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.)

5 files changed, 61 insertions, 2 deletions

diff --git a/compiler/rustc_hir/src/attrs/data_structures.rs b/compiler/rustc_hir/src/attrs/data_structures.rs
index 31715955ed3..a17350f0392 100644
--- a/compiler/rustc_hir/src/attrs/data_structures.rs
+++ b/compiler/rustc_hir/src/attrs/data_structures.rs
@@ -1,7 +1,11 @@
+use std::borrow::Cow;
+use std::path::PathBuf;
+
 pub use ReprAttr::*;
 use rustc_abi::Align;
 use rustc_ast::token::CommentKind;
 use rustc_ast::{AttrStyle, ast};
+use rustc_error_messages::{DiagArgValue, IntoDiagArg};
 use rustc_macros::{Decodable, Encodable, HashStable_Generic, PrintAttribute};
 use rustc_span::def_id::DefId;
 use rustc_span::hygiene::Transparency;
@@ -213,6 +217,17 @@ pub enum MirDialect {
     Runtime,
 }
 
+impl IntoDiagArg for MirDialect {
+    fn into_diag_arg(self, _path: &mut Option<PathBuf>) -> DiagArgValue {
+        let arg = match self {
+            MirDialect::Analysis => "analysis",
+            MirDialect::Built => "built",
+            MirDialect::Runtime => "runtime",
+        };
+        DiagArgValue::Str(Cow::Borrowed(arg))
+    }
+}
+
 #[derive(Clone, Copy, Decodable, Debug, Encodable, PartialEq)]
 #[derive(HashStable_Generic, PrintAttribute)]
 pub enum MirPhase {
@@ -221,6 +236,17 @@ pub enum MirPhase {
     Optimized,
 }
 
+impl IntoDiagArg for MirPhase {
+    fn into_diag_arg(self, _path: &mut Option<PathBuf>) -> DiagArgValue {
+        let arg = match self {
+            MirPhase::Initial => "initial",
+            MirPhase::PostCleanup => "post-cleanup",
+            MirPhase::Optimized => "optimized",
+        };
+        DiagArgValue::Str(Cow::Borrowed(arg))
+    }
+}
+
 /// Represents parsed *built-in* inert attributes.
 ///
 /// ## Overview
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;
 
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 2c8986b7c7d..39696f74d51 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -1,4 +1,5 @@
 // ignore-tidy-filelength
+use std::borrow::Cow;
 use std::fmt;
 
 use rustc_abi::ExternAbi;
@@ -17,6 +18,7 @@ pub use rustc_ast::{
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::sorted_map::SortedMap;
 use rustc_data_structures::tagged_ptr::TaggedRef;
+use rustc_error_messages::{DiagArgValue, IntoDiagArg};
 use rustc_index::IndexVec;
 use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 use rustc_span::def_id::LocalDefId;
@@ -2259,8 +2261,15 @@ impl fmt::Display for ConstContext {
     }
 }
 
-// NOTE: `IntoDiagArg` impl for `ConstContext` lives in `rustc_errors`
-// due to a cyclical dependency between hir and that crate.
+impl IntoDiagArg for ConstContext {
+    fn into_diag_arg(self, _: &mut Option<std::path::PathBuf>) -> DiagArgValue {
+        DiagArgValue::Str(Cow::Borrowed(match self {
+            ConstContext::ConstFn => "const_fn",
+            ConstContext::Static(_) => "static",
+            ConstContext::Const { .. } => "const",
+        }))
+    }
+}
 
 /// A literal.
 pub type Lit = Spanned<LitKind>;
diff --git a/compiler/rustc_hir/src/target.rs b/compiler/rustc_hir/src/target.rs
index f68dad3a5e8..dcac51b10b4 100644
--- a/compiler/rustc_hir/src/target.rs
+++ b/compiler/rustc_hir/src/target.rs
@@ -79,6 +79,8 @@ impl Display for Target {
     }
 }
 
+rustc_error_messages::into_diag_arg_using_display!(Target);
+
 impl Target {
     pub fn is_associated_item(self) -> bool {
         match self {
diff --git a/compiler/rustc_hir/src/version.rs b/compiler/rustc_hir/src/version.rs
index ab5ab026b4c..bc2c38a4935 100644
--- a/compiler/rustc_hir/src/version.rs
+++ b/compiler/rustc_hir/src/version.rs
@@ -1,6 +1,8 @@
+use std::borrow::Cow;
 use std::fmt::{self, Display};
 use std::sync::OnceLock;
 
+use rustc_error_messages::{DiagArgValue, IntoDiagArg};
 use rustc_macros::{
     Decodable, Encodable, HashStable_Generic, PrintAttribute, current_rustc_version,
 };
@@ -45,3 +47,9 @@ impl Display for RustcVersion {
         write!(formatter, "{}.{}.{}", self.major, self.minor, self.patch)
     }
 }
+
+impl IntoDiagArg for RustcVersion {
+    fn into_diag_arg(self, _: &mut Option<std::path::PathBuf>) -> DiagArgValue {
+        DiagArgValue::Str(Cow::Owned(self.to_string()))
+    }
+}