emit suggestion byte literal is passed to `format!`

1 files changed, 22 insertions, 7 deletions

diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index a2035ee3c6e..43b94e239eb 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -9,7 +9,7 @@ use rustc_ast::{self as ast, AstLike, Attribute, Item, NodeId, PatKind};
 use rustc_attr::{self as attr, Deprecation, Stability};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::sync::{self, Lrc};
-use rustc_errors::{DiagnosticBuilder, ErrorReported};
+use rustc_errors::{Applicability, DiagnosticBuilder, ErrorReported};
 use rustc_lint_defs::builtin::PROC_MACRO_BACK_COMPAT;
 use rustc_lint_defs::BuiltinLintDiagnostics;
 use rustc_parse::{self, nt_to_tokenstream, parser, MACRO_ARGUMENTS};
@@ -1133,13 +1133,15 @@ impl<'a> ExtCtxt<'a> {
 }
 
 /// Extracts a string literal from the macro expanded version of `expr`,
-/// emitting `err_msg` if `expr` is not a string literal. This does not stop
-/// compilation on error, merely emits a non-fatal error and returns `None`.
+/// returning a diagnostic error of `err_msg` if `expr` is not a string literal.
+/// The returned bool indicates whether an applicable suggestion has already been
+/// added to the diagnostic to avoid emitting multiple suggestions. `Err(None)`
+/// indicates that an ast error was encountered.
 pub fn expr_to_spanned_string<'a>(
     cx: &'a mut ExtCtxt<'_>,
     expr: P<ast::Expr>,
     err_msg: &str,
-) -> Result<(Symbol, ast::StrStyle, Span), Option<DiagnosticBuilder<'a>>> {
+) -> Result<(Symbol, ast::StrStyle, Span), Option<(DiagnosticBuilder<'a>, bool)>> {
     // Perform eager expansion on the expression.
     // We want to be able to handle e.g., `concat!("foo", "bar")`.
     let expr = cx.expander().fully_expand_fragment(AstFragment::Expr(expr)).make_expr();
@@ -1147,14 +1149,27 @@ pub fn expr_to_spanned_string<'a>(
     Err(match expr.kind {
         ast::ExprKind::Lit(ref l) => match l.kind {
             ast::LitKind::Str(s, style) => return Ok((s, style, expr.span)),
+            ast::LitKind::ByteStr(_) => {
+                let mut err = cx.struct_span_err(l.span, err_msg);
+                err.span_suggestion(
+                    expr.span.shrink_to_lo(),
+                    "consider removing the leading `b`",
+                    String::new(),
+                    Applicability::MaybeIncorrect,
+                );
+                Some((err, true))
+            }
             ast::LitKind::Err(_) => None,
-            _ => Some(cx.struct_span_err(l.span, err_msg)),
+            _ => Some((cx.struct_span_err(l.span, err_msg), false)),
         },
         ast::ExprKind::Err => None,
-        _ => Some(cx.struct_span_err(expr.span, err_msg)),
+        _ => Some((cx.struct_span_err(expr.span, err_msg), false)),
     })
 }
 
+/// Extracts a string literal from the macro expanded version of `expr`,
+/// emitting `err_msg` if `expr` is not a string literal. This does not stop
+/// compilation on error, merely emits a non-fatal error and returns `None`.
 pub fn expr_to_string(
     cx: &mut ExtCtxt<'_>,
     expr: P<ast::Expr>,
@@ -1162,7 +1177,7 @@ pub fn expr_to_string(
 ) -> Option<(Symbol, ast::StrStyle)> {
     expr_to_spanned_string(cx, expr, err_msg)
         .map_err(|err| {
-            err.map(|mut err| {
+            err.map(|(mut err, _)| {
                 err.emit();
             })
         })