1 files changed, 83 insertions, 0 deletions

diff --git a/crates/ra_hir/src/debug.rs b/crates/ra_hir/src/debug.rs
new file mode 100644
index 000000000..87f3180c3
--- /dev/null
+++ b/crates/ra_hir/src/debug.rs
@@ -0,0 +1,83 @@
+//! printf debugging infrastructure for rust-analyzer.
+//!
+//! When you print a hir type, like a module, using `eprintln!("{:?}", module)`,
+//! you usually get back a numeric ID, which doesn't tell you much:
+//! `Module(92)`.
+//!
+//! This module adds convenience `debug` methods to various types, which resolve
+//! the id to a human-readable location info:
+//!
+//! ```not_rust
+//! eprintln!("{:?}", module.debug(db));
+//! =>
+//! Module { name: collections, path: "liballoc/collections/mod.rs" }
+//! ```
+//!
+//! Note that to get this info, we might need to execute queries! So
+//!
+//! * don't use the `debug` methods for logging
+//! * when debugging, be aware that interference is possible.
+
+use std::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 Fn(&mut fmt::Formatter<'_>) -> fmt::Result) -> impl fmt::Debug {
+    struct DebugFn<F>(F);
+
+    impl<F: Fn(&mut fmt::Formatter<'_>) -> fmt::Result> fmt::Debug for DebugFn<F> {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            (&self.0)(fmt)
+        }
+    }
+
+    DebugFn(f)
+}