Auto merge of #96085 - jsgf:deny-unused-deps, r=compiler-errors

Make sure `-Dunused-crate-dependencies --json unused-externs` makes rustc exit with error status

This PR:
- fixes compiletest to understand unused extern notifications
- adds tests for `--json unused-externs`
- makes sure that deny-level unused externs notifications are treated as compile errors
  - refactors the `emit_unused_externs` callstack to plumb through the level as an enum as a string, and adds `Level::is_error`

Update: adds `--json unused-externs-silent` with the original behaviour since Cargo needs it. Should address `@est31's` concerns.

Fixes: https://github.com/rust-lang/rust/issues/96068

3 files changed, 22 insertions, 5 deletions

diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 47cdf39cd52..5dd743e8d00 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -212,7 +212,12 @@ pub trait Emitter {
     fn emit_future_breakage_report(&mut self, _diags: Vec<Diagnostic>) {}
 
     /// Emit list of unused externs
-    fn emit_unused_externs(&mut self, _lint_level: &str, _unused_externs: &[&str]) {}
+    fn emit_unused_externs(
+        &mut self,
+        _lint_level: rustc_lint_defs::Level,
+        _unused_externs: &[&str],
+    ) {
+    }
 
     /// Checks if should show explanations about "rustc --explain"
     fn should_show_explain(&self) -> bool {
diff --git a/compiler/rustc_errors/src/json.rs b/compiler/rustc_errors/src/json.rs
index d680e7fab70..6ff52182d6b 100644
--- a/compiler/rustc_errors/src/json.rs
+++ b/compiler/rustc_errors/src/json.rs
@@ -171,7 +171,8 @@ impl Emitter for JsonEmitter {
         }
     }
 
-    fn emit_unused_externs(&mut self, lint_level: &str, unused_externs: &[&str]) {
+    fn emit_unused_externs(&mut self, lint_level: rustc_lint_defs::Level, unused_externs: &[&str]) {
+        let lint_level = lint_level.as_str();
         let data = UnusedExterns { lint_level, unused_extern_names: unused_externs };
         let result = if self.pretty {
             writeln!(&mut self.dst, "{}", as_pretty_json(&data))
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 4e6ab0edf66..a64133bb7f4 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -969,8 +969,19 @@ impl Handler {
         self.inner.borrow_mut().emitter.emit_future_breakage_report(diags)
     }
 
-    pub fn emit_unused_externs(&self, lint_level: &str, unused_externs: &[&str]) {
-        self.inner.borrow_mut().emit_unused_externs(lint_level, unused_externs)
+    pub fn emit_unused_externs(
+        &self,
+        lint_level: rustc_lint_defs::Level,
+        loud: bool,
+        unused_externs: &[&str],
+    ) {
+        let mut inner = self.inner.borrow_mut();
+
+        if loud && lint_level.is_error() {
+            inner.bump_err_count();
+        }
+
+        inner.emit_unused_externs(lint_level, unused_externs)
     }
 
     pub fn update_unstable_expectation_id(
@@ -1141,7 +1152,7 @@ impl HandlerInner {
         self.emitter.emit_artifact_notification(path, artifact_type);
     }
 
-    fn emit_unused_externs(&mut self, lint_level: &str, unused_externs: &[&str]) {
+    fn emit_unused_externs(&mut self, lint_level: rustc_lint_defs::Level, unused_externs: &[&str]) {
         self.emitter.emit_unused_externs(lint_level, unused_externs);
     }