provide more useful info for DefId Debug

compiler/rustc_smir/src/rustc_smir/mod.rs

@@ -37,9 +37,14 @@ fn find_crate(&self, name: &str) -> Option<stable_mir::Crate> {
         })
     }
 
+    fn name_of_def_id(&self, def_id: stable_mir::DefId) -> String {
+        self.tcx.def_path_str(self[def_id])
+    }
+
     fn all_local_items(&mut self) -> stable_mir::CrateItems {
         self.tcx.mir_keys(()).iter().map(|item| self.crate_item(item.to_def_id())).collect()
     }
+
     fn entry_fn(&mut self) -> Option<stable_mir::CrateItem> {
         Some(self.crate_item(self.tcx.entry_fn(())?.0))
     }

compiler/rustc_smir/src/stable_mir/mod.rs

@@ -12,6 +12,8 @@
 //! If you need an internal construct, consider using `rustc_internal` or `rustc_smir`.
 
 use std::cell::Cell;
+use std::fmt;
+use std::fmt::Debug;
 
 use self::ty::{
     GenericPredicates, Generics, ImplDef, ImplTrait, Span, TraitDecl, TraitDef, Ty, TyKind,
@@ -29,9 +31,18 @@
 pub type CrateNum = usize;
 
 /// A unique identification number for each item accessible for the current compilation unit.
-#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq)]
 pub struct DefId(pub(crate) usize);
 
+impl Debug for DefId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("DefId:")
+            .field("id", &self.0)
+            .field("name", &with(|cx| cx.name_of_def_id(*self)))
+            .finish()
+    }
+}
+
 /// A unique identification number for each provenance
 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
 pub struct AllocId(pub(crate) usize);
@@ -127,6 +138,9 @@ pub trait Context {
     /// Find a crate with the given name.
     fn find_crate(&self, name: &str) -> Option<Crate>;
 
+    /// Prints the name of given `DefId`
+    fn name_of_def_id(&self, def_id: DefId) -> String;
+
     /// Obtain the representation of a type.
     fn ty_kind(&mut self, ty: Ty) -> TyKind;