Rollup merge of #141213 - xizheyin:issue-141136, r=nnethercote

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

Fixes #141136

Changes can be seen in the second commit: 9de7fff

r? compiler

Author: matthiaskrgr

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -765,12 +765,24 @@ 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, _| {
+                                    Ok(s.get(start - 1..start) == Some("{"))
+                                });
+                            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::MaybeIncorrect,
+                                );
+                            }
                         } 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.rs

@@ -0,0 +1,15 @@
+struct Foo {
+    x: i32
+}
+
+impl Foo {
+    fn foo(&self) {
+        let _ = format!("{x}"); //~ ERROR cannot find value `x` in this scope [E0425]
+        let _ = format!("{x }"); //~ ERROR cannot find value `x` in this scope [E0425]
+        let _ = format!("{ x}"); //~ ERROR invalid format string: expected `}`, found `x`
+        let _ = format!("{}", x); //~ ERROR cannot find value `x` in this scope [E0425]
+        println!("{x}"); //~ ERROR cannot find value `x` in this scope [E0425]
+    }
+}
+
+fn main(){}

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

@@ -0,0 +1,48 @@
+error: invalid format string: expected `}`, found `x`
+  --> $DIR/sugg-field-in-format-string-issue-141136.rs:9:28
+   |
+LL |         let _ = format!("{ x}");
+   |                          - ^ expected `}` in format string
+   |                          |
+   |                          because of this opening brace
+   |
+   = note: if you intended to print `{`, you can escape it using `{{`
+
+error[E0425]: cannot find value `x` in this scope
+  --> $DIR/sugg-field-in-format-string-issue-141136.rs:7:27
+   |
+LL |         let _ = format!("{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 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
+   |
+LL |         let _ = format!("{}", x);
+   |                               ^
+   |
+help: you might have meant to use the available field
+   |
+LL |         let _ = format!("{}", self.x);
+   |                               +++++
+
+error[E0425]: cannot find value `x` in this scope
+  --> $DIR/sugg-field-in-format-string-issue-141136.rs:11:20
+   |
+LL |         println!("{x}");
+   |                    ^
+   |
+   = help: you might have meant to use the available field in a format string: `"{}", self.x`
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0425`.

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