Auto merge of #3556 - lucasloisp:bool-ord-comparison, r=oli-obk

Implements lint for order comparisons against bool (#3438)

As described on issue #3438, this change implements linting for `>` and `<` comparisons against both `boolean` literals and between expressions.

4 files changed, 153 insertions, 25 deletions

diff --git a/clippy_lints/src/needless_bool.rs b/clippy_lints/src/needless_bool.rs
index 3bb87fbf5e9..1ad7f4c5540 100644
--- a/clippy_lints/src/needless_bool.rs
+++ b/clippy_lints/src/needless_bool.rs
@@ -45,8 +45,9 @@ declare_clippy_lint! {
     "if-statements with plain booleans in the then- and else-clause, e.g. `if p { true } else { false }`"
 }
 
-/// **What it does:** Checks for expressions of the form `x == true` and
-/// `x != true` (or vice versa) and suggest using the variable directly.
+/// **What it does:** Checks for expressions of the form `x == true`,
+/// `x != true` and order comparisons such as `x < true` (or vice versa) and
+/// suggest using the variable directly.
 ///
 /// **Why is this bad?** Unnecessary code.
 ///
@@ -143,22 +144,54 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {
         }
 
         if let ExprKind::Binary(Spanned { node, .. }, ..) = e.node {
+            let ignore_case = None::<(fn(_) -> _, &str)>;
+            let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
             match node {
-                BinOpKind::Eq => check_comparison(
+                BinOpKind::Eq => {
+                    let true_case = Some((|h| h, "equality checks against true are unnecessary"));
+                    let false_case = Some((
+                        |h: Sugg<'_>| !h,
+                        "equality checks against false can be replaced by a negation",
+                    ));
+                    check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
+                },
+                BinOpKind::Ne => {
+                    let true_case = Some((
+                        |h: Sugg<'_>| !h,
+                        "inequality checks against true can be replaced by a negation",
+                    ));
+                    let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
+                    check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
+                },
+                BinOpKind::Lt => check_comparison(
                     cx,
                     e,
-                    "equality checks against true are unnecessary",
-                    "equality checks against false can be replaced by a negation",
-                    |h| h,
-                    |h| !h,
+                    ignore_case,
+                    Some((|h| h, "greater than checks against false are unnecessary")),
+                    Some((
+                        |h: Sugg<'_>| !h,
+                        "less than comparison against true can be replaced by a negation",
+                    )),
+                    ignore_case,
+                    Some((
+                        |l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
+                        "order comparisons between booleans can be simplified",
+                    )),
                 ),
-                BinOpKind::Ne => check_comparison(
+                BinOpKind::Gt => check_comparison(
                     cx,
                     e,
-                    "inequality checks against true can be replaced by a negation",
-                    "inequality checks against false are unnecessary",
-                    |h| !h,
-                    |h| h,
+                    Some((
+                        |h: Sugg<'_>| !h,
+                        "less than comparison against true can be replaced by a negation",
+                    )),
+                    ignore_case,
+                    ignore_case,
+                    Some((|h| h, "greater than checks against false are unnecessary")),
+                    Some((
+                        |l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
+                        "order comparisons between booleans can be simplified",
+                    )),
                 ),
                 _ => (),
             }
@@ -169,22 +202,45 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {
 fn check_comparison<'a, 'tcx>(
     cx: &LateContext<'a, 'tcx>,
     e: &'tcx Expr,
-    true_message: &str,
-    false_message: &str,
-    true_hint: impl FnOnce(Sugg<'_>) -> Sugg<'_>,
-    false_hint: impl FnOnce(Sugg<'_>) -> Sugg<'_>,
+    left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
+    left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
+    right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
+    right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
+    no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
 ) {
     use self::Expression::*;
 
     if let ExprKind::Binary(_, ref left_side, ref right_side) = e.node {
-        let applicability = Applicability::MachineApplicable;
+        let mut applicability = Applicability::MachineApplicable;
         match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
-            (Bool(true), Other) => suggest_bool_comparison(cx, e, right_side, applicability, true_message, true_hint),
-            (Other, Bool(true)) => suggest_bool_comparison(cx, e, left_side, applicability, true_message, true_hint),
-            (Bool(false), Other) => {
-                suggest_bool_comparison(cx, e, right_side, applicability, false_message, false_hint)
-            },
-            (Other, Bool(false)) => suggest_bool_comparison(cx, e, left_side, applicability, false_message, false_hint),
+            (Bool(true), Other) => left_true.map_or((), |(h, m)| {
+                suggest_bool_comparison(cx, e, right_side, applicability, m, h)
+            }),
+            (Other, Bool(true)) => right_true.map_or((), |(h, m)| {
+                suggest_bool_comparison(cx, e, left_side, applicability, m, h)
+            }),
+            (Bool(false), Other) => left_false.map_or((), |(h, m)| {
+                suggest_bool_comparison(cx, e, right_side, applicability, m, h)
+            }),
+            (Other, Bool(false)) => right_false.map_or((), |(h, m)| {
+                suggest_bool_comparison(cx, e, left_side, applicability, m, h)
+            }),
+            (Other, Other) => no_literal.map_or((), |(h, m)| {
+                let (l_ty, r_ty) = (cx.tables.expr_ty(left_side), cx.tables.expr_ty(right_side));
+                if l_ty.is_bool() && r_ty.is_bool() {
+                    let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
+                    let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
+                    span_lint_and_sugg(
+                        cx,
+                        BOOL_COMPARISON,
+                        e.span,
+                        m,
+                        "try simplifying it as shown",
+                        h(left_side, right_side).to_string(),
+                        applicability,
+                    )
+                }
+            }),
             _ => (),
         }
     }
@@ -196,7 +252,7 @@ fn suggest_bool_comparison<'a, 'tcx>(
     expr: &Expr,
     mut applicability: Applicability,
     message: &str,
-    conv_hint: impl FnOnce(Sugg<'_>) -> Sugg<'_>,
+    conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
 ) {
     let hint = Sugg::hir_with_applicability(cx, expr, "..", &mut applicability);
     span_lint_and_sugg(
diff --git a/clippy_lints/src/utils/sugg.rs b/clippy_lints/src/utils/sugg.rs
index c5f4a61fe8c..66f18b51f21 100644
--- a/clippy_lints/src/utils/sugg.rs
+++ b/clippy_lints/src/utils/sugg.rs
@@ -174,6 +174,11 @@ impl<'a> Sugg<'a> {
         make_binop(ast::BinOpKind::And, &self, rhs)
     }
 
+    /// Convenience method to create the `<lhs> & <rhs>` suggestion.
+    pub fn bit_and(self, rhs: &Self) -> Sugg<'static> {
+        make_binop(ast::BinOpKind::BitAnd, &self, rhs)
+    }
+
     /// Convenience method to create the `<lhs> as <rhs>` suggestion.
     pub fn as_ty<R: Display>(self, rhs: R) -> Sugg<'static> {
         make_assoc(AssocOp::As, &self, &Sugg::NonParen(rhs.to_string().into()))
diff --git a/tests/ui/bool_comparison.rs b/tests/ui/bool_comparison.rs
index 30b5acf2d97..2a28d0af1b2 100644
--- a/tests/ui/bool_comparison.rs
+++ b/tests/ui/bool_comparison.rs
@@ -50,4 +50,35 @@ fn main() {
     } else {
         "no"
     };
+    if x < true {
+        "yes"
+    } else {
+        "no"
+    };
+    if false < x {
+        "yes"
+    } else {
+        "no"
+    };
+    if x > false {
+        "yes"
+    } else {
+        "no"
+    };
+    if true > x {
+        "yes"
+    } else {
+        "no"
+    };
+    let y = true;
+    if x < y {
+        "yes"
+    } else {
+        "no"
+    };
+    if x > y {
+        "yes"
+    } else {
+        "no"
+    };
 }
diff --git a/tests/ui/bool_comparison.stderr b/tests/ui/bool_comparison.stderr
index d136bc656b6..9a12a8f089a 100644
--- a/tests/ui/bool_comparison.stderr
+++ b/tests/ui/bool_comparison.stderr
@@ -48,5 +48,41 @@ error: inequality checks against false are unnecessary
 48 |     if false != x {
    |        ^^^^^^^^^^ help: try simplifying it as shown: `x`
 
-error: aborting due to 8 previous errors
+error: less than comparison against true can be replaced by a negation
+  --> $DIR/bool_comparison.rs:53:8
+   |
+53 |     if x < true {
+   |        ^^^^^^^^ help: try simplifying it as shown: `!x`
+
+error: greater than checks against false are unnecessary
+  --> $DIR/bool_comparison.rs:58:8
+   |
+58 |     if false < x {
+   |        ^^^^^^^^^ help: try simplifying it as shown: `x`
+
+error: greater than checks against false are unnecessary
+  --> $DIR/bool_comparison.rs:63:8
+   |
+63 |     if x > false {
+   |        ^^^^^^^^^ help: try simplifying it as shown: `x`
+
+error: less than comparison against true can be replaced by a negation
+  --> $DIR/bool_comparison.rs:68:8
+   |
+68 |     if true > x {
+   |        ^^^^^^^^ help: try simplifying it as shown: `!x`
+
+error: order comparisons between booleans can be simplified
+  --> $DIR/bool_comparison.rs:74:8
+   |
+74 |     if x < y {
+   |        ^^^^^ help: try simplifying it as shown: `!x & y`
+
+error: order comparisons between booleans can be simplified
+  --> $DIR/bool_comparison.rs:79:8
+   |
+79 |     if x > y {
+   |        ^^^^^ help: try simplifying it as shown: `x & !y`
+
+error: aborting due to 14 previous errors