JOKE: Add lint to check for expressions that could be compile time

Author: GnomedDev

CHANGELOG.md

@@ -5727,6 +5727,7 @@ Released 2018-09-13
 [`misrefactored_assign_op`]: https://rust-lang.github.io/rust-clippy/master/index.html#misrefactored_assign_op
 [`missing_assert_message`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_assert_message
 [`missing_asserts_for_indexing`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_asserts_for_indexing
+[`missing_const_for_expr`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_const_for_expr
 [`missing_const_for_fn`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_const_for_fn
 [`missing_const_for_thread_local`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_const_for_thread_local
 [`missing_docs_in_private_items`]: https://rust-lang.github.io/rust-clippy/master/index.html#missing_docs_in_private_items

clippy_lints/src/declared_lints.rs

@@ -513,6 +513,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::mismatching_type_param_order::MISMATCHING_TYPE_PARAM_ORDER_INFO,
     crate::missing_assert_message::MISSING_ASSERT_MESSAGE_INFO,
     crate::missing_asserts_for_indexing::MISSING_ASSERTS_FOR_INDEXING_INFO,
+    crate::missing_const_for_expr::MISSING_CONST_FOR_EXPR_INFO,
     crate::missing_const_for_fn::MISSING_CONST_FOR_FN_INFO,
     crate::missing_const_for_thread_local::MISSING_CONST_FOR_THREAD_LOCAL_INFO,
     crate::missing_doc::MISSING_DOCS_IN_PRIVATE_ITEMS_INFO,

clippy_lints/src/lib.rs

@@ -1,3 +1,4 @@
+#![deny(clippy::missing_const_for_expr)]
 #![feature(array_windows)]
 #![feature(binary_heap_into_iter_sorted)]
 #![feature(box_patterns)]
@@ -232,6 +233,7 @@ mod misc_early;
 mod mismatching_type_param_order;
 mod missing_assert_message;
 mod missing_asserts_for_indexing;
+mod missing_const_for_expr;
 mod missing_const_for_fn;
 mod missing_const_for_thread_local;
 mod missing_doc;
@@ -951,5 +953,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(|_| Box::new(manual_ignore_case_cmp::ManualIgnoreCaseCmp));
     store.register_late_pass(|_| Box::new(unnecessary_literal_bound::UnnecessaryLiteralBound));
     store.register_late_pass(move |_| Box::new(arbitrary_source_item_ordering::ArbitrarySourceItemOrdering::new(conf)));
+    store.register_late_pass(|_| Box::new(missing_const_for_expr::MissingConstForExpr));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }

clippy_lints/src/missing_const_for_expr.rs

@@ -0,0 +1,67 @@
+use std::ops::ControlFlow;
+
+use clippy_utils::consts::ConstEvalCtxt;
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet_opt;
+use clippy_utils::visitors::Descend;
+use rustc_errors::Applicability;
+use rustc_hir::def_id::LocalDefId;
+use rustc_hir::intravisit::FnKind;
+use rustc_hir::{Body, ExprKind, FnDecl};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::declare_lint_pass;
+use rustc_span::Span;
+
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// ### Why restrict this?
+    ///
+    /// ### Example
+    /// ```no_run
+    /// // example code where clippy issues a warning
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// // example code which does not raise clippy warning
+    /// ```
+    #[clippy::version = "1.84.0"]
+    pub MISSING_CONST_FOR_EXPR,
+    restriction,
+    "not the default lint description"
+}
+
+declare_lint_pass!(MissingConstForExpr => [MISSING_CONST_FOR_EXPR]);
+
+impl LateLintPass<'_> for MissingConstForExpr {
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'_>,
+        _: FnKind<'_>,
+        _: &FnDecl<'_>,
+        body: &Body<'_>,
+        _: Span,
+        _: LocalDefId,
+    ) {
+        clippy_utils::visitors::for_each_expr_without_closures::<!, Descend>(body, |expr| {
+            if !matches!(expr.kind, ExprKind::ConstBlock(_))
+                && ConstEvalCtxt::new(cx).eval(expr).is_some()
+                && let Some(snippet) = snippet_opt(cx, expr.span)
+            {
+                span_lint_and_sugg(
+                    cx,
+                    MISSING_CONST_FOR_EXPR,
+                    expr.span,
+                    "this expression could be inside a `const` block",
+                    "replace with",
+                    format!("const {{ {snippet} }}"),
+                    Applicability::MachineApplicable,
+                );
+
+                ControlFlow::Continue(Descend::No)
+            } else {
+                ControlFlow::Continue(Descend::Yes)
+            }
+        });
+    }
+}

tests/ui/missing_const_for_expr.rs

@@ -0,0 +1,5 @@
+#![warn(clippy::missing_const_for_expr)]
+
+fn main() {
+    // test code goes here
+}