Stabilize -Zcheck-cfg as always enabled-by-default

src/cargo/core/compiler/build_runner/mod.rs

@@ -246,7 +246,7 @@ impl<'a, 'gctx> BuildRunner<'a, 'gctx> {
                 let mut args = compiler::extern_args(&self, unit, &mut unstable_opts)?;
                 args.extend(compiler::lto_args(&self, unit));
                 args.extend(compiler::features_args(unit));
-                args.extend(compiler::check_cfg_args(&self, unit));
+                args.extend(compiler::check_cfg_args(unit));
 
                 let script_meta = self.find_build_script_metadata(unit);
                 if let Some(meta) = script_meta {
@@ -256,12 +256,9 @@ impl<'a, 'gctx> BuildRunner<'a, 'gctx> {
                             args.push(cfg.into());
                         }
 
-                        if !output.check_cfgs.is_empty() {
-                            args.push("-Zunstable-options".into());
-                            for check_cfg in &output.check_cfgs {
-                                args.push("--check-cfg".into());
-                                args.push(check_cfg.into());
-                            }
+                        for check_cfg in &output.check_cfgs {
+                            args.push("--check-cfg".into());
+                            args.push(check_cfg.into());
                         }
 
                         for (lt, arg) in &output.linker_args {

src/cargo/core/compiler/custom_build.rs

@@ -408,7 +408,6 @@ fn build_work(build_runner: &mut BuildRunner<'_, '_>, unit: &Unit) -> CargoResul
     paths::create_dir_all(&script_out_dir)?;
 
     let nightly_features_allowed = build_runner.bcx.gctx.nightly_features_allowed;
-    let extra_check_cfg = build_runner.bcx.gctx.cli_unstable().check_cfg;
     let targets: Vec<Target> = unit.pkg.targets().to_vec();
     let msrv = unit.pkg.rust_version().cloned();
     // Need a separate copy for the fresh closure.
@@ -556,7 +555,6 @@ fn build_work(build_runner: &mut BuildRunner<'_, '_>, unit: &Unit) -> CargoResul
             &pkg_descr,
             &script_out_dir,
             &script_out_dir,
-            extra_check_cfg,
             nightly_features_allowed,
             &targets,
             &msrv,
@@ -585,7 +583,6 @@ fn build_work(build_runner: &mut BuildRunner<'_, '_>, unit: &Unit) -> CargoResul
                 &pkg_descr,
                 &prev_script_out_dir,
                 &script_out_dir,
-                extra_check_cfg,
                 nightly_features_allowed,
                 &targets_fresh,
                 &msrv_fresh,
@@ -642,7 +639,6 @@ impl BuildOutput {
         pkg_descr: &str,
         script_out_dir_when_generated: &Path,
         script_out_dir: &Path,
-        extra_check_cfg: bool,
         nightly_features_allowed: bool,
         targets: &[Target],
         msrv: &Option<RustVersion>,
@@ -654,7 +650,6 @@ impl BuildOutput {
             pkg_descr,
             script_out_dir_when_generated,
             script_out_dir,
-            extra_check_cfg,
             nightly_features_allowed,
             targets,
             msrv,
@@ -665,17 +660,13 @@ impl BuildOutput {
     ///
     /// * `pkg_descr` --- for error messages
     /// * `library_name` --- for determining if `RUSTC_BOOTSTRAP` should be allowed
-    /// * `extra_check_cfg` --- for unstable feature [`-Zcheck-cfg`]
-    ///
-    /// [`-Zcheck-cfg`]: https://doc.rust-lang.org/cargo/reference/unstable.html#check-cfg
     pub fn parse(
         input: &[u8],
         // Takes String instead of InternedString so passing `unit.pkg.name()` will give a compile error.
         library_name: Option<String>,
         pkg_descr: &str,
         script_out_dir_when_generated: &Path,
         script_out_dir: &Path,
-        extra_check_cfg: bool,
         nightly_features_allowed: bool,
         targets: &[Target],
         msrv: &Option<RustVersion>,
@@ -908,12 +899,7 @@ impl BuildOutput {
                 }
                 "rustc-cfg" => cfgs.push(value.to_string()),
                 "rustc-check-cfg" => {
-                    if extra_check_cfg {
-                        check_cfgs.push(value.to_string());
-                    } else {
-                        // silently ignoring the instruction to try to
-                        // minimise MSRV annoyance when stabilizing -Zcheck-cfg
-                    }
+                    check_cfgs.push(value.to_string());
                 }
                 "rustc-env" => {
                     let (key, val) = BuildOutput::parse_rustc_env(&value, &whence)?;
@@ -1255,7 +1241,6 @@ fn prev_build_output(
             &unit.pkg.to_string(),
             &prev_script_out_dir,
             &script_out_dir,
-            build_runner.bcx.gctx.cli_unstable().check_cfg,
             build_runner.bcx.gctx.nightly_features_allowed,
             unit.pkg.targets(),
             &unit.pkg.rust_version().cloned(),

src/cargo/core/compiler/fingerprint/mod.rs

@@ -1454,14 +1454,7 @@ fn calculate_normal(
         // actually affect the output artifact so there's no need to hash it.
         path: util::hash_u64(path_args(build_runner.bcx.ws, unit).0),
         features: format!("{:?}", unit.features),
-        // Note we curently only populate `declared_features` when `-Zcheck-cfg`
-        // is passed since it's the only user-facing toggle that will make this
-        // fingerprint relevant.
-        declared_features: if build_runner.bcx.gctx.cli_unstable().check_cfg {
-            format!("{declared_features:?}")
-        } else {
-            "".to_string()
-        },
+        declared_features: format!("{declared_features:?}"),
         deps,
         local: Mutex::new(local),
         memoized_hash: Mutex::new(None),

src/cargo/core/compiler/mod.rs

@@ -732,7 +732,7 @@ fn prepare_rustdoc(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> CargoResu
     let doc_dir = build_runner.files().out_dir(unit);
     rustdoc.arg("-o").arg(&doc_dir);
     rustdoc.args(&features_args(unit));
-    rustdoc.args(&check_cfg_args(build_runner, unit));
+    rustdoc.args(&check_cfg_args(unit));
 
     add_error_format_and_color(build_runner, &mut rustdoc);
     add_allow_features(build_runner, &mut rustdoc);
@@ -1125,7 +1125,7 @@ fn build_base_args(
     }
 
     cmd.args(&features_args(unit));
-    cmd.args(&check_cfg_args(build_runner, unit));
+    cmd.args(&check_cfg_args(unit));
 
     let meta = build_runner.files().metadata(unit);
     cmd.arg("-C").arg(&format!("metadata={}", meta));
@@ -1310,57 +1310,51 @@ fn trim_paths_args(
 }
 
 /// Generates the `--check-cfg` arguments for the `unit`.
-/// See unstable feature [`check-cfg`].
 ///
 /// [`check-cfg`]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#check-cfg
-fn check_cfg_args(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> Vec<OsString> {
-    if build_runner.bcx.gctx.cli_unstable().check_cfg {
-        // The routine below generates the --check-cfg arguments. Our goals here are to
-        // enable the checking of conditionals and pass the list of declared features.
-        //
-        // In the simplified case, it would resemble something like this:
-        //
-        //   --check-cfg=cfg() --check-cfg=cfg(feature, values(...))
-        //
-        // but having `cfg()` is redundant with the second argument (as well-known names
-        // and values are implicitly enabled when one or more `--check-cfg` argument is
-        // passed) so we don't emit it and just pass:
-        //
-        //   --check-cfg=cfg(feature, values(...))
-        //
-        // This way, even if there are no declared features, the config `feature` will
-        // still be expected, meaning users would get "unexpected value" instead of name.
-        // This wasn't always the case, see rust-lang#119930 for some details.
+fn check_cfg_args(unit: &Unit) -> Vec<OsString> {
+    // The routine below generates the --check-cfg arguments. Our goals here are to
+    // enable the checking of conditionals and pass the list of declared features.
+    //
+    // In the simplified case, it would resemble something like this:
+    //
+    //   --check-cfg=cfg() --check-cfg=cfg(feature, values(...))
+    //
+    // but having `cfg()` is redundant with the second argument (as well-known names
+    // and values are implicitly enabled when one or more `--check-cfg` argument is
+    // passed) so we don't emit it and just pass:
+    //
+    //   --check-cfg=cfg(feature, values(...))
+    //
+    // This way, even if there are no declared features, the config `feature` will
+    // still be expected, meaning users would get "unexpected value" instead of name.
+    // This wasn't always the case, see rust-lang#119930 for some details.
 
-        let gross_cap_estimation = unit.pkg.summary().features().len() * 7 + 25;
-        let mut arg_feature = OsString::with_capacity(gross_cap_estimation);
+    let gross_cap_estimation = unit.pkg.summary().features().len() * 7 + 25;
+    let mut arg_feature = OsString::with_capacity(gross_cap_estimation);
 
-        arg_feature.push("cfg(feature, values(");
-        for (i, feature) in unit.pkg.summary().features().keys().enumerate() {
-            if i != 0 {
-                arg_feature.push(", ");
-            }
-            arg_feature.push("\"");
-            arg_feature.push(feature);
-            arg_feature.push("\"");
+    arg_feature.push("cfg(feature, values(");
+    for (i, feature) in unit.pkg.summary().features().keys().enumerate() {
+        if i != 0 {
+            arg_feature.push(", ");
         }
-        arg_feature.push("))");
-
-        // We also include the `docsrs` cfg from the docs.rs service. We include it here
-        // (in Cargo) instead of rustc, since there is a much closer relationship between
-        // Cargo and docs.rs than rustc and docs.rs. In particular, all users of docs.rs use
-        // Cargo, but not all users of rustc (like Rust-for-Linux) use docs.rs.
-
-        vec![
-            OsString::from("-Zunstable-options"),
-            OsString::from("--check-cfg"),
-            OsString::from("cfg(docsrs)"),
-            OsString::from("--check-cfg"),
-            arg_feature,
-        ]
-    } else {
-        Vec::new()
-    }
+        arg_feature.push("\"");
+        arg_feature.push(feature);
+        arg_feature.push("\"");
+    }
+    arg_feature.push("))");
+
+    // We also include the `docsrs` cfg from the docs.rs service. We include it here
+    // (in Cargo) instead of rustc, since there is a much closer relationship between
+    // Cargo and docs.rs than rustc and docs.rs. In particular, all users of docs.rs use
+    // Cargo, but not all users of rustc (like Rust-for-Linux) use docs.rs.
+
+    vec![
+        OsString::from("--check-cfg"),
+        OsString::from("cfg(docsrs)"),
+        OsString::from("--check-cfg"),
+        arg_feature,
+    ]
 }
 
 /// Adds LTO related codegen flags.

src/cargo/core/features.rs

@@ -752,7 +752,6 @@ unstable_cli_options!(
     #[serde(deserialize_with = "deserialize_build_std")]
     build_std: Option<Vec<String>>  = ("Enable Cargo to compile the standard library itself as part of a crate graph compilation"),
     build_std_features: Option<Vec<String>>  = ("Configure features enabled for the standard library itself when building the standard library"),
-    check_cfg: bool = ("Enable compile-time checking of `cfg` names/values/features"),
     codegen_backend: bool = ("Enable the `codegen-backend` option in profiles in .cargo/config.toml file"),
     config_include: bool = ("Enable the `include` key in config files"),
     direct_minimal_versions: bool = ("Resolve minimal dependency versions instead of maximum (direct dependencies only)"),
@@ -854,6 +853,9 @@ const STABILIZED_CREDENTIAL_PROCESS: &str =
 const STABILIZED_REGISTRY_AUTH: &str =
     "Authenticated registries are available if a credential provider is configured.";
 
+const STABILIZED_CHECK_CFG: &str =
+    "Compile-time checking of conditional (a.k.a. `-Zcheck-cfg`) is now always enabled.";
+
 fn deserialize_build_std<'de, D>(deserializer: D) -> Result<Option<Vec<String>>, D::Error>
 where
     D: serde::Deserializer<'de>,
@@ -1107,6 +1109,7 @@ impl CliUnstable {
             "doctest-in-workspace" => stabilized_warn(k, "1.72", STABILIZED_DOCTEST_IN_WORKSPACE),
             "credential-process" => stabilized_warn(k, "1.74", STABILIZED_CREDENTIAL_PROCESS),
             "registry-auth" => stabilized_warn(k, "1.74", STABILIZED_REGISTRY_AUTH),
+            "check-cfg" => stabilized_warn(k, "CURRENT_CARGO_VERSION", STABILIZED_CHECK_CFG),
 
             // Unstable features
             // Sorted alphabetically:
@@ -1119,9 +1122,6 @@ impl CliUnstable {
                 self.build_std = Some(crate::core::compiler::standard_lib::parse_unstable_flag(v))
             }
             "build-std-features" => self.build_std_features = Some(parse_features(v)),
-            "check-cfg" => {
-                self.check_cfg = parse_empty(k, v)?;
-            }
             "codegen-backend" => self.codegen_backend = parse_empty(k, v)?,
             "config-include" => self.config_include = parse_empty(k, v)?,
             "direct-minimal-versions" => self.direct_minimal_versions = parse_empty(k, v)?,

src/cargo/util/context/target.rs

@@ -135,7 +135,7 @@ fn load_config_table(gctx: &GlobalContext, prefix: &str) -> CargoResult<TargetCo
 fn parse_links_overrides(
     target_key: &ConfigKey,
     links: HashMap<String, CV>,
-    gctx: &GlobalContext,
+    _gctx: &GlobalContext,
 ) -> CargoResult<BTreeMap<String, BuildOutput>> {
     let mut links_overrides = BTreeMap::new();
 
@@ -204,13 +204,8 @@ fn parse_links_overrides(
                     output.cfgs.extend(list.iter().map(|v| v.0.clone()));
                 }
                 "rustc-check-cfg" => {
-                    if gctx.cli_unstable().check_cfg {
-                        let list = value.list(key)?;
-                        output.check_cfgs.extend(list.iter().map(|v| v.0.clone()));
-                    } else {
-                        // silently ignoring the instruction to try to
-                        // minimise MSRV annoyance when stabilizing -Zcheck-cfg
-                    }
+                    let list = value.list(key)?;
+                    output.check_cfgs.extend(list.iter().map(|v| v.0.clone()));
                 }
                 "rustc-env" => {
                     for (name, val) in value.table(key)?.0 {