Make --check-cfg use a different lint for CLI --cfg checking

compiler/rustc_lint/src/builtin.rs

@@ -2890,22 +2890,55 @@ impl EarlyLintPass for SpecialModuleName {
     }
 }
 
-pub use rustc_session::lint::builtin::UNEXPECTED_CFGS;
+declare_lint! {
+    /// The `unexpected_cli_cfgs` lint detects unexpected conditional compilation given
+    /// in the command line.
+    ///
+    /// ### Example
+    ///
+    /// ```text
+    /// rustc --cfg 'foo' --check-cfg 'cfg()'
+    /// ```
+    ///
+    /// ```rust,ignore (needs command line option)
+    /// fn main() {}
+    /// ```
+    ///
+    /// This will produce:
+    ///
+    /// ```text
+    /// warning: unexpected `foo` as condition name
+    ///    |
+    ///    = help: was set with `--cfg` but isn't in the `--check-cfg` expected names
+    /// ```
+    ///
+    /// ### Explanation
+    ///
+    /// This lint is only active when a `--check-cfg='cfg(...)'` option has been passed
+    /// to the compiler and triggers whenever an unknown condition name or value is used
+    /// on `--cfg` command line arguments.
+    pub UNEXPECTED_CLI_CFGS,
+    Allow,
+    "detects unexpected names and values in `--cfg`",
+}
 
-declare_lint_pass!(UnexpectedCfgs => [UNEXPECTED_CFGS]);
+declare_lint_pass!(UnexpectedCliCfgs => [UNEXPECTED_CLI_CFGS]);
 
-impl EarlyLintPass for UnexpectedCfgs {
+impl EarlyLintPass for UnexpectedCliCfgs {
     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 {
             match check_cfg.expecteds.get(&name) {
                 Some(ExpectedValues::Some(values)) if !values.contains(&value) => {
                     let value = value.unwrap_or(kw::Empty);
-                    cx.emit_lint(UNEXPECTED_CFGS, BuiltinUnexpectedCliConfigValue { name, value });
+                    cx.emit_lint(
+                        UNEXPECTED_CLI_CFGS,
+                        BuiltinUnexpectedCliConfigValue { name, value },
+                    );
                 }
                 None if check_cfg.exhaustive_names => {
-                    cx.emit_lint(UNEXPECTED_CFGS, BuiltinUnexpectedCliConfigName { name });
+                    cx.emit_lint(UNEXPECTED_CLI_CFGS, BuiltinUnexpectedCliConfigName { name });
                 }
                 _ => { /* expected */ }
             }

compiler/rustc_lint/src/lib.rs

@@ -179,7 +179,7 @@ early_lint_methods!(
             IncompleteInternalFeatures: IncompleteInternalFeatures,
             RedundantSemicolons: RedundantSemicolons,
             UnusedDocComment: UnusedDocComment,
-            UnexpectedCfgs: UnexpectedCfgs,
+            UnexpectedCliCfgs: UnexpectedCliCfgs,
         ]
     ]
 );

compiler/rustc_lint_defs/src/builtin.rs

@@ -3438,6 +3438,7 @@ declare_lint_pass! {
         UNCONDITIONAL_PANIC,
         UNCONDITIONAL_RECURSION,
         UNDEFINED_NAKED_FUNCTION_ABI,
+        UNEXPECTED_CFGS,
         UNFULFILLED_LINT_EXPECTATIONS,
         UNINHABITED_STATIC,
         UNKNOWN_CRATE_TYPES,

tests/ui/check-cfg/unexpected-cli-cfg.rs

@@ -0,0 +1,23 @@
+// Check for unexpected configuration value in the code.
+//
+// check-pass
+// compile-flags: -Z unstable-options
+// compile-flags: --cfg foo --cfg bar --cfg feature="bar"
+// compile-flags: --check-cfg=cfg(feature,values("serde","full"))
+//
+// error-pattern: unexpected `foo` as condition name
+// error-pattern: unexpected `bar` as condition name
+// error-pattern: unexpected condition value `bar` for condition name `feature`
+// error-pattern: was set with `--cfg` but isn't in the `--check-cfg` expected
+
+#![warn(unexpected_cli_cfgs)]
+
+#[cfg(feature = "bar")]
+//~^ WARNING unexpected `cfg` condition value
+pub fn f() {}
+
+#[cfg(foo)]
+//~^ WARNING unexpected `cfg` condition name
+pub fn foo() {}
+
+pub fn main() {}

tests/ui/check-cfg/unexpected-cli-cfg.stderr

@@ -0,0 +1,36 @@
+warning: unexpected `cfg` condition value: `bar`
+  --> $DIR/unexpected-cli-cfg.rs:15:7
+   |
+LL | #[cfg(feature = "bar")]
+   |       ^^^^^^^^^^^^^^^
+   |
+   = note: expected values for `feature` are: `full`, `serde`
+   = note: `#[warn(unexpected_cfgs)]` on by default
+
+warning: unexpected `cfg` condition name: `foo`
+  --> $DIR/unexpected-cli-cfg.rs:19:7
+   |
+LL | #[cfg(foo)]
+   |       ^^^
+   |
+   = help: expected names are: `debug_assertions`, `doc`, `doctest`, `feature`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `sanitize`, `target_abi`, `target_arch`, `target_endian`, `target_env`, `target_family`, `target_feature`, `target_has_atomic`, `target_has_atomic_equal_alignment`, `target_has_atomic_load_store`, `target_os`, `target_pointer_width`, `target_thread_local`, `target_vendor`, `test`, `unix`, `windows`
+
+warning: unexpected `foo` as condition name
+   |
+   = help: was set with `--cfg` but isn't in the `--check-cfg` expected names
+note: the lint level is defined here
+  --> $DIR/unexpected-cli-cfg.rs:13:9
+   |
+LL | #![warn(unexpected_cli_cfgs)]
+   |         ^^^^^^^^^^^^^^^^^^^
+
+warning: unexpected `bar` as condition name
+   |
+   = help: was set with `--cfg` but isn't in the `--check-cfg` expected names
+
+warning: unexpected condition value `bar` for condition name `feature`
+   |
+   = help: was set with `--cfg` but isn't in the `--check-cfg` expected values
+
+warning: 5 warnings emitted
+