Make VFS join methods fallible

crates/ra_hir_def/src/nameres/tests/mod_resolution.rs

@@ -334,6 +334,22 @@ fn module_resolution_relative_path_2() {
     "###);
 }
 
+#[test]
+fn module_resolution_relative_path_outside_root() {
+    let map = def_map(
+        r###"
+        //- /main.rs
+
+        #[path="../../../../../outside.rs"]
+        mod foo;
+        "###,
+    );
+
+    assert_snapshot!(map, @r###"
+        ⋮crate
+    "###);
+}
+
 #[test]
 fn module_resolution_explicit_path_mod_rs_2() {
     let map = def_map(

crates/rust-analyzer/src/global_state.rs

@@ -213,7 +213,7 @@ impl GlobalStateSnapshot {
     pub(crate) fn anchored_path(&self, file_id: FileId, path: &str) -> Url {
         let mut base = self.vfs.read().0.file_path(file_id);
         base.pop();
-        let path = base.join(path);
+        let path = base.join(path).unwrap();
         let path = path.as_path().unwrap();
         url_from_abs_path(&path)
     }

crates/vfs/src/file_set.rs

@@ -18,7 +18,7 @@ impl FileSet {
     pub fn resolve_path(&self, anchor: FileId, path: &str) -> Option<FileId> {
         let mut base = self.paths[&anchor].clone();
         base.pop();
-        let path = base.join(path);
+        let path = base.join(path)?;
         let res = self.files.get(&path).copied();
         res
     }

crates/vfs/src/vfs_path.rs

@@ -22,15 +22,15 @@ impl VfsPath {
             VfsPathRepr::VirtualPath(_) => None,
         }
     }
-    pub fn join(&self, path: &str) -> VfsPath {
+    pub fn join(&self, path: &str) -> Option<VfsPath> {
         match &self.0 {
             VfsPathRepr::PathBuf(it) => {
                 let res = it.join(path).normalize();
-                VfsPath(VfsPathRepr::PathBuf(res))
+                Some(VfsPath(VfsPathRepr::PathBuf(res)))
             }
             VfsPathRepr::VirtualPath(it) => {
-                let res = it.join(path);
-                VfsPath(VfsPathRepr::VirtualPath(res))
+                let res = it.join(path)?;
+                Some(VfsPath(VfsPathRepr::VirtualPath(res)))
             }
         }
     }
@@ -101,13 +101,15 @@ impl VirtualPath {
         self.0 = self.0[..pos].to_string();
         true
     }
-    fn join(&self, mut path: &str) -> VirtualPath {
+    fn join(&self, mut path: &str) -> Option<VirtualPath> {
         let mut res = self.clone();
         while path.starts_with("../") {
-            assert!(res.pop());
+            if !res.pop() {
+                return None;
+            }
             path = &path["../".len()..]
         }
         res.0 = format!("{}/{}", res.0, path);
-        res
+        Some(res)
     }
 }