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

Author: Urgau

src/cargo/core/compiler/build_context/target_info.rs

@@ -55,6 +55,11 @@ pub struct TargetInfo {
     pub rustflags: Vec<String>,
     /// Extra flags to pass to `rustdoc`, see [`extra_args`].
     pub rustdocflags: Vec<String>,
+    /// Whether or not rustc (stably) supports the `--check-cfg` flag.
+    ///
+    /// Can be removed once the minimum supported rustc version of Cargo is
+    /// at minimum 1.80.0.
+    pub support_check_cfg: bool,
 }
 
 /// Kind of each file generated by a Unit, part of `FileType`.
@@ -199,6 +204,13 @@ impl TargetInfo {
                 process.arg("--crate-type").arg(crate_type.as_str());
             }
 
+            let support_check_cfg = rustc
+                .cached_output(
+                    process.clone().arg("--check-cfg").arg("cfg()"),
+                    extra_fingerprint,
+                )
+                .is_ok();
+
             process.arg("--print=sysroot");
             process.arg("--print=split-debuginfo");
             process.arg("--print=crate-name"); // `___` as a delimiter.
@@ -310,6 +322,7 @@ impl TargetInfo {
                 )?,
                 cfg,
                 support_split_debuginfo,
+                support_check_cfg,
             });
         }
     }

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

@@ -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 +408,11 @@ 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 extra_check_cfg = build_runner
+        .bcx
+        .target_data
+        .info(unit.kind)
+        .support_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.
@@ -665,9 +669,7 @@ 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
+    /// * `extra_check_cfg` --- for `--check-cfg` (if supported)
     pub fn parse(
         input: &[u8],
         // Takes String instead of InternedString so passing `unit.pkg.name()` will give a compile error.
@@ -910,8 +912,8 @@ impl BuildOutput {
                     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
+                        // silently ignoring the instruction because the rustc version
+                        // we are using does not support --check-cfg stably
                     }
                 }
                 "rustc-env" => {
@@ -1254,7 +1256,11 @@ 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
+                .target_data
+                .info(unit.kind)
+                .support_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

@@ -1310,11 +1310,13 @@ 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 {
+    if build_runner
+        .bcx
+        .target_data
+        .info(unit.kind)
+        .support_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.
         //
@@ -1352,7 +1354,6 @@ fn check_cfg_args(build_runner: &BuildRunner<'_, '_>, unit: &Unit) -> Vec<OsStri
         // 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"),
@@ -1476,11 +1477,8 @@ fn add_custom_flags(
             for cfg in output.cfgs.iter() {
                 cmd.arg("--cfg").arg(cfg);
             }
-            if !output.check_cfgs.is_empty() {
-                cmd.arg("-Zunstable-options");
-                for check_cfg in &output.check_cfgs {
-                    cmd.arg("--check-cfg").arg(check_cfg);
-                }
+            for check_cfg in &output.check_cfgs {
+                cmd.arg("--check-cfg").arg(check_cfg);
             }
             for (name, value) in output.env.iter() {
                 cmd.env(name, value);

src/cargo/core/features.rs

@@ -753,7 +753,6 @@ unstable_cli_options!(
     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"),
     cargo_lints: bool = ("Enable the `[lints.cargo]` table"),
-    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)"),
@@ -855,6 +854,9 @@ const STABILIZED_REGISTRY_AUTH: &str =
 
 const STABILIZED_LINTS: &str = "The `[lints]` table is now always available.";
 
+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>,
@@ -1109,6 +1111,7 @@ impl CliUnstable {
             "credential-process" => stabilized_warn(k, "1.74", STABILIZED_CREDENTIAL_PROCESS),
             "lints" => stabilized_warn(k, "1.74", STABILIZED_LINTS),
             "registry-auth" => stabilized_warn(k, "1.74", STABILIZED_REGISTRY_AUTH),
+            "check-cfg" => stabilized_warn(k, "1.80", STABILIZED_CHECK_CFG),
 
             // Unstable features
             // Sorted alphabetically:
@@ -1122,9 +1125,6 @@ impl CliUnstable {
             }
             "build-std-features" => self.build_std_features = Some(parse_features(v)),
             "cargo-lints" => self.cargo_lints = parse_empty(k, 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

@@ -120,7 +120,7 @@ fn load_config_table(gctx: &GlobalContext, prefix: &str) -> CargoResult<TargetCo
     // Links do not support environment variables.
     let target_key = ConfigKey::from_str(prefix);
     let links_overrides = match gctx.get_table(&target_key)? {
-        Some(links) => parse_links_overrides(&target_key, links.val, gctx)?,
+        Some(links) => parse_links_overrides(&target_key, links.val)?,
         None => BTreeMap::new(),
     };
     Ok(TargetConfig {
@@ -135,7 +135,6 @@ fn load_config_table(gctx: &GlobalContext, prefix: &str) -> CargoResult<TargetCo
 fn parse_links_overrides(
     target_key: &ConfigKey,
     links: HashMap<String, CV>,
-    gctx: &GlobalContext,
 ) -> CargoResult<BTreeMap<String, BuildOutput>> {
     let mut links_overrides = BTreeMap::new();
 
@@ -204,13 +203,8 @@ 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 {