Enforce crate level attributes checks

compiler/rustc_passes/src/check_attr.rs

@@ -19,8 +19,8 @@ use rustc_hir::{
 use rustc_hir::{MethodKind, Target};
 use rustc_session::lint::builtin::{CONFLICTING_REPR_HINTS, UNUSED_ATTRIBUTES};
 use rustc_session::parse::feature_err;
-use rustc_span::symbol::sym;
-use rustc_span::Span;
+use rustc_span::symbol::{sym, Symbol};
+use rustc_span::{Span, DUMMY_SP};
 
 pub(crate) fn target_from_impl_item<'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -821,17 +821,45 @@ fn is_c_like_enum(item: &Item<'_>) -> bool {
     }
 }
 
+fn check_invalid_crate_level_attr(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
+    const ATTRS_TO_CHECK: &[Symbol] = &[
+        sym::macro_export,
+        sym::repr,
+        sym::path,
+        sym::automatically_derived,
+        sym::start,
+        sym::main,
+    ];
+
+    for attr in attrs {
+        for attr_to_check in ATTRS_TO_CHECK {
+            if tcx.sess.check_name(attr, *attr_to_check) {
+                tcx.sess
+                    .struct_span_err(
+                        attr.span,
+                        &format!(
+                            "`{}` attribute cannot be used at crate level",
+                            attr_to_check.to_ident_string()
+                        ),
+                    )
+                    .emit();
+            }
+        }
+    }
+}
+
 fn check_mod_attrs(tcx: TyCtxt<'_>, module_def_id: LocalDefId) {
     tcx.hir()
         .visit_item_likes_in_module(module_def_id, &mut CheckAttrVisitor { tcx }.as_deep_visitor());
     if module_def_id.is_top_level_module() {
         CheckAttrVisitor { tcx }.check_attributes(
             CRATE_HIR_ID,
             tcx.hir().krate_attrs(),
-            &tcx.hir().span(CRATE_HIR_ID),
+            &DUMMY_SP,
             Target::Mod,
             None,
         );
+        check_invalid_crate_level_attr(tcx, tcx.hir().krate_attrs());
     }
 }
 

compiler/rustc_passes/src/entry.rs

@@ -78,29 +78,38 @@ fn entry_fn(tcx: TyCtxt<'_>, cnum: CrateNum) -> Option<(LocalDefId, EntryFnType)
 // Beware, this is duplicated in `librustc_builtin_macros/test_harness.rs`
 // (with `ast::Item`), so make sure to keep them in sync.
 fn entry_point_type(sess: &Session, item: &Item<'_>, at_root: bool) -> EntryPointType {
-    match item.kind {
-        ItemKind::Fn(..) => {
-            if sess.contains_name(&item.attrs, sym::start) {
-                EntryPointType::Start
-            } else if sess.contains_name(&item.attrs, sym::main) {
-                EntryPointType::MainAttr
-            } else if item.ident.name == sym::main {
-                if at_root {
-                    // This is a top-level function so can be `main`.
-                    EntryPointType::MainNamed
-                } else {
-                    EntryPointType::OtherMain
-                }
-            } else {
-                EntryPointType::None
-            }
+    if sess.contains_name(&item.attrs, sym::start) {
+        EntryPointType::Start
+    } else if sess.contains_name(&item.attrs, sym::main) {
+        EntryPointType::MainAttr
+    } else if item.ident.name == sym::main {
+        if at_root {
+            // This is a top-level function so can be `main`.
+            EntryPointType::MainNamed
+        } else {
+            EntryPointType::OtherMain
         }
-        _ => EntryPointType::None,
+    } else {
+        EntryPointType::None
     }
 }
 
+fn throw_attr_err(sess: &Session, span: Span, attr: &str) {
+    sess.struct_span_err(span, &format!("`{}` attribute can only be used on functions", attr))
+        .emit();
+}
+
 fn find_item(item: &Item<'_>, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
     match entry_point_type(&ctxt.session, item, at_root) {
+        EntryPointType::None => (),
+        _ if !matches!(item.kind, ItemKind::Fn(..)) => {
+            if let Some(attr) = ctxt.session.find_by_name(item.attrs, sym::start) {
+                throw_attr_err(&ctxt.session, attr.span, "start");
+            }
+            if let Some(attr) = ctxt.session.find_by_name(item.attrs, sym::main) {
+                throw_attr_err(&ctxt.session, attr.span, "main");
+            }
+        }
         EntryPointType::MainNamed => {
             if ctxt.main_fn.is_none() {
                 ctxt.main_fn = Some((item.hir_id, item.span));
@@ -137,7 +146,6 @@ fn find_item(item: &Item<'_>, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
                     .emit();
             }
         }
-        EntryPointType::None => (),
     }
 }
 

compiler/rustc_session/src/lint/builtin.rs

@@ -518,7 +518,7 @@ declare_lint! {
     /// ### Example
     ///
     /// ```rust
-    /// #![macro_export]
+    /// #![ignore]
     /// ```
     ///
     /// {{produces}}

src/test/rustdoc-ui/doc-alias-crate-level.rs

@@ -1,3 +1,6 @@
 #![feature(doc_alias)]
 
-#![doc(alias = "shouldn't work!")] //~ ERROR
+#![doc(alias = "crate-level-not-working")] //~ ERROR
+
+#[doc(alias = "shouldn't work!")] //~ ERROR
+pub fn foo() {}

src/test/rustdoc-ui/doc-alias-crate-level.stderr

@@ -1,8 +1,14 @@
+error: '\'' character isn't allowed in `#[doc(alias = "...")]`
+  --> $DIR/doc-alias-crate-level.rs:5:7
+   |
+LL | #[doc(alias = "shouldn't work!")]
+   |       ^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error: `#![doc(alias = "...")]` isn't allowed as a crate level attribute
   --> $DIR/doc-alias-crate-level.rs:3:8
    |
-LL | #![doc(alias = "shouldn't work!")]
-   |        ^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #![doc(alias = "crate-level-not-working")]
+   |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error: aborting due to 2 previous errors
 

src/test/ui/doc-alias-crate-level.stderr

@@ -1,4 +1,4 @@
-error: `#![doc(alias = "...")]` isn't allowed as a crate level attribute
+error: '\'' character isn't allowed in `#[doc(alias = "...")]`
   --> $DIR/doc-alias-crate-level.rs:7:8
    |
 LL | #![doc(alias = "shouldn't work!")]

src/test/ui/feature-gate/issue-43106-gating-of-builtin-attrs-error.rs

@@ -1,3 +1,6 @@
+//~ NOTE: not an `extern crate` item
+//~^ NOTE: not a function or static
+//~^^ NOTE: not a function or closure
 // This is testing whether various builtin attributes signals an
 // error or warning when put in "weird" places.
 //
@@ -7,22 +10,19 @@
 
 // ignore-tidy-linelength
 
-#![deny(unused_attributes)]
-//~^ NOTE not a function or static
-//~^^ NOTE the lint level is defined here
-//~^^^ NOTE not an `extern crate` item
-//~^^^^ NOTE not a function or static
-//~^^^^^ NOTE not a function or closure
-
 #![macro_export]
+//~^ ERROR: `macro_export` attribute cannot be used at crate level
 #![main]
+//~^ ERROR: `main` attribute cannot be used at crate level
 #![start]
+//~^ ERROR: `start` attribute cannot be used at crate level
 #![repr()]
+//~^ ERROR: `repr` attribute cannot be used at crate level
 #![path = "3800"]
+//~^ ERROR: `path` attribute cannot be used at crate level
 #![automatically_derived]
+//~^ ERROR: `automatically_derived` attribute cannot be used at crate level
 #![no_mangle]
-//~^ ERROR attribute should be applied to a function or static
-//~^^ WARN
 #![no_link]
 //~^ ERROR: attribute should be applied to an `extern crate` item
 #![export_name = "2200"]
@@ -107,4 +107,40 @@ mod export_name {
     //~| NOTE not a function or static
 }
 
+#[main]
+//~^ ERROR: `main` attribute can only be used on functions
+mod main {
+    mod inner { #![main] }
+    //~^ ERROR: `main` attribute can only be used on functions
+
+    // for `fn f()` case, see feature-gate-main.rs
+
+    #[main] struct S;
+    //~^ ERROR: `main` attribute can only be used on functions
+
+    #[main] type T = S;
+    //~^ ERROR: `main` attribute can only be used on functions
+
+    #[main] impl S { }
+    //~^ ERROR: `main` attribute can only be used on functions
+}
+
+#[start]
+//~^ ERROR: `start` attribute can only be used on functions
+mod start {
+    mod inner { #![start] }
+    //~^ ERROR: `start` attribute can only be used on functions
+
+    // for `fn f()` case, see feature-gate-start.rs
+
+    #[start] struct S;
+    //~^ ERROR: `start` attribute can only be used on functions
+
+    #[start] type T = S;
+    //~^ ERROR: `start` attribute can only be used on functions
+
+    #[start] impl S { }
+    //~^ ERROR: `start` attribute can only be used on functions
+}
+
 fn main() {}