Add global_variables lint

Author: EFanZh

CHANGELOG.md

@@ -5729,6 +5729,7 @@ Released 2018-09-13
 [`get_first`]: https://rust-lang.github.io/rust-clippy/master/index.html#get_first
 [`get_last_with_len`]: https://rust-lang.github.io/rust-clippy/master/index.html#get_last_with_len
 [`get_unwrap`]: https://rust-lang.github.io/rust-clippy/master/index.html#get_unwrap
+[`global_variables`]: https://rust-lang.github.io/rust-clippy/master/index.html#global_variables
 [`host_endian_bytes`]: https://rust-lang.github.io/rust-clippy/master/index.html#host_endian_bytes
 [`identity_conversion`]: https://rust-lang.github.io/rust-clippy/master/index.html#identity_conversion
 [`identity_op`]: https://rust-lang.github.io/rust-clippy/master/index.html#identity_op

clippy_lints/src/declared_lints.rs

@@ -192,6 +192,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::functions::TOO_MANY_ARGUMENTS_INFO,
     crate::functions::TOO_MANY_LINES_INFO,
     crate::future_not_send::FUTURE_NOT_SEND_INFO,
+    crate::global_variables::GLOBAL_VARIABLES_INFO,
     crate::if_let_mutex::IF_LET_MUTEX_INFO,
     crate::if_not_else::IF_NOT_ELSE_INFO,
     crate::if_then_some_else_none::IF_THEN_SOME_ELSE_NONE_INFO,

clippy_lints/src/global_variables.rs

@@ -0,0 +1,61 @@
+use clippy_utils::diagnostics;
+use rustc_hir::{Item, ItemKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::declare_lint_pass;
+
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// Checks whether a global variable defined.
+    ///
+    /// ### Why restrict this?
+    ///
+    /// - Global variables can be modified from any part of the program, making it difficult to
+    ///   track and control their state.
+    /// - Global variables introduce implicit dependencies that are not visible in function
+    ///   signatures, making the code harder to understand and maintain.
+    /// - Global variables introduce persistent state, complicating unit tests and making them
+    ///   prone to side effects.
+    /// - Global variables create tight coupling between different parts of the program, making it
+    ///   harder to modify one part without affecting others.
+    ///
+    /// ### Example
+    ///
+    /// ```no_run
+    /// static STATE: State = Mutex::new(State::new());
+    ///
+    /// fn foo() {
+    ///    // Access global variable `STATE`.
+    /// }
+    /// ```
+    ///
+    /// Use instead:
+    ///
+    /// ```no_run
+    /// fn foo(state: &mut State) {
+    ///    // Access `state` argument instead of a global variable.
+    /// }
+    /// ```
+    #[clippy::version = "1.88.0"]
+    pub GLOBAL_VARIABLES,
+    nursery,
+    "global variables are discouraged"
+}
+
+declare_lint_pass!(GlobalVariables => [GLOBAL_VARIABLES]);
+
+impl<'tcx> LateLintPass<'tcx> for GlobalVariables {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
+        if matches!(item.kind, ItemKind::Static(..)) {
+            let tcx = cx.tcx;
+
+            if !tcx
+                .type_of(item.owner_id.def_id)
+                .skip_binder()
+                .is_freeze(tcx, cx.typing_env())
+            {
+                diagnostics::span_lint(cx, GLOBAL_VARIABLES, item.span, "found global variable");
+            }
+        }
+    }
+}

clippy_lints/src/lib.rs

@@ -155,6 +155,7 @@ mod from_raw_with_void_ptr;
 mod from_str_radix_10;
 mod functions;
 mod future_not_send;
+mod global_variables;
 mod if_let_mutex;
 mod if_not_else;
 mod if_then_some_else_none;
@@ -943,5 +944,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(manual_option_as_slice::ManualOptionAsSlice::new(conf)));
     store.register_late_pass(|_| Box::new(single_option_map::SingleOptionMap));
     store.register_late_pass(move |_| Box::new(redundant_test_prefix::RedundantTestPrefix));
+    store.register_late_pass(|_| Box::new(global_variables::GlobalVariables));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }

tests/ui/global_variables.rs

@@ -0,0 +1,28 @@
+#![warn(clippy::global_variables)]
+
+use std::sync::Mutex;
+use std::sync::atomic::AtomicU32;
+
+macro_rules! define_global_variable_with_macro {
+    () => {
+        static GLOBAL_VARIABLE_0: AtomicU32 = AtomicU32::new(2);
+        //~^ global_variables
+
+        static GLOBAL_VARIABLE_1: Mutex<u32> = Mutex::new(3);
+        //~^ global_variables
+    };
+}
+
+fn main() {
+    define_global_variable_with_macro!();
+
+    static GLOBAL_VARIABLE_2: AtomicU32 = AtomicU32::new(2);
+    //~^ global_variables
+
+    static GLOBAL_VARIABLE_3: Mutex<u32> = Mutex::new(3);
+    //~^ global_variables
+
+    static NOT_GLOBAL_VARIABLE_0: u32 = 1;
+    static NOT_GLOBAL_VARIABLE_1: Vec<AtomicU32> = Vec::new();
+    static NOT_GLOBAL_VARIABLE_2: Vec<Mutex<u32>> = Vec::new();
+}

tests/ui/global_variables.stderr

@@ -0,0 +1,38 @@
+error: found global variable
+  --> tests/ui/global_variables.rs:8:9
+   |
+LL |         static GLOBAL_VARIABLE_0: AtomicU32 = AtomicU32::new(2);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     define_global_variable_with_macro!();
+   |     ------------------------------------ in this macro invocation
+   |
+   = note: `-D clippy::global-variables` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::global_variables)]`
+   = note: this error originates in the macro `define_global_variable_with_macro` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: found global variable
+  --> tests/ui/global_variables.rs:11:9
+   |
+LL |         static GLOBAL_VARIABLE_1: Mutex<u32> = Mutex::new(3);
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     define_global_variable_with_macro!();
+   |     ------------------------------------ in this macro invocation
+   |
+   = note: this error originates in the macro `define_global_variable_with_macro` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: found global variable
+  --> tests/ui/global_variables.rs:19:5
+   |
+LL |     static GLOBAL_VARIABLE_2: AtomicU32 = AtomicU32::new(2);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: found global variable
+  --> tests/ui/global_variables.rs:22:5
+   |
+LL |     static GLOBAL_VARIABLE_3: Mutex<u32> = Mutex::new(3);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors
+