New lint: always_true_conditions

CHANGELOG.md

@@ -5458,6 +5458,7 @@ Released 2018-09-13
 [`almost_complete_letter_range`]: https://rust-lang.github.io/rust-clippy/master/index.html#almost_complete_letter_range
 [`almost_complete_range`]: https://rust-lang.github.io/rust-clippy/master/index.html#almost_complete_range
 [`almost_swapped`]: https://rust-lang.github.io/rust-clippy/master/index.html#almost_swapped
+[`always_true_conditions`]: https://rust-lang.github.io/rust-clippy/master/index.html#always_true_conditions
 [`approx_constant`]: https://rust-lang.github.io/rust-clippy/master/index.html#approx_constant
 [`arbitrary_source_item_ordering`]: https://rust-lang.github.io/rust-clippy/master/index.html#arbitrary_source_item_ordering
 [`arc_with_non_send_sync`]: https://rust-lang.github.io/rust-clippy/master/index.html#arc_with_non_send_sync

clippy_lints/src/always_true_conditions.rs

@@ -0,0 +1,61 @@
+use clippy_utils::diagnostics::span_lint;
+use rustc_hir::{BinOpKind, Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::declare_lint_pass;
+
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// ### Why is this bad?
+    ///
+    /// ### Example
+    /// ```no_run
+    /// let foo = "anything";
+    /// if foo != "thing1" || foo != "thing2" {
+    ///     println!("always executes");
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```no_run
+    /// let foo = "anything";
+    /// if foo != "thing1" && foo != "thing2" {
+    ///     println!("sometimes executes");
+    /// }
+    /// ```
+    #[clippy::version = "1.87.0"]
+    pub ALWAYS_TRUE_CONDITIONS,
+    nursery,
+    "checks for if statement conditions which are always true"
+}
+
+declare_lint_pass!(AlwaysTrueConditions => [ALWAYS_TRUE_CONDITIONS]);
+
+fn context_applicable(expr: &Expr<'_>) -> bool {
+    if let ExprKind::Binary(new_op, new_f, new_l) = expr.kind {
+        if new_op.node == BinOpKind::Or {
+            //only continue DOWN if its an or.give me the zuck
+            let f = context_applicable(new_f);
+            let l = context_applicable(new_l);
+            l && f
+        } else {
+            new_op.node == BinOpKind::Ne
+        }
+    } else {
+        false
+    }
+}
+
+impl LateLintPass<'_> for AlwaysTrueConditions {
+    fn check_expr(&mut self, cx: &LateContext<'_>, e: &Expr<'_>) {
+        if let ExprKind::If(cond, _, _) = e.kind
+            && let ExprKind::DropTemps(cond) = cond.kind
+            && let ExprKind::Binary(f_op_kind, f_cond, l_cond) = cond.kind
+            && let BinOpKind::Or = f_op_kind.node
+        {
+            let msg = "expression will always be true, did you mean &&?";
+            if context_applicable(f_cond) && context_applicable(l_cond) {
+                span_lint(cx, ALWAYS_TRUE_CONDITIONS, e.span, msg);
+            }
+        }
+    }
+}

clippy_lints/src/declared_lints.rs

@@ -35,6 +35,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::utils::internal_lints::unsorted_clippy_utils_paths::UNSORTED_CLIPPY_UTILS_PATHS_INFO,
     crate::absolute_paths::ABSOLUTE_PATHS_INFO,
     crate::almost_complete_range::ALMOST_COMPLETE_RANGE_INFO,
+    crate::always_true_conditions::ALWAYS_TRUE_CONDITIONS_INFO,
     crate::approx_const::APPROX_CONSTANT_INFO,
     crate::arbitrary_source_item_ordering::ARBITRARY_SOURCE_ITEM_ORDERING_INFO,
     crate::arc_with_non_send_sync::ARC_WITH_NON_SEND_SYNC_INFO,

clippy_lints/src/lib.rs

@@ -75,6 +75,7 @@ pub mod deprecated_lints;
 // begin lints modules, do not remove this comment, it’s used in `update_lints`
 mod absolute_paths;
 mod almost_complete_range;
+mod always_true_conditions;
 mod approx_const;
 mod arbitrary_source_item_ordering;
 mod arc_with_non_send_sync;
@@ -984,5 +985,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
     store.register_late_pass(move |_| Box::new(non_std_lazy_statics::NonStdLazyStatic::new(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(|_| Box::new(always_true_conditions::AlwaysTrueConditions));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }

tests/ui/always_true_conditions.rs

@@ -0,0 +1,36 @@
+#![warn(clippy::always_true_conditions)]
+#[allow(clippy::needless_if)]
+fn foo_m(name: &str) {
+    if name != "Min" || name != "Max" || name != "Middle" {
+        //~^ always_true_conditions
+        println!("always prints");
+    } else {
+        println!("never prints");
+    }
+    if name != "Min" && name != "Max" {
+        println!("condition satisfied");
+    } else {
+        println!("else");
+    }
+}
+
+fn foo_s(name: &str) {
+    if name != "Min" || name != "Max" {
+        //~^ always_true_conditions
+        println!("always prints");
+    } else {
+        println!("never prints");
+    }
+    if name != "Min" && name != "Max" {
+        println!("condition satisfied");
+    } else {
+        println!("else");
+    }
+}
+
+fn catch_fails(input: &str) {
+    let b = true;
+    if b || input != "foo" {
+        println!("should not fire!");
+    }
+}

tests/ui/always_true_conditions.stderr

@@ -0,0 +1,27 @@
+error: expression will always be true, did you mean &&?
+  --> tests/ui/always_true_conditions.rs:4:5
+   |
+LL | /     if name != "Min" || name != "Max" || name != "Middle" {
+LL | |
+LL | |         println!("always prints");
+LL | |     } else {
+LL | |         println!("never prints");
+LL | |     }
+   | |_____^
+   |
+   = note: `-D clippy::always-true-conditions` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::always_true_conditions)]`
+
+error: expression will always be true, did you mean &&?
+  --> tests/ui/always_true_conditions.rs:18:5
+   |
+LL | /     if name != "Min" || name != "Max" {
+LL | |
+LL | |         println!("always prints");
+LL | |     } else {
+LL | |         println!("never prints");
+LL | |     }
+   | |_____^
+
+error: aborting due to 2 previous errors
+