From b65fab62999e96acd3683826ffd4140091f185f2 Mon Sep 17 00:00:00 2001
From: Josh Triplett <josh@joshtriplett.org>
Date: Thu, 14 Aug 2025 00:28:44 -0700
Subject: Move `IntoDiagArg` earlier in the dependency chains

`rustc_errors` depends on numerous crates, solely to implement its
`IntoDiagArg` trait on types from those crates. Many crates depend on
`rustc_errors`, and it's on the critical path.

We can't swap things around to make all of those crates depend on
`rustc_errors` instead, because `rustc_errors` would end up in
dependency cycles.

Instead, move `IntoDiagArg` into `rustc_error_messages`, which has far
fewer dependencies, and then have most of these crates depend on
`rustc_error_messages`.

This allows `rustc_errors` to drop dependencies on several crates,
including the large `rustc_target`.

(This doesn't fully reduce dependency chains yet, as `rustc_errors`
still depends on `rustc_hir` which depends on `rustc_target`. That will
get fixed in a subsequent commit.)
---
 compiler/rustc_hir/src/def.rs | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

(limited to 'compiler/rustc_hir/src/def.rs')

diff --git a/compiler/rustc_hir/src/def.rs b/compiler/rustc_hir/src/def.rs
index 79319e24266..8af4740f376 100644
--- a/compiler/rustc_hir/src/def.rs
+++ b/compiler/rustc_hir/src/def.rs
@@ -1,10 +1,12 @@
 use std::array::IntoIter;
+use std::borrow::Cow;
 use std::fmt::Debug;
 
 use rustc_ast as ast;
 use rustc_ast::NodeId;
 use rustc_data_structures::stable_hasher::ToStableHashKey;
 use rustc_data_structures::unord::UnordMap;
+use rustc_error_messages::{DiagArgValue, IntoDiagArg};
 use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 use rustc_span::Symbol;
 use rustc_span::def_id::{DefId, LocalDefId};
@@ -586,6 +588,12 @@ pub enum Res<Id = hir::HirId> {
     Err,
 }
 
+impl<Id> IntoDiagArg for Res<Id> {
+    fn into_diag_arg(self, _: &mut Option<std::path::PathBuf>) -> DiagArgValue {
+        DiagArgValue::Str(Cow::Borrowed(self.descr()))
+    }
+}
+
 /// The result of resolving a path before lowering to HIR,
 /// with "module" segments resolved and associated item
 /// segments deferred to type checking.
@@ -673,6 +681,12 @@ impl Namespace {
     }
 }
 
+impl IntoDiagArg for Namespace {
+    fn into_diag_arg(self, _: &mut Option<std::path::PathBuf>) -> DiagArgValue {
+        DiagArgValue::Str(Cow::Borrowed(self.descr()))
+    }
+}
+
 impl<CTX: crate::HashStableContext> ToStableHashKey<CTX> for Namespace {
     type KeyType = Namespace;
 
-- 
cgit 1.4.1-3-g733a5