emit unreachable pattern lint

compiler/rustc_hir/src/attrs/mod.rs

@@ -77,8 +77,11 @@ macro_rules! find_attr {
                     rustc_hir::Attribute::Parsed($pattern) $(if $guard)? => {
                         break 'done Some($e);
                     }
-                    // FIXME: doesn't actually trigger in other crates :/
-                    // https://github.com/rust-lang/rust/issues/110613
+                    rustc_hir::Attribute::Unparsed(..) => {}
+                    // In lint emitting, there's a specific exception for this warning.
+                    // It's not usually emitted from inside macros from other crates
+                    // (see https://github.com/rust-lang/rust/issues/110613)
+                    // But this one is!
                     #[deny(unreachable_patterns)]
                     _ => {}
                 }

compiler/rustc_middle/src/lint.rs

@@ -9,7 +9,7 @@
 use rustc_session::Session;
 use rustc_session::lint::builtin::{self, FORBIDDEN_LINT_GROUPS};
 use rustc_session::lint::{FutureIncompatibilityReason, Level, Lint, LintExpectationId, LintId};
-use rustc_span::{DUMMY_SP, Span, Symbol, kw};
+use rustc_span::{DUMMY_SP, ExpnKind, Span, Symbol, kw};
 use tracing::instrument;
 
 use crate::ty::TyCtxt;
@@ -380,7 +380,17 @@ fn lint_level_impl(
             // allow individual lints to opt-out from being reported.
             let incompatible = future_incompatible.is_some_and(|f| f.reason.edition().is_none());
 
-            if !incompatible && !lint.report_in_external_macro {
+            // In rustc, for the find_attr macro, we want to always emit this.
+            // This completely circumvents normal lint checking, which usually doesn't happen for macros from other crates.
+            // However, we kind of want that when using find_attr from another rustc crate. So we cheat a little.
+            let is_in_find_attr = sess.enable_internal_lints()
+                && err.span.primary_spans().iter().any(|s| {
+                    s.source_callee().is_some_and(
+                    |i| matches!(i.kind, ExpnKind::Macro(_, name) if name.as_str() == "find_attr")
+                    )
+                });
+
+            if !incompatible && !lint.report_in_external_macro && !is_in_find_attr {
                 err.cancel();
 
                 // Don't continue further, since we don't want to have

tests/ui-fulldeps/internal-lints/find_attr.rs

@@ -21,4 +21,7 @@ fn main() {
     //~^ ERROR use of `AttributeKind` in `find_attr!(...)` invocation
     find_attr!(attrs, AttributeKind::Inline(..) if true => todo!());
     //~^ ERROR use of `AttributeKind` in `find_attr!(...)` invocation
+
+    find_attr!(attrs, wildcard);
+    //~^ ERROR unreachable pattern
 }

tests/ui-fulldeps/internal-lints/find_attr.stderr

@@ -48,5 +48,27 @@ LL |     find_attr!(attrs, AttributeKind::Inline(..) if true => todo!());
    = note: `find_attr!(...)` already imports `AttributeKind::*`
    = help: remote `AttributeKind`
 
-error: aborting due to 5 previous errors
+error: unreachable pattern
+  --> $DIR/find_attr.rs:25:5
+   |
+LL |     find_attr!(attrs, wildcard);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^ no value can reach this
+   |
+note: multiple earlier patterns match some of the same values
+  --> $DIR/find_attr.rs:25:5
+   |
+LL |     find_attr!(attrs, wildcard);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |     |
+   |     matches some of the same values
+   |     matches some of the same values
+   |     collectively making this unreachable
+note: the lint level is defined here
+  --> $DIR/find_attr.rs:25:5
+   |
+LL |     find_attr!(attrs, wildcard);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: this error originates in the macro `$crate::find_attr` which comes from the expansion of the macro `find_attr` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 6 previous errors