Add a future incompat warning for #[no_link]

This is a pre-1.0 attribute that accidentally got stabilized. It was
only meant for compiler plugins which we no longer support, not for
regular crates. It is rather fragile and can easily lead to linker
errors depending on where rustc decides to codegen functions and
statics, which varies between rustc versions. It might also be unsound
if a crate for example expects a global constructor it defined to run.
Using it doesn't have an effect on the size of the produced binaries
except when it defines a `#[used]` static given that we remove all
unused functions and statics at link time already.

Author: bjorn3

compiler/rustc_attr_parsing/src/attributes/no_link.rs

@@ -1,6 +1,8 @@
 use rustc_feature::AttributeStability;
+use rustc_lint_defs::builtin::NO_LINK_ATTRIBUTES;
 
 use super::prelude::*;
+use crate::diagnostics::NoLinkAttrUsed;
 
 pub(crate) struct NoLinkParser;
 impl NoArgsAttributeParser for NoLinkParser {
@@ -14,4 +16,8 @@ impl NoArgsAttributeParser for NoLinkParser {
     ]);
     const STABILITY: AttributeStability = AttributeStability::Stable;
     const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::NoLink;
+
+    fn finalize_check(cx: &mut FinalizeCheckContext<'_, '_>, attr_span: Span) {
+        cx.emit_lint(NO_LINK_ATTRIBUTES, NoLinkAttrUsed, attr_span);
+    }
 }

compiler/rustc_attr_parsing/src/diagnostics.rs

@@ -2132,3 +2132,7 @@ pub(crate) enum MacroExport {
     #[note("declarative macros follow the same exporting rules as regular items")]
     OnDeclMacro,
 }
+
+#[derive(Diagnostic)]
+#[diag("use of deprecated `no_link` attribute")]
+pub(crate) struct NoLinkAttrUsed;

compiler/rustc_lint_defs/src/builtin.rs

@@ -83,6 +83,7 @@ pub mod hardwired {
             NEVER_TYPE_FALLBACK_FLOWING_INTO_UNSAFE,
             NON_CONTIGUOUS_RANGE_ENDPOINTS,
             NON_EXHAUSTIVE_OMITTED_PATTERNS,
+            NO_LINK_ATTRIBUTES,
             OUT_OF_SCOPE_MACRO_CALLS,
             OVERLAPPING_RANGE_ENDPOINTS,
             PARTIAL_STACK_PROTECTOR,
@@ -6019,3 +6020,35 @@ declare_lint! {
     r#"detects default field values on types that have const parameters"#,
     @feature_gate = default_field_values;
 }
+
+declare_lint! {
+    /// The `no_link_attr_used` lint detects that you used `#[no_link]` on an
+    /// `extern crate` item.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #[no_link]
+    /// extern crate std;
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// This is a pre-1.0 attribute that accidentally got stabilized. It was only meant
+    /// for compiler plugins which we no longer support, not for regular crates. It is
+    /// rather fragile and can easily lead to linker errors depending on where rustc
+    /// decides to codegen functions and statics, which varies between rustc versions. It
+    /// might also be unsound if a crate for example expects a global constructor it
+    /// defined to run. Using it doesn't have an effect on the size of the produced
+    /// binaries except when it defines a `#[used]` static given that we remove all unused
+    /// functions and statics at link time already.
+    pub NO_LINK_ATTRIBUTES,
+    Deny,
+    "detects usage of `#[no_link]` on `extern crate` items",
+    @future_incompatible = FutureIncompatibleInfo {
+        reason: fcw!(FutureReleaseError #164032),
+        report_in_deps: true,
+    };
+}

tests/ui/attributes/malformed-attrs.rs

@@ -207,6 +207,8 @@ static mut TLS: u8 = 42;
 
 #[no_link()]
 //~^ ERROR malformed
+//~| ERROR use of deprecated `no_link` attribute
+//~| WARN this was previously accepted by the compiler
 #[macro_use = 1]
 //~^ ERROR malformed
 extern crate wloop;

tests/ui/attributes/malformed-attrs.stderr

@@ -23,7 +23,7 @@ LL | #[cfg_attr(predicate, attr1, attr2, ...)]
    |           ++++++++++++++++++++++++++++++
 
 error[E0463]: can't find crate for `wloop`
-  --> $DIR/malformed-attrs.rs:212:1
+  --> $DIR/malformed-attrs.rs:214:1
    |
 LL | extern crate wloop;
    | ^^^^^^^^^^^^^^^^^^^ can't find crate
@@ -783,7 +783,7 @@ LL + #[no_link]
    |
 
 error[E0539]: malformed `macro_use` attribute input
-  --> $DIR/malformed-attrs.rs:210:3
+  --> $DIR/malformed-attrs.rs:212:3
    |
 LL | #[macro_use = 1]
    |   ^^^^^^^^^^---
@@ -801,7 +801,7 @@ LL + #[macro_use(name1, name2, ...)]
    |
 
 error[E0539]: malformed `macro_export` attribute input
-  --> $DIR/malformed-attrs.rs:215:3
+  --> $DIR/malformed-attrs.rs:217:3
    |
 LL | #[macro_export = 18]
    |   ^^^^^^^^^^^^^----
@@ -818,7 +818,7 @@ LL + #[macro_export(local_inner_macros)]
    |
 
 error[E0658]: the `allow_internal_unsafe` attribute side-steps the `unsafe_code` lint
-  --> $DIR/malformed-attrs.rs:217:3
+  --> $DIR/malformed-attrs.rs:219:3
    |
 LL | #[allow_internal_unsafe = 1]
    |   ^^^^^^^^^^^^^^^^^^^^^
@@ -827,7 +827,7 @@ LL | #[allow_internal_unsafe = 1]
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
 error[E0565]: malformed `allow_internal_unsafe` attribute input
-  --> $DIR/malformed-attrs.rs:217:3
+  --> $DIR/malformed-attrs.rs:219:3
    |
 LL | #[allow_internal_unsafe = 1]
    |   ^^^^^^^^^^^^^^^^^^^^^^---
@@ -964,8 +964,18 @@ LL | #[automatically_derived = 18]
    = help: the `automatically_derived` attribute can only be applied to trait impl blocks
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
 
+error: use of deprecated `no_link` attribute
+  --> $DIR/malformed-attrs.rs:208:1
+   |
+LL | #[no_link()]
+   | ^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
+   = note: `#[deny(no_link_attributes)]` (part of `#[deny(future_incompatible)]`) on by default
+
 error: valid forms for the attribute are `ignore` and `ignore = "reason"`
-  --> $DIR/malformed-attrs.rs:224:3
+  --> $DIR/malformed-attrs.rs:226:3
    |
 LL | #[ignore = 1]
    |   ^^^^^^^^^^
@@ -984,7 +994,7 @@ LL |     #[coroutine = 63] || {}
    = note: expected unit type `()`
               found coroutine `{coroutine@$DIR/malformed-attrs.rs:117:23: 117:25}`
 
-error: aborting due to 74 previous errors; 8 warnings emitted
+error: aborting due to 75 previous errors; 8 warnings emitted
 
 Some errors have detailed explanations: E0308, E0463, E0539, E0565, E0658, E0805.
 For more information about an error, try `rustc --explain E0308`.
@@ -1010,9 +1020,20 @@ LL | #[ignore()]
    = note: for more information, see issue #57571 <https://github.com/rust-lang/rust/issues/57571>
    = note: `#[deny(ill_formed_attribute_input)]` (part of `#[deny(future_incompatible)]`) on by default
 
+Future breakage diagnostic:
+error: use of deprecated `no_link` attribute
+  --> $DIR/malformed-attrs.rs:208:1
+   |
+LL | #[no_link()]
+   | ^^^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
+   = note: `#[deny(no_link_attributes)]` (part of `#[deny(future_incompatible)]`) on by default
+
 Future breakage diagnostic:
 error: valid forms for the attribute are `ignore` and `ignore = "reason"`
-  --> $DIR/malformed-attrs.rs:224:3
+  --> $DIR/malformed-attrs.rs:226:3
    |
 LL | #[ignore = 1]
    |   ^^^^^^^^^^

tests/ui/attributes/no_link/auxiliary/no_link-crate.rs

@@ -1,6 +1,7 @@
 //@ no-prefer-dynamic
 
 #![crate_type = "rlib"]
+#![warn(no_link_attributes)]
 
 #[macro_use] #[no_link] extern crate empty_crate_1 as t1;
 #[macro_use] extern crate empty_crate_2 as t2;

tests/ui/attributes/no_link/no-link-struct.rs

@@ -1,7 +1,11 @@
 //@ check-pass
 //@ aux-build:empty-struct.rs
 
+#![warn(no_link_attributes)]
+
 #[no_link]
+//~^ WARN use of deprecated `no_link` attribute
+//~| WARN this was previously accepted by the compiler
 extern crate empty_struct;
 
 fn main() {

tests/ui/attributes/no_link/no-link-struct.stderr

@@ -0,0 +1,31 @@
+warning: use of deprecated `no_link` attribute
+  --> $DIR/no-link-struct.rs:6:1
+   |
+LL | #[no_link]
+   | ^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
+note: the lint level is defined here
+  --> $DIR/no-link-struct.rs:4:9
+   |
+LL | #![warn(no_link_attributes)]
+   |         ^^^^^^^^^^^^^^^^^^
+
+warning: 1 warning emitted
+
+Future incompatibility report: Future breakage diagnostic:
+warning: use of deprecated `no_link` attribute
+  --> $DIR/no-link-struct.rs:6:1
+   |
+LL | #[no_link]
+   | ^^^^^^^^^^
+   |
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
+note: the lint level is defined here
+  --> $DIR/no-link-struct.rs:4:9
+   |
+LL | #![warn(no_link_attributes)]
+   |         ^^^^^^^^^^^^^^^^^^
+

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

@@ -29,6 +29,10 @@
 //~| WARN previously accepted
 #![no_link]
 //~^ ERROR: the `no_link` attribute cannot be used on crates
+//~| ERROR use of deprecated `no_link` attribute
+//~| WARN this was previously accepted by the compiler
+//~| NOTE `#[deny(no_link_attributes)]` (part of `#[deny(future_incompatible)]`) on by default
+//~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
 #![export_name = "2200"]
 //~^ ERROR: attribute cannot be used on
 //~| NOTE takes precedence
@@ -58,38 +62,65 @@ mod inline {
 
 #[no_link]
 //~^ ERROR the `no_link` attribute cannot be used on modules
+//~| ERROR use of deprecated `no_link` attribute
+//~| WARN this was previously accepted by the compiler
+//~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
 mod no_link {
     mod inner { #![no_link] }
     //~^ ERROR the `no_link` attribute cannot be used on modules
+    //~| ERROR use of deprecated `no_link` attribute
+    //~| WARN this was previously accepted by the compiler
+    //~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
 
     #[no_link] fn f() {
         //~^ ERROR the `no_link` attribute cannot be used on functions
+        //~| ERROR use of deprecated `no_link` attribute
+        //~| WARN this was previously accepted by the compiler
+        //~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
         match () {
             #[no_link]
             //~^ WARN the `no_link` attribute cannot be used on match arms [unused_attributes]
             //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+            //~| ERROR use of deprecated `no_link` attribute
+            //~| WARN this was previously accepted by the compiler
+            //~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
             _ => ()
         }
     }
 
     #[no_link]
     //~^ ERROR the `no_link` attribute cannot be used on structs
+    //~| ERROR use of deprecated `no_link` attribute
+    //~| WARN this was previously accepted by the compiler
+    //~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
     struct S {
         #[no_link]
         //~^ WARN the `no_link` attribute cannot be used on struct fields [unused_attributes]
         //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+        //~| ERROR use of deprecated `no_link` attribute
+        //~| WARN this was previously accepted by the compiler
+        //~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
         field: ()
     }
 
     #[no_link]type T = S;
     //~^ ERROR the `no_link` attribute cannot be used on type aliases
+    //~| ERROR use of deprecated `no_link` attribute
+    //~| WARN this was previously accepted by the compiler
+    //~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
 
     #[no_link] impl S { }
     //~^ ERROR the `no_link` attribute cannot be used on inherent impl blocks
+    //~| ERROR use of deprecated `no_link` attribute
+    //~| WARN this was previously accepted by the compiler
+    //~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
 
     #[no_link]
     //~^ WARN the `no_link` attribute cannot be used on macro defs
     //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    //~| ERROR use of deprecated `no_link` attribute
+    //~| WARN this was previously accepted by the compiler
+    //~| NOTE for more information, see issue #164032 <https://github.com/rust-lang/rust/issues/164032>
     macro_rules! m{() => {}}
 }