Make comma separated lists of anything easier to make for errors

Provide a new function `listify`, meant to be used in cases similar to `pluralize!`. When you have a slice of arbitrary elements that need to be presented to the user, `listify` allows you to turn that into a list of comma separated strings.

This reduces a lot of redundant logic that happens often in diagnostics.

1 files changed, 8 insertions, 10 deletions

diff --git a/compiler/rustc_builtin_macros/src/format.rs b/compiler/rustc_builtin_macros/src/format.rs
index 7c746bd719f..90447da6680 100644
--- a/compiler/rustc_builtin_macros/src/format.rs
+++ b/compiler/rustc_builtin_macros/src/format.rs
@@ -8,7 +8,9 @@ use rustc_ast::{
     token,
 };
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::{Applicability, Diag, MultiSpan, PResult, SingleLabelManySpans};
+use rustc_errors::{
+    Applicability, Diag, MultiSpan, PResult, SingleLabelManySpans, listify, pluralize,
+};
 use rustc_expand::base::*;
 use rustc_lint_defs::builtin::NAMED_ARGUMENTS_USED_POSITIONALLY;
 use rustc_lint_defs::{BufferedEarlyLint, BuiltinLintDiag, LintId};
@@ -975,15 +977,11 @@ fn report_invalid_references(
         } else {
             MultiSpan::from_spans(invalid_refs.iter().filter_map(|&(_, span, _, _)| span).collect())
         };
-        let arg_list = if let &[index] = &indexes[..] {
-            format!("argument {index}")
-        } else {
-            let tail = indexes.pop().unwrap();
-            format!(
-                "arguments {head} and {tail}",
-                head = indexes.into_iter().map(|i| i.to_string()).collect::<Vec<_>>().join(", ")
-            )
-        };
+        let arg_list = format!(
+            "argument{} {}",
+            pluralize!(indexes.len()),
+            listify(&indexes, |i: &usize| i.to_string()).unwrap_or_default()
+        );
         e = ecx.dcx().struct_span_err(
             span,
             format!("invalid reference to positional {arg_list} ({num_args_desc})"),