Adjust -Zcheck-cfg for new rustc syntax and behavior

src/cargo/core/compiler/custom_build.rs

@@ -403,10 +403,7 @@ fn build_work(cx: &mut Context<'_, '_>, unit: &Unit) -> CargoResult<Job> {
     paths::create_dir_all(&script_out_dir)?;
 
     let nightly_features_allowed = cx.bcx.config.nightly_features_allowed;
-    let extra_check_cfg = match cx.bcx.config.cli_unstable().check_cfg {
-        Some((_, _, _, output)) => output,
-        None => false,
-    };
+    let extra_check_cfg = cx.bcx.config.cli_unstable().check_cfg;
     let targets: Vec<Target> = unit.pkg.targets().to_vec();
     // Need a separate copy for the fresh closure.
     let targets_fresh = targets.clone();
@@ -1126,10 +1123,7 @@ fn prev_build_output(cx: &mut Context<'_, '_>, unit: &Unit) -> (Option<BuildOutp
             &unit.pkg.to_string(),
             &prev_script_out_dir,
             &script_out_dir,
-            match cx.bcx.config.cli_unstable().check_cfg {
-                Some((_, _, _, output)) => output,
-                None => false,
-            },
+            cx.bcx.config.cli_unstable().check_cfg,
             cx.bcx.config.nightly_features_allowed,
             unit.pkg.targets(),
         )

src/cargo/core/compiler/mod.rs

@@ -1167,39 +1167,32 @@ fn features_args(unit: &Unit) -> Vec<OsString> {
 ///
 /// [`check-cfg`]: https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#check-cfg
 fn check_cfg_args(cx: &Context<'_, '_>, unit: &Unit) -> Vec<OsString> {
-    if let Some((features, well_known_names, well_known_values, _output)) =
-        cx.bcx.config.cli_unstable().check_cfg
-    {
-        let mut args = Vec::with_capacity(unit.pkg.summary().features().len() * 2 + 4);
-        args.push(OsString::from("-Zunstable-options"));
-
-        if features {
-            // This generate something like this:
-            //  - values(feature)
-            //  - values(feature, "foo", "bar")
-            let mut arg = OsString::from("values(feature");
-            for (&feat, _) in unit.pkg.summary().features() {
-                arg.push(", \"");
-                arg.push(&feat);
-                arg.push("\"");
+    if cx.bcx.config.cli_unstable().check_cfg {
+        // This generate something like this:
+        //  - cfg(feature, values())
+        //  - cfg(feature, values("foo", "bar"))
+        //
+        // NOTE: Despite only explicitly specifying `feature`, well known names and values
+        // are implicitly enabled when one or more `--check-cfg` argument is passed.
+
+        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.push(")");
-
-            args.push(OsString::from("--check-cfg"));
-            args.push(arg);
-        }
-
-        if well_known_names {
-            args.push(OsString::from("--check-cfg"));
-            args.push(OsString::from("names()"));
-        }
-
-        if well_known_values {
-            args.push(OsString::from("--check-cfg"));
-            args.push(OsString::from("values()"));
+            arg_feature.push("\"");
+            arg_feature.push(feature);
+            arg_feature.push("\"");
         }
+        arg_feature.push("))");
 
-        args
+        vec![
+            OsString::from("-Zunstable-options"),
+            OsString::from("--check-cfg"),
+            arg_feature,
+        ]
     } else {
         Vec::new()
     }

src/cargo/core/features.rs

@@ -731,8 +731,7 @@ 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"),
-    #[serde(deserialize_with = "deserialize_check_cfg")]
-    check_cfg: Option<(/*features:*/ bool, /*well_known_names:*/ bool, /*well_known_values:*/ bool, /*output:*/ bool)> = ("Specify scope of compile-time checking of `cfg` names/values"),
+    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)"),
@@ -842,20 +841,6 @@ where
     ))
 }
 
-fn deserialize_check_cfg<'de, D>(
-    deserializer: D,
-) -> Result<Option<(bool, bool, bool, bool)>, D::Error>
-where
-    D: serde::Deserializer<'de>,
-{
-    use serde::de::Error;
-    let Some(crates) = <Option<Vec<String>>>::deserialize(deserializer)? else {
-        return Ok(None);
-    };
-
-    parse_check_cfg(crates.into_iter()).map_err(D::Error::custom)
-}
-
 #[derive(Debug, Copy, Clone, Default, Deserialize)]
 pub struct GitoxideFeatures {
     /// All fetches are done with `gitoxide`, which includes git dependencies as well as the crates index.
@@ -924,32 +909,6 @@ fn parse_gitoxide(
     Ok(Some(out))
 }
 
-fn parse_check_cfg(
-    it: impl Iterator<Item = impl AsRef<str>>,
-) -> CargoResult<Option<(bool, bool, bool, bool)>> {
-    let mut features = false;
-    let mut well_known_names = false;
-    let mut well_known_values = false;
-    let mut output = false;
-
-    for e in it {
-        match e.as_ref() {
-            "features" => features = true,
-            "names" => well_known_names = true,
-            "values" => well_known_values = true,
-            "output" => output = true,
-            _ => bail!("unstable check-cfg only takes `features`, `names`, `values` or `output` as valid inputs"),
-        }
-    }
-
-    Ok(Some((
-        features,
-        well_known_names,
-        well_known_values,
-        output,
-    )))
-}
-
 impl CliUnstable {
     pub fn parse(
         &mut self,
@@ -1107,7 +1066,7 @@ impl CliUnstable {
             }
             "build-std-features" => self.build_std_features = Some(parse_features(v)),
             "check-cfg" => {
-                self.check_cfg = v.map_or(Ok(None), |v| parse_check_cfg(v.split(',')))?
+                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)?,

src/cargo/util/config/target.rs

@@ -137,10 +137,6 @@ fn parse_links_overrides(
     config: &Config,
 ) -> CargoResult<BTreeMap<String, BuildOutput>> {
     let mut links_overrides = BTreeMap::new();
-    let extra_check_cfg = match config.cli_unstable().check_cfg {
-        Some((_, _, _, output)) => output,
-        None => false,
-    };
 
     for (lib_name, value) in links {
         // Skip these keys, it shares the namespace with `TargetConfig`.
@@ -207,7 +203,7 @@ fn parse_links_overrides(
                     output.cfgs.extend(list.iter().map(|v| v.0.clone()));
                 }
                 "rustc-check-cfg" => {
-                    if extra_check_cfg {
+                    if config.cli_unstable().check_cfg {
                         let list = value.list(key)?;
                         output.check_cfgs.extend(list.iter().map(|v| v.0.clone()));
                     } else {