Stabilize -Zcheck-cfg as always enabled

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 {

src/doc/src/reference/build-script-examples.md

@@ -456,6 +456,9 @@ values](https://github.com/sfackler/rust-openssl/blob/dc72a8e2c429e46c275e528b61
 ```rust,ignore
 // (portion of build.rs)
 
+println!("cargo::rustc-check-cfg=cfg(ossl101,ossl102)");
+println!("cargo::rustc-check-cfg=cfg(ossl110,ossl110g,ossl111)");
+
 if let Ok(version) = env::var("DEP_OPENSSL_VERSION_NUMBER") {
     let version = u64::from_str_radix(&version, 16).unwrap();
 

src/doc/src/reference/build-scripts.md

@@ -130,6 +130,8 @@ one detailed below.
   compiler.
 * [`cargo::rustc-cfg=KEY[="VALUE"]`](#rustc-cfg) --- Enables compile-time `cfg`
   settings.
+* [`cargo::rustc-check-cfg=CHECK_CFG`](#rustc-check-cfg) -- Register custom `cfg`s as
+  expected for compile-time checking of configs. 
 * [`cargo::rustc-env=VAR=VALUE`](#rustc-env) --- Sets an environment variable.
 * [`cargo::rustc-cdylib-link-arg=FLAG`](#rustc-cdylib-link-arg) --- Passes custom
   flags to a linker for cdylib crates.
@@ -233,7 +235,10 @@ equivalent to using [`rustc-link-lib`](#rustc-link-lib) and
 
 The `rustc-cfg` instruction tells Cargo to pass the given value to the
 [`--cfg` flag][option-cfg] to the compiler. This may be used for compile-time
-detection of features to enable [conditional compilation].
+detection of features to enable [conditional compilation]. Custom cfgs
+must either be expected using the [`cargo::rustc-check-cfg`](#rustc-check-cfg)
+instruction or usage will need to allow the [`unexpected_cfgs`][unexpected-cfgs]
+lint to avoid unexpected cfgs warnings.
 
 Note that this does *not* affect Cargo's dependency resolution. This cannot be
 used to enable an optional dependency, or enable other Cargo features.
@@ -249,6 +254,41 @@ identifier, the value should be a string.
 [cargo features]: features.md
 [conditional compilation]: ../../reference/conditional-compilation.md
 [option-cfg]: ../../rustc/command-line-arguments.md#option-cfg
+[unexpected-cfgs]: ../../rustc/lints/listing/warn-by-default.md#unexpected-cfgs
+
+### `cargo::rustc-check-cfg=CHECK_CFG` {#rustc-check-cfg}
+
+Add to the list of expected config names and values that is used when checking
+the _reachable_ cfg expressions.
+
+For details on the syntax of `CHECK_CFG`, see `rustc` [`--check-cfg` flag][option-check-cfg].
+See also the [`unexpected_cfgs`][unexpected-cfgs] lint.
+
+The instruction can be used like this:
+
+```rust,no_run
+// build.rs
+println!("cargo::rustc-check-cfg=cfg(foo, values(\"bar\"))");
+```
+
+Note that all possible cfgs should be defined, regardless of which cfgs are
+currently enabled. This includes all possible values of a given cfg name.
+
+It is recommended to group the `cargo::rustc-check-cfg` and
+[`cargo::rustc-cfg`][option-cfg] instructions as closely as possible in order to
+avoid typos, missing check-cfg, stalled cfgs...
+
+#### Example of using `cargo::rustc-check-cfg` and `cargo::rustc-cfg` together
+
+```rust,no_run
+// build.rs
+println!("cargo::rustc-check-cfg=cfg(foo, values(\"bar\"))");
+if foo_bar_condition {
+    println!("cargo::rustc-cfg=foo=\"bar\"");
+}
+```
+
+[option-check-cfg]: ../../rustc/command-line-arguments.md#option-check-cfg
 
 ### `cargo::rustc-env=VAR=VALUE` {#rustc-env}
 

src/doc/src/reference/unstable.md

@@ -83,7 +83,6 @@ For the latest nightly, see the [nightly version] of this page.
     * [build-std-features](#build-std-features) --- Sets features to use with the standard library.
     * [binary-dep-depinfo](#binary-dep-depinfo) --- Causes the dep-info file to track binary dependencies.
     * [panic-abort-tests](#panic-abort-tests) --- Allows running tests with the "abort" panic strategy.
-    * [check-cfg](#check-cfg) --- Compile-time validation of `cfg` expressions.
     * [host-config](#host-config) --- Allows setting `[target]`-like configuration settings for host build targets.
     * [target-applies-to-host](#target-applies-to-host) --- Alters whether certain flags will be passed to host build targets.
     * [gc](#gc) --- Global cache garbage collection.
@@ -1154,44 +1153,6 @@ You can use the flag like this:
 cargo rustdoc -Z unstable-options --output-format json
 ```
 
-## check-cfg
-
-* RFC: [#3013](https://github.com/rust-lang/rfcs/pull/3013)
-* Tracking Issue: [#10554](https://github.com/rust-lang/cargo/issues/10554)
-
-`-Z check-cfg` command line enables compile time checking of Cargo features as well as `rustc`
-well known names and values in `#[cfg]`, `cfg!`, `#[link]` and `#[cfg_attr]` with the `rustc`
-and `rustdoc` unstable `--check-cfg` command line.
-
-You can use the flag like this:
-
-```
-cargo check -Z unstable-options -Z check-cfg
-```
-
-### `cargo::rustc-check-cfg=CHECK_CFG`
-
-The `rustc-check-cfg` instruction tells Cargo to pass the given value to the
-`--check-cfg` flag to the compiler. This may be used for compile-time
-detection of unexpected conditional compilation name and/or values.
-
-This can only be used in combination with `-Zcheck-cfg` otherwise it is ignored
-with a warning.
-
-If you want to integrate with Cargo features, only use `-Zcheck-cfg` instead of
-trying to do it manually with this option.
-
-You can use the instruction like this:
-
-```rust,no_run
-// build.rs
-println!("cargo::rustc-check-cfg=cfg(foo, bar)");
-```
-
-```
-cargo check -Z unstable-options -Z check-cfg
-```
-
 ## codegen-backend
 
 The `codegen-backend` feature makes it possible to select the codegen backend used by rustc using a profile.
@@ -1798,3 +1759,11 @@ The `-Z registry-auth` feature has been stabilized in the 1.74 release with the
 requirement that a credential-provider is configured.
 
 See [Registry Authentication](registry-authentication.md) documentation for details.
+
+## check-cfg
+
+The `-Z check-cfg` feature has been stabilized in the 1.80 release by making it the
+default behavior.
+
+See the [build script documentation](build-scripts.md#rustc-check-cfg) for informations
+about specifying custom cfgs.

tests/testsuite/build_script.rs

@@ -2609,7 +2609,10 @@ fn cfg_test() {
         )
         .file(
             "build.rs",
-            r#"fn main() { println!("cargo::rustc-cfg=foo"); }"#,
+            r#"fn main() {
+                println!("cargo::rustc-cfg=foo");
+                println!("cargo::rustc-check-cfg=cfg(foo)");
+            }"#,
         )
         .file(
             "src/lib.rs",
@@ -2714,6 +2717,9 @@ fn cfg_override_test() {
                 authors = []
                 build = "build.rs"
                 links = "a"
+
+                [lints.rust]
+                unexpected_cfgs = "allow" # bc of override, stable/nightly, tests
             "#,
         )
         .file("build.rs", "")
@@ -5590,9 +5596,10 @@ fn build_script_rerun_when_target_rustflags_change() {
             use std::env;
 
             fn main() {
+                println!("cargo::rustc-check-cfg=cfg(enable)");
                 if let Ok(rustflags) = env::var("CARGO_ENCODED_RUSTFLAGS") {
                     if !rustflags.is_empty() {
-                        println!("cargo::rustc-cfg=enable")
+                        println!("cargo::rustc-cfg=enable");
                     }
                 }
             }