(crate) fn parent_link(self, tree: &ModuleTree) -> Option<LinkId> {
+        tree.module(self).parent
+     }
+    pub(crate) fn parent(self, tree: &ModuleTree) -> Option<ModuleId> {
+        let link = self.parent_link(tree)?;
+        Some(tree.link(link).owner)
+    }
+    pub(crate) fn root(self, tree: &ModuleTree) -> ModuleId {
+        let mut curr = self;
+        let mut i = 0;
+        while let Some(next) = curr.parent(tree) {
+            curr = next;
+            i += 1;
+            if i > 100 {
+                return self;
+            }
+        }
+        curr
+    }
+    pub(crate) fn child(self, tree: &ModuleTree, name: &str) -> Option<ModuleId> {
+        let link = tree.module(self)
+            .children
+            .iter()
+            .map(|&it| tree.link(it))
+            .find(|it| it.name == name)?;
+        Some(*link.points_to.first()?)
+    }
+    pub(crate) fn problems(
+        self,
+        tree: &ModuleTree,
+        root: ast::Root,
+    ) -> Vec<(SyntaxNode, Problem)> {
+        tree.module(self)
+            .children
+            .iter()
+            .filter_map(|&it| {
+                let p = tree.link(it).problem.clone()?;
+                let s = it.bind_source(tree, root);
+                let s = s.name().unwrap().syntax().owned();
+                Some((s, p))
+            })
+            .collect()
+    }
+}
+
+impl LinkId {
+    pub(crate) fn name(self, tree: &ModuleTree) -> SmolStr {
+        tree.link(self).name.clone()
+    }
+    pub(crate) fn owner(self, tree: &ModuleTree) -> ModuleId {
+        tree.link(self).owner
+    }
+    fn points_to(self, tree: &ModuleTree) -> &[ModuleId] {
+        &tree.link(self).points_to
+    }
+    pub(crate) fn bind_source<'a>(
+        self,
+        tree: &ModuleTree,
+        root: ast::Root<'a>,
+    ) -> ast::Module<'a> {
+        imp::modules(root)
+            .find(|(name, _)| name == &tree.link(self).name)
+            .unwrap()
+            .1
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Hash)]
+struct ModuleData {
+    file_id: FileId,
+    parent: Option<LinkId>,
+    children: Vec<LinkId>,
+}
+
+#[derive(Hash, Debug, PartialEq, Eq)]
+struct LinkData {
+    owner: ModuleId,
+    name: SmolStr,
+    points_to: Vec<ModuleId>,
+    problem: Option<Problem>,
+}
+
+
+impl ModuleTree {
+    fn module(&self, id: ModuleId) -> &ModuleData {
+        &self.mods[id.0 as usize]
+    }
+    fn module_mut(&mut self, id: ModuleId) -> &mut ModuleData {
+        &mut self.mods[id.0 as usize]
+    }
+    fn link(&self, id: LinkId) -> &LinkData {
+        &self.links[id.0 as usize]
+    }
+    fn link_mut(&mut self, id: LinkId) -> &mut LinkData {
+        &mut self.links[id.0 as usize]
+    }
+
+    fn push_mod(&mut self, data: ModuleData) -> ModuleId {
+        let id = ModuleId(self.mods.len() as u32);
+        self.mods.push(data);
+        id
+    }
+    fn push_link(&mut self, data: LinkData) -> LinkId {
+        let id = LinkId(self.links.len() as u32);
+        self.mods[data.owner.0 as usize].children.push(id);
+        self.links.push(data);
+        id
+    }
+}
+