Adjust -Zcheck-cfg for new rustc syntax and behavior

This commit removes all the -Zcheck-cfg options (features, names,
values, output), as they don't make much sense now since features, names
and values are all combine together for upstream rustc and the output
option was only here because the other were.

Now the new behavior from cargo is to always pass one `--check-cfg`
argument to rustc for the `feature`s which implicitly enables well known
names and values.

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 {