Suggest use "{}", self.x instead of {self.x} when resolve x as field of self

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

Author: xizheyin

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -751,12 +751,30 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                 match candidate {
                     AssocSuggestion::Field(field_span) => {
                         if self_is_available {
-                            err.span_suggestion_verbose(
-                                span.shrink_to_lo(),
-                                "you might have meant to use the available field",
-                                format!("{pre}self."),
-                                Applicability::MachineApplicable,
-                            );
+                            let source_map = self.r.tcx.sess.source_map();
+                            // check if the field is used in a format string, such as `"{x}"`
+                            let field_is_format_named_arg =
+                                source_map.span_to_source(span, |s, start, _| {
+                                    if let Some(expanded_expr) = s.get(start - 1..start)
+                                        && expanded_expr.starts_with("{")
+                                    {
+                                        Ok(true)
+                                    } else {
+                                        Ok(false)
+                                    }
+                                });
+                            if let Ok(true) = field_is_format_named_arg {
+                                err.help(
+                                    format!("you might have meant to use the available field in a format string: `\"{{}}\", self.{}`", segment.ident.name),
+                                );
+                            } else {
+                                err.span_suggestion_verbose(
+                                    span.shrink_to_lo(),
+                                    "you might have meant to use the available field",
+                                    format!("{pre}self."),
+                                    Applicability::MachineApplicable,
+                                );
+                            }
                         } else {
                             err.span_label(field_span, "a field by that name exists in `Self`");
                         }

tests/ui/resolve/suggestions/sugg-field-in-format-string-issue-141136.stderr

@@ -14,21 +14,15 @@ error[E0425]: cannot find value `x` in this scope
 LL |         let _ = format!("{x}");
    |                           ^
    |
-help: you might have meant to use the available field
-   |
-LL |         let _ = format!("{self.x}");
-   |                           +++++
+   = help: you might have meant to use the available field in a format string: `"{}", self.x`
 
 error[E0425]: cannot find value `x` in this scope
   --> $DIR/sugg-field-in-format-string-issue-141136.rs:8:27
    |
 LL |         let _ = format!("{x }");
    |                           ^^
    |
-help: you might have meant to use the available field
-   |
-LL |         let _ = format!("{self.x }");
-   |                           +++++
+   = help: you might have meant to use the available field in a format string: `"{}", self.x`
 
 error[E0425]: cannot find value `x` in this scope
   --> $DIR/sugg-field-in-format-string-issue-141136.rs:10:31

tests/ui/resolve/typo-suggestion-for-variable-with-name-similar-to-struct-field.stderr

@@ -20,17 +20,9 @@ error[E0425]: cannot find value `config` in this scope
   --> $DIR/typo-suggestion-for-variable-with-name-similar-to-struct-field.rs:15:20
    |
 LL |         println!("{config}");
-   |                    ^^^^^^
-   |
-help: you might have meant to use the available field
-   |
-LL |         println!("{self.config}");
-   |                    +++++
-help: a local variable with a similar name exists
-   |
-LL -         println!("{config}");
-LL +         println!("{cofig}");
+   |                    ^^^^^^ help: a local variable with a similar name exists: `cofig`
    |
+   = help: you might have meant to use the available field in a format string: `"{}", self.config`
 
 error[E0425]: cannot find value `bah` in this scope
   --> $DIR/typo-suggestion-for-variable-with-name-similar-to-struct-field.rs:33:9