1 files changed, 56 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty/display.rs b/crates/ra_hir/src/ty/display.rs
new file mode 100644
index 000000000..63ec9d7e1
--- /dev/null
+++ b/crates/ra_hir/src/ty/display.rs
@@ -0,0 +1,56 @@
+use std::fmt;
+
+use crate::db::HirDatabase;
+
+pub struct HirFormatter<'a, 'b, DB> {
+    pub db: &'a DB,
+    fmt: &'a mut fmt::Formatter<'b>,
+}
+
+pub trait HirDisplay {
+    fn hir_fmt(&self, f: &mut HirFormatter<impl HirDatabase>) -> fmt::Result;
+    fn display<'a, DB>(&'a self, db: &'a DB) -> HirDisplayWrapper<'a, DB, Self>
+    where
+        Self: Sized,
+    {
+        HirDisplayWrapper(db, self)
+    }
+}
+
+impl<'a, 'b, DB> HirFormatter<'a, 'b, DB>
+where
+    DB: HirDatabase,
+{
+    pub fn write_joined<T: HirDisplay>(
+        &mut self,
+        iter: impl IntoIterator<Item = T>,
+        sep: &str,
+    ) -> fmt::Result {
+        let mut first = true;
+        for e in iter {
+            if !first {
+                write!(self, "{}", sep)?;
+            }
+            first = false;
+            e.hir_fmt(self)?;
+        }
+        Ok(())
+    }
+
+    /// This allows using the `write!` macro directly with a `HirFormatter`.
+    pub fn write_fmt(&mut self, args: fmt::Arguments) -> fmt::Result {
+        fmt::write(self.fmt, args)
+    }
+}
+
+pub struct HirDisplayWrapper<'a, DB, T>(&'a DB, &'a T);
+
+impl<'a, DB, T> fmt::Display for HirDisplayWrapper<'a, DB, T>
+where
+    DB: HirDatabase,
+    T: HirDisplay,
+{
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.1.hir_fmt(&mut HirFormatter { db: self.0, fmt: f })
+    }
+}