Auto merge of #9412 - xFrednet:jst-r-bool-to-int-lint, r=xFrednet

New lint `bool_to_int_with_if`

This is a rebased version of #9086 I could sadly not push directly push to the PR branch as it's protected.

The lint implementation comes from `@jst-r.` Thank you for the work you put into this :)

---

Closes: #8131
Closes: #9086

changelog: Add lint [`bool_to_int_with_if`]

r? `@ghost`

Author: bors

CHANGELOG.md

@@ -3603,6 +3603,7 @@ Released 2018-09-13
 [`blocks_in_if_conditions`]: https://rust-lang.github.io/rust-clippy/master/index.html#blocks_in_if_conditions
 [`bool_assert_comparison`]: https://rust-lang.github.io/rust-clippy/master/index.html#bool_assert_comparison
 [`bool_comparison`]: https://rust-lang.github.io/rust-clippy/master/index.html#bool_comparison
+[`bool_to_int_with_if`]: https://rust-lang.github.io/rust-clippy/master/index.html#bool_to_int_with_if
 [`borrow_as_ptr`]: https://rust-lang.github.io/rust-clippy/master/index.html#borrow_as_ptr
 [`borrow_deref_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#borrow_deref_ref
 [`borrow_interior_mutable_const`]: https://rust-lang.github.io/rust-clippy/master/index.html#borrow_interior_mutable_const

clippy_lints/src/bool_to_int_with_if.rs

@@ -0,0 +1,125 @@
+use rustc_ast::{ExprPrecedence, LitKind};
+use rustc_hir::{Block, ExprKind};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+
+use clippy_utils::{diagnostics::span_lint_and_then, is_else_clause, source::snippet_block_with_applicability};
+use rustc_errors::Applicability;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Instead of using an if statement to convert a bool to an int,
+    /// this lint suggests using a `from()` function or an `as` coercion.
+    ///
+    /// ### Why is this bad?
+    /// Coercion or `from()` is idiomatic way to convert bool to a number.
+    /// Both methods are guaranteed to return 1 for true, and 0 for false.
+    ///
+    /// See https://doc.rust-lang.org/std/primitive.bool.html#impl-From%3Cbool%3E
+    ///
+    /// ### Example
+    /// ```rust
+    /// # let condition = false;
+    /// if condition {
+    ///     1_i64
+    /// } else {
+    ///     0
+    /// };
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// # let condition = false;
+    /// i64::from(condition);
+    /// ```
+    /// or
+    /// ```rust
+    /// # let condition = false;
+    /// condition as i64;
+    /// ```
+    #[clippy::version = "1.65.0"]
+    pub BOOL_TO_INT_WITH_IF,
+    style,
+    "using if to convert bool to int"
+}
+declare_lint_pass!(BoolToIntWithIf => [BOOL_TO_INT_WITH_IF]);
+
+impl<'tcx> LateLintPass<'tcx> for BoolToIntWithIf {
+    fn check_expr(&mut self, ctx: &LateContext<'tcx>, expr: &'tcx rustc_hir::Expr<'tcx>) {
+        if !expr.span.from_expansion() {
+            check_if_else(ctx, expr);
+        }
+    }
+}
+
+fn check_if_else<'tcx>(ctx: &LateContext<'tcx>, expr: &'tcx rustc_hir::Expr<'tcx>) {
+    if let ExprKind::If(check, then, Some(else_)) = expr.kind
+        && let Some(then_lit) = int_literal(then)
+        && let Some(else_lit) = int_literal(else_)
+        && check_int_literal_equals_val(then_lit, 1)
+        && check_int_literal_equals_val(else_lit, 0)
+    {
+        let mut applicability = Applicability::MachineApplicable;
+        let snippet = snippet_block_with_applicability(ctx, check.span, "..", None, &mut applicability);
+        let snippet_with_braces = {
+            let need_parens = should_have_parentheses(check);
+            let (left_paren, right_paren) = if need_parens {("(", ")")} else {("", "")};
+            format!("{left_paren}{snippet}{right_paren}")
+        };
+
+        let ty = ctx.typeck_results().expr_ty(then_lit); // then and else must be of same type
+
+        let suggestion = {
+            let wrap_in_curly = is_else_clause(ctx.tcx, expr);
+            let (left_curly, right_curly) = if wrap_in_curly {("{", "}")} else {("", "")};
+            format!(
+                "{left_curly}{ty}::from({snippet}){right_curly}"
+            )
+        }; // when used in else clause if statement should be wrapped in curly braces
+
+        span_lint_and_then(ctx,
+            BOOL_TO_INT_WITH_IF,
+            expr.span,
+            "boolean to int conversion using if",
+            |diag| {
+            diag.span_suggestion(
+                expr.span,
+                "replace with from",
+                suggestion,
+                applicability,
+            );
+            diag.note(format!("`{snippet_with_braces} as {ty}` or `{snippet_with_braces}.into()` can also be valid options"));
+        });
+    };
+}
+
+// If block contains only a int literal expression, return literal expression
+fn int_literal<'tcx>(expr: &'tcx rustc_hir::Expr<'tcx>) -> Option<&'tcx rustc_hir::Expr<'tcx>> {
+    if let ExprKind::Block(block, _) = expr.kind
+        && let Block {
+            stmts: [],       // Shouldn't lint if statements with side effects
+            expr: Some(expr),
+            ..
+        } = block
+        && let ExprKind::Lit(lit) = &expr.kind
+        && let LitKind::Int(_, _) = lit.node
+    {
+        Some(expr)
+    } else {
+        None
+    }
+}
+
+fn check_int_literal_equals_val<'tcx>(expr: &'tcx rustc_hir::Expr<'tcx>, expected_value: u128) -> bool {
+    if let ExprKind::Lit(lit) = &expr.kind
+        && let LitKind::Int(val, _) = lit.node
+        && val == expected_value
+    {
+        true
+    } else {
+        false
+    }
+}
+
+fn should_have_parentheses<'tcx>(check: &'tcx rustc_hir::Expr<'tcx>) -> bool {
+    check.precedence().order() < ExprPrecedence::Cast.order()
+}

clippy_lints/src/lib.register_all.rs

@@ -17,6 +17,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
     LintId::of(await_holding_invalid::AWAIT_HOLDING_REFCELL_REF),
     LintId::of(blocks_in_if_conditions::BLOCKS_IN_IF_CONDITIONS),
     LintId::of(bool_assert_comparison::BOOL_ASSERT_COMPARISON),
+    LintId::of(bool_to_int_with_if::BOOL_TO_INT_WITH_IF),
     LintId::of(booleans::NONMINIMAL_BOOL),
     LintId::of(booleans::OVERLY_COMPLEX_BOOL_EXPR),
     LintId::of(borrow_deref_ref::BORROW_DEREF_REF),

clippy_lints/src/lib.register_lints.rs

@@ -56,6 +56,7 @@ store.register_lints(&[
     await_holding_invalid::AWAIT_HOLDING_REFCELL_REF,
     blocks_in_if_conditions::BLOCKS_IN_IF_CONDITIONS,
     bool_assert_comparison::BOOL_ASSERT_COMPARISON,
+    bool_to_int_with_if::BOOL_TO_INT_WITH_IF,
     booleans::NONMINIMAL_BOOL,
     booleans::OVERLY_COMPLEX_BOOL_EXPR,
     borrow_deref_ref::BORROW_DEREF_REF,

clippy_lints/src/lib.register_style.rs

@@ -6,6 +6,7 @@ store.register_group(true, "clippy::style", Some("clippy_style"), vec![
     LintId::of(assertions_on_constants::ASSERTIONS_ON_CONSTANTS),
     LintId::of(blocks_in_if_conditions::BLOCKS_IN_IF_CONDITIONS),
     LintId::of(bool_assert_comparison::BOOL_ASSERT_COMPARISON),
+    LintId::of(bool_to_int_with_if::BOOL_TO_INT_WITH_IF),
     LintId::of(casts::FN_TO_NUMERIC_CAST),
     LintId::of(casts::FN_TO_NUMERIC_CAST_WITH_TRUNCATION),
     LintId::of(collapsible_if::COLLAPSIBLE_ELSE_IF),

clippy_lints/src/lib.rs

@@ -178,6 +178,7 @@ mod attrs;
 mod await_holding_invalid;
 mod blocks_in_if_conditions;
 mod bool_assert_comparison;
+mod bool_to_int_with_if;
 mod booleans;
 mod borrow_deref_ref;
 mod cargo;
@@ -900,6 +901,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
     store.register_late_pass(|| Box::new(manual_string_new::ManualStringNew));
     store.register_late_pass(|| Box::new(unused_peekable::UnusedPeekable));
     store.register_early_pass(|| Box::new(multi_assignments::MultiAssignments));
+    store.register_late_pass(|| Box::new(bool_to_int_with_if::BoolToIntWithIf));
     // add lints here, do not remove this comment, it's used in `new_lint`
 }
 

clippy_lints/src/matches/single_match.rs

@@ -201,12 +201,8 @@ fn form_exhaustive_matches<'a>(cx: &LateContext<'a>, ty: Ty<'a>, left: &Pat<'_>,
             // in the arms, so we need to evaluate the correct offsets here in order to iterate in
             // both arms at the same time.
             let len = max(
-                left_in.len() + {
-                    if left_pos.is_some() { 1 } else { 0 }
-                },
-                right_in.len() + {
-                    if right_pos.is_some() { 1 } else { 0 }
-                },
+                left_in.len() + usize::from(left_pos.is_some()),
+                right_in.len() + usize::from(right_pos.is_some()),
             );
             let mut left_pos = left_pos.unwrap_or(usize::MAX);
             let mut right_pos = right_pos.unwrap_or(usize::MAX);

clippy_lints/src/only_used_in_recursion.rs

@@ -234,11 +234,7 @@ impl<'tcx> LateLintPass<'tcx> for OnlyUsedInRecursion {
             })) => (
                 def_id.to_def_id(),
                 FnKind::TraitFn,
-                if sig.decl.implicit_self.has_implicit_self() {
-                    1
-                } else {
-                    0
-                },
+                usize::from(sig.decl.implicit_self.has_implicit_self()),
             ),
             Some(Node::ImplItem(&ImplItem {
                 kind: ImplItemKind::Fn(ref sig, _),
@@ -253,11 +249,7 @@ impl<'tcx> LateLintPass<'tcx> for OnlyUsedInRecursion {
                     (
                         trait_item_id,
                         FnKind::ImplTraitFn(cx.tcx.erase_regions(trait_ref.substs) as *const _ as usize),
-                        if sig.decl.implicit_self.has_implicit_self() {
-                            1
-                        } else {
-                            0
-                        },
+                        usize::from(sig.decl.implicit_self.has_implicit_self()),
                     )
                 } else {
                     (def_id.to_def_id(), FnKind::Fn, 0)

tests/ui/author/struct.rs

@@ -1,4 +1,9 @@
-#[allow(clippy::unnecessary_operation, clippy::single_match)]
+#![allow(
+    clippy::unnecessary_operation,
+    clippy::single_match,
+    clippy::no_effect,
+    clippy::bool_to_int_with_if
+)]
 fn main() {
     struct Test {
         field: u32,

tests/ui/bool_to_int_with_if.fixed

@@ -0,0 +1,85 @@
+// run-rustfix
+
+#![warn(clippy::bool_to_int_with_if)]
+#![allow(unused, dead_code, clippy::unnecessary_operation, clippy::no_effect)]
+
+fn main() {
+    let a = true;
+    let b = false;
+
+    let x = 1;
+    let y = 2;
+
+    // Should lint
+    // precedence
+    i32::from(a);
+    i32::from(!a);
+    i32::from(a || b);
+    i32::from(cond(a, b));
+    i32::from(x + y < 4);
+
+    // if else if
+    if a {
+        123
+    } else {i32::from(b)};
+
+    // Shouldn't lint
+
+    if a {
+        1
+    } else if b {
+        0
+    } else {
+        3
+    };
+
+    if a {
+        3
+    } else if b {
+        1
+    } else {
+        -2
+    };
+
+    if a {
+        3
+    } else {
+        0
+    };
+    if a {
+        side_effect();
+        1
+    } else {
+        0
+    };
+    if a {
+        1
+    } else {
+        side_effect();
+        0
+    };
+
+    // multiple else ifs
+    if a {
+        123
+    } else if b {
+        1
+    } else if a | b {
+        0
+    } else {
+        123
+    };
+
+    some_fn(a);
+}
+
+// Lint returns and type inference
+fn some_fn(a: bool) -> u8 {
+    u8::from(a)
+}
+
+fn side_effect() {}
+
+fn cond(a: bool, b: bool) -> bool {
+    a || b
+}