Implement IntoDiagnosticArg for rustc_ast::Path

Cargo.lock

@@ -3438,6 +3438,8 @@ version = "0.0.0"
 dependencies = [
  "annotate-snippets",
  "atty",
+ "rustc_ast",
+ "rustc_ast_pretty",
  "rustc_data_structures",
  "rustc_error_messages",
  "rustc_hir",

compiler/rustc_errors/Cargo.toml

@@ -8,6 +8,8 @@ doctest = false
 
 [dependencies]
 tracing = "0.1"
+rustc_ast = { path = "../rustc_ast" }
+rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_error_messages = { path = "../rustc_error_messages" }
 rustc_serialize = { path = "../rustc_serialize" }
 rustc_span = { path = "../rustc_span" }

compiler/rustc_errors/src/diagnostic.rs

@@ -3,6 +3,8 @@ use crate::{
     CodeSuggestion, DiagnosticMessage, EmissionGuarantee, Level, LintDiagnosticBuilder, MultiSpan,
     SubdiagnosticMessage, Substitution, SubstitutionPart, SuggestionStyle,
 };
+use rustc_ast as ast;
+use rustc_ast_pretty::pprust;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_error_messages::FluentValue;
 use rustc_hir as hir;
@@ -175,6 +177,12 @@ impl IntoDiagnosticArg for hir::ConstContext {
     }
 }
 
+impl IntoDiagnosticArg for ast::Path {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        DiagnosticArgValue::Str(Cow::Owned(pprust::path_to_string(&self)))
+    }
+}
+
 /// Trait implemented by error types. This should not be implemented manually. Instead, use
 /// `#[derive(Subdiagnostic)]` -- see [rustc_macros::Subdiagnostic].
 #[cfg_attr(bootstrap, rustc_diagnostic_item = "AddSubdiagnostic")]