6 files changed, 47 insertions, 5 deletions
diff --git a/compiler/rustc_error_messages/locales/en-US/lint.ftl b/compiler/rustc_error_messages/locales/en-US/lint.ftl
index 27ad3e45366..7f9918e4f12 100644
--- a/compiler/rustc_error_messages/locales/en-US/lint.ftl
+++ b/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
diff --git a/compiler/rustc_lint/src/builtin.rs b/compiler/rustc_lint/src/builtin.rs
index 4e9c209a584..48942211eba 100644
--- a/compiler/rustc_lint/src/builtin.rs
+++ b/compiler/rustc_lint/src/builtin.rs
@@ -3250,3 +3250,39 @@ impl EarlyLintPass for SpecialModuleName {
         }
     }
 }
+
+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();
+                        });
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/compiler/rustc_lint/src/lib.rs b/compiler/rustc_lint/src/lib.rs
index 8cbfc82c0f0..370a75cf700 100644
--- a/compiler/rustc_lint/src/lib.rs
+++ b/compiler/rustc_lint/src/lib.rs
@@ -146,6 +146,7 @@ macro_rules! early_lint_passes {
                 IncompleteFeatures: IncompleteFeatures,
                 RedundantSemicolons: RedundantSemicolons,
                 UnusedDocComment: UnusedDocComment,
+                UnexpectedCfgs: UnexpectedCfgs,
             ]
         );
     };
diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 845563338ea..ca01599acc8 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -3365,7 +3365,6 @@ declare_lint_pass! {
         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,
diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs
index 7fa4294e5cf..04bd685f190 100644
--- a/compiler/rustc_session/src/config.rs
+++ b/compiler/rustc_session/src/config.rs
@@ -901,7 +901,7 @@ fn default_configuration(sess: &Session) -> CrateConfig {
         sess.fatal(&err);
     });
 
-    let mut ret = FxHashSet::default();
+    let mut ret = CrateConfig::default();
     ret.reserve(7); // the minimum number of insertions
     // Target bindings.
     ret.insert((sym::target_os, Some(Symbol::intern(os))));
diff --git a/compiler/rustc_session/src/parse.rs b/compiler/rustc_session/src/parse.rs
index ebec754dcff..5b95d73bd4d 100644
--- a/compiler/rustc_session/src/parse.rs
+++ b/compiler/rustc_session/src/parse.rs
@@ -8,7 +8,7 @@ use crate::lint::{
 };
 use crate::SessionDiagnostic;
 use rustc_ast::node_id::NodeId;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_data_structures::sync::{Lock, Lrc};
 use rustc_errors::{emitter::SilentEmitter, ColorConfig, Handler};
 use rustc_errors::{
@@ -25,7 +25,7 @@ use std::str;
 
 /// The set of keys (and, optionally, values) that define the compilation
 /// environment of the crate, used to drive conditional compilation.
-pub type CrateConfig = FxHashSet<(Symbol, Option<Symbol>)>;
+pub type CrateConfig = FxIndexSet<(Symbol, Option<Symbol>)>;
 pub type CrateCheckConfig = CheckCfg<Symbol>;
 
 /// Collected spans during parsing for places where a certain feature was
@@ -241,7 +241,7 @@ impl ParseSess {
         Self {
             span_diagnostic: handler,
             unstable_features: UnstableFeatures::from_environment(None),
-            config: FxHashSet::default(),
+            config: FxIndexSet::default(),
             check_config: CrateCheckConfig::default(),
             edition: ExpnId::root().expn_data().edition,
             raw_identifier_spans: Lock::new(Vec::new()),