Convert no_std and no_core to the new attribute infrastructure

compiler/rustc_attr_parsing/src/attributes/crate_level.rs

@@ -176,3 +176,27 @@ impl<S: Stage> SingleAttributeParser<S> for PatternComplexityLimitParser {
         })
     }
 }
+
+pub(crate) struct NoCoreParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for NoCoreParser {
+    const PATH: &[Symbol] = &[sym::no_core];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    // because it's a crate-level attribute, we already warn about it.
+    // Putting target limitations here would give duplicate warnings
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS);
+    const CREATE: fn(Span) -> AttributeKind = AttributeKind::NoCore;
+    const TYPE: AttributeType = AttributeType::CrateLevel;
+}
+
+pub(crate) struct NoStdParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for NoStdParser {
+    const PATH: &[Symbol] = &[sym::no_std];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Warn;
+    // because it's a crate-level attribute, we already warn about it.
+    // Putting target limitations here would give duplicate warnings
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(ALL_TARGETS);
+    const CREATE: fn(Span) -> AttributeKind = AttributeKind::NoStd;
+    const TYPE: AttributeType = AttributeType::CrateLevel;
+}

compiler/rustc_attr_parsing/src/context.rs

@@ -25,8 +25,8 @@ use crate::attributes::codegen_attrs::{
 };
 use crate::attributes::confusables::ConfusablesParser;
 use crate::attributes::crate_level::{
-    CrateNameParser, MoveSizeLimitParser, PatternComplexityLimitParser, RecursionLimitParser,
-    TypeLengthLimitParser,
+    CrateNameParser, MoveSizeLimitParser, NoCoreParser, NoStdParser, PatternComplexityLimitParser,
+    RecursionLimitParser, TypeLengthLimitParser,
 };
 use crate::attributes::deprecation::DeprecationParser;
 use crate::attributes::dummy::DummyParser;
@@ -222,8 +222,10 @@ attribute_parsers!(
         Single<WithoutArgs<MacroEscapeParser>>,
         Single<WithoutArgs<MarkerParser>>,
         Single<WithoutArgs<MayDangleParser>>,
+        Single<WithoutArgs<NoCoreParser>>,
         Single<WithoutArgs<NoImplicitPreludeParser>>,
         Single<WithoutArgs<NoMangleParser>>,
+        Single<WithoutArgs<NoStdParser>>,
         Single<WithoutArgs<NonExhaustiveParser>>,
         Single<WithoutArgs<ParenSugarParser>>,
         Single<WithoutArgs<PassByValueParser>>,

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -579,12 +579,18 @@ pub enum AttributeKind {
     /// Represents `#[naked]`
     Naked(Span),
 
+    /// Represents `#[no_core]`
+    NoCore(Span),
+
     /// Represents `#[no_implicit_prelude]`
     NoImplicitPrelude(Span),
 
     /// Represents `#[no_mangle]`
     NoMangle(Span),
 
+    /// Represents `#[no_std]`
+    NoStd(Span),
+
     /// Represents `#[non_exhaustive]`
     NonExhaustive(Span),
 

compiler/rustc_hir/src/attrs/encode_cross_crate.rs

@@ -64,8 +64,10 @@ impl AttributeKind {
             MoveSizeLimit { .. } => No,
             MustUse { .. } => Yes,
             Naked(..) => No,
+            NoCore(..) => No,
             NoImplicitPrelude(..) => No,
-            NoMangle(..) => Yes,      // Needed for rustdoc
+            NoMangle(..) => Yes, // Needed for rustdoc
+            NoStd(..) => No,
             NonExhaustive(..) => Yes, // Needed for rustdoc
             Optimize(..) => No,
             ParenSugar(..) => No,

compiler/rustc_passes/src/check_attr.rs

@@ -274,6 +274,8 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
                     | AttributeKind::MoveSizeLimit { .. }
                     | AttributeKind::TypeLengthLimit { .. }
                     | AttributeKind::PatternComplexityLimit { .. }
+                    | AttributeKind::NoCore { .. }
+                    | AttributeKind::NoStd { .. }
                 ) => { /* do nothing  */ }
                 Attribute::Unparsed(attr_item) => {
                     style = Some(attr_item.style);

src/tools/clippy/clippy_utils/src/lib.rs

@@ -2133,17 +2133,11 @@ pub fn std_or_core(cx: &LateContext<'_>) -> Option<&'static str> {
 }
 
 pub fn is_no_std_crate(cx: &LateContext<'_>) -> bool {
-    cx.tcx
-        .hir_attrs(hir::CRATE_HIR_ID)
-        .iter()
-        .any(|attr| attr.has_name(sym::no_std))
+    find_attr!(cx.tcx.hir_attrs(hir::CRATE_HIR_ID), AttributeKind::NoStd(..))
 }
 
 pub fn is_no_core_crate(cx: &LateContext<'_>) -> bool {
-    cx.tcx
-        .hir_attrs(hir::CRATE_HIR_ID)
-        .iter()
-        .any(|attr| attr.has_name(sym::no_core))
+    find_attr!(cx.tcx.hir_attrs(hir::CRATE_HIR_ID), AttributeKind::NoCore(..))
 }
 
 /// Check if parent of a hir node is a trait implementation block.

tests/ui/attributes/malformed-no-std.rs

@@ -0,0 +1,25 @@
+#![feature(no_core)]
+// these all still apply no_std and then later error
+#![no_std = "foo"]
+//~^ ERROR malformed `no_std` attribute input
+#![no_std("bar")]
+//~^ ERROR malformed `no_std` attribute input
+#![no_std(foo = "bar")]
+//~^ ERROR malformed `no_std` attribute input
+#![no_core = "foo"]
+//~^ ERROR malformed `no_core` attribute input
+#![no_core("bar")]
+//~^ ERROR malformed `no_core` attribute input
+#![no_core(foo = "bar")]
+//~^ ERROR malformed `no_core` attribute input
+
+#[deny(unused_attributes)]
+#[no_std]
+//~^ ERROR crate-level attribute should be an inner attribute: add an exclamation mark:
+#[no_core]
+//~^ ERROR crate-level attribute should be an inner attribute: add an exclamation mark:
+// to fix compilation
+extern crate core;
+extern crate std;
+
+fn main() {}

tests/ui/attributes/malformed-no-std.stderr

@@ -0,0 +1,86 @@
+error[E0565]: malformed `no_std` attribute input
+  --> $DIR/malformed-no-std.rs:3:1
+   |
+LL | #![no_std = "foo"]
+   | ^^^^^^^^^^-------^
+   | |         |
+   | |         didn't expect any arguments here
+   | help: must be of the form: `#![no_std]`
+
+error[E0565]: malformed `no_std` attribute input
+  --> $DIR/malformed-no-std.rs:5:1
+   |
+LL | #![no_std("bar")]
+   | ^^^^^^^^^-------^
+   | |        |
+   | |        didn't expect any arguments here
+   | help: must be of the form: `#![no_std]`
+
+error[E0565]: malformed `no_std` attribute input
+  --> $DIR/malformed-no-std.rs:7:1
+   |
+LL | #![no_std(foo = "bar")]
+   | ^^^^^^^^^-------------^
+   | |        |
+   | |        didn't expect any arguments here
+   | help: must be of the form: `#![no_std]`
+
+error[E0565]: malformed `no_core` attribute input
+  --> $DIR/malformed-no-std.rs:9:1
+   |
+LL | #![no_core = "foo"]
+   | ^^^^^^^^^^^-------^
+   | |          |
+   | |          didn't expect any arguments here
+   | help: must be of the form: `#![no_core]`
+
+error[E0565]: malformed `no_core` attribute input
+  --> $DIR/malformed-no-std.rs:11:1
+   |
+LL | #![no_core("bar")]
+   | ^^^^^^^^^^-------^
+   | |         |
+   | |         didn't expect any arguments here
+   | help: must be of the form: `#![no_core]`
+
+error[E0565]: malformed `no_core` attribute input
+  --> $DIR/malformed-no-std.rs:13:1
+   |
+LL | #![no_core(foo = "bar")]
+   | ^^^^^^^^^^-------------^
+   | |         |
+   | |         didn't expect any arguments here
+   | help: must be of the form: `#![no_core]`
+
+error: crate-level attribute should be an inner attribute: add an exclamation mark: `#![no_std]`
+  --> $DIR/malformed-no-std.rs:17:1
+   |
+LL | #[no_std]
+   | ^^^^^^^^^
+   |
+note: This attribute does not have an `!`, which means it is applied to this extern crate
+  --> $DIR/malformed-no-std.rs:22:1
+   |
+LL | extern crate core;
+   | ^^^^^^^^^^^^^^^^^^
+note: the lint level is defined here
+  --> $DIR/malformed-no-std.rs:16:8
+   |
+LL | #[deny(unused_attributes)]
+   |        ^^^^^^^^^^^^^^^^^
+
+error: crate-level attribute should be an inner attribute: add an exclamation mark: `#![no_core]`
+  --> $DIR/malformed-no-std.rs:19:1
+   |
+LL | #[no_core]
+   | ^^^^^^^^^^
+   |
+note: This attribute does not have an `!`, which means it is applied to this extern crate
+  --> $DIR/malformed-no-std.rs:22:1
+   |
+LL | extern crate core;
+   | ^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 8 previous errors
+
+For more information about this error, try `rustc --explain E0565`.

tests/ui/feature-gates/issue-43106-gating-of-builtin-attrs.rs

@@ -539,26 +539,26 @@ mod macro_escape {
 
 #[no_std]
 //~^ WARN crate-level attribute should be an inner attribute
-//~| HELP add a `!`
 mod no_std {
+    //~^ NOTE This attribute does not have an `!`, which means it is applied to this module
     mod inner { #![no_std] }
-//~^ WARN crate-level attribute should be in the root module
+//~^ WARN the `#![no_std]` attribute can only be used at the crate root
 
     #[no_std] fn f() { }
     //~^ WARN crate-level attribute should be an inner attribute
-    //~| HELP add a `!`
+    //~| NOTE This attribute does not have an `!`, which means it is applied to this function
 
     #[no_std] struct S;
     //~^ WARN crate-level attribute should be an inner attribute
-    //~| HELP add a `!`
+    //~| NOTE This attribute does not have an `!`, which means it is applied to this struct
 
     #[no_std] type T = S;
     //~^ WARN crate-level attribute should be an inner attribute
-    //~| HELP add a `!`
+    //~| NOTE This attribute does not have an `!`, which means it is applied to this type alias
 
     #[no_std] impl S { }
     //~^ WARN crate-level attribute should be an inner attribute
-    //~| HELP add a `!`
+    //~| NOTE This attribute does not have an `!`, which means it is applied to this implementation block
 }
 
 // At time of authorship, #[proc_macro_derive = "2500"] signals error