From ff9fd36aa4ed90051424560268108370bbb3749b Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 28 Jun 2022 22:09:59 -0700
Subject: [PATCH] Implement IntoDiagnosticArg for hir::ConstContext

---
 Cargo.lock                              |  1 +
 compiler/rustc_errors/Cargo.toml        |  1 +
 compiler/rustc_errors/src/diagnostic.rs | 11 +++++++++++
 compiler/rustc_hir/src/hir.rs           |  3 +++
 4 files changed, 16 insertions(+)

diff --git a/Cargo.lock b/Cargo.lock
index 86936b25d8a..268af59aa89 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3813,6 +3813,7 @@ dependencies = [
  "atty",
  "rustc_data_structures",
  "rustc_error_messages",
+ "rustc_hir",
  "rustc_lint_defs",
  "rustc_macros",
  "rustc_serialize",
diff --git a/compiler/rustc_errors/Cargo.toml b/compiler/rustc_errors/Cargo.toml
index 89557626057..7d7e92c5229 100644
--- a/compiler/rustc_errors/Cargo.toml
+++ b/compiler/rustc_errors/Cargo.toml
@@ -13,6 +13,7 @@ rustc_serialize = { path = "../rustc_serialize" }
 rustc_span = { path = "../rustc_span" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_data_structures = { path = "../rustc_data_structures" }
+rustc_hir = { path = "../rustc_hir" }
 rustc_lint_defs = { path = "../rustc_lint_defs" }
 unicode-width = "0.1.4"
 atty = "0.2"
diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 0d1d017d874..9429ad1a897 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -5,6 +5,7 @@ use crate::{
 };
 use rustc_data_structures::stable_map::FxHashMap;
 use rustc_error_messages::FluentValue;
+use rustc_hir as hir;
 use rustc_lint_defs::{Applicability, LintExpectationId};
 use rustc_span::edition::LATEST_STABLE_EDITION;
 use rustc_span::symbol::{Ident, Symbol};
@@ -160,6 +161,16 @@ impl<'source> Into<FluentValue<'source>> for DiagnosticArgValue<'source> {
     }
 }
 
+impl IntoDiagnosticArg for hir::ConstContext {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        DiagnosticArgValue::Str(Cow::Borrowed(match self {
+            hir::ConstContext::ConstFn => "constant function",
+            hir::ConstContext::Static(_) => "static",
+            hir::ConstContext::Const => "constant",
+        }))
+    }
+}
+
 /// Trait implemented by error types. This should not be implemented manually. Instead, use
 /// `#[derive(SessionSubdiagnostic)]` -- see [rustc_macros::SessionSubdiagnostic].
 #[rustc_diagnostic_item = "AddSubdiagnostic"]
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index a2ef158ce8d..acd77f5d2ee 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -1595,6 +1595,9 @@ impl fmt::Display for ConstContext {
     }
 }
 
+// NOTE: `IntoDiagnosticArg` impl for `ConstContext` lives in `rustc_errors`
+// due to a cyclical dependency between hir that crate.
+
 /// A literal.
 pub type Lit = Spanned<LitKind>;