Migrations for rustc_expand transcribe.rs

compiler/rustc_error_messages/locales/en-US/expand.ftl

@@ -3,3 +3,12 @@ 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
+
+expand_must_repeat_once = 
+    this must repeat at least once
+
+count_repetition_misplaced =
+    `count` can not be placed inside the inner-most repetition

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -7,6 +7,7 @@ use rustc_ast::tokenstream::{DelimSpan, Spacing, TokenStream, TokenTree};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::{pluralize, PResult};
 use rustc_errors::{DiagnosticBuilder, ErrorGuaranteed};
+use rustc_macros::SessionDiagnostic;
 use rustc_span::hygiene::{LocalExpnId, Transparency};
 use rustc_span::symbol::{sym, Ident, MacroRulesNormalizedIdent};
 use rustc_span::Span;
@@ -53,6 +54,20 @@ impl<'a> Iterator for Frame<'a> {
     }
 }
 
+#[derive(SessionDiagnostic)]
+#[error(expand::expr_repeat_no_syntax_vars)]
+struct NoSyntaxVarsExprRepeat {
+    #[primary_span]
+    span: Span,
+}
+
+#[derive(SessionDiagnostic)]
+#[error(expand::must_repeat_once)]
+struct MustRepeatOnce {
+    #[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 +180,7 @@ 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) => {
@@ -193,10 +204,7 @@ pub(super) fn transcribe<'a>(
                                 // FIXME: this really ought to be caught at macro definition
                                 // time... It happens when the Kleene operator in the matcher and
                                 // the body for the same meta-variable do not match.
-                                return Err(cx.struct_span_err(
-                                    sp.entire(),
-                                    "this must repeat at least once",
-                                ));
+                                return Err(cx.create_err(MustRepeatOnce { span: sp.entire() }));
                             }
                         } else {
                             // 0 is the initial counter (we have done 0 repetitions so far). `len`
@@ -420,6 +428,13 @@ fn lockstep_iter_size(
     }
 }
 
+#[derive(SessionDiagnostic)]
+#[error(expand::count_repetition_misplaced)]
+struct CountRepetitionMisplaced {
+    #[primary_span]
+    span: Span,
+}
+
 /// Used solely by the `count` meta-variable expression, counts the outer-most repetitions at a
 /// given optional nested depth.
 ///
@@ -448,10 +463,7 @@ fn count_repetitions<'a>(
         match matched {
             MatchedTokenTree(_) | MatchedNonterminal(_) => {
                 if declared_lhs_depth == 0 {
-                    return Err(cx.struct_span_err(
-                        sp.entire(),
-                        "`count` can not be placed inside the inner-most repetition",
-                    ));
+                    return Err(cx.create_err(CountRepetitionMisplaced { span: sp.entire() }));
                 }
                 match depth_opt {
                     None => Ok(1),