Auto merge of rust-lang#94584 - pnkfelix:inject-use-suggestion-sites, r=ekuber

More robust fallback for `use` suggestion

Our old way to suggest where to add `use`s would first look for pre-existing `use`s in the relevant crate/module, and if there are *no* uses, it would fallback on trying to use another item as the basis for the suggestion.

But this was fragile, as illustrated in issue rust-lang#87613

This PR instead identifies span of the first token after any inner attributes, and uses *that* as the fallback for the `use` suggestion.

Fix rust-lang#87613

Author: bors

src/modules.rs

@@ -124,7 +124,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
         mut self,
         krate: &'ast ast::Crate,
     ) -> Result<FileModMap<'ast>, ModuleResolutionError> {
-        let root_filename = self.parse_sess.span_to_filename(krate.span);
+        let root_filename = self.parse_sess.span_to_filename(krate.spans.inner_span);
         self.directory.path = match root_filename {
             FileName::Real(ref p) => p.parent().unwrap_or(Path::new("")).to_path_buf(),
             _ => PathBuf::new(),
@@ -135,7 +135,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
             self.visit_mod_from_ast(&krate.items)?;
         }
 
-        let snippet_provider = self.parse_sess.snippet_provider(krate.span);
+        let snippet_provider = self.parse_sess.snippet_provider(krate.spans.inner_span);
 
         self.file_map.insert(
             root_filename,

src/parse/parser.rs

@@ -113,7 +113,7 @@ impl<'a> Parser<'a> {
         let result = catch_unwind(AssertUnwindSafe(|| {
             let mut parser = new_parser_from_file(sess.inner(), path, Some(span));
             match parser.parse_mod(&TokenKind::Eof) {
-                Ok(result) => Some(result),
+                Ok((a, i, spans)) => Some((a, i, spans.inner_span)),
                 Err(mut e) => {
                     e.emit();
                     if sess.can_reset_errors() {

src/visitor.rs

@@ -915,7 +915,11 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
         let ident_str = rewrite_ident(&self.get_context(), ident).to_owned();
         self.push_str(&ident_str);
 
-        if let ast::ModKind::Loaded(ref items, ast::Inline::Yes, inner_span) = mod_kind {
+        if let ast::ModKind::Loaded(ref items, ast::Inline::Yes, ref spans) = mod_kind {
+            let ast::ModSpans {
+                inner_span,
+                inject_use_span: _,
+            } = *spans;
             match self.config.brace_style() {
                 BraceStyle::AlwaysNextLine => {
                     let indent_str = self.block_indent.to_string_with_newline(self.config);