Lint against empty cfg(any()/all())

Author: jamie-osec

compiler/rustc_attr_parsing/src/attributes/cfg.rs

@@ -7,6 +7,7 @@ use rustc_errors::{Applicability, Diagnostic, PResult, msg};
 use rustc_feature::{Features, GatedCfg, find_gated_cfg};
 use rustc_hir::attrs::CfgEntry;
 use rustc_hir::{AttrPath, RustcVersion, Target};
+use rustc_lint_defs::builtin::EMPTY_CFG_PREDICATE;
 use rustc_parse::parser::{ForceCollect, Parser, Recovery};
 use rustc_parse::{exp, parse_in};
 use rustc_session::Session;
@@ -19,6 +20,7 @@ use thin_vec::ThinVec;
 
 use crate::attributes::AttributeSafety;
 use crate::context::{AcceptContext, ShouldEmit};
+use crate::diagnostics::EmptyCfgPredictate;
 use crate::parser::{
     AllowExprMetavar, ArgParser, MetaItemListParser, MetaItemOrLitParser, NameValueParser,
 };
@@ -92,14 +94,42 @@ pub fn parse_cfg_entry(
                     };
                     CfgEntry::Not(Box::new(parse_cfg_entry(cx, single)?), list.span)
                 }
-                Some(sym::any) => CfgEntry::Any(
-                    list.mixed().flat_map(|sub_item| parse_cfg_entry(cx, sub_item)).collect(),
-                    list.span,
-                ),
-                Some(sym::all) => CfgEntry::All(
-                    list.mixed().flat_map(|sub_item| parse_cfg_entry(cx, sub_item)).collect(),
-                    list.span,
-                ),
+                Some(sym::any) => {
+                    if list.is_empty() && !list.span.from_expansion() {
+                        let span = meta.span();
+                        cx.emit_lint(
+                            EMPTY_CFG_PREDICATE,
+                            EmptyCfgPredictate {
+                                predicate_span: span,
+                                predicate: sym::any,
+                                lit: false,
+                            },
+                            span,
+                        );
+                    }
+                    CfgEntry::Any(
+                        list.mixed().flat_map(|sub_item| parse_cfg_entry(cx, sub_item)).collect(),
+                        list.span,
+                    )
+                }
+                Some(sym::all) => {
+                    if list.is_empty() && !list.span.from_expansion() {
+                        let span = meta.span();
+                        cx.emit_lint(
+                            EMPTY_CFG_PREDICATE,
+                            EmptyCfgPredictate {
+                                predicate_span: span,
+                                predicate: sym::all,
+                                lit: true,
+                            },
+                            span,
+                        );
+                    }
+                    CfgEntry::All(
+                        list.mixed().flat_map(|sub_item| parse_cfg_entry(cx, sub_item)).collect(),
+                        list.span,
+                    )
+                }
                 Some(sym::target) => parse_cfg_entry_target(cx, list, meta.span())?,
                 Some(sym::version) => parse_cfg_entry_version(cx, list, meta.span())?,
                 _ => {

compiler/rustc_attr_parsing/src/diagnostics.rs

@@ -782,6 +782,23 @@ pub(crate) mod unexpected_cfg_value {
     }
 }
 
+#[derive(Diagnostic)]
+#[diag("use of empty `cfg({$predicate}())`")]
+#[note(
+    "this used to be a common pattern before `cfg(true)` and `cfg(false)` were added to the language in Rust 1.88"
+)]
+pub(crate) struct EmptyCfgPredictate {
+    #[suggestion(
+        "consider using a boolean literal",
+        code = "{lit}",
+        applicability = "machine-applicable",
+        style = "verbose"
+    )]
+    pub predicate_span: Span,
+    pub predicate: Symbol,
+    pub lit: bool,
+}
+
 #[derive(Diagnostic)]
 pub(crate) enum InvalidOnClause {
     #[diag("empty `on`-clause in `#[rustc_on_unimplemented]`", code = E0232)]

compiler/rustc_lint_defs/src/builtin.rs

@@ -46,6 +46,7 @@ pub mod hardwired {
             DUPLICATE_MACRO_ATTRIBUTES,
             ELIDED_LIFETIMES_IN_ASSOCIATED_CONSTANT,
             ELIDED_LIFETIMES_IN_PATHS,
+            EMPTY_CFG_PREDICATE,
             EXPLICIT_BUILTIN_CFGS_IN_FLAGS,
             EXPORTED_PRIVATE_DEPENDENCIES,
             FFI_UNWIND_CALLS,
@@ -5578,3 +5579,31 @@ declare_lint! {
     "usage of `unsafe` code and other potentially unsound constructs",
     @eval_always = true
 }
+
+declare_lint! {
+    /// The `empty_cfg_predicate` lint detects the use of empty `cfg` predicate lists.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![deny(empty_cfg_predicate)]
+    /// #[cfg(any())]
+    /// fn foo() {}
+    ///
+    /// #[cfg(all())]
+    /// fn bar() {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// The meaning of `cfg(any())` and `cfg(all())` is not immediately obvious;
+    /// `cfg(false)` and `cfg(true)` respectively may be used instead.
+    /// This used to be a common pattern before `cfg(true)` and `cfg(false)`
+    /// were added to the language in Rust 1.88
+    pub EMPTY_CFG_PREDICATE,
+    Warn,
+    "detects use of empty `cfg(any())` and `cfg(all())`",
+    @msrv = "1.88.0";
+}

library/std/src/os/raw/mod.rs

@@ -9,7 +9,7 @@ macro_rules! alias_core_ffi {
     ($($t:ident)*) => {$(
         #[stable(feature = "raw_os", since = "1.1.0")]
         #[doc = include_str!(concat!("../../../../core/src/ffi/", stringify!($t), ".md"))]
-        #[doc(cfg(all()))]
+        #[doc(cfg(true))]
         pub type $t = core::ffi::$t;
     )*}
 }

library/std/src/os/windows/raw.rs

@@ -7,10 +7,10 @@ use crate::os::raw::c_void;
 #[stable(feature = "raw_ext", since = "1.1.0")]
 pub type HANDLE = *mut c_void;
 #[cfg(target_pointer_width = "32")]
-#[doc(cfg(all()))]
+#[doc(cfg(true))]
 #[stable(feature = "raw_ext", since = "1.1.0")]
 pub type SOCKET = u32;
 #[cfg(target_pointer_width = "64")]
-#[doc(cfg(all()))]
+#[doc(cfg(true))]
 #[stable(feature = "raw_ext", since = "1.1.0")]
 pub type SOCKET = u64;

src/tools/clippy/tests/ui-toml/toml_inconsistent_struct_constructor/conf_inconsistent_struct_constructor.fixed

@@ -44,6 +44,7 @@ mod field_attributes {
 // https://github.com/rust-lang/rust-clippy/pull/13737#discussion_r1874539800
 mod cfgs_between_fields {
     #[allow(clippy::non_minimal_cfg)]
+    #[allow(empty_cfg_predicate)]
     fn cfg_all() {
         struct S {
             a: i32,
@@ -62,6 +63,7 @@ mod cfgs_between_fields {
         };
     }
 
+    #[allow(empty_cfg_predicate)]
     fn cfg_any() {
         struct S {
             a: i32,

src/tools/clippy/tests/ui-toml/toml_inconsistent_struct_constructor/conf_inconsistent_struct_constructor.rs

@@ -44,6 +44,7 @@ mod field_attributes {
 // https://github.com/rust-lang/rust-clippy/pull/13737#discussion_r1874539800
 mod cfgs_between_fields {
     #[allow(clippy::non_minimal_cfg)]
+    #[allow(empty_cfg_predicate)]
     fn cfg_all() {
         struct S {
             a: i32,
@@ -62,6 +63,7 @@ mod cfgs_between_fields {
         };
     }
 
+    #[allow(empty_cfg_predicate)]
     fn cfg_any() {
         struct S {
             a: i32,

src/tools/clippy/tests/ui-toml/toml_inconsistent_struct_constructor/conf_inconsistent_struct_constructor.stderr

@@ -40,7 +40,7 @@ LL ~             expn_depth: if condition { 1 } else { 0 },
    |
 
 error: struct constructor field order is inconsistent with struct definition field order
-  --> tests/ui-toml/toml_inconsistent_struct_constructor/conf_inconsistent_struct_constructor.rs:56:13
+  --> tests/ui-toml/toml_inconsistent_struct_constructor/conf_inconsistent_struct_constructor.rs:57:13
    |
 LL | /             d: 0,
 LL | |
@@ -61,7 +61,7 @@ LL ~             d: 0,
    |
 
 error: struct constructor field order is inconsistent with struct definition field order
-  --> tests/ui-toml/toml_inconsistent_struct_constructor/conf_inconsistent_struct_constructor.rs:74:13
+  --> tests/ui-toml/toml_inconsistent_struct_constructor/conf_inconsistent_struct_constructor.rs:76:13
    |
 LL | /             d: 0,
 LL | |

src/tools/clippy/tests/ui/double_must_use_unfixable.rs

@@ -2,13 +2,13 @@
 #![expect(clippy::result_unit_err)]
 #![feature(never_type)]
 
-#[cfg_attr(all(), must_use, deprecated)]
+#[cfg_attr(true, must_use, deprecated)]
 pub fn issue_12320() -> Result<(), ()> {
     //~^ double_must_use
     unimplemented!();
 }
 
-#[cfg_attr(all(), deprecated, must_use)]
+#[cfg_attr(true, deprecated, must_use)]
 pub fn issue_12320_2() -> Result<(), ()> {
     //~^ double_must_use
     unimplemented!();

src/tools/clippy/tests/ui/double_must_use_unfixable.stderr

@@ -5,10 +5,10 @@ LL | pub fn issue_12320() -> Result<(), ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 help: remove `must_use`
-  --> tests/ui/double_must_use_unfixable.rs:5:19
+  --> tests/ui/double_must_use_unfixable.rs:5:18
    |
-LL | #[cfg_attr(all(), must_use, deprecated)]
-   |                   ^^^^^^^^
+LL | #[cfg_attr(true, must_use, deprecated)]
+   |                  ^^^^^^^^
    = note: alternatively, you may add an explicit reason to the `must_use` attribute
    = note: `-D clippy::double-must-use` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::double_must_use)]`
@@ -20,10 +20,10 @@ LL | pub fn issue_12320_2() -> Result<(), ()> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 help: remove `must_use`
-  --> tests/ui/double_must_use_unfixable.rs:11:31
+  --> tests/ui/double_must_use_unfixable.rs:11:30
    |
-LL | #[cfg_attr(all(), deprecated, must_use)]
-   |                               ^^^^^^^^
+LL | #[cfg_attr(true, deprecated, must_use)]
+   |                              ^^^^^^^^
    = note: alternatively, you may add an explicit reason to the `must_use` attribute
 
 error: aborting due to 2 previous errors