extract "expected string literal" special case to its own subfunction

Author: scrabsha

compiler/rustc_attr_parsing/src/session_diagnostics.rs

@@ -595,6 +595,23 @@ pub(crate) struct AttributeParseError<'a> {
 }
 
 impl<'a> AttributeParseError<'a> {
+    fn render_expected_string_literal<G>(&self, diag: &mut Diag<'_, G>, byte_string: Option<Span>)
+    where
+        G: EmissionGuarantee,
+    {
+        if let Some(start_point_span) = byte_string {
+            diag.span_suggestion(
+                start_point_span,
+                "consider removing the prefix",
+                "",
+                Applicability::MaybeIncorrect,
+            );
+            diag.note("expected a normal string literal, not a byte string literal");
+        } else {
+            diag.span_label(self.span, "expected a string literal here");
+        }
+    }
+
     fn render_expected_specific_argument<G>(
         &self,
         diag: &mut Diag<'_, G>,
@@ -685,19 +702,7 @@ impl<'a, G: EmissionGuarantee> Diagnostic<'a, G> for AttributeParseError<'_> {
         diag.code(E0539);
         match &self.reason {
             AttributeParseErrorReason::ExpectedStringLiteral { byte_string } => {
-                if let Some(start_point_span) = byte_string {
-                    diag.span_suggestion(
-                        start_point_span,
-                        "consider removing the prefix",
-                        "",
-                        Applicability::MaybeIncorrect,
-                    );
-                    diag.note("expected a normal string literal, not a byte string literal");
-
-                    return diag;
-                } else {
-                    diag.span_label(self.span, "expected a string literal here");
-                }
+                self.render_expected_string_literal(&mut diag, *byte_string);
             }
             AttributeParseErrorReason::ExpectedFilenameLiteral => {
                 diag.span_label(self.span, "expected a filename string literal here");

tests/ui/conditional-compilation/cfg-attr-syntax-validation.rs

@@ -44,6 +44,7 @@ struct S8;
 
 #[cfg(a = b"hi")]  //~ ERROR malformed `cfg` attribute input
 //~^ NOTE expected a normal string literal, not a byte string literal
+//~| NOTE for more information, visit
 struct S9;
 
 macro_rules! generate_s10 {

tests/ui/conditional-compilation/cfg-attr-syntax-validation.stderr

@@ -85,14 +85,23 @@ error[E0539]: malformed `cfg` attribute input
   --> $DIR/cfg-attr-syntax-validation.rs:45:1
    |
 LL | #[cfg(a = b"hi")]
-   | ^^^^^^^^^^-^^^^^^
-   |           |
-   |           help: consider removing the prefix
+   | ^^^^^^^^^^^^^^^^^
    |
    = note: expected a normal string literal, not a byte string literal
+   = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg-attribute>
+help: consider removing the prefix
+   |
+LL - #[cfg(a = b"hi")]
+LL + #[cfg(a = "hi")]
+   |
+help: must be of the form
+   |
+LL - #[cfg(a = b"hi")]
+LL + #[cfg(predicate)]
+   |
 
 error: expected a literal (`1u8`, `1.0f32`, `"string"`, etc.) here, found `expr` metavariable
-  --> $DIR/cfg-attr-syntax-validation.rs:51:25
+  --> $DIR/cfg-attr-syntax-validation.rs:52:25
    |
 LL |         #[cfg(feature = $expr)]
    |                         ^^^^^

tests/ui/conditional-compilation/cfg_attr-attr-syntax-validation.stderr

@@ -74,11 +74,20 @@ error[E0539]: malformed `cfg_attr` attribute input
   --> $DIR/cfg_attr-attr-syntax-validation.rs:25:1
    |
 LL | #[cfg_attr(a = b"hi")]
-   | ^^^^^^^^^^^^^^^-^^^^^^
-   |                |
-   |                help: consider removing the prefix
+   | ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: expected a normal string literal, not a byte string literal
+   = note: for more information, visit <https://doc.rust-lang.org/reference/conditional-compilation.html#the-cfg_attr-attribute>
+help: consider removing the prefix
+   |
+LL - #[cfg_attr(a = b"hi")]
+LL + #[cfg_attr(a = "hi")]
+   |
+help: must be of the form
+   |
+LL - #[cfg_attr(a = b"hi")]
+LL + #[cfg_attr(predicate, attr1, attr2, ...)]
+   |
 
 error: expected `,`, found end of `cfg_attr` input
   --> $DIR/cfg_attr-attr-syntax-validation.rs:38:16