--- /dev/null
+//! Checks for needless boolean results of if-else expressions
+//!
+//! This lint is **warn** by default
+
+use crate::utils::sugg::Sugg;
+use crate::utils::{is_expn_of, parent_node_is_if_expr, snippet_with_applicability, span_lint, span_lint_and_sugg};
+use rustc_ast::ast::LitKind;
+use rustc_errors::Applicability;
+use rustc_hir::{BinOpKind, Block, Expr, ExprKind, StmtKind, UnOp};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::source_map::Spanned;
+use rustc_span::Span;
+
+declare_clippy_lint! {
+ /// **What it does:** Checks for expressions of the form `if c { true } else {
+ /// false }` (or vice versa) and suggests using the condition directly.
+ ///
+ /// **Why is this bad?** Redundant code.
+ ///
+ /// **Known problems:** Maybe false positives: Sometimes, the two branches are
+ /// painstakingly documented (which we, of course, do not detect), so they *may*
+ /// have some value. Even then, the documentation can be rewritten to match the
+ /// shorter code.
+ ///
+ /// **Example:**
+ /// ```rust,ignore
+ /// if x {
+ /// false
+ /// } else {
+ /// true
+ /// }
+ /// ```
+ /// Could be written as
+ /// ```rust,ignore
+ /// !x
+ /// ```
+ pub NEEDLESS_BOOL,
+ complexity,
+ "if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"
+}
+
+declare_clippy_lint! {
+ /// **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.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ /// ```rust,ignore
+ /// if x == true {}
+ /// if y == false {}
+ /// ```
+ /// use `x` directly:
+ /// ```rust,ignore
+ /// if x {}
+ /// if !y {}
+ /// ```
+ pub BOOL_COMPARISON,
+ complexity,
+ "comparing a variable to a boolean, e.g., `if x == true` or `if x != true`"
+}
+
+declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
+
+impl<'tcx> LateLintPass<'tcx> for NeedlessBool {
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
+ use self::Expression::{Bool, RetBool};
+ if let ExprKind::If(ref pred, ref then_block, Some(ref else_expr)) = e.kind {
+ let reduce = |ret, not| {
+ let mut applicability = Applicability::MachineApplicable;
+ let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
+ let mut snip = if not { !snip } else { snip };
+
+ if ret {
+ snip = snip.make_return();
+ }
+
+ if parent_node_is_if_expr(&e, &cx) {
+ snip = snip.blockify()
+ }
+
+ span_lint_and_sugg(
+ cx,
+ NEEDLESS_BOOL,
+ e.span,
+ "this if-then-else expression returns a bool literal",
+ "you can reduce it to",
+ snip.to_string(),
+ applicability,
+ );
+ };
+ if let ExprKind::Block(ref then_block, _) = then_block.kind {
+ match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
+ (RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
+ span_lint(
+ cx,
+ NEEDLESS_BOOL,
+ e.span,
+ "this if-then-else expression will always return true",
+ );
+ },
+ (RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
+ span_lint(
+ cx,
+ NEEDLESS_BOOL,
+ e.span,
+ "this if-then-else expression will always return false",
+ );
+ },
+ (RetBool(true), RetBool(false)) => reduce(true, false),
+ (Bool(true), Bool(false)) => reduce(false, false),
+ (RetBool(false), RetBool(true)) => reduce(true, true),
+ (Bool(false), Bool(true)) => reduce(false, true),
+ _ => (),
+ }
+ } else {
+ panic!("IfExpr `then` node is not an `ExprKind::Block`");
+ }
+ }
+ }
+}
+
+declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
+
+impl<'tcx> LateLintPass<'tcx> for BoolComparison {
+ fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
+ if e.span.from_expansion() {
+ return;
+ }
+
+ if let ExprKind::Binary(Spanned { node, .. }, ..) = e.kind {
+ let ignore_case = None::<(fn(_) -> _, &str)>;
+ let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
+ match node {
+ 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,
+ 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::Gt => check_comparison(
+ cx,
+ e,
+ 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",
+ )),
+ ),
+ _ => (),
+ }
+ }
+ }
+}
+
+struct ExpressionInfoWithSpan {
+ one_side_is_unary_not: bool,
+ left_span: Span,
+ right_span: Span,
+}
+
+fn is_unary_not(e: &Expr<'_>) -> (bool, Span) {
+ if let ExprKind::Unary(UnOp::Not, operand) = e.kind {
+ return (true, operand.span);
+ }
+ (false, e.span)
+}
+
+fn one_side_is_unary_not<'tcx>(left_side: &'tcx Expr<'_>, right_side: &'tcx Expr<'_>) -> ExpressionInfoWithSpan {
+ let left = is_unary_not(left_side);
+ let right = is_unary_not(right_side);
+
+ ExpressionInfoWithSpan {
+ one_side_is_unary_not: left.0 != right.0,
+ left_span: left.1,
+ right_span: right.1,
+ }
+}
+
+fn check_comparison<'a, 'tcx>(
+ cx: &LateContext<'tcx>,
+ e: &'tcx Expr<'_>,
+ 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::{Bool, Other};
+
+ if let ExprKind::Binary(op, ref left_side, ref right_side) = e.kind {
+ let (l_ty, r_ty) = (
+ cx.typeck_results().expr_ty(left_side),
+ cx.typeck_results().expr_ty(right_side),
+ );
+ if is_expn_of(left_side.span, "cfg").is_some() || is_expn_of(right_side.span, "cfg").is_some() {
+ return;
+ }
+ if l_ty.is_bool() && r_ty.is_bool() {
+ let mut applicability = Applicability::MachineApplicable;
+
+ if let BinOpKind::Eq = op.node {
+ let expression_info = one_side_is_unary_not(&left_side, &right_side);
+ if expression_info.one_side_is_unary_not {
+ span_lint_and_sugg(
+ cx,
+ BOOL_COMPARISON,
+ e.span,
+ "this comparison might be written more concisely",
+ "try simplifying it as shown",
+ format!(
+ "{} != {}",
+ snippet_with_applicability(cx, expression_info.left_span, "..", &mut applicability),
+ snippet_with_applicability(cx, expression_info.right_span, "..", &mut applicability)
+ ),
+ applicability,
+ )
+ }
+ }
+
+ match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
+ (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 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,
+ )
+ }),
+ _ => (),
+ }
+ }
+ }
+}
+
+fn suggest_bool_comparison<'a, 'tcx>(
+ cx: &LateContext<'tcx>,
+ e: &'tcx Expr<'_>,
+ expr: &Expr<'_>,
+ mut applicability: Applicability,
+ message: &str,
+ conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
+) {
+ let hint = if expr.span.from_expansion() {
+ if applicability != Applicability::Unspecified {
+ applicability = Applicability::MaybeIncorrect;
+ }
+ Sugg::hir_with_macro_callsite(cx, expr, "..")
+ } else {
+ Sugg::hir_with_applicability(cx, expr, "..", &mut applicability)
+ };
+ span_lint_and_sugg(
+ cx,
+ BOOL_COMPARISON,
+ e.span,
+ message,
+ "try simplifying it as shown",
+ conv_hint(hint).to_string(),
+ applicability,
+ );
+}
+
+enum Expression {
+ Bool(bool),
+ RetBool(bool),
+ Other,
+}
+
+fn fetch_bool_block(block: &Block<'_>) -> Expression {
+ match (&*block.stmts, block.expr.as_ref()) {
+ (&[], Some(e)) => fetch_bool_expr(&**e),
+ (&[ref e], None) => {
+ if let StmtKind::Semi(ref e) = e.kind {
+ if let ExprKind::Ret(_) = e.kind {
+ fetch_bool_expr(&**e)
+ } else {
+ Expression::Other
+ }
+ } else {
+ Expression::Other
+ }
+ },
+ _ => Expression::Other,
+ }
+}
+
+fn fetch_bool_expr(expr: &Expr<'_>) -> Expression {
+ match expr.kind {
+ ExprKind::Block(ref block, _) => fetch_bool_block(block),
+ ExprKind::Lit(ref lit_ptr) => {
+ if let LitKind::Bool(value) = lit_ptr.node {
+ Expression::Bool(value)
+ } else {
+ Expression::Other
+ }
+ },
+ ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
+ Expression::Bool(value) => Expression::RetBool(value),
+ _ => Expression::Other,
+ },
+ _ => Expression::Other,
+ }
+}
projects / rustc.git / blobdiff