2 files changed, 98 insertions, 23 deletions

diff --git a/crates/ide/src/completion/complete_mod.rs b/crates/ide/src/completion/complete_mod.rs
index 4c1e79603..da3d93bad 100644
--- a/crates/ide/src/completion/complete_mod.rs
+++ b/crates/ide/src/completion/complete_mod.rs
@@ -1,35 +1,61 @@
 //! Completes mod declarations.
 
-use base_db::FileLoader;
-use hir::ModuleSource;
+use base_db::{SourceDatabaseExt, VfsPath};
+use hir::{Module, ModuleSource};
+use ide_db::RootDatabase;
 
 use super::{completion_context::CompletionContext, completion_item::Completions};
 
 /// Complete mod declaration, i.e. `mod <|> ;`
 pub(super) fn complete_mod(acc: &mut Completions, ctx: &CompletionContext) {
     let module_names_for_import = ctx
-        .sema
-        // TODO kb this is wrong, since we need not the file module
-        .to_module_def(ctx.position.file_id)
+        .scope
+        .module()
         .and_then(|current_module| {
-            dbg!(current_module.name(ctx.db));
-            dbg!(current_module.definition_source(ctx.db));
-            dbg!(current_module.declaration_source(ctx.db));
-            let mut zz = Vec::new();
-            let mut vv = Some(current_module);
-            while let Some(ModuleSource::Module(_)) =
-                vv.map(|vv| vv.definition_source(ctx.db).value)
-            {
-                zz.push(current_module.name(ctx.db));
-                vv = current_module.parent(ctx.db);
-            }
-            dbg!(zz);
-            let definition_source = current_module.definition_source(ctx.db);
+            let module_path = path_to_closest_containing_module_file(current_module, ctx.db);
             // TODO kb filter out declarations in possible_sudmobule_names
             // let declaration_source = current_module.declaration_source(ctx.db);
-            let module_definition_source_file = definition_source.file_id.original_file(ctx.db);
-            let mod_declaration_candidates =
-                ctx.db.possible_sudmobule_names(module_definition_source_file);
+            let module_definition_source_file =
+                current_module.definition_source(ctx.db).file_id.original_file(ctx.db);
+
+            let source_root_id = ctx.db.file_source_root(module_definition_source_file);
+            let source_root = ctx.db.source_root(source_root_id);
+            let directory_to_look_for_submodules = source_root
+                .path_for_file(&module_definition_source_file)
+                .and_then(|module_file_path| get_directory_with_submodules(module_file_path))?;
+
+            let mod_declaration_candidates = source_root
+                .iter()
+                .filter(|submodule_file| submodule_file != &module_definition_source_file)
+                .filter_map(|submodule_file| {
+                    let submodule_path = source_root.path_for_file(&submodule_file)?;
+                    if submodule_path.parent()? == directory_to_look_for_submodules {
+                        submodule_path.file_name_and_extension()
+                    } else {
+                        None
+                    }
+                })
+                .filter_map(|file_name_and_extension| {
+                    match file_name_and_extension {
+                        // TODO kb wrong resolution for nested non-file modules (mod tests { mod <|> })
+                        // TODO kb in src/bin when a module is included into another,
+                        // the included file gets "moved" into a directory below and now cannot add any other modules
+                        ("mod", Some("rs")) | ("lib", Some("rs")) | ("main", Some("rs")) => None,
+                        (file_name, Some("rs")) => Some(file_name.to_owned()),
+                        (subdirectory_name, None) => {
+                            let mod_rs_path = directory_to_look_for_submodules
+                                .join(subdirectory_name)?
+                                .join("mod.rs")?;
+                            if source_root.file_for_path(&mod_rs_path).is_some() {
+                                Some(subdirectory_name.to_owned())
+                            } else {
+                                None
+                            }
+                        }
+                        _ => None,
+                    }
+                })
+                .collect::<Vec<_>>();
             dbg!(mod_declaration_candidates);
             // TODO kb exlude existing children from the candidates
             let existing_children = current_module.children(ctx.db).collect::<Vec<_>>();
@@ -37,3 +63,51 @@ pub(super) fn complete_mod(acc: &mut Completions, ctx: &CompletionContext) {
         })
         .unwrap_or_default();
 }
+
+fn path_to_closest_containing_module_file(
+    current_module: Module,
+    db: &RootDatabase,
+) -> Vec<Module> {
+    let mut path = Vec::new();
+
+    let mut current_module = Some(current_module);
+    while let Some(ModuleSource::Module(_)) =
+        current_module.map(|module| module.definition_source(db).value)
+    {
+        if let Some(module) = current_module {
+            path.insert(0, module);
+            current_module = module.parent(db);
+        } else {
+            current_module = None;
+        }
+    }
+
+    path
+}
+
+fn get_directory_with_submodules(module_file_path: &VfsPath) -> Option<VfsPath> {
+    let module_directory_path = module_file_path.parent()?;
+    match module_file_path.file_name_and_extension()? {
+        ("mod", Some("rs")) | ("lib", Some("rs")) | ("main", Some("rs")) => {
+            Some(module_directory_path)
+        }
+        (regular_rust_file_name, Some("rs")) => {
+            if matches!(
+                (
+                    module_directory_path
+                        .parent()
+                        .as_ref()
+                        .and_then(|path| path.file_name_and_extension()),
+                    module_directory_path.file_name_and_extension(),
+                ),
+                (Some(("src", None)), Some(("bin", None)))
+            ) {
+                // files in /src/bin/ can import each other directly
+                Some(module_directory_path)
+            } else {
+                module_directory_path.join(regular_rust_file_name)
+            }
+        }
+        _ => None,
+    }
+}
diff --git a/crates/ide/src/completion/completion_context.rs b/crates/ide/src/completion/completion_context.rs
index 31886942a..47355d5dc 100644
--- a/crates/ide/src/completion/completion_context.rs
+++ b/crates/ide/src/completion/completion_context.rs
@@ -1,7 +1,7 @@
 //! FIXME: write short doc here
 
-use base_db::{FileLoader, SourceDatabase};
-use hir::{ModuleSource, Semantics, SemanticsScope, Type};
+use base_db::SourceDatabase;
+use hir::{Semantics, SemanticsScope, Type};
 use ide_db::RootDatabase;
 use syntax::{
     algo::{find_covering_element, find_node_at_offset},
@@ -112,6 +112,7 @@ impl<'a> CompletionContext<'a> {
         };
         let fake_ident_token =
             file_with_fake_ident.syntax().token_at_offset(position.offset).right_biased().unwrap();
+
         let krate = sema.to_module_def(position.file_id).map(|m| m.krate());
         let original_token =
             original_file.syntax().token_at_offset(position.offset).left_biased()?;