Consistent no_prelude attribute

compiler/rustc_expand/src/base.rs

@@ -727,7 +727,7 @@ pub struct SyntaxExtension {
     /// Edition of the crate in which this macro is defined.
     pub edition: Edition,
     /// Built-in macros have a couple of special properties like availability
-    /// in `#[no_implicit_prelude]` modules, so we have to keep this flag.
+    /// in `#[no_prelude]` modules, so we have to keep this flag.
     pub builtin_name: Option<Symbol>,
 }
 

compiler/rustc_feature/src/active.rs

@@ -620,6 +620,9 @@ declare_features! (
     /// Allows arbitrary expressions in key-value attributes at parse time.
     (active, extended_key_value_attributes, "1.50.0", Some(78835), None),
 
+    /// Allow #![no_prelude] to disable prelude for current module
+    (active, no_prelude, "1.51.0", Some(20561), None),
+
     /// `:pat2018` and `:pat2021` macro matchers.
     (active, edition_macro_pats, "1.51.0", Some(54883), None),
 

compiler/rustc_feature/src/builtin_attrs.rs

@@ -253,6 +253,10 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     ungated!(path, Normal, template!(NameValueStr: "file")),
     ungated!(no_std, CrateLevel, template!(Word)),
     ungated!(no_implicit_prelude, Normal, template!(Word)),
+    gated!(
+        no_prelude, Normal, template!(Word),
+        "experimental feature: replacement for #![no_implicit_prelude] that is not inherited by descendants"
+    ),
     ungated!(non_exhaustive, AssumedUsed, template!(Word)),
 
     // Runtime

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -761,10 +761,13 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
 
             ItemKind::Mod(..) => {
                 let module_kind = ModuleKind::Def(DefKind::Mod, def_id, ident.name);
+                let inheritable_no_prelude = parent.pass_on_no_prelude
+                    || self.r.session.contains_name(&item.attrs, sym::no_implicit_prelude);
+                let local_no_prelude = inheritable_no_prelude
+                    || self.r.session.contains_name(&item.attrs, sym::no_prelude);
                 let module = self.r.arenas.alloc_module(ModuleData {
-                    no_implicit_prelude: parent.no_implicit_prelude || {
-                        self.r.session.contains_name(&item.attrs, sym::no_implicit_prelude)
-                    },
+                    pass_on_no_prelude: inheritable_no_prelude,
+                    no_prelude: local_no_prelude,
                     ..ModuleData::new(Some(parent), module_kind, def_id, expansion, item.span)
                 });
                 self.r.define(parent, ident, TypeNS, (module, vis, sp, expansion));

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1174,7 +1174,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                         // We can see through blocks
                     } else {
                         // Items from the prelude
-                        if !module.no_implicit_prelude {
+                        if !module.no_prelude {
                             let extern_prelude = self.r.extern_prelude.clone();
                             names.extend(extern_prelude.iter().flat_map(|(ident, _)| {
                                 self.r.crate_loader.maybe_process_path_extern(ident.name).and_then(

compiler/rustc_resolve/src/lib.rs

@@ -493,7 +493,12 @@ pub struct ModuleData<'a> {
     unexpanded_invocations: RefCell<FxHashSet<ExpnId>>,
 
     /// Whether `#[no_implicit_prelude]` is active.
-    no_implicit_prelude: bool,
+    /// And should therefore be active in decendant modules
+    pass_on_no_prelude: bool,
+
+    /// Whether `#[no_prelude]` or `#[no_implicit_prelude]` is active.
+    /// And therefore the current modul should use no prelude
+    no_prelude: bool,
 
     glob_importers: RefCell<Vec<&'a Import<'a>>>,
     globs: RefCell<Vec<&'a Import<'a>>>,
@@ -524,7 +529,8 @@ impl<'a> ModuleData<'a> {
             lazy_resolutions: Default::default(),
             populate_on_access: Cell::new(!nearest_parent_mod.is_local()),
             unexpanded_invocations: Default::default(),
-            no_implicit_prelude: false,
+            pass_on_no_prelude: false,
+            no_prelude: false,
             glob_importers: RefCell::new(Vec::new()),
             globs: RefCell::new(Vec::new()),
             traits: RefCell::new(None),
@@ -1207,13 +1213,18 @@ impl<'a> Resolver<'a> {
         let root_local_def_id = LocalDefId { local_def_index: CRATE_DEF_INDEX };
         let root_def_id = root_local_def_id.to_def_id();
         let root_module_kind = ModuleKind::Def(DefKind::Mod, root_def_id, kw::Empty);
+        let inheritable_no_prelude = session.contains_name(&krate.attrs, sym::no_implicit_prelude);
+        let local_no_prelude =
+            inheritable_no_prelude || session.contains_name(&krate.attrs, sym::no_prelude);
         let graph_root = arenas.alloc_module(ModuleData {
-            no_implicit_prelude: session.contains_name(&krate.attrs, sym::no_implicit_prelude),
+            pass_on_no_prelude: inheritable_no_prelude,
+            no_prelude: local_no_prelude,
             ..ModuleData::new(None, root_module_kind, root_def_id, ExpnId::root(), krate.span)
         });
         let empty_module_kind = ModuleKind::Def(DefKind::Mod, root_def_id, kw::Empty);
         let empty_module = arenas.alloc_module(ModuleData {
-            no_implicit_prelude: true,
+            pass_on_no_prelude: true,
+            no_prelude: true,
             ..ModuleData::new(
                 Some(graph_root),
                 empty_module_kind,
@@ -1724,7 +1735,7 @@ impl<'a> Resolver<'a> {
             MacroNS => Scope::DeriveHelpers(parent_scope.expansion),
         };
         let mut ctxt = ctxt.normalize_to_macros_2_0();
-        let mut use_prelude = !module.no_implicit_prelude;
+        let mut use_prelude = !module.no_prelude;
 
         loop {
             let visit = match scope {
@@ -1795,7 +1806,7 @@ impl<'a> Resolver<'a> {
                     ValueNS | MacroNS => break,
                 },
                 Scope::Module(module) => {
-                    use_prelude = !module.no_implicit_prelude;
+                    use_prelude = !module.no_prelude;
                     match self.hygienic_lexical_parent(module, &mut ctxt) {
                         Some(parent_module) => Scope::Module(parent_module),
                         None => {
@@ -1967,7 +1978,7 @@ impl<'a> Resolver<'a> {
             }
         }
 
-        if !module.no_implicit_prelude {
+        if !module.no_prelude {
             ident.span.adjust(ExpnId::root());
             if ns == TypeNS {
                 if let Some(binding) = self.extern_prelude_get(ident, !record_used) {

compiler/rustc_span/src/symbol.rs

@@ -753,6 +753,7 @@ symbols! {
         no_main,
         no_mangle,
         no_niche,
+        no_prelude,
         no_sanitize,
         no_stack_check,
         no_start,

src/test/ui/associated-types/associated-types-impl-redirect.rs

@@ -8,8 +8,8 @@
 // for `ByRef`. The right answer was to consider the result ambiguous
 // until more type information was available.
 
-#![feature(lang_items)]
-#![no_implicit_prelude]
+#![feature(no_prelude, lang_items)]
+#![no_prelude]
 
 use std::marker::Sized;
 use std::option::Option::{None, Some, self};

src/test/ui/associated-types/associated-types-issue-20346.rs

@@ -1,7 +1,8 @@
 // Test that we reliably check the value of the associated type.
 
 #![crate_type = "lib"]
-#![no_implicit_prelude]
+#![feature(no_prelude)]
+#![no_prelude]
 
 use std::option::Option::{self, None, Some};
 use std::vec::Vec;

src/test/ui/associated-types/associated-types-issue-20346.stderr

@@ -1,5 +1,5 @@
 error[E0271]: type mismatch resolving `<Adapter<I> as Iterator>::Item == Option<T>`
-  --> $DIR/associated-types-issue-20346.rs:34:5
+  --> $DIR/associated-types-issue-20346.rs:35:5
    |
 LL | fn is_iterator_of<A, I: Iterator<Item=A>>(_: &I) {}
    |                                  ------ required by this bound in `is_iterator_of`

src/test/ui/associated-types/associated-types-where-clause-impl-ambiguity.rs

@@ -7,8 +7,8 @@
 // for `ByRef`. The right answer was to consider the result ambiguous
 // until more type information was available.
 
-#![feature(lang_items)]
-#![no_implicit_prelude]
+#![feature(no_prelude, lang_items)]
+#![no_prelude]
 
 use std::marker::Sized;
 use std::option::Option::{None, Some, self};

src/test/ui/attributes/no-prelude-nested.rs

@@ -0,0 +1,63 @@
+#![feature(no_prelude)]
+
+// Test that things from the prelude aren't in scope. Use many of them
+// so that renaming some things won't magically make this test fail
+// for the wrong reason (e.g. if `Add` changes to `Addition`, and
+// `no_prelude` stops working, then the `impl Add` will still
+// fail with the same error message).
+//
+// Unlike `no_implicit_prelude`, `no_prelude` doesn't cascade into nested
+// modules, this makes the impl in foo::baz work.
+
+#[no_prelude]
+mod foo {
+    mod baz {
+        struct Test;
+        impl From<Test> for Test {
+            fn from(t: Test) {
+                Test
+            }
+        }
+        impl Clone for Test {
+            fn clone(&self) {
+                Test
+            }
+        }
+        impl Eq for Test {}
+
+        fn foo() {
+            drop(2)
+        }
+    }
+
+    struct Test;
+    impl From for Test {} //~ ERROR: cannot find trait
+    impl Clone for Test {} //~ ERROR: expected trait, found derive macro
+    impl Iterator for Test {} //~ ERROR: cannot find trait
+    impl ToString for Test {} //~ ERROR: cannot find trait
+    impl Eq for Test {} //~ ERROR: expected trait, found derive macro
+
+    fn foo() {
+        drop(2) //~ ERROR: cannot find function `drop`
+    }
+}
+
+fn qux() {
+    #[no_prelude]
+    mod qux_inner {
+        struct Test;
+        impl From for Test {} //~ ERROR: cannot find trait
+        impl Clone for Test {} //~ ERROR: expected trait, found derive macro
+        impl Iterator for Test {} //~ ERROR: cannot find trait
+        impl ToString for Test {} //~ ERROR: cannot find trait
+        impl Eq for Test {} //~ ERROR: expected trait, found derive macro
+        fn foo() {
+            drop(2) //~ ERROR: cannot find function `drop`
+        }
+    }
+}
+
+fn main() {
+    // these should work fine
+    drop(2)
+}

src/test/ui/attributes/no-prelude-nested.stderr

@@ -0,0 +1,136 @@
+error[E0405]: cannot find trait `From` in this scope
+  --> $DIR/no-prelude-nested.rs:34:10
+   |
+LL |     impl From for Test {}
+   |          ^^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+LL |     use std::convert::From;
+   |
+
+error[E0404]: expected trait, found derive macro `Clone`
+  --> $DIR/no-prelude-nested.rs:35:10
+   |
+LL |     impl Clone for Test {}
+   |          ^^^^^ not a trait
+   |
+help: consider importing this trait instead
+   |
+LL |     use std::clone::Clone;
+   |
+
+error[E0405]: cannot find trait `Iterator` in this scope
+  --> $DIR/no-prelude-nested.rs:36:10
+   |
+LL |     impl Iterator for Test {}
+   |          ^^^^^^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+LL |     use std::iter::Iterator;
+   |
+
+error[E0405]: cannot find trait `ToString` in this scope
+  --> $DIR/no-prelude-nested.rs:37:10
+   |
+LL |     impl ToString for Test {}
+   |          ^^^^^^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+LL |     use std::string::ToString;
+   |
+
+error[E0404]: expected trait, found derive macro `Eq`
+  --> $DIR/no-prelude-nested.rs:38:10
+   |
+LL |     impl Eq for Test {}
+   |          ^^ not a trait
+   |
+help: consider importing this trait instead
+   |
+LL |     use std::cmp::Eq;
+   |
+
+error[E0425]: cannot find function `drop` in this scope
+  --> $DIR/no-prelude-nested.rs:41:9
+   |
+LL |         drop(2)
+   |         ^^^^ not found in this scope
+   |
+help: consider importing this function
+   |
+LL |     use std::mem::drop;
+   |
+
+error[E0405]: cannot find trait `From` in this scope
+  --> $DIR/no-prelude-nested.rs:49:14
+   |
+LL |         impl From for Test {}
+   |              ^^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+LL |         use std::convert::From;
+   |
+
+error[E0404]: expected trait, found derive macro `Clone`
+  --> $DIR/no-prelude-nested.rs:50:14
+   |
+LL |         impl Clone for Test {}
+   |              ^^^^^ not a trait
+   |
+help: consider importing this trait instead
+   |
+LL |         use std::clone::Clone;
+   |
+
+error[E0405]: cannot find trait `Iterator` in this scope
+  --> $DIR/no-prelude-nested.rs:51:14
+   |
+LL |         impl Iterator for Test {}
+   |              ^^^^^^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+LL |         use std::iter::Iterator;
+   |
+
+error[E0405]: cannot find trait `ToString` in this scope
+  --> $DIR/no-prelude-nested.rs:52:14
+   |
+LL |         impl ToString for Test {}
+   |              ^^^^^^^^ not found in this scope
+   |
+help: consider importing this trait
+   |
+LL |         use std::string::ToString;
+   |
+
+error[E0404]: expected trait, found derive macro `Eq`
+  --> $DIR/no-prelude-nested.rs:53:14
+   |
+LL |         impl Eq for Test {}
+   |              ^^ not a trait
+   |
+help: consider importing this trait instead
+   |
+LL |         use std::cmp::Eq;
+   |
+
+error[E0425]: cannot find function `drop` in this scope
+  --> $DIR/no-prelude-nested.rs:55:13
+   |
+LL |             drop(2)
+   |             ^^^^ not found in this scope
+   |
+help: consider importing this function
+   |
+LL |         use std::mem::drop;
+   |
+
+error: aborting due to 12 previous errors
+
+Some errors have detailed explanations: E0404, E0405, E0425.
+For more information about an error, try `rustc --explain E0404`.

src/test/ui/attributes/no-prelude.rs

@@ -0,0 +1,19 @@
+#![feature(no_prelude)]
+#![no_prelude]
+
+// Test that things from the prelude aren't in scope. Use many of them
+// so that renaming some things won't magically make this test fail
+// for the wrong reason (e.g. if `Add` changes to `Addition`, and
+// `no_prelude` stops working, then the `impl Add` will still
+// fail with the same error message).
+
+struct Test;
+impl Add for Test {} //~ ERROR: cannot find trait
+impl Clone for Test {} //~ ERROR: expected trait, found derive macro
+impl Iterator for Test {} //~ ERROR: cannot find trait
+impl ToString for Test {} //~ ERROR: cannot find trait
+impl Writer for Test {} //~ ERROR: cannot find trait
+
+fn main() {
+    drop(2) //~ ERROR: cannot find function `drop`
+}