Auto merge of #65588 - Centril:rollup-9k55k3t, r=Centril

Rollup of 6 pull requests

Successful merges:

 - #65174 (Fix zero-size uninitialized boxes)
 - #65252 (expand: Simplify expansion of derives)
 - #65485 (Suppress ICE when validators disagree on `LiveDrop`s in presence of `&mut`)
 - #65542 (Refer to "associated functions" instead of "static methods")
 - #65545 (More symbol cleanups)
 - #65576 (Don't add `argc` and `argv` arguments to `main` on WASI.)

Failed merges:

r? @ghost

src/liballoc/boxed.rs

@@ -142,6 +142,9 @@ impl<T> Box<T> {
     #[unstable(feature = "new_uninit", issue = "63291")]
     pub fn new_uninit() -> Box<mem::MaybeUninit<T>> {
         let layout = alloc::Layout::new::<mem::MaybeUninit<T>>();
+        if layout.size() == 0 {
+            return Box(NonNull::dangling().into())
+        }
         let ptr = unsafe {
             Global.alloc(layout)
                 .unwrap_or_else(|_| alloc::handle_alloc_error(layout))
@@ -182,9 +185,16 @@ impl<T> Box<[T]> {
     #[unstable(feature = "new_uninit", issue = "63291")]
     pub fn new_uninit_slice(len: usize) -> Box<[mem::MaybeUninit<T>]> {
         let layout = alloc::Layout::array::<mem::MaybeUninit<T>>(len).unwrap();
-        let ptr = unsafe { alloc::alloc(layout) };
-        let unique = Unique::new(ptr).unwrap_or_else(|| alloc::handle_alloc_error(layout));
-        let slice = unsafe { slice::from_raw_parts_mut(unique.cast().as_ptr(), len) };
+        let ptr = if layout.size() == 0 {
+            NonNull::dangling()
+        } else {
+            unsafe {
+                Global.alloc(layout)
+                    .unwrap_or_else(|_| alloc::handle_alloc_error(layout))
+                    .cast()
+            }
+        };
+        let slice = unsafe { slice::from_raw_parts_mut(ptr.as_ptr(), len) };
         Box(Unique::from(slice))
     }
 }

src/liballoc/tests/boxed.rs

@@ -0,0 +1,18 @@
+use std::ptr::NonNull;
+use std::mem::MaybeUninit;
+
+#[test]
+fn unitialized_zero_size_box() {
+    assert_eq!(
+        &*Box::<()>::new_uninit() as *const _,
+        NonNull::<MaybeUninit<()>>::dangling().as_ptr(),
+    );
+    assert_eq!(
+        Box::<[()]>::new_uninit_slice(4).as_ptr(),
+        NonNull::<MaybeUninit<()>>::dangling().as_ptr(),
+    );
+    assert_eq!(
+        Box::<[String]>::new_uninit_slice(0).as_ptr(),
+        NonNull::<MaybeUninit<String>>::dangling().as_ptr(),
+    );
+}

src/liballoc/tests/lib.rs

@@ -2,6 +2,7 @@
 #![feature(box_syntax)]
 #![feature(drain_filter)]
 #![feature(exact_size_is_empty)]
+#![feature(new_uninit)]
 #![feature(option_flattening)]
 #![feature(pattern)]
 #![feature(trusted_len)]
@@ -14,6 +15,7 @@ use std::collections::hash_map::DefaultHasher;
 
 mod arc;
 mod binary_heap;
+mod boxed;
 mod btree;
 mod cow_str;
 mod fmt;

src/librustc/hir/map/def_collector.rs

@@ -90,7 +90,7 @@ impl<'a> DefCollector<'a> {
         }
     }
 
-    pub fn visit_macro_invoc(&mut self, id: NodeId) {
+    fn visit_macro_invoc(&mut self, id: NodeId) {
         self.definitions.set_invocation_parent(id.placeholder_to_expn_id(), self.parent_def);
     }
 }

src/librustc/hir/map/definitions.rs

@@ -111,7 +111,7 @@ pub struct Definitions {
 /// A unique identifier that we can use to lookup a definition
 /// precisely. It combines the index of the definition's parent (if
 /// any) with a `DisambiguatedDefPathData`.
-#[derive(Clone, PartialEq, Debug, Hash, RustcEncodable, RustcDecodable)]
+#[derive(Clone, PartialEq, Debug, RustcEncodable, RustcDecodable)]
 pub struct DefKey {
     /// The parent path.
     pub parent: Option<DefIndex>,
@@ -162,13 +162,13 @@ impl DefKey {
 /// between them. This introduces some artificial ordering dependency
 /// but means that if you have, e.g., two impls for the same type in
 /// the same module, they do get distinct `DefId`s.
-#[derive(Clone, PartialEq, Debug, Hash, RustcEncodable, RustcDecodable)]
+#[derive(Clone, PartialEq, Debug, RustcEncodable, RustcDecodable)]
 pub struct DisambiguatedDefPathData {
     pub data: DefPathData,
     pub disambiguator: u32
 }
 
-#[derive(Clone, Debug, Hash, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
 pub struct DefPath {
     /// The path leading from the crate root to the item.
     pub data: Vec<DisambiguatedDefPathData>,

src/librustc_codegen_ssa/base.rs

@@ -414,8 +414,11 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(cx: &'
         rust_main_def_id: DefId,
         use_start_lang_item: bool,
     ) {
-        let llfty =
-            cx.type_func(&[cx.type_int(), cx.type_ptr_to(cx.type_i8p())], cx.type_int());
+        let llfty = if cx.sess().target.target.options.main_needs_argc_argv {
+            cx.type_func(&[cx.type_int(), cx.type_ptr_to(cx.type_i8p())], cx.type_int())
+        } else {
+            cx.type_func(&[], cx.type_int())
+        };
 
         let main_ret_ty = cx.tcx().fn_sig(rust_main_def_id).output();
         // Given that `main()` has no arguments,
@@ -445,11 +448,19 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(cx: &'
 
         bx.insert_reference_to_gdb_debug_scripts_section_global();
 
-        // Params from native main() used as args for rust start function
-        let param_argc = bx.get_param(0);
-        let param_argv = bx.get_param(1);
-        let arg_argc = bx.intcast(param_argc, cx.type_isize(), true);
-        let arg_argv = param_argv;
+        let (arg_argc, arg_argv) = if cx.sess().target.target.options.main_needs_argc_argv {
+            // Params from native main() used as args for rust start function
+            let param_argc = bx.get_param(0);
+            let param_argv = bx.get_param(1);
+            let arg_argc = bx.intcast(param_argc, cx.type_isize(), true);
+            let arg_argv = param_argv;
+            (arg_argc, arg_argv)
+        } else {
+            // The Rust start function doesn't need argc and argv, so just pass zeros.
+            let arg_argc = bx.const_int(cx.type_int(), 0);
+            let arg_argv = bx.const_null(cx.type_ptr_to(cx.type_i8p()));
+            (arg_argc, arg_argv)
+        };
 
         let (start_fn, args) = if use_start_lang_item {
             let start_def_id = cx.tcx().require_lang_item(StartFnLangItem, None);

src/librustc_mir/lib.rs

@@ -14,6 +14,7 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![feature(core_intrinsics)]
 #![feature(const_fn)]
 #![feature(decl_macro)]
+#![feature(drain_filter)]
 #![feature(exhaustive_patterns)]
 #![feature(never_type)]
 #![feature(specialization)]

src/librustc_mir/transform/qualify_consts.rs

@@ -1024,23 +1024,12 @@ impl<'a, 'tcx> Checker<'a, 'tcx> {
             new_errors.dedup();
 
             if self.errors != new_errors {
-                error!("old validator: {:?}", self.errors);
-                error!("new validator: {:?}", new_errors);
-
-                // ICE on nightly if the validators do not emit exactly the same errors.
-                // Users can supress this panic with an unstable compiler flag (hopefully after
-                // filing an issue).
-                let opts = &self.tcx.sess.opts;
-                let trigger_ice = opts.unstable_features.is_nightly_build()
-                    && !opts.debugging_opts.suppress_const_validation_back_compat_ice;
-
-                if trigger_ice {
-                    span_bug!(
-                        body.span,
-                        "{}",
-                        VALIDATOR_MISMATCH_ERR,
-                    );
-                }
+                validator_mismatch(
+                    self.tcx,
+                    body,
+                    std::mem::replace(&mut self.errors, vec![]),
+                    new_errors,
+                );
             }
         }
 
@@ -1870,6 +1859,58 @@ fn args_required_const(tcx: TyCtxt<'_>, def_id: DefId) -> Option<FxHashSet<usize
     Some(ret)
 }
 
+fn validator_mismatch(
+    tcx: TyCtxt<'tcx>,
+    body: &Body<'tcx>,
+    mut old_errors: Vec<(Span, String)>,
+    mut new_errors: Vec<(Span, String)>,
+) {
+    error!("old validator: {:?}", old_errors);
+    error!("new validator: {:?}", new_errors);
+
+    // ICE on nightly if the validators do not emit exactly the same errors.
+    // Users can supress this panic with an unstable compiler flag (hopefully after
+    // filing an issue).
+    let opts = &tcx.sess.opts;
+    let strict_validation_enabled = opts.unstable_features.is_nightly_build()
+        && !opts.debugging_opts.suppress_const_validation_back_compat_ice;
+
+    if !strict_validation_enabled {
+        return;
+    }
+
+    // If this difference would cause a regression from the old to the new or vice versa, trigger
+    // the ICE.
+    if old_errors.is_empty() || new_errors.is_empty() {
+        span_bug!(body.span, "{}", VALIDATOR_MISMATCH_ERR);
+    }
+
+    // HACK: Borrows that would allow mutation are forbidden in const contexts, but they cause the
+    // new validator to be more conservative about when a dropped local has been moved out of.
+    //
+    // Supress the mismatch ICE in cases where the validators disagree only on the number of
+    // `LiveDrop` errors and both observe the same sequence of `MutBorrow`s.
+
+    let is_live_drop = |(_, s): &mut (_, String)| s.starts_with("LiveDrop");
+    let is_mut_borrow = |(_, s): &&(_, String)| s.starts_with("MutBorrow");
+
+    let old_live_drops: Vec<_> = old_errors.drain_filter(is_live_drop).collect();
+    let new_live_drops: Vec<_> = new_errors.drain_filter(is_live_drop).collect();
+
+    let only_live_drops_differ = old_live_drops != new_live_drops && old_errors == new_errors;
+
+    let old_mut_borrows = old_errors.iter().filter(is_mut_borrow);
+    let new_mut_borrows = new_errors.iter().filter(is_mut_borrow);
+
+    let at_least_one_mut_borrow = old_mut_borrows.clone().next().is_some();
+
+    if only_live_drops_differ && at_least_one_mut_borrow && old_mut_borrows.eq(new_mut_borrows) {
+        return;
+    }
+
+    span_bug!(body.span, "{}", VALIDATOR_MISMATCH_ERR);
+}
+
 const VALIDATOR_MISMATCH_ERR: &str =
     r"Disagreement between legacy and dataflow-based const validators.
     After filing an issue, use `-Zsuppress-const-validation-back-compat-ice` to compile your code.";

src/librustc_privacy/lib.rs

@@ -880,11 +880,11 @@ impl Visitor<'tcx> for EmbargoVisitor<'tcx> {
             self.tcx,
             self.tcx.hir().local_def_id(md.hir_id)
         ).unwrap();
-        let mut module_id = self.tcx.hir().as_local_hir_id(macro_module_def_id).unwrap();
-        if !self.tcx.hir().is_hir_id_module(module_id) {
-            // `module_id` doesn't correspond to a `mod`, return early (#63164).
-            return;
-        }
+        let mut module_id = match self.tcx.hir().as_local_hir_id(macro_module_def_id) {
+            Some(module_id) if self.tcx.hir().is_hir_id_module(module_id) => module_id,
+            // `module_id` doesn't correspond to a `mod`, return early (#63164, #65252).
+            _ => return,
+        };
         let level = if md.vis.node.is_pub() { self.get(module_id) } else { None };
         let new_level = self.update(md.hir_id, level);
         if new_level.is_none() {

src/librustc_resolve/build_reduced_graph.rs

@@ -163,25 +163,15 @@ impl<'a> Resolver<'a> {
         Some(ext)
     }
 
-    // FIXME: `extra_placeholders` should be included into the `fragment` as regular placeholders.
     crate fn build_reduced_graph(
         &mut self,
         fragment: &AstFragment,
-        extra_placeholders: &[NodeId],
         parent_scope: ParentScope<'a>,
     ) -> LegacyScope<'a> {
         let mut def_collector = DefCollector::new(&mut self.definitions, parent_scope.expansion);
         fragment.visit_with(&mut def_collector);
-        for placeholder in extra_placeholders {
-            def_collector.visit_macro_invoc(*placeholder);
-        }
-
         let mut visitor = BuildReducedGraphVisitor { r: self, parent_scope };
         fragment.visit_with(&mut visitor);
-        for placeholder in extra_placeholders {
-            visitor.parent_scope.legacy = visitor.visit_invoc(*placeholder);
-        }
-
         visitor.parent_scope.legacy
     }
 
@@ -1064,8 +1054,17 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
         None
     }
 
+    // Mark the given macro as unused unless its name starts with `_`.
+    // Macro uses will remove items from this set, and the remaining
+    // items will be reported as `unused_macros`.
+    fn insert_unused_macro(&mut self, ident: Ident, node_id: NodeId, span: Span) {
+        if !ident.as_str().starts_with("_") {
+            self.r.unused_macros.insert(node_id, span);
+        }
+    }
+
     fn define_macro(&mut self, item: &ast::Item) -> LegacyScope<'a> {
-        let parent_scope = &self.parent_scope;
+        let parent_scope = self.parent_scope;
         let expansion = parent_scope.expansion;
         let (ext, ident, span, is_legacy) = match &item.kind {
             ItemKind::MacroDef(def) => {
@@ -1105,7 +1104,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                             (res, vis, span, expansion, IsMacroExport));
             } else {
                 self.r.check_reserved_macro_name(ident, res);
-                self.r.unused_macros.insert(item.id, span);
+                self.insert_unused_macro(ident, item.id, span);
             }
             LegacyScope::Binding(self.r.arenas.alloc_legacy_binding(LegacyBinding {
                 parent_legacy_scope: parent_scope.legacy, binding, ident
@@ -1114,7 +1113,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
             let module = parent_scope.module;
             let vis = self.resolve_visibility(&item.vis);
             if vis != ty::Visibility::Public {
-                self.r.unused_macros.insert(item.id, span);
+                self.insert_unused_macro(ident, item.id, span);
             }
             self.r.define(module, ident, MacroNS, (res, vis, span, expansion));
             self.parent_scope.legacy

src/librustc_resolve/error_codes.rs

@@ -1013,33 +1013,42 @@ fn h1() -> i32 {
 "##,
 
 E0424: r##"
-The `self` keyword was used in a static method.
+The `self` keyword was used inside of an associated function without a "`self`
+receiver" parameter.
 
 Erroneous code example:
 
 ```compile_fail,E0424
 struct Foo;
 
 impl Foo {
-    fn bar(self) {}
+    // `bar` is a method, because it has a receiver parameter.
+    fn bar(&self) {}
 
+    // `foo` is not a method, because it has no receiver parameter.
     fn foo() {
-        self.bar(); // error: `self` is not available in a static method.
+        self.bar(); // error: `self` value is a keyword only available in
+                    //        methods with a `self` parameter
     }
 }
 ```
 
-Please check if the method's argument list should have contained `self`,
-`&self`, or `&mut self` (in case you didn't want to create a static
-method), and add it if so. Example:
+The `self` keyword can only be used inside methods, which are associated
+functions (functions defined inside of a `trait` or `impl` block) that have a
+`self` receiver as its first parameter, like `self`, `&self`, `&mut self` or
+`self: &mut Pin<Self>` (this last one is an example of an ["abitrary `self`
+type"](https://github.com/rust-lang/rust/issues/44874)).
+
+Check if the associated function's parameter list should have contained a `self`
+receiver for it to be a method, and add it if so. Example:
 
 ```
 struct Foo;
 
 impl Foo {
-    fn bar(self) {}
+    fn bar(&self) {}
 
-    fn foo(self) {
+    fn foo(self) { // `foo` is now a method.
         self.bar(); // ok!
     }
 }