Improve check-cfg expected names diagnostic

compiler/rustc_lint/src/early/diagnostics/check_cfg.rs

@@ -10,19 +10,35 @@ use crate::lints;
 
 const MAX_CHECK_CFG_NAMES_OR_VALUES: usize = 35;
 
+enum FilterWellKnownNames {
+    Yes,
+    No,
+}
+
 fn sort_and_truncate_possibilities(
     sess: &Session,
     mut possibilities: Vec<Symbol>,
+    filter_well_known_names: FilterWellKnownNames,
 ) -> (Vec<Symbol>, usize) {
+    let possibilities_len = possibilities.len();
+
     let n_possibilities = if sess.opts.unstable_opts.check_cfg_all_expected {
         possibilities.len()
     } else {
+        match filter_well_known_names {
+            FilterWellKnownNames::Yes => {
+                possibilities.retain(|cfg_name| {
+                    !sess.psess.check_config.well_known_names.contains(cfg_name)
+                });
+            }
+            FilterWellKnownNames::No => {}
+        };
         std::cmp::min(possibilities.len(), MAX_CHECK_CFG_NAMES_OR_VALUES)
     };
 
     possibilities.sort_by(|s1, s2| s1.as_str().cmp(s2.as_str()));
 
-    let and_more = possibilities.len().saturating_sub(n_possibilities);
+    let and_more = possibilities_len.saturating_sub(n_possibilities);
     possibilities.truncate(n_possibilities);
     (possibilities, and_more)
 }
@@ -198,8 +214,10 @@ pub(super) fn unexpected_cfg_name(
         } else {
             vec![]
         };
+
+        let (possibilities, and_more) =
+            sort_and_truncate_possibilities(sess, possibilities, FilterWellKnownNames::Yes);
         let expected_names = if !possibilities.is_empty() {
-            let (possibilities, and_more) = sort_and_truncate_possibilities(sess, possibilities);
             let possibilities: Vec<_> =
                 possibilities.into_iter().map(|s| Ident::new(s, name_span)).collect();
             Some(lints::unexpected_cfg_name::ExpectedNames {
@@ -269,8 +287,11 @@ pub(super) fn unexpected_cfg_value(
     // for names as the possibilities could be very long
     let code_sugg = if !possibilities.is_empty() {
         let expected_values = {
-            let (possibilities, and_more) =
-                sort_and_truncate_possibilities(sess, possibilities.clone());
+            let (possibilities, and_more) = sort_and_truncate_possibilities(
+                sess,
+                possibilities.clone(),
+                FilterWellKnownNames::No,
+            );
             lints::unexpected_cfg_value::ExpectedValues {
                 name,
                 have_none_possibility,

src/doc/rustc/src/check-cfg/cargo-specifics.md

@@ -13,6 +13,8 @@ the `unexpected_cfgs` lint and `--check-cfg` flag. It is not intended to provide
 individual details, for that refer to the [`--check-cfg` documentation](../check-cfg.md) and
 to the [Cargo book](../../cargo/index.html).
 
+> The full list of well known cfgs (aka builtins) can be found under [Checking conditional configurations / Well known names and values](../check-cfg.md#well-known-names-and-values).
+
 ## Cargo feature
 
 *See the [`[features]` section in the Cargo book][cargo-features] for more details.*

tests/ui/check-cfg/allow-same-level.rs

@@ -1,12 +1,24 @@
-// This test check that #[allow(unexpected_cfgs)] doesn't work if put on the same level
+// This test check that #[allow(unexpected_cfgs)] **doesn't work**
+// when put on the same level as the #[cfg] attribute.
+//
+// It should work, but due to interactions between how #[cfg]s are
+// expanded, the lint machinery and the check-cfg impl, we
+// miss the #[allow], althrough we probably shoudln't.
+//
+// cf. https://github.com/rust-lang/rust/issues/124735
 //
 //@ check-pass
 //@ no-auto-check-cfg
-//@ compile-flags: --check-cfg=cfg()
+//@ compile-flags: --check-cfg=cfg() --cfg=unknown_but_active_cfg
 
 #[allow(unexpected_cfgs)]
 #[cfg(FALSE)]
 //~^ WARNING unexpected `cfg` condition name
 fn bar() {}
 
+#[allow(unexpected_cfgs)]
+#[cfg(unknown_but_active_cfg)]
+//~^ WARNING unexpected `cfg` condition name
+fn bar() {}
+
 fn main() {}

tests/ui/check-cfg/allow-same-level.stderr

@@ -1,13 +1,21 @@
 warning: unexpected `cfg` condition name: `FALSE`
-  --> $DIR/allow-same-level.rs:8:7
+  --> $DIR/allow-same-level.rs:15:7
    |
 LL | #[cfg(FALSE)]
    |       ^^^^^
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
    = help: to expect this configuration use `--check-cfg=cfg(FALSE)`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default
 
-warning: 1 warning emitted
+warning: unexpected `cfg` condition name: `unknown_but_active_cfg`
+  --> $DIR/allow-same-level.rs:20:7
+   |
+LL | #[cfg(unknown_but_active_cfg)]
+   |       ^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: to expect this configuration use `--check-cfg=cfg(unknown_but_active_cfg)`
+   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
+
+warning: 2 warnings emitted
 

tests/ui/check-cfg/cargo-build-script.stderr

@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `has_foo`
 LL | #[cfg(has_foo)]
    |       ^^^^^^^
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `fmt_debug`, `has_bar`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
+   = help: expected names are: `has_bar` and 30 more
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]

tests/ui/check-cfg/cargo-feature.none.stderr

@@ -1,5 +1,5 @@
 warning: unexpected `cfg` condition value: `serde`
-  --> $DIR/cargo-feature.rs:14:7
+  --> $DIR/cargo-feature.rs:15:7
    |
 LL | #[cfg(feature = "serde")]
    |       ^^^^^^^^^^^^^^^^^ help: remove the condition
@@ -10,7 +10,7 @@ LL | #[cfg(feature = "serde")]
    = note: `#[warn(unexpected_cfgs)]` on by default
 
 warning: unexpected `cfg` condition value: (none)
-  --> $DIR/cargo-feature.rs:18:7
+  --> $DIR/cargo-feature.rs:19:7
    |
 LL | #[cfg(feature)]
    |       ^^^^^^^ help: remove the condition
@@ -20,12 +20,12 @@ LL | #[cfg(feature)]
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition name: `tokio_unstable`
-  --> $DIR/cargo-feature.rs:22:7
+  --> $DIR/cargo-feature.rs:23:7
    |
 LL | #[cfg(tokio_unstable)]
    |       ^^^^^^^^^^^^^^
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `feature`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
+   = help: expected names are: `docsrs`, `feature`, and `test` and 30 more
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
@@ -34,7 +34,7 @@ LL | #[cfg(tokio_unstable)]
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition name: `CONFIG_NVME`
-  --> $DIR/cargo-feature.rs:26:7
+  --> $DIR/cargo-feature.rs:27:7
    |
 LL | #[cfg(CONFIG_NVME = "m")]
    |       ^^^^^^^^^^^^^^^^^

tests/ui/check-cfg/cargo-feature.rs

@@ -6,6 +6,7 @@
 //@ no-auto-check-cfg
 //@ revisions: some none
 //@ rustc-env:CARGO_CRATE_NAME=foo
+//@ compile-flags: --check-cfg=cfg(docsrs,test)
 //@ [none]compile-flags: --check-cfg=cfg(feature,values())
 //@ [some]compile-flags: --check-cfg=cfg(feature,values("bitcode"))
 //@ [some]compile-flags: --check-cfg=cfg(CONFIG_NVME,values("y"))

tests/ui/check-cfg/cargo-feature.some.stderr

@@ -1,5 +1,5 @@
 warning: unexpected `cfg` condition value: `serde`
-  --> $DIR/cargo-feature.rs:14:7
+  --> $DIR/cargo-feature.rs:15:7
    |
 LL | #[cfg(feature = "serde")]
    |       ^^^^^^^^^^^^^^^^^
@@ -10,7 +10,7 @@ LL | #[cfg(feature = "serde")]
    = note: `#[warn(unexpected_cfgs)]` on by default
 
 warning: unexpected `cfg` condition value: (none)
-  --> $DIR/cargo-feature.rs:18:7
+  --> $DIR/cargo-feature.rs:19:7
    |
 LL | #[cfg(feature)]
    |       ^^^^^^^- help: specify a config value: `= "bitcode"`
@@ -20,12 +20,12 @@ LL | #[cfg(feature)]
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition name: `tokio_unstable`
-  --> $DIR/cargo-feature.rs:22:7
+  --> $DIR/cargo-feature.rs:23:7
    |
 LL | #[cfg(tokio_unstable)]
    |       ^^^^^^^^^^^^^^
    |
-   = help: expected names are: `CONFIG_NVME`, `clippy`, `debug_assertions`, `doc`, `doctest`, `feature`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
+   = help: expected names are: `CONFIG_NVME`, `docsrs`, `feature`, and `test` and 30 more
    = help: consider using a Cargo feature instead
    = help: or consider adding in `Cargo.toml` the `check-cfg` lint config for the lint:
             [lints.rust]
@@ -34,7 +34,7 @@ LL | #[cfg(tokio_unstable)]
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg/cargo-specifics.html> for more information about checking conditional configuration
 
 warning: unexpected `cfg` condition value: `m`
-  --> $DIR/cargo-feature.rs:26:7
+  --> $DIR/cargo-feature.rs:27:7
    |
 LL | #[cfg(CONFIG_NVME = "m")]
    |       ^^^^^^^^^^^^^^---

tests/ui/check-cfg/cfg-value-for-cfg-name-duplicate.stderr

@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `value`
 LL | #[cfg(value)]
    |       ^^^^^
    |
-   = help: expected names are: `bar`, `bee`, `clippy`, `cow`, `debug_assertions`, `doc`, `doctest`, `fmt_debug`, `foo`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
+   = help: expected names are: `bar`, `bee`, `cow`, and `foo` and 30 more
    = help: to expect this configuration use `--check-cfg=cfg(value)`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

tests/ui/check-cfg/cfg-value-for-cfg-name-multiple.stderr

@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `my_value`
 LL | #[cfg(my_value)]
    |       ^^^^^^^^
    |
-   = help: expected names are: `bar`, `clippy`, `debug_assertions`, `doc`, `doctest`, `fmt_debug`, `foo`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
+   = help: expected names are: `bar` and `foo` and 30 more
    = help: to expect this configuration use `--check-cfg=cfg(my_value)`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

tests/ui/check-cfg/cfg-value-for-cfg-name.stderr

@@ -4,7 +4,6 @@ warning: unexpected `cfg` condition name: `linux`
 LL | #[cfg(linux)]
    |       ^^^^^ help: found config with similar value: `target_os = "linux"`
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
    = help: to expect this configuration use `--check-cfg=cfg(linux)`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

tests/ui/check-cfg/compact-names.stderr

@@ -4,7 +4,6 @@ warning: unexpected `cfg` condition name: `target_architecture`
 LL | #[cfg(target(os = "linux", architecture = "arm"))]
    |                            ^^^^^^^^^^^^^^^^^^^^
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
    = help: to expect this configuration use `--check-cfg=cfg(target_architecture, values("arm"))`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

tests/ui/check-cfg/exhaustive-names-values.empty_cfg.stderr

@@ -4,7 +4,6 @@ warning: unexpected `cfg` condition name: `unknown_key`
 LL | #[cfg(unknown_key = "value")]
    |       ^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
    = help: to expect this configuration use `--check-cfg=cfg(unknown_key, values("value"))`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

tests/ui/check-cfg/exhaustive-names-values.feature.stderr

@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `unknown_key`
 LL | #[cfg(unknown_key = "value")]
    |       ^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `feature`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
+   = help: expected names are: `feature` and 30 more
    = help: to expect this configuration use `--check-cfg=cfg(unknown_key, values("value"))`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

tests/ui/check-cfg/exhaustive-names-values.full.stderr

@@ -4,7 +4,7 @@ warning: unexpected `cfg` condition name: `unknown_key`
 LL | #[cfg(unknown_key = "value")]
    |       ^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `feature`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
+   = help: expected names are: `feature` and 30 more
    = help: to expect this configuration use `--check-cfg=cfg(unknown_key, values("value"))`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

tests/ui/check-cfg/exhaustive-names.stderr

@@ -4,7 +4,6 @@ warning: unexpected `cfg` condition name: `unknown_key`
 LL | #[cfg(unknown_key = "value")]
    |       ^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
    = help: to expect this configuration use `--check-cfg=cfg(unknown_key, values("value"))`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
    = note: `#[warn(unexpected_cfgs)]` on by default

tests/ui/check-cfg/mix.stderr

@@ -44,7 +44,7 @@ warning: unexpected `cfg` condition name: `uu`
 LL | #[cfg_attr(uu, unix)]
    |            ^^
    |
-   = help: expected names are: `clippy`, `debug_assertions`, `doc`, `doctest`, `feature`, `fmt_debug`, `miri`, `overflow_checks`, `panic`, `proc_macro`, `relocation_model`, `rustfmt`, `sanitize`, `sanitizer_cfi_generalize_pointers`, `sanitizer_cfi_normalize_integers`, `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`, `ub_checks`, `unix`, and `windows`
+   = help: expected names are: `feature` and 30 more
    = help: to expect this configuration use `--check-cfg=cfg(uu)`
    = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration