1 files changed, 154 insertions, 0 deletions

diff --git a/crates/ide/src/diagnostics/unlinked_file.rs b/crates/ide/src/diagnostics/unlinked_file.rs
new file mode 100644
index 000000000..f6dc671b9
--- /dev/null
+++ b/crates/ide/src/diagnostics/unlinked_file.rs
@@ -0,0 +1,154 @@
+use hir::{
+    db::DefDatabase,
+    diagnostics::{Diagnostic, DiagnosticCode},
+    InFile,
+};
+use ide_db::{
+    base_db::{FileId, FileLoader, SourceDatabase, SourceDatabaseExt},
+    source_change::SourceChange,
+    RootDatabase,
+};
+use syntax::{
+    ast::{self, ModuleItemOwner, NameOwner},
+    AstNode, SyntaxNodePtr,
+};
+use text_edit::TextEdit;
+
+use crate::Fix;
+
+use super::fixes::DiagnosticWithFix;
+
+#[derive(Debug)]
+pub struct UnlinkedFile {
+    pub file_id: FileId,
+    pub node: SyntaxNodePtr,
+}
+
+impl Diagnostic for UnlinkedFile {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("unlinked-file")
+    }
+
+    fn message(&self) -> String {
+        "file not included in module tree".to_string()
+    }
+
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file_id.into(), self.node.clone())
+    }
+
+    fn as_any(&self) -> &(dyn std::any::Any + Send + 'static) {
+        self
+    }
+}
+
+impl DiagnosticWithFix for UnlinkedFile {
+    fn fix(&self, sema: &hir::Semantics<RootDatabase>) -> Option<Fix> {
+        // If there's an existing module that could add a `mod` item to include the unlinked file,
+        // suggest that as a fix.
+
+        let source_root = sema.db.source_root(sema.db.file_source_root(self.file_id));
+        let our_path = source_root.path_for_file(&self.file_id)?;
+        let module_name = our_path.name_and_extension()?.0;
+
+        // Candidates to look for:
+        // - `mod.rs` in the same folder
+        //   - we also check `main.rs` and `lib.rs`
+        // - `$dir.rs` in the parent folder, where `$dir` is the directory containing `self.file_id`
+        let parent = our_path.parent()?;
+        let mut paths =
+            vec![parent.join("mod.rs")?, parent.join("main.rs")?, parent.join("lib.rs")?];
+
+        // `submod/bla.rs` -> `submod.rs`
+        if let Some(newmod) = (|| {
+            let name = parent.name_and_extension()?.0;
+            parent.parent()?.join(&format!("{}.rs", name))
+        })() {
+            paths.push(newmod);
+        }
+
+        for path in &paths {
+            if let Some(parent_id) = source_root.file_for_path(path) {
+                for krate in sema.db.relevant_crates(*parent_id).iter() {
+                    let crate_def_map = sema.db.crate_def_map(*krate);
+                    for (_, module) in crate_def_map.modules() {
+                        if module.origin.is_inline() {
+                            // We don't handle inline `mod parent {}`s, they use different paths.
+                            continue;
+                        }
+
+                        if module.origin.file_id() == Some(*parent_id) {
+                            return make_fix(sema.db, *parent_id, module_name, self.file_id);
+                        }
+                    }
+                }
+            }
+        }
+
+        None
+    }
+}
+
+fn make_fix(
+    db: &RootDatabase,
+    parent_file_id: FileId,
+    new_mod_name: &str,
+    added_file_id: FileId,
+) -> Option<Fix> {
+    fn is_outline_mod(item: &ast::Item) -> bool {
+        matches!(item, ast::Item::Module(m) if m.item_list().is_none())
+    }
+
+    let mod_decl = format!("mod {};", new_mod_name);
+    let ast: ast::SourceFile = db.parse(parent_file_id).tree();
+
+    let mut builder = TextEdit::builder();
+
+    // If there's an existing `mod m;` statement matching the new one, don't emit a fix (it's
+    // probably `#[cfg]`d out).
+    for item in ast.items() {
+        if let ast::Item::Module(m) = item {
+            if let Some(name) = m.name() {
+                if m.item_list().is_none() && name.to_string() == new_mod_name {
+                    cov_mark::hit!(unlinked_file_skip_fix_when_mod_already_exists);
+                    return None;
+                }
+            }
+        }
+    }
+
+    // If there are existing `mod m;` items, append after them (after the first group of them, rather).
+    match ast
+        .items()
+        .skip_while(|item| !is_outline_mod(item))
+        .take_while(|item| is_outline_mod(item))
+        .last()
+    {
+        Some(last) => {
+            cov_mark::hit!(unlinked_file_append_to_existing_mods);
+            builder.insert(last.syntax().text_range().end(), format!("\n{}", mod_decl));
+        }
+        None => {
+            // Prepend before the first item in the file.
+            match ast.items().next() {
+                Some(item) => {
+                    cov_mark::hit!(unlinked_file_prepend_before_first_item);
+                    builder.insert(item.syntax().text_range().start(), format!("{}\n\n", mod_decl));
+                }
+                None => {
+                    // No items in the file, so just append at the end.
+                    cov_mark::hit!(unlinked_file_empty_file);
+                    builder.insert(ast.syntax().text_range().end(), format!("{}\n", mod_decl));
+                }
+            }
+        }
+    }
+
+    let edit = builder.finish();
+    let trigger_range = db.parse(added_file_id).tree().syntax().text_range();
+    Some(Fix::new(
+        &format!("Insert `{}`", mod_decl),
+        SourceChange::from_text_edit(parent_file_id, edit),
+        trigger_range,
+    ))
+}