Allow #[deny] inside #[forbid] as a no-op with a warning

compiler/rustc_error_codes/src/error_codes/E0453.md

@@ -1,3 +1,5 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 A lint check attribute was overruled by a `forbid` directive set as an
 attribute on an enclosing scope, or on the command line with the `-F` option.
 

compiler/rustc_lint/src/errors.rs

@@ -6,18 +6,6 @@ use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::lint::Level;
 use rustc_span::{Span, Symbol};
 
-#[derive(Diagnostic)]
-#[diag(lint_overruled_attribute, code = E0453)]
-pub struct OverruledAttribute<'a> {
-    #[primary_span]
-    pub span: Span,
-    #[label]
-    pub overruled: Span,
-    pub lint_level: &'a str,
-    pub lint_source: Symbol,
-    #[subdiagnostic]
-    pub sub: OverruledAttributeSub,
-}
 //
 pub enum OverruledAttributeSub {
     DefaultSource { id: String },

compiler/rustc_lint/src/levels.rs

@@ -9,8 +9,9 @@ use crate::{
     fluent_generated as fluent,
     late::unerased_lint_store,
     lints::{
-        DeprecatedLintName, IgnoredUnlessCrateSpecified, OverruledAttributeLint, RemovedLint,
-        RenamedLint, RenamedLintSuggestion, UnknownLint, UnknownLintSuggestion,
+        DeprecatedLintName, IgnoredUnlessCrateSpecified, OverruledAttributeFcw,
+        OverruledAttributeLint, RemovedLint, RenamedLint, RenamedLintSuggestion, UnknownLint,
+        UnknownLintSuggestion,
     },
 };
 use rustc_ast as ast;
@@ -29,6 +30,7 @@ use rustc_middle::lint::{
 };
 use rustc_middle::query::Providers;
 use rustc_middle::ty::{RegisteredTools, TyCtxt};
+use rustc_session::lint::builtin::UNOVERRIDABLE_LINT_LEVEL;
 use rustc_session::lint::{
     builtin::{
         self, FORBIDDEN_LINT_GROUPS, RENAMED_AND_REMOVED_LINTS, SINGLE_USE_LIFETIMES,
@@ -42,8 +44,7 @@ use rustc_span::symbol::{sym, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 
 use crate::errors::{
-    MalformedAttribute, MalformedAttributeSub, OverruledAttribute, OverruledAttributeSub,
-    UnknownToolInScopedLint,
+    MalformedAttribute, MalformedAttributeSub, OverruledAttributeSub, UnknownToolInScopedLint,
 };
 
 /// Collection of lint levels for the whole crate.
@@ -637,11 +638,13 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
         {
             *id = id.normalize();
         }
-        // Setting to a non-forbid level is an error if the lint previously had
+        // Setting to a non-forbid level is a mistake if the lint previously had
         // a forbid level. Note that this is not necessarily true even with a
         // `#[forbid(..)]` attribute present, as that is overridden by `--cap-lints`.
+        // While this could be a hard error (and was in the past), this causes issues
+        // with macros expanding to deny() in contexts where it's already forbid().
         //
-        // This means that this only errors if we're truly lowering the lint
+        // This means that this only warns if we're truly lowering the lint
         // level from forbid.
         if self.lint_added_lints && level != Level::Forbid {
             if let Level::Forbid = old_level {
@@ -674,18 +677,21 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
                     LintLevelSource::CommandLine(_, _) => OverruledAttributeSub::CommandLineSource,
                 };
                 if !fcw_warning {
-                    self.sess.dcx().emit_err(OverruledAttribute {
-                        span: src.span(),
-                        overruled: src.span(),
-                        lint_level: level.as_str(),
-                        lint_source: src.name(),
-                        sub,
-                    });
+                    self.emit_span_lint(
+                        UNOVERRIDABLE_LINT_LEVEL,
+                        src.span().into(),
+                        OverruledAttributeLint {
+                            overruled: src.span(),
+                            lint_level: level.as_str(),
+                            lint_source: src.name(),
+                            sub,
+                        },
+                    );
                 } else {
                     self.emit_span_lint(
                         FORBIDDEN_LINT_GROUPS,
                         src.span().into(),
-                        OverruledAttributeLint {
+                        OverruledAttributeFcw {
                             overruled: src.span(),
                             lint_level: level.as_str(),
                             lint_source: src.name(),

compiler/rustc_lint/src/lints.rs

@@ -991,6 +991,17 @@ impl AddToDiagnostic for NonBindingLetSub {
 // levels.rs
 #[derive(LintDiagnostic)]
 #[diag(lint_overruled_attribute)]
+pub struct OverruledAttributeFcw<'a> {
+    #[label]
+    pub overruled: Span,
+    pub lint_level: &'a str,
+    pub lint_source: Symbol,
+    #[subdiagnostic]
+    pub sub: OverruledAttributeSub,
+}
+
+#[derive(LintDiagnostic)]
+#[diag(lint_overruled_attribute, code = E0453)]
 pub struct OverruledAttributeLint<'a> {
     #[label]
     pub overruled: Span,

compiler/rustc_lint_defs/src/builtin.rs

@@ -166,7 +166,7 @@ declare_lint! {
     Warn,
     "applying forbid to lint-groups",
     @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
+        reason: FutureIncompatibilityReason::FutureReleaseSemanticsChange,
         reference: "issue #81670 <https://github.com/rust-lang/rust/issues/81670>",
     };
 }
@@ -4534,3 +4534,30 @@ declare_lint! {
         reference: "issue #120192 <https://github.com/rust-lang/rust/issues/120192>",
     };
 }
+
+declare_lint! {
+    /// The `unoverridable_lint_level` lint detects attempts at overriding a `forbid()`
+    /// lint. This does **nothing**, as `forbid()` cannot be overridden.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #![forbid(unsafe_code)]
+    ///
+    /// #[deny(unsafe_code)]
+    /// fn main() {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Then `forbid()` is used on a lint, this lint is guaranteed to be a hard error
+    /// and cannot be overriden. But because macros may use their own `deny()` in their
+    /// expanded output, which might get expanded into a context that is `forbid()` already,
+    /// this is not a hard error.
+    /// As lints in macros are suppressed, so this lint will not show up in these cases.
+    pub UNOVERRIDABLE_LINT_LEVEL,
+    Warn,
+    "attempting to overriding a forbid lint",
+}

tests/ui/lint/auxiliary/deny-macro.rs

@@ -0,0 +1,7 @@
+#[macro_export]
+macro_rules! emit_deny {
+    () => {
+        #[deny(unsafe_code)]
+        let _so_safe = 0;
+    };
+}

tests/ui/lint/forbid-group-group-2.rs

@@ -6,9 +6,9 @@
 
 #[allow(nonstandard_style)]
 //~^ ERROR incompatible with previous
-//~| WARNING previously accepted by the compiler
+//~| WARNING this will change its meaning in a future release!
 //~| ERROR incompatible with previous
-//~| WARNING previously accepted by the compiler
+//~| WARNING this will change its meaning in a future release!
 //~| ERROR incompatible with previous
-//~| WARNING previously accepted by the compiler
+//~| WARNING this will change its meaning in a future release!
 fn main() {}

tests/ui/lint/forbid-group-group-2.stderr

@@ -7,7 +7,7 @@ LL | #![forbid(warnings)]
 LL | #[allow(nonstandard_style)]
    |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this will change its meaning in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
 note: the lint level is defined here
   --> $DIR/forbid-group-group-2.rs:5:9
@@ -24,7 +24,7 @@ LL | #![forbid(warnings)]
 LL | #[allow(nonstandard_style)]
    |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this will change its meaning in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
@@ -37,7 +37,7 @@ LL | #![forbid(warnings)]
 LL | #[allow(nonstandard_style)]
    |         ^^^^^^^^^^^^^^^^^ overruled by previous forbid
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this will change its meaning in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 

tests/ui/lint/forbid-group-member.rs

@@ -7,7 +7,7 @@
 
 #[allow(unused_variables)]
 //~^ WARNING incompatible with previous forbid
-//~| WARNING previously accepted
+//~| WARNING this will change its meaning in a future release!
 fn main() {
     let a: ();
 }

tests/ui/lint/forbid-group-member.stderr

@@ -7,7 +7,7 @@ LL |
 LL | #[allow(unused_variables)]
    |         ^^^^^^^^^^^^^^^^ overruled by previous forbid
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this will change its meaning in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
    = note: `#[warn(forbidden_lint_groups)]` on by default
 

tests/ui/lint/forbid-member-group.rs

@@ -1,10 +1,11 @@
 // Check what happens when we forbid a member of
 // a group but then allow the group.
+//@ check-pass
 
 #![forbid(unused_variables)]
 
 #[allow(unused)]
-//~^ ERROR incompatible with previous forbid
+//~^ WARNING incompatible with previous forbid
 fn main() {
     let a: ();
 }

tests/ui/lint/forbid-member-group.stderr

@@ -1,12 +1,14 @@
-error[E0453]: allow(unused) incompatible with previous forbid
-  --> $DIR/forbid-member-group.rs:6:9
+warning[E0453]: allow(unused) incompatible with previous forbid
+  --> $DIR/forbid-member-group.rs:7:9
    |
 LL | #![forbid(unused_variables)]
    |           ---------------- `forbid` level set here
 LL |
 LL | #[allow(unused)]
    |         ^^^^^^ overruled by previous forbid
+   |
+   = note: `#[warn(unoverridable_lint_level)]` on by default
 
-error: aborting due to 1 previous error
+warning: 1 warning emitted
 
 For more information about this error, try `rustc --explain E0453`.

tests/ui/lint/forbid-with-macro-deny.rs

@@ -0,0 +1,10 @@
+//@ aux-build:deny-macro.rs
+//@ check-pass
+
+#![forbid(unsafe_code)]
+
+extern crate deny_macro;
+
+fn main() {
+    deny_macro::emit_deny! {}
+}

tests/ui/lint/issue-70819-dont-override-forbid-in-same-scope.rs

@@ -20,7 +20,7 @@ fn forbid_first(num: i32) -> i32 {
     #![forbid(unused)]
     #![deny(unused)]
     //~^ ERROR: deny(unused) incompatible with previous forbid
-    //~| WARNING being phased out
+    //~| WARNING this will change its meaning in a future release!
     #![warn(unused)]
     #![allow(unused)]
 

tests/ui/lint/issue-70819-dont-override-forbid-in-same-scope.stderr

@@ -6,7 +6,7 @@ LL |     #![forbid(unused)]
 LL |     #![deny(unused)]
    |             ^^^^^^ overruled by previous forbid
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this will change its meaning in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
 note: the lint level is defined here
   --> $DIR/issue-70819-dont-override-forbid-in-same-scope.rs:17:11

tests/ui/lint/issue-80988.rs

@@ -6,5 +6,5 @@
 
 #[deny(warnings)]
 //~^ WARNING incompatible with previous forbid
-//~| WARNING being phased out
+//~| WARNING this will change its meaning in a future release!
 fn main() {}

tests/ui/lint/issue-80988.stderr

@@ -7,7 +7,7 @@ LL |
 LL | #[deny(warnings)]
    |        ^^^^^^^^ overruled by previous forbid
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = warning: this will change its meaning in a future release!
    = note: for more information, see issue #81670 <https://github.com/rust-lang/rust/issues/81670>
    = note: `#[warn(forbidden_lint_groups)]` on by default
 

tests/ui/lint/lint-forbid-attr.rs

@@ -1,6 +1,7 @@
+//@ check-pass
 #![forbid(deprecated)]
 
 #[allow(deprecated)]
-//~^ ERROR allow(deprecated) incompatible
+//~^ WARNING allow(deprecated) incompatible
 fn main() {
 }

tests/ui/lint/lint-forbid-attr.stderr

@@ -1,12 +1,14 @@
-error[E0453]: allow(deprecated) incompatible with previous forbid
-  --> $DIR/lint-forbid-attr.rs:3:9
+warning[E0453]: allow(deprecated) incompatible with previous forbid
+  --> $DIR/lint-forbid-attr.rs:4:9
    |
 LL | #![forbid(deprecated)]
    |           ---------- `forbid` level set here
 LL |
 LL | #[allow(deprecated)]
    |         ^^^^^^^^^^ overruled by previous forbid
+   |
+   = note: `#[warn(unoverridable_lint_level)]` on by default
 
-error: aborting due to 1 previous error
+warning: 1 warning emitted
 
 For more information about this error, try `rustc --explain E0453`.

tests/ui/lint/lint-forbid-cmdline.rs

@@ -1,5 +1,6 @@
 //@ compile-flags: -F deprecated
+//@ check-pass
 
-#[allow(deprecated)] //~ ERROR allow(deprecated) incompatible
+#[allow(deprecated)] //~ WARNING allow(deprecated) incompatible
 fn main() {
 }

tests/ui/lint/lint-forbid-cmdline.stderr

@@ -1,11 +1,12 @@
-error[E0453]: allow(deprecated) incompatible with previous forbid
-  --> $DIR/lint-forbid-cmdline.rs:3:9
+warning[E0453]: allow(deprecated) incompatible with previous forbid
+  --> $DIR/lint-forbid-cmdline.rs:4:9
    |
 LL | #[allow(deprecated)]
    |         ^^^^^^^^^^ overruled by previous forbid
    |
    = note: `forbid` lint level was set on command line
+   = note: `#[warn(unoverridable_lint_level)]` on by default
 
-error: aborting due to 1 previous error
+warning: 1 warning emitted
 
 For more information about this error, try `rustc --explain E0453`.

tests/ui/lint/outer-forbid.rs

@@ -19,14 +19,15 @@
 
 #[allow(unused_variables)]
 //~^ ERROR incompatible with previous
-//~| WARNING this was previously accepted by the compiler
+//~| WARNING this will change its meaning in a future release!
 fn foo() {}
+//~^ ERROR function `foo` is never used
 
 #[allow(unused)] //~ ERROR incompatible with previous
-//~^ WARNING this was previously accepted by the compiler
+//~^ WARNING this will change its meaning in a future release!
 fn bar() {}
 
-#[allow(nonstandard_style)] //~ ERROR incompatible with previous
+#[allow(nonstandard_style)] //~ WARNING incompatible with previous
 fn main() {
     println!("hello forbidden world")
 }