4 files changed, 90 insertions, 3 deletions

diff --git a/crates/ra_hir/src/db.rs b/crates/ra_hir/src/db.rs
index 7b7974f5b..f7f124904 100644
--- a/crates/ra_hir/src/db.rs
+++ b/crates/ra_hir/src/db.rs
@@ -5,6 +5,7 @@ use ra_syntax::{ast, Parse, SmolStr, SyntaxNode};
 
 use crate::{
     adt::{EnumData, StructData},
+    debug::HirDebugDatabase,
     generics::{GenericDef, GenericParams},
     ids,
     impl_block::{ImplBlock, ImplSourceMap, ModuleImplBlocks},
@@ -83,7 +84,7 @@ pub trait AstDatabase: InternDatabase {
 // This database uses `AstDatabase` internally,
 #[salsa::query_group(DefDatabaseStorage)]
 #[salsa::requires(AstDatabase)]
-pub trait DefDatabase: InternDatabase {
+pub trait DefDatabase: InternDatabase + HirDebugDatabase {
     #[salsa::invoke(crate::adt::StructData::struct_data_query)]
     fn struct_data(&self, s: Struct) -> Arc<StructData>;
 
diff --git a/crates/ra_hir/src/debug.rs b/crates/ra_hir/src/debug.rs
new file mode 100644
index 000000000..5a835741d
--- /dev/null
+++ b/crates/ra_hir/src/debug.rs
@@ -0,0 +1,64 @@
+use std::{cell::Cell, fmt};
+
+use ra_db::{CrateId, FileId};
+
+use crate::{db::HirDatabase, Crate, Module, Name};
+
+impl Crate {
+    pub fn debug(self, db: &impl HirDebugDatabase) -> impl fmt::Debug + '_ {
+        debug_fn(move |fmt| db.debug_crate(self, fmt))
+    }
+}
+
+impl Module {
+    pub fn debug(self, db: &impl HirDebugDatabase) -> impl fmt::Debug + '_ {
+        debug_fn(move |fmt| db.debug_module(self, fmt))
+    }
+}
+
+pub trait HirDebugHelper: HirDatabase {
+    fn crate_name(&self, _krate: CrateId) -> Option<String> {
+        None
+    }
+    fn file_path(&self, _file_id: FileId) -> Option<String> {
+        None
+    }
+}
+
+pub trait HirDebugDatabase {
+    fn debug_crate(&self, krate: Crate, fmt: &mut fmt::Formatter<'_>) -> fmt::Result;
+    fn debug_module(&self, module: Module, fmt: &mut fmt::Formatter<'_>) -> fmt::Result;
+}
+
+impl<DB: HirDebugHelper> HirDebugDatabase for DB {
+    fn debug_crate(&self, krate: Crate, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let mut builder = fmt.debug_tuple("Crate");
+        match self.crate_name(krate.crate_id) {
+            Some(name) => builder.field(&name),
+            None => builder.field(&krate.crate_id),
+        }
+        .finish()
+    }
+
+    fn debug_module(&self, module: Module, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let file_id = module.definition_source(self).file_id.original_file(self);
+        let path = self.file_path(file_id);
+        fmt.debug_struct("Module")
+            .field("name", &module.name(self).unwrap_or_else(Name::missing))
+            .field("path", &path.unwrap_or_else(|| "N/A".to_string()))
+            .finish()
+    }
+}
+
+fn debug_fn(f: impl FnOnce(&mut fmt::Formatter<'_>) -> fmt::Result) -> impl fmt::Debug {
+    struct DebugFn<F>(Cell<Option<F>>);
+
+    impl<F: FnOnce(&mut fmt::Formatter<'_>) -> fmt::Result> fmt::Debug for DebugFn<F> {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            let f = self.0.take().unwrap();
+            f(fmt)
+        }
+    }
+
+    DebugFn(Cell::new(Some(f)))
+}
diff --git a/crates/ra_hir/src/lib.rs b/crates/ra_hir/src/lib.rs
index 7c2a68992..24ee84f86 100644
--- a/crates/ra_hir/src/lib.rs
+++ b/crates/ra_hir/src/lib.rs
@@ -20,6 +20,7 @@ macro_rules! impl_froms {
 }
 
 mod either;
+pub mod debug;
 
 pub mod db;
 #[macro_use]
diff --git a/crates/ra_hir/src/mock.rs b/crates/ra_hir/src/mock.rs
index 972f0ece5..8dcea5071 100644
--- a/crates/ra_hir/src/mock.rs
+++ b/crates/ra_hir/src/mock.rs
@@ -2,13 +2,14 @@ use std::{panic, sync::Arc};
 
 use parking_lot::Mutex;
 use ra_db::{
-    salsa, CrateGraph, Edition, FileId, FilePosition, SourceDatabase, SourceRoot, SourceRootId,
+    salsa, CrateGraph, CrateId, Edition, FileId, FilePosition, SourceDatabase, SourceRoot,
+    SourceRootId,
 };
 use relative_path::RelativePathBuf;
 use rustc_hash::FxHashMap;
 use test_utils::{extract_offset, parse_fixture, CURSOR_MARKER};
 
-use crate::{db, diagnostics::DiagnosticSink};
+use crate::{db, debug::HirDebugHelper, diagnostics::DiagnosticSink};
 
 pub const WORKSPACE: SourceRootId = SourceRootId(0);
 
@@ -24,10 +25,22 @@ pub struct MockDatabase {
     events: Mutex<Option<Vec<salsa::Event<MockDatabase>>>>,
     runtime: salsa::Runtime<MockDatabase>,
     files: FxHashMap<String, FileId>,
+    crate_names: Arc<FxHashMap<CrateId, String>>,
+    file_paths: Arc<FxHashMap<FileId, String>>,
 }
 
 impl panic::RefUnwindSafe for MockDatabase {}
 
+impl HirDebugHelper for MockDatabase {
+    fn crate_name(&self, krate: CrateId) -> Option<String> {
+        self.crate_names.get(&krate).cloned()
+    }
+
+    fn file_path(&self, file_id: FileId) -> Option<String> {
+        self.file_paths.get(&file_id).cloned()
+    }
+}
+
 impl MockDatabase {
     pub fn with_files(fixture: &str) -> MockDatabase {
         let (db, position) = MockDatabase::from_fixture(fixture);
@@ -62,6 +75,7 @@ impl MockDatabase {
         for (crate_name, (crate_root, edition, _)) in graph.0.iter() {
             let crate_root = self.file_id_of(&crate_root);
             let crate_id = crate_graph.add_crate_root(crate_root, *edition);
+            Arc::make_mut(&mut self.crate_names).insert(crate_id, crate_name.clone());
             ids.insert(crate_name, crate_id);
         }
         for (crate_name, (_, _, deps)) in graph.0.iter() {
@@ -151,8 +165,11 @@ impl MockDatabase {
         let is_crate_root = rel_path == "lib.rs" || rel_path == "/main.rs";
 
         let file_id = FileId(self.files.len() as u32);
+
         let prev = self.files.insert(path.to_string(), file_id);
         assert!(prev.is_none(), "duplicate files in the text fixture");
+        Arc::make_mut(&mut self.file_paths).insert(file_id, path.to_string());
+
         let text = Arc::new(text.to_string());
         self.set_file_text(file_id, text);
         self.set_file_relative_path(file_id, rel_path.clone());
@@ -200,6 +217,8 @@ impl Default for MockDatabase {
             events: Default::default(),
             runtime: salsa::Runtime::default(),
             files: FxHashMap::default(),
+            crate_names: Default::default(),
+            file_paths: Default::default(),
         };
         db.set_crate_graph(Default::default());
         db
@@ -213,6 +232,8 @@ impl salsa::ParallelDatabase for MockDatabase {
             runtime: self.runtime.snapshot(self),
             // only the root database can be used to get file_id by path.
             files: FxHashMap::default(),
+            file_paths: Arc::clone(&self.file_paths),
+            crate_names: Arc::clone(&self.crate_names),
         })
     }
 }