Report the configured Polonius default in -Z help

compiler/rustc_session/src/config.rs

@@ -3647,11 +3647,14 @@ pub enum Polonius {
 
 impl Default for Polonius {
     fn default() -> Self {
-        if option_env!("CFG_DEFAULT_POLONIUS_NEXT").is_some() { Self::Next } else { Self::Off }
+        Self::DEFAULT
     }
 }
 
 impl Polonius {
+    pub(crate) const DEFAULT: Self =
+        if option_env!("CFG_DEFAULT_POLONIUS_NEXT").is_some() { Self::Next } else { Self::Off };
+
     /// Returns whether the legacy version of polonius is enabled
     pub fn is_legacy_enabled(&self) -> bool {
         matches!(self, Polonius::Legacy)

compiler/rustc_session/src/options.rs

@@ -510,7 +510,7 @@ macro_rules! options {
                 $( { TARGET_MODIFIER: $tmod_variant:ident } )?
                 $( { MITIGATION: $mitigation_variant:ident } )?
                 ,
-                $desc:literal
+                $desc:expr
                 $(, removed: $removed:ident )?
             ),
         )*
@@ -2350,6 +2350,12 @@ options! {
     // - src/doc/rustc/src/codegen-options/index.md
 }
 
+const POLONIUS_HELP: &str = match Polonius::DEFAULT {
+    Polonius::Off => "enable polonius-based borrow-checker (default: no)",
+    Polonius::Next => "enable polonius-based borrow-checker (default: next)",
+    Polonius::Legacy => panic!("Polonius::Legacy is not a valid default value"),
+};
+
 options! {
     UnstableOptions, UnstableOptionsTargetModifiers, Z_OPTIONS, dbopts, "Z", "unstable",
 
@@ -2750,7 +2756,7 @@ options! {
         `vt-ptr-type-discrimination - incorporate type discrimination in authenticated vtable pointers
         Example: `-Zpointer-authentication=+calls,-init-fini`."),
     polonius: Polonius = (Polonius::default(), parse_polonius, [TRACKED],
-        "enable polonius-based borrow-checker (default: no)"),
+        POLONIUS_HELP),
     pre_link_arg: (/* redirected to pre_link_args */) = ((), parse_string_push, [UNTRACKED],
         "a single extra argument to prepend the linker invocation (can be used several times)"),
     pre_link_args: Vec<String> = (Vec::new(), parse_list, [UNTRACKED],

tests/run-make/rustc-help/polonius-help-stable.stdout

@@ -0,0 +1 @@
+    -Z                                      polonius=val -- enable polonius-based borrow-checker (default: no)

tests/run-make/rustc-help/polonius-help.stdout

@@ -0,0 +1 @@
+    -Z                                      polonius=val -- enable polonius-based borrow-checker (default: next)

tests/run-make/rustc-help/rmake.rs

@@ -5,6 +5,7 @@ use run_make_support::{bare_rustc, diff, similar};
 fn main() {
     // `rustc --help`
     let help = bare_rustc().arg("--help").run().stdout_utf8();
+
     diff().expected_file("help.stdout").actual_text("(rustc --help)", &help).run();
 
     // `rustc` should be the same as `rustc --help`
@@ -22,6 +23,20 @@ fn main() {
     // Check that all help options can be invoked at once
     let codegen_help = bare_rustc().arg("-Chelp").run().stdout_utf8();
     let unstable_help = bare_rustc().arg("-Zhelp").run().stdout_utf8();
+
+    let polonius_help =
+        format!("{}\n", unstable_help.lines().find(|line| line.contains("polonius=val")).unwrap());
+    let version = bare_rustc().arg("--version").run().stdout_utf8();
+    let expected_file = if version.contains("-nightly") || version.contains("-dev") {
+        "polonius-help.stdout"
+    } else {
+        "polonius-help-stable.stdout"
+    };
+    diff()
+        .expected_file(expected_file)
+        .actual_text("rustc -Zhelp (polonius)", &polonius_help)
+        .run();
+
     let lints_help = bare_rustc().arg("-Whelp").run().stdout_utf8();
     let expected_all = format!("{help}{codegen_help}{unstable_help}{lints_help}");
     let all_help = bare_rustc().args(["--help", "-Chelp", "-Zhelp", "-Whelp"]).run().stdout_utf8();