Rollup merge of #91313 - petrochenkov:cratexp, r=Aaron1011

expand: Turn `ast::Crate` into a first class expansion target

And stop creating a fake `mod` item for the crate root when expanding a crate, thus addressing FIXMEs left in https://github.com/rust-lang/rust/pull/82238, and making a step towards a proper support for crate-level macro attributes (cc #54726).

I haven't added token collection support for the whole crate in this PR, maybe later.
r? `@Aaron1011`

compiler/rustc_ast/src/ast.rs

@@ -517,6 +517,8 @@ pub struct Crate {
     pub attrs: Vec<Attribute>,
     pub items: Vec<P<Item>>,
     pub span: Span,
+    // Placeholder ID if the crate node is a macro placeholder.
+    pub is_placeholder: Option<NodeId>,
 }
 
 /// Possible values inside of compile-time attribute lists.

compiler/rustc_ast/src/ast_like.rs

@@ -1,7 +1,7 @@
 use super::ptr::P;
 use super::token::Nonterminal;
 use super::tokenstream::LazyTokenStream;
-use super::{Arm, ExprField, FieldDef, GenericParam, Param, PatField, Variant};
+use super::{Arm, Crate, ExprField, FieldDef, GenericParam, Param, PatField, Variant};
 use super::{AssocItem, Expr, ForeignItem, Item, Local, MacCallStmt};
 use super::{AttrItem, AttrKind, Block, Pat, Path, Ty, Visibility};
 use super::{AttrVec, Attribute, Stmt, StmtKind};
@@ -276,7 +276,7 @@ fn tokens_mut(&mut self) -> Option<&mut Option<LazyTokenStream>> {
 // These ast nodes only support inert attributes, so they don't
 // store tokens (since nothing can observe them)
 derive_has_attrs_no_tokens! {
-    FieldDef, Arm, ExprField, PatField, Variant, Param, GenericParam
+    FieldDef, Arm, ExprField, PatField, Variant, Param, GenericParam, Crate
 }
 
 // These AST nodes don't support attributes, but can

compiler/rustc_ast/src/mut_visit.rs

@@ -284,6 +284,10 @@ fn visit_span(&mut self, _sp: &mut Span) {
 /// Use a map-style function (`FnOnce(T) -> T`) to overwrite a `&mut T`. Useful
 /// when using a `flat_map_*` or `filter_map_*` method within a `visit_`
 /// method. Abort the program if the closure panics.
+///
+/// FIXME: Abort on panic means that any fatal error inside `visit_clobber` will abort the compiler.
+/// Instead of aborting on catching a panic we need to reset the visited node to some valid but
+/// possibly meaningless value and rethrow the panic.
 //
 // No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
 pub fn visit_clobber<T, F>(t: &mut T, f: F)
@@ -1105,36 +1109,11 @@ pub fn noop_visit_fn_header<T: MutVisitor>(header: &mut FnHeader, vis: &mut T) {
     visit_unsafety(unsafety, vis);
 }
 
-// FIXME: Avoid visiting the crate as a `Mod` item, flat map only the inner items if possible,
-// or make crate visiting first class if necessary.
 pub fn noop_visit_crate<T: MutVisitor>(krate: &mut Crate, vis: &mut T) {
-    visit_clobber(krate, |Crate { attrs, items, span }| {
-        let item_vis =
-            Visibility { kind: VisibilityKind::Public, span: span.shrink_to_lo(), tokens: None };
-        let item = P(Item {
-            ident: Ident::empty(),
-            attrs,
-            id: DUMMY_NODE_ID,
-            vis: item_vis,
-            span,
-            kind: ItemKind::Mod(Unsafe::No, ModKind::Loaded(items, Inline::Yes, span)),
-            tokens: None,
-        });
-        let items = vis.flat_map_item(item);
-
-        let len = items.len();
-        if len == 0 {
-            Crate { attrs: vec![], items: vec![], span }
-        } else if len == 1 {
-            let Item { attrs, span, kind, .. } = items.into_iter().next().unwrap().into_inner();
-            match kind {
-                ItemKind::Mod(_, ModKind::Loaded(items, ..)) => Crate { attrs, items, span },
-                _ => panic!("visitor converted a module to not a module"),
-            }
-        } else {
-            panic!("a crate cannot expand to more than one item");
-        }
-    });
+    let Crate { attrs, items, span, is_placeholder: _ } = krate;
+    visit_attrs(attrs, vis);
+    items.flat_map_in_place(|item| vis.flat_map_item(item));
+    vis.visit_span(span);
 }
 
 // Mutates one item into possibly many items.

compiler/rustc_ast/src/visit.rs

@@ -211,6 +211,9 @@ fn visit_expr_field(&mut self, f: &'ast ExprField) {
     fn visit_pat_field(&mut self, fp: &'ast PatField) {
         walk_pat_field(self, fp)
     }
+    fn visit_crate(&mut self, krate: &'ast Crate) {
+        walk_crate(self, krate)
+    }
 }
 
 #[macro_export]

compiler/rustc_ast_pretty/src/pprust/mod.rs

@@ -75,3 +75,12 @@ pub fn attribute_to_string(attr: &ast::Attribute) -> String {
 pub fn to_string(f: impl FnOnce(&mut State<'_>)) -> String {
     State::new().to_string(f)
 }
+
+pub fn crate_to_string_for_macros(krate: &ast::Crate) -> String {
+    State::new().to_string(|s| {
+        s.print_inner_attributes(&krate.attrs);
+        for item in &krate.items {
+            s.print_item(item);
+        }
+    })
+}

compiler/rustc_builtin_macros/src/cfg_eval.rs

@@ -77,6 +77,10 @@ fn flat_map_annotatable(
         Annotatable::Param(param) => vis.flat_map_param(param).pop().map(Annotatable::Param),
         Annotatable::FieldDef(sf) => vis.flat_map_field_def(sf).pop().map(Annotatable::FieldDef),
         Annotatable::Variant(v) => vis.flat_map_variant(v).pop().map(Annotatable::Variant),
+        Annotatable::Crate(mut krate) => {
+            vis.visit_crate(&mut krate);
+            Some(Annotatable::Crate(krate))
+        }
     }
 }
 
@@ -101,6 +105,7 @@ fn has_cfg_or_cfg_attr(annotatable: &Annotatable) -> bool {
             Annotatable::Param(param) => finder.visit_param(&param),
             Annotatable::FieldDef(field) => finder.visit_field_def(&field),
             Annotatable::Variant(variant) => finder.visit_variant(&variant),
+            Annotatable::Crate(krate) => finder.visit_crate(krate),
         };
         finder.has_cfg_or_cfg_attr
     }

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -84,9 +84,35 @@ struct TestHarnessGenerator<'a> {
     tests: Vec<Test>,
 }
 
+impl TestHarnessGenerator<'_> {
+    fn add_test_cases(&mut self, node_id: ast::NodeId, span: Span, prev_tests: Vec<Test>) {
+        let mut tests = mem::replace(&mut self.tests, prev_tests);
+
+        if !tests.is_empty() {
+            // Create an identifier that will hygienically resolve the test
+            // case name, even in another module.
+            let expn_id = self.cx.ext_cx.resolver.expansion_for_ast_pass(
+                span,
+                AstPass::TestHarness,
+                &[],
+                Some(node_id),
+            );
+            for test in &mut tests {
+                // See the comment on `mk_main` for why we're using
+                // `apply_mark` directly.
+                test.ident.span =
+                    test.ident.span.apply_mark(expn_id.to_expn_id(), Transparency::Opaque);
+            }
+            self.cx.test_cases.extend(tests);
+        }
+    }
+}
+
 impl<'a> MutVisitor for TestHarnessGenerator<'a> {
     fn visit_crate(&mut self, c: &mut ast::Crate) {
+        let prev_tests = mem::take(&mut self.tests);
         noop_visit_crate(c, self);
+        self.add_test_cases(ast::CRATE_NODE_ID, c.span, prev_tests);
 
         // Create a main function to run our tests
         c.items.push(mk_main(&mut self.cx));
@@ -103,34 +129,10 @@ fn visit_crate(&mut self, c: &mut ast::Crate) {
 
         // We don't want to recurse into anything other than mods, since
         // mods or tests inside of functions will break things
-        if let ast::ItemKind::Mod(..) = item.kind {
-            let tests = mem::take(&mut self.tests);
+        if let ast::ItemKind::Mod(_, ModKind::Loaded(.., span)) = item.kind {
+            let prev_tests = mem::take(&mut self.tests);
             noop_visit_item_kind(&mut item.kind, self);
-            let mut tests = mem::replace(&mut self.tests, tests);
-
-            if !tests.is_empty() {
-                let parent =
-                    if item.id == ast::DUMMY_NODE_ID { ast::CRATE_NODE_ID } else { item.id };
-                // Create an identifier that will hygienically resolve the test
-                // case name, even in another module.
-                let inner_span = match item.kind {
-                    ast::ItemKind::Mod(_, ModKind::Loaded(.., span)) => span,
-                    _ => unreachable!(),
-                };
-                let expn_id = self.cx.ext_cx.resolver.expansion_for_ast_pass(
-                    inner_span,
-                    AstPass::TestHarness,
-                    &[],
-                    Some(parent),
-                );
-                for test in &mut tests {
-                    // See the comment on `mk_main` for why we're using
-                    // `apply_mark` directly.
-                    test.ident.span =
-                        test.ident.span.apply_mark(expn_id.to_expn_id(), Transparency::Opaque);
-                }
-                self.cx.test_cases.extend(tests);
-            }
+            self.add_test_cases(item.id, span, prev_tests);
         }
         smallvec![P(item)]
     }
@@ -146,7 +148,7 @@ fn entry_point_type(sess: &Session, item: &ast::Item, depth: usize) -> EntryPoin
             } else if sess.contains_name(&item.attrs, sym::rustc_main) {
                 EntryPointType::MainAttr
             } else if item.ident.name == sym::main {
-                if depth == 1 {
+                if depth == 0 {
                     // This is a top-level function so can be 'main'
                     EntryPointType::MainNamed
                 } else {

compiler/rustc_expand/src/base.rs

@@ -48,6 +48,7 @@ pub enum Annotatable {
     Param(ast::Param),
     FieldDef(ast::FieldDef),
     Variant(ast::Variant),
+    Crate(ast::Crate),
 }
 
 impl Annotatable {
@@ -66,6 +67,7 @@ pub fn span(&self) -> Span {
             Annotatable::Param(ref p) => p.span,
             Annotatable::FieldDef(ref sf) => sf.span,
             Annotatable::Variant(ref v) => v.span,
+            Annotatable::Crate(ref c) => c.span,
         }
     }
 
@@ -84,6 +86,7 @@ pub fn visit_attrs(&mut self, f: impl FnOnce(&mut Vec<Attribute>)) {
             Annotatable::Param(p) => p.visit_attrs(f),
             Annotatable::FieldDef(sf) => sf.visit_attrs(f),
             Annotatable::Variant(v) => v.visit_attrs(f),
+            Annotatable::Crate(c) => c.visit_attrs(f),
         }
     }
 
@@ -102,6 +105,7 @@ pub fn visit_with<'a, V: Visitor<'a>>(&'a self, visitor: &mut V) {
             Annotatable::Param(p) => visitor.visit_param(p),
             Annotatable::FieldDef(sf) => visitor.visit_field_def(sf),
             Annotatable::Variant(v) => visitor.visit_variant(v),
+            Annotatable::Crate(c) => visitor.visit_crate(c),
         }
     }
 
@@ -122,7 +126,8 @@ pub fn into_nonterminal(self) -> Nonterminal {
             | Annotatable::GenericParam(..)
             | Annotatable::Param(..)
             | Annotatable::FieldDef(..)
-            | Annotatable::Variant(..) => panic!("unexpected annotatable"),
+            | Annotatable::Variant(..)
+            | Annotatable::Crate(..) => panic!("unexpected annotatable"),
         }
     }
 
@@ -220,6 +225,13 @@ pub fn expect_variant(self) -> ast::Variant {
             _ => panic!("expected variant"),
         }
     }
+
+    pub fn expect_crate(self) -> ast::Crate {
+        match self {
+            Annotatable::Crate(krate) => krate,
+            _ => panic!("expected krate"),
+        }
+    }
 }
 
 /// Result of an expansion that may need to be retried.
@@ -419,6 +431,11 @@ fn make_ty(self: Box<Self>) -> Option<P<ast::Ty>> {
     fn make_variants(self: Box<Self>) -> Option<SmallVec<[ast::Variant; 1]>> {
         None
     }
+
+    fn make_crate(self: Box<Self>) -> Option<ast::Crate> {
+        // Fn-like macros cannot produce a crate.
+        unreachable!()
+    }
 }
 
 macro_rules! make_MacEager {

compiler/rustc_expand/src/expand.rs

@@ -14,13 +14,13 @@
 use rustc_ast::visit::{self, AssocCtxt, Visitor};
 use rustc_ast::{AstLike, Block, Inline, ItemKind, MacArgs, MacCall};
 use rustc_ast::{MacCallStmt, MacStmtStyle, MetaItemKind, ModKind, NestedMetaItem};
-use rustc_ast::{NodeId, PatKind, Path, StmtKind, Unsafe};
+use rustc_ast::{NodeId, PatKind, Path, StmtKind};
 use rustc_ast_pretty::pprust;
 use rustc_attr::is_builtin_attr;
 use rustc_data_structures::map_in_place::MapInPlace;
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{Applicability, FatalError, PResult};
+use rustc_errors::{Applicability, PResult};
 use rustc_feature::Features;
 use rustc_parse::parser::{
     AttemptLocalParseRecovery, ForceCollect, Parser, RecoverColon, RecoverComma,
@@ -33,7 +33,7 @@
 use rustc_span::symbol::{sym, Ident};
 use rustc_span::{FileName, LocalExpnId, Span};
 
-use smallvec::{smallvec, SmallVec};
+use smallvec::SmallVec;
 use std::ops::DerefMut;
 use std::path::PathBuf;
 use std::rc::Rc;
@@ -205,6 +205,7 @@ impl<'a> MacResult for crate::mbe::macro_rules::ParserAnyMacro<'a> {
     Variants(SmallVec<[ast::Variant; 1]>) {
         "variant"; many fn flat_map_variant; fn visit_variant(); fn make_variants;
     }
+    Crate(ast::Crate) { "crate"; one fn visit_crate; fn visit_crate; fn make_crate; }
 }
 
 pub enum SupportsMacroExpansion {
@@ -227,9 +228,8 @@ pub fn supports_macro_expansion(self) -> SupportsMacroExpansion {
             AstFragmentKind::Items
             | AstFragmentKind::TraitItems
             | AstFragmentKind::ImplItems
-            | AstFragmentKind::ForeignItems => {
-                SupportsMacroExpansion::Yes { supports_inner_attrs: true }
-            }
+            | AstFragmentKind::ForeignItems
+            | AstFragmentKind::Crate => SupportsMacroExpansion::Yes { supports_inner_attrs: true },
             AstFragmentKind::Arms
             | AstFragmentKind::Fields
             | AstFragmentKind::FieldPats
@@ -288,6 +288,9 @@ fn expect_from_annotatables<I: IntoIterator<Item = Annotatable>>(
             AstFragmentKind::OptExpr => {
                 AstFragment::OptExpr(items.next().map(Annotatable::expect_expr))
             }
+            AstFragmentKind::Crate => {
+                AstFragment::Crate(items.next().expect("expected exactly one crate").expect_crate())
+            }
             AstFragmentKind::Pat | AstFragmentKind::Ty => {
                 panic!("patterns and types aren't annotatable")
             }
@@ -359,9 +362,7 @@ pub fn new(cx: &'a mut ExtCtxt<'b>, monotonic: bool) -> Self {
         MacroExpander { cx, monotonic }
     }
 
-    // FIXME: Avoid visiting the crate as a `Mod` item,
-    // make crate a first class expansion target instead.
-    pub fn expand_crate(&mut self, mut krate: ast::Crate) -> ast::Crate {
+    pub fn expand_crate(&mut self, krate: ast::Crate) -> ast::Crate {
         let file_path = match self.cx.source_map().span_to_filename(krate.span) {
             FileName::Real(name) => name
                 .into_local_path()
@@ -375,52 +376,7 @@ pub fn expand_crate(&mut self, mut krate: ast::Crate) -> ast::Crate {
             file_path_stack: vec![file_path],
             dir_path,
         });
-
-        let krate_item = AstFragment::Items(smallvec![P(ast::Item {
-            attrs: krate.attrs,
-            span: krate.span,
-            kind: ast::ItemKind::Mod(
-                Unsafe::No,
-                ModKind::Loaded(krate.items, Inline::Yes, krate.span)
-            ),
-            ident: Ident::empty(),
-            id: ast::DUMMY_NODE_ID,
-            vis: ast::Visibility {
-                span: krate.span.shrink_to_lo(),
-                kind: ast::VisibilityKind::Public,
-                tokens: None,
-            },
-            tokens: None,
-        })]);
-
-        match self.fully_expand_fragment(krate_item).make_items().pop().map(P::into_inner) {
-            Some(ast::Item {
-                attrs,
-                kind: ast::ItemKind::Mod(_, ModKind::Loaded(items, ..)),
-                ..
-            }) => {
-                krate.attrs = attrs;
-                krate.items = items;
-            }
-            None => {
-                // Resolution failed so we return an empty expansion
-                krate.attrs = vec![];
-                krate.items = vec![];
-            }
-            Some(ast::Item { span, kind, .. }) => {
-                krate.attrs = vec![];
-                krate.items = vec![];
-                self.cx.span_err(
-                    span,
-                    &format!(
-                        "expected crate top-level item to be a module after macro expansion, found {} {}",
-                        kind.article(), kind.descr()
-                    ),
-                );
-                // FIXME: this workaround issue #84569
-                FatalError.raise();
-            }
-        };
+        let krate = self.fully_expand_fragment(AstFragment::Crate(krate)).make_crate();
         self.cx.trace_macros_diag();
         krate
     }
@@ -708,26 +664,32 @@ fn expand_invoc(
                 SyntaxExtensionKind::Attr(expander) => {
                     self.gate_proc_macro_input(&item);
                     self.gate_proc_macro_attr_item(span, &item);
-                    let mut fake_tokens = false;
-                    if let Annotatable::Item(item_inner) = &item {
-                        if let ItemKind::Mod(_, mod_kind) = &item_inner.kind {
-                            // FIXME: Collect tokens and use them instead of generating
-                            // fake ones. These are unstable, so it needs to be
-                            // fixed prior to stabilization
-                            // Fake tokens when we are invoking an inner attribute, and:
-                            fake_tokens = matches!(attr.style, ast::AttrStyle::Inner) &&
-                                // We are invoking an attribute on the crate root, or an outline
-                                // module
-                                (item_inner.ident.name.is_empty() || !matches!(mod_kind, ast::ModKind::Loaded(_, Inline::Yes, _)));
-                        }
-                    }
-                    let tokens = if fake_tokens {
-                        rustc_parse::fake_token_stream(
+                    let tokens = match &item {
+                        // FIXME: Collect tokens and use them instead of generating
+                        // fake ones. These are unstable, so it needs to be
+                        // fixed prior to stabilization
+                        // Fake tokens when we are invoking an inner attribute, and
+                        // we are invoking it on an out-of-line module or crate.
+                        Annotatable::Crate(krate) => rustc_parse::fake_token_stream_for_crate(
                             &self.cx.sess.parse_sess,
-                            &item.into_nonterminal(),
-                        )
-                    } else {
-                        item.into_tokens(&self.cx.sess.parse_sess)
+                            krate,
+                        ),
+                        Annotatable::Item(item_inner)
+                            if matches!(attr.style, ast::AttrStyle::Inner)
+                                && matches!(
+                                    item_inner.kind,
+                                    ItemKind::Mod(
+                                        _,
+                                        ModKind::Unloaded | ModKind::Loaded(_, Inline::No, _),
+                                    )
+                                ) =>
+                        {
+                            rustc_parse::fake_token_stream(
+                                &self.cx.sess.parse_sess,
+                                &item.into_nonterminal(),
+                            )
+                        }
+                        _ => item.into_tokens(&self.cx.sess.parse_sess),
                     };
                     let attr_item = attr.unwrap_normal_item();
                     if let MacArgs::Eq(..) = attr_item.args {
@@ -804,7 +766,8 @@ fn gate_proc_macro_attr_item(&self, span: Span, item: &Annotatable) {
             Annotatable::Item(_)
             | Annotatable::TraitItem(_)
             | Annotatable::ImplItem(_)
-            | Annotatable::ForeignItem(_) => return,
+            | Annotatable::ForeignItem(_)
+            | Annotatable::Crate(..) => return,
             Annotatable::Stmt(stmt) => {
                 // Attributes are stable on item statements,
                 // but unstable on all other kinds of statements
@@ -949,6 +912,7 @@ pub fn parse_ast_fragment<'a>(
             RecoverComma::No,
             RecoverColon::Yes,
         )?),
+        AstFragmentKind::Crate => AstFragment::Crate(this.parse_crate_mod()?),
         AstFragmentKind::Arms
         | AstFragmentKind::Fields
         | AstFragmentKind::FieldPats
@@ -1195,6 +1159,30 @@ macro_rules! assign_id {
 }
 
 impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
+    fn visit_crate(&mut self, krate: &mut ast::Crate) {
+        let span = krate.span;
+        let empty_crate =
+            || ast::Crate { attrs: Vec::new(), items: Vec::new(), span, is_placeholder: None };
+        let mut fold_crate = |krate: ast::Crate| {
+            let mut krate = match self.configure(krate) {
+                Some(krate) => krate,
+                None => return empty_crate(),
+            };
+
+            if let Some(attr) = self.take_first_attr(&mut krate) {
+                return self
+                    .collect_attr(attr, Annotatable::Crate(krate), AstFragmentKind::Crate)
+                    .make_crate();
+            }
+
+            noop_visit_crate(&mut krate, self);
+            krate
+        };
+
+        // Cannot use `visit_clobber` here, see the FIXME on it.
+        *krate = fold_crate(mem::replace(krate, empty_crate()));
+    }
+
     fn visit_expr(&mut self, expr: &mut P<ast::Expr>) {
         self.cfg.configure_expr(expr);
         visit_clobber(expr.deref_mut(), |mut expr| {

compiler/rustc_expand/src/placeholders.rs

@@ -46,6 +46,12 @@ fn mac_placeholder() -> ast::MacCall {
         || P(ast::Pat { id, kind: ast::PatKind::MacCall(mac_placeholder()), span, tokens: None });
 
     match kind {
+        AstFragmentKind::Crate => AstFragment::Crate(ast::Crate {
+            attrs: Default::default(),
+            items: Default::default(),
+            span,
+            is_placeholder: Some(id),
+        }),
         AstFragmentKind::Expr => AstFragment::Expr(expr_placeholder()),
         AstFragmentKind::OptExpr => AstFragment::OptExpr(Some(expr_placeholder())),
         AstFragmentKind::Items => AstFragment::Items(smallvec![P(ast::Item {
@@ -354,4 +360,12 @@ fn visit_ty(&mut self, ty: &mut P<ast::Ty>) {
             _ => noop_visit_ty(ty, self),
         }
     }
+
+    fn visit_crate(&mut self, krate: &mut ast::Crate) {
+        if let Some(id) = krate.is_placeholder {
+            *krate = self.remove(id).make_crate();
+        } else {
+            noop_visit_crate(krate, self)
+        }
+    }
 }

compiler/rustc_interface/src/passes.rs

@@ -323,7 +323,7 @@ pub fn configure_and_expand(
 
         let crate_attrs = krate.attrs.clone();
         let extern_mod_loaded = |ident: Ident, attrs, items, span| {
-            let krate = ast::Crate { attrs, items, span };
+            let krate = ast::Crate { attrs, items, span, is_placeholder: None };
             pre_expansion_lint(sess, lint_store, &krate, &crate_attrs, &ident.name.as_str());
             (krate.attrs, krate.items)
         };

compiler/rustc_parse/src/lib.rs

@@ -326,6 +326,12 @@ pub fn fake_token_stream(sess: &ParseSess, nt: &Nonterminal) -> TokenStream {
     parse_stream_from_source_str(filename, source, sess, Some(nt.span()))
 }
 
+pub fn fake_token_stream_for_crate(sess: &ParseSess, krate: &ast::Crate) -> TokenStream {
+    let source = pprust::crate_to_string_for_macros(krate);
+    let filename = FileName::macro_expansion_source_code(&source);
+    parse_stream_from_source_str(filename, source, sess, Some(krate.span))
+}
+
 pub fn parse_cfg_attr(
     attr: &Attribute,
     parse_sess: &ParseSess,

compiler/rustc_parse/src/parser/item.rs

@@ -26,7 +26,7 @@ impl<'a> Parser<'a> {
     /// Parses a source module as a crate. This is the main entry point for the parser.
     pub fn parse_crate_mod(&mut self) -> PResult<'a, ast::Crate> {
         let (attrs, items, span) = self.parse_mod(&token::Eof)?;
-        Ok(ast::Crate { attrs, items, span })
+        Ok(ast::Crate { attrs, items, span, is_placeholder: None })
     }
 
     /// Parses a `mod <foo> { ... }` or `mod <foo>;` item.

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -651,11 +651,6 @@ fn build_reduced_graph_for_use_tree(
 
     /// Constructs the reduced graph for one item.
     fn build_reduced_graph_for_item(&mut self, item: &'b Item) {
-        if matches!(item.kind, ItemKind::Mod(..)) && item.ident.name == kw::Empty {
-            // Fake crate root item from expand.
-            return;
-        }
-
         let parent_scope = &self.parent_scope;
         let parent = parent_scope.module;
         let expansion = parent_scope.expansion;
@@ -1499,4 +1494,13 @@ fn visit_variant(&mut self, variant: &'b ast::Variant) {
 
         visit::walk_variant(self, variant);
     }
+
+    fn visit_crate(&mut self, krate: &'b ast::Crate) {
+        if let Some(id) = krate.is_placeholder {
+            self.visit_invoc_in_module(id);
+        } else {
+            visit::walk_crate(self, krate);
+            self.contains_macro_use(&krate.attrs);
+        }
+    }
 }

compiler/rustc_resolve/src/def_collector.rs

@@ -7,7 +7,7 @@
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::definitions::*;
 use rustc_span::hygiene::LocalExpnId;
-use rustc_span::symbol::{kw, sym};
+use rustc_span::symbol::sym;
 use rustc_span::Span;
 use tracing::debug;
 
@@ -92,10 +92,6 @@ fn visit_item(&mut self, i: &'a Item) {
         // information we encapsulate into, the better
         let def_data = match &i.kind {
             ItemKind::Impl { .. } => DefPathData::Impl,
-            ItemKind::Mod(..) if i.ident.name == kw::Empty => {
-                // Fake crate root item from expand.
-                return visit::walk_item(self, i);
-            }
             ItemKind::Mod(..)
             | ItemKind::Trait(..)
             | ItemKind::TraitAlias(..)
@@ -346,4 +342,12 @@ fn visit_param(&mut self, p: &'a Param) {
     fn visit_field_def(&mut self, field: &'a FieldDef) {
         self.collect_field(field, None);
     }
+
+    fn visit_crate(&mut self, krate: &'a Crate) {
+        if let Some(id) = krate.is_placeholder {
+            self.visit_macro_invoc(id)
+        } else {
+            visit::walk_crate(self, krate)
+        }
+    }
 }

src/test/ui/ast-json/ast-json-noexpand-output.stdout

@@ -1 +1 @@
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src/test/ui/ast-json/ast-json-output.stdout

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src/test/ui/proc-macro/crate-attrs-multiple.rs

@@ -0,0 +1,14 @@
+// Multiple custom crate-level attributes, both inert and active.
+
+// check-pass
+// aux-crate:test_macros=test-macros.rs
+
+#![feature(custom_inner_attributes)]
+#![feature(prelude_import)]
+
+#![test_macros::identity_attr]
+#![rustfmt::skip]
+#![test_macros::identity_attr]
+#![rustfmt::skip]
+
+fn main() {}

src/test/ui/proc-macro/issue-59191-replace-root-with-fn.rs

@@ -1,7 +1,10 @@
-// edition:2018
-// aux-crate:issue_59191=issue-59191.rs
 // Test that using a macro to replace the entire crate tree with a non-'mod' item errors out nicely.
 // `issue_59191::no_main` replaces whatever's passed in with `fn main() {}`.
+
+// edition:2018
+// aux-crate:issue_59191=issue-59191.rs
+// error-pattern: requires `sized` lang_item
+
 #![feature(custom_inner_attributes)]
 #![issue_59191::no_main]
-//~^ ERROR expected crate top-level item to be a module after macro expansion, found a function
+#![issue_59191::no_main]

src/test/ui/proc-macro/issue-59191-replace-root-with-fn.stderr

@@ -1,10 +1,4 @@
-error: expected crate top-level item to be a module after macro expansion, found a function
-  --> $DIR/issue-59191-replace-root-with-fn.rs:6:1
-   |
-LL | #![issue_59191::no_main]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: this error originates in the attribute macro `issue_59191::no_main` (in Nightly builds, run with -Z macro-backtrace for more info)
+error: requires `sized` lang_item
 
 error: aborting due to previous error