Fix #104086, Tighten the 'introduce new binding' suggestion

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1810,18 +1810,27 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
  false
  }
 
- fn let_binding_suggestion(&self, err: &mut Diagnostic, ident_span: Span) -> bool {
+ fn let_binding_suggestion(&mut self, err: &mut Diagnostic, ident_span: Span) -> bool {
  // try to give a suggestion for this pattern: `name = 1`, which is common in other languages
  let mut added_suggestion = false;
- if let Some(Expr { kind: ExprKind::Assign(lhs, _rhs, _), .. }) = self.diagnostic_metadata.in_assignment &&
- let ast::ExprKind::Path(None, _) = lhs.kind {
+ if let Some(Expr { kind: ExprKind::Assign(lhs, rhs, _), .. }) =
+ self.diagnostic_metadata.in_assignment
+ {
+ let is_rhs_assign = match rhs.kind {
+ ExprKind::Assign(..) => true,
+ _ => false,
+ };
+
+ if let ast::ExprKind::Path(None, _) = lhs.kind && !is_rhs_assign {
  let sm = self.r.session.source_map();
  let line_span = sm.span_extend_to_line(ident_span);
  let ident_name = sm.span_to_snippet(ident_span).unwrap();
- // HACK(chenyukang): make sure ident_name is at the starting of the line to protect against macros
- if sm
- .span_to_snippet(line_span)
- .map_or(false, |s| s.trim().starts_with(&ident_name))
+ // HACK(chenyukang): make sure ident_name is at the starting of the line to protect against macros,
+ // and avoid some special cases like `x = x = x`
+ if let Ok(line) = sm.span_to_snippet(line_span) &&
+ let stripped = line.split_whitespace().collect::<String>() &&
+ stripped.trim().starts_with(&ident_name) &&
+ stripped.matches(&format!("{}=", &ident_name)).count() == 1
  {
  err.span_suggestion_verbose(
  ident_span.shrink_to_lo(),
@@ -1832,6 +1841,8 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
  added_suggestion = true;
  }
  }
+ self.diagnostic_metadata.in_assignment = None;
+ }
  added_suggestion
  }
 

src/test/ui/suggestions/issue-104086-suggest-let.rs

@@ -0,0 +1,10 @@
+// error-pattern: not found in this scope
+
+fn main() {
+ x = x = x;
+ x = y = y = y;
+ x = y = y;
+ x = x = y;
+ x = x; // will suggest add `let`
+ x = y // will suggest add `let`
+}

src/test/ui/suggestions/issue-104086-suggest-let.stderr

@@ -0,0 +1,81 @@
+error[E0425]: cannot find value `x` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:4:5
+ |
+LL | x = x = x;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `x` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:4:9
+ |
+LL | x = x = x;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `x` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:4:13
+ |
+LL | x = x = x;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `x` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:5:5
+ |
+LL | x = y = y = y;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `y` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:5:9
+ |
+LL | x = y = y = y;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `y` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:5:13
+ |
+LL | x = y = y = y;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `y` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:5:17
+ |
+LL | x = y = y = y;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `x` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:6:5
+ |
+LL | x = y = y;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `y` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:6:9
+ |
+LL | x = y = y;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `y` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:6:13
+ |
+LL | x = y = y;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `x` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:7:5
+ |
+LL | x = x = y;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `x` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:7:9
+ |
+LL | x = x = y;
+ | ^ not found in this scope
+
+error[E0425]: cannot find value `y` in this scope
+ --> $DIR/issue-104086-suggest-let.rs:7:13
+ |
+LL | x = x = y;
+ | ^ not found in this scope
+
+error: aborting due to 13 previous errors
+
+For more information about this error, try `rustc --explain E0425`.