Add --json unused-externs-silent with original behaviour

Since Cargo wants to do its own fatal error handling for unused
dependencies, add the option `--json unused-externs-silent` which
has the original behaviour of not indicating non-zero exit status for
`deny`/`forbid`-level unused dependencies.

4 files changed, 15 insertions, 4 deletions

diff --git a/src/librustdoc/config.rs b/src/librustdoc/config.rs
index cee3dcb416f..1ff2c8191e5 100644
--- a/src/librustdoc/config.rs
+++ b/src/librustdoc/config.rs
@@ -10,7 +10,9 @@ use rustc_session::config::{
     self, parse_crate_types_from_list, parse_externs, parse_target_triple, CrateType,
 };
 use rustc_session::config::{get_cmd_lint_options, nightly_options};
-use rustc_session::config::{CodegenOptions, DebuggingOptions, ErrorOutputType, Externs};
+use rustc_session::config::{
+    CodegenOptions, DebuggingOptions, ErrorOutputType, Externs, JsonUnusedExterns,
+};
 use rustc_session::getopts;
 use rustc_session::lint::Level;
 use rustc_session::search_paths::SearchPath;
@@ -147,7 +149,7 @@ crate struct Options {
     /// documentation.
     crate run_check: bool,
     /// Whether doctests should emit unused externs
-    crate json_unused_externs: bool,
+    crate json_unused_externs: JsonUnusedExterns,
     /// Whether to skip capturing stdout and stderr of tests.
     crate nocapture: bool,
 
diff --git a/src/librustdoc/doctest.rs b/src/librustdoc/doctest.rs
index 45ac16e75aa..82e367427ef 100644
--- a/src/librustdoc/doctest.rs
+++ b/src/librustdoc/doctest.rs
@@ -168,7 +168,7 @@ crate fn run(options: RustdocOptions) -> Result<(), ErrorGuaranteed> {
 
     // Collect and warn about unused externs, but only if we've gotten
     // reports for each doctest
-    if json_unused_externs {
+    if json_unused_externs.is_enabled() {
         let unused_extern_reports: Vec<_> =
             std::mem::take(&mut unused_extern_reports.lock().unwrap());
         if unused_extern_reports.len() == compiling_test_count {
@@ -337,7 +337,7 @@ fn run_test(
     if lang_string.test_harness {
         compiler.arg("--test");
     }
-    if rustdoc_options.json_unused_externs && !lang_string.compile_fail {
+    if rustdoc_options.json_unused_externs.is_enabled() && !lang_string.compile_fail {
         compiler.arg("--error-format=json");
         compiler.arg("--json").arg("unused-externs");
         compiler.arg("-Z").arg("unstable-options");
diff --git a/src/test/ui/unused-crate-deps/deny-cmdline-json-silent.rs b/src/test/ui/unused-crate-deps/deny-cmdline-json-silent.rs
new file mode 100644
index 00000000000..fd9a61d6caa
--- /dev/null
+++ b/src/test/ui/unused-crate-deps/deny-cmdline-json-silent.rs
@@ -0,0 +1,8 @@
+// Check for unused crate dep, json event, deny but we're not reporting that in exit status
+
+// edition:2018
+// check-pass
+// compile-flags: -Dunused-crate-dependencies -Zunstable-options --json unused-externs-silent --error-format=json
+// aux-crate:bar=bar.rs
+
+fn main() {}
diff --git a/src/test/ui/unused-crate-deps/deny-cmdline-json-silent.stderr b/src/test/ui/unused-crate-deps/deny-cmdline-json-silent.stderr
new file mode 100644
index 00000000000..595619f3a8a
--- /dev/null
+++ b/src/test/ui/unused-crate-deps/deny-cmdline-json-silent.stderr
@@ -0,0 +1 @@
+{"lint_level":"deny","unused_extern_names":["bar"]}