From 7e15fbab75ab919238ec86011fd54cba7ad78e68 Mon Sep 17 00:00:00 2001
From: nidnogg <henriquevt98@gmail.com>
Date: Tue, 16 Aug 2022 18:34:13 -0300
Subject: [PATCH] Added first migration for repeated expressions without syntax
 vars

---
 .../rustc_error_messages/locales/en-US/expand.ftl  |  3 +++
 compiler/rustc_expand/src/mbe/transcribe.rs        | 14 +++++++++-----
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/compiler/rustc_error_messages/locales/en-US/expand.ftl b/compiler/rustc_error_messages/locales/en-US/expand.ftl
index bdfa22e77eb..42519fd22ce 100644
--- a/compiler/rustc_error_messages/locales/en-US/expand.ftl
+++ b/compiler/rustc_error_messages/locales/en-US/expand.ftl
@@ -3,3 +3,6 @@ expand_explain_doc_comment_outer =
 
 expand_explain_doc_comment_inner =
     inner doc comments expand to `#![doc = "..."]`, which is what this macro attempted to match
+
+expand_expr_repeat_no_syntax_vars = 
+    attempted to repeat an expression containing no syntax variables matched as repeating at this depth
diff --git a/compiler/rustc_expand/src/mbe/transcribe.rs b/compiler/rustc_expand/src/mbe/transcribe.rs
index e47ea83ac38..69090cb457e 100644
--- a/compiler/rustc_expand/src/mbe/transcribe.rs
+++ b/compiler/rustc_expand/src/mbe/transcribe.rs
@@ -9,6 +9,7 @@
 use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed};
 use rustc_span::hygiene::{LocalExpnId, Transparency};
 use rustc_span::symbol::{sym, Ident, MacroRulesNormalizedIdent};
+use rustc_macros::SessionDiagnostic;
 use rustc_span::Span;
 
 use smallvec::{smallvec, SmallVec};
@@ -53,6 +54,13 @@ fn next(&mut self) -> Option<&'a mbe::TokenTree> {
     }
 }
 
+#[derive(SessionDiagnostic)]
+#[error(expand::expr_repeat_no_syntax_vars)]
+struct NoSyntaxVarsExprRepeat {
+    #[primary_span]
+    span: Span,
+}
+
 /// This can do Macro-By-Example transcription.
 /// - `interp` is a map of meta-variables to the tokens (non-terminals) they matched in the
 ///   invocation. We are assuming we already know there is a match.
@@ -165,11 +173,7 @@ pub(super) fn transcribe<'a>(
             seq @ mbe::TokenTree::Sequence(_, delimited) => {
                 match lockstep_iter_size(&seq, interp, &repeats) {
                     LockstepIterSize::Unconstrained => {
-                        return Err(cx.struct_span_err(
-                            seq.span(), /* blame macro writer */
-                            "attempted to repeat an expression containing no syntax variables \
-                             matched as repeating at this depth",
-                        ));
+                        return Err(cx.create_err(NoSyntaxVarsExprRepeat { span: seq.span() }));
                     }
 
                     LockstepIterSize::Contradiction(msg) => {