Add warning against unexpected --cfg with --check-cfg

compiler/rustc_error_messages/locales/en-US/lint.ftl

@@ -354,6 +354,12 @@ lint_builtin_unreachable_pub = unreachable `pub` {$what}
     .suggestion = consider restricting its visibility
     .help = or consider exporting it for use by other crates
 
+lint_builtin_unexpected_cli_config_name = unexpected `{$name}` as condition name
+    .help = was set with `--cfg` but isn't in the `--check-cfg` expected names
+
+lint_builtin_unexpected_cli_config_value = unexpected condition value `{$value}` for condition name `{$name}`
+    .help = was set with `--cfg` but isn't in the `--check-cfg` expected values
+
 lint_builtin_type_alias_bounds_help = use fully disambiguated paths (i.e., `<T as Trait>::Assoc`) to refer to associated types in type aliases
 
 lint_builtin_type_alias_where_clause = where clauses are not enforced in type aliases

compiler/rustc_lint/src/builtin.rs

@@ -3250,3 +3250,39 @@ fn check_crate(&mut self, cx: &EarlyContext<'_>, krate: &ast::Crate) {
         }
     }
 }
+
+pub use rustc_session::lint::builtin::UNEXPECTED_CFGS;
+
+declare_lint_pass!(UnexpectedCfgs => [UNEXPECTED_CFGS]);
+
+impl EarlyLintPass for UnexpectedCfgs {
+    fn check_crate(&mut self, cx: &EarlyContext<'_>, _: &ast::Crate) {
+        let cfg = &cx.sess().parse_sess.config;
+        let check_cfg = &cx.sess().parse_sess.check_config;
+        for &(name, value) in cfg {
+            if let Some(names_valid) = &check_cfg.names_valid {
+                if !names_valid.contains(&name) {
+                    cx.lookup(UNEXPECTED_CFGS, None::<MultiSpan>, |diag| {
+                        diag.build(fluent::lint::builtin_unexpected_cli_config_name)
+                            .help(fluent::lint::help)
+                            .set_arg("name", name)
+                            .emit();
+                    });
+                }
+            }
+            if let Some(value) = value {
+                if let Some(values) = &check_cfg.values_valid.get(&name) {
+                    if !values.contains(&value) {
+                        cx.lookup(UNEXPECTED_CFGS, None::<MultiSpan>, |diag| {
+                            diag.build(fluent::lint::builtin_unexpected_cli_config_value)
+                                .help(fluent::lint::help)
+                                .set_arg("name", name)
+                                .set_arg("value", value)
+                                .emit();
+                        });
+                    }
+                }
+            }
+        }
+    }
+}

compiler/rustc_lint/src/lib.rs

@@ -144,6 +144,7 @@ macro_rules! early_lint_passes {
                 IncompleteFeatures: IncompleteFeatures,
                 RedundantSemicolons: RedundantSemicolons,
                 UnusedDocComment: UnusedDocComment,
+                UnexpectedCfgs: UnexpectedCfgs,
             ]
         );
     };

compiler/rustc_lint_defs/src/builtin.rs

@@ -3365,7 +3365,6 @@
         DEPRECATED_CFG_ATTR_CRATE_TYPE_NAME,
         DUPLICATE_MACRO_ATTRIBUTES,
         SUSPICIOUS_AUTO_TRAIT_IMPLS,
-        UNEXPECTED_CFGS,
         DEPRECATED_WHERE_CLAUSE_LOCATION,
         TEST_UNSTABLE_LINT,
         FFI_UNWIND_CALLS,

src/test/ui/check-cfg/allow-at-crate-level.rs

@@ -0,0 +1,8 @@
+// This test check that #![allow(unexpected_cfgs)] works with --cfg
+//
+// check-pass
+// compile-flags: --cfg=unexpected --check-cfg=names() -Z unstable-options
+
+#![allow(unexpected_cfgs)]
+
+fn main() {}

src/test/ui/check-cfg/invalid-cfg-value.stderr

@@ -15,5 +15,9 @@ LL | #[cfg(feature = "rand")]
    |
    = note: expected values for `feature` are: full, serde
 
-warning: 2 warnings emitted
+warning: unexpected condition value `rand` for condition name `feature`
+   |
+   = help: was set with `--cfg` but isn't in the `--check-cfg` expected values
+
+warning: 3 warnings emitted
 

src/test/ui/check-cfg/mix.rs

@@ -3,7 +3,7 @@
 // we correctly lint on the `cfg!` macro and `cfg_attr` attribute.
 //
 // check-pass
-// compile-flags: --check-cfg=names() --check-cfg=values(feature,"foo") --cfg feature="bar" -Z unstable-options
+// compile-flags: --check-cfg=names() --check-cfg=values(feature,"foo") --cfg feature="bar" --cfg unknown_name -Z unstable-options
 
 #[cfg(windows)]
 fn do_windows_stuff() {}

src/test/ui/check-cfg/mix.stderr

@@ -28,6 +28,14 @@ warning: unexpected `cfg` condition name
 LL | #[cfg_attr(uu, test)]
    |            ^^
 
+warning: unexpected condition value `bar` for condition name `feature`
+   |
+   = help: was set with `--cfg` but isn't in the `--check-cfg` expected values
+
+warning: unexpected `unknown_name` as condition name
+   |
+   = help: was set with `--cfg` but isn't in the `--check-cfg` expected names
+
 warning: unexpected `cfg` condition name
   --> $DIR/mix.rs:35:10
    |
@@ -170,5 +178,5 @@ LL |     cfg!(all(feature = "zebra", feature = "zebra", feature = "zebra"));
    |
    = note: expected values for `feature` are: foo
 
-warning: 25 warnings emitted
+warning: 27 warnings emitted