Auto merge of rust-lang#12387 - 00nktk:fix-mod-rename, r=Veykril

fix(ide-db): correct single-file module rename

Fixes a bug where rust-analyzer would emit `WorkspaceEdit`s with paths to dirs instead of files for the following project layout.

lib.rs
```rust
mod foo;
```

foo.rs
```rust
mod bar {
    struct Bar;
}
```
Also fixes emitted paths for modules with mod.rs.
The bug resulted in panic in helix editor when attempting to rename a module.

Author: bors

crates/hir/src/has_source.rs

@@ -39,6 +39,11 @@ impl Module {
         }
     }
 
+    pub fn is_inline(self, db: &dyn HirDatabase) -> bool {
+        let def_map = self.id.def_map(db.upcast());
+        def_map[self.id.local_id].origin.is_inline()
+    }
+
     /// Returns a node which declares this module, either a `mod foo;` or a `mod foo {}`.
     /// `None` for the crate root.
     pub fn declaration_source(self, db: &dyn HirDatabase) -> Option<InFile<ast::Module>> {

crates/ide-db/src/rename.rs

@@ -180,15 +180,33 @@ fn rename_mod(
     let InFile { file_id, value: def_source } = module.definition_source(sema.db);
     if let ModuleSource::SourceFile(..) = def_source {
         let anchor = file_id.original_file(sema.db);
-        // not mod.rs and doesn't has children, rename file only
-        if !module.is_mod_rs(sema.db) && module.children(sema.db).next().is_none() {
+
+        let is_mod_rs = module.is_mod_rs(sema.db);
+        let has_detached_child = module.children(sema.db).any(|child| !child.is_inline(sema.db));
+
+        // Module exists in a named file
+        if !is_mod_rs {
             let path = format!("{}.rs", new_name);
             let dst = AnchoredPathBuf { anchor, path };
             source_change.push_file_system_edit(FileSystemEdit::MoveFile { src: anchor, dst })
-        } else if let Some(mod_name) = module.name(sema.db) {
-            // is mod.rs or has children, rename dir
-            let src = AnchoredPathBuf { anchor, path: mod_name.to_string() };
-            let dst = AnchoredPathBuf { anchor, path: new_name.to_string() };
+        }
+
+        // Rename the dir if:
+        //  - Module source is in mod.rs
+        //  - Module has submodules defined in separate files
+        let dir_paths = match (is_mod_rs, has_detached_child, module.name(sema.db)) {
+            // Go up one level since the anchor is inside the dir we're trying to rename
+            (true, _, Some(mod_name)) => {
+                Some((format!("../{}", mod_name), format!("../{}", new_name)))
+            }
+            // The anchor is on the same level as target dir
+            (false, true, Some(mod_name)) => Some((mod_name.to_string(), new_name.to_string())),
+            _ => None,
+        };
+
+        if let Some((src, dst)) = dir_paths {
+            let src = AnchoredPathBuf { anchor, path: src };
+            let dst = AnchoredPathBuf { anchor, path: dst };
             source_change.push_file_system_edit(FileSystemEdit::MoveDir {
                 src,
                 src_id: anchor,

crates/ide/src/rename.rs

@@ -973,7 +973,7 @@ mod fo$0o;
                                 anchor: FileId(
                                     1,
                                 ),
-                                path: "foo",
+                                path: "../foo",
                             },
                             src_id: FileId(
                                 1,
@@ -982,7 +982,7 @@ mod fo$0o;
                                 anchor: FileId(
                                     1,
                                 ),
-                                path: "foo2",
+                                path: "../foo2",
                             },
                         },
                     ],
@@ -1158,6 +1158,17 @@ mod quux;
                         },
                     },
                     file_system_edits: [
+                        MoveFile {
+                            src: FileId(
+                                1,
+                            ),
+                            dst: AnchoredPathBuf {
+                                anchor: FileId(
+                                    1,
+                                ),
+                                path: "foo2.rs",
+                            },
+                        },
                         MoveDir {
                             src: AnchoredPathBuf {
                                 anchor: FileId(