293 lines
11 KiB
Rust
293 lines
11 KiB
Rust
//! Checks for needless boolean results of if-else expressions
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//!
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//! This lint is **warn** by default
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use crate::utils::sugg::Sugg;
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use crate::utils::{higher, parent_node_is_if_expr, span_lint, span_lint_and_sugg};
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use rustc::lint::{LateContext, LateLintPass};
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use rustc_errors::Applicability;
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use rustc_hir::*;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::source_map::Spanned;
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use syntax::ast::LitKind;
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declare_clippy_lint! {
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/// **What it does:** Checks for expressions of the form `if c { true } else {
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/// false }`
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/// (or vice versa) and suggest using the condition directly.
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///
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/// **Why is this bad?** Redundant code.
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///
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/// **Known problems:** Maybe false positives: Sometimes, the two branches are
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/// painstakingly documented (which we, of course, do not detect), so they *may*
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/// have some value. Even then, the documentation can be rewritten to match the
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/// shorter code.
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///
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/// **Example:**
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/// ```rust,ignore
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/// if x {
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/// false
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/// } else {
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/// true
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/// }
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/// ```
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/// Could be written as
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/// ```rust,ignore
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/// !x
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/// ```
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pub NEEDLESS_BOOL,
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complexity,
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"if-statements with plain booleans in the then- and else-clause, e.g., `if p { true } else { false }`"
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for expressions of the form `x == true`,
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/// `x != true` and order comparisons such as `x < true` (or vice versa) and
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/// suggest using the variable directly.
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///
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/// **Why is this bad?** Unnecessary code.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust,ignore
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/// if x == true {} // could be `if x { }`
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/// ```
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pub BOOL_COMPARISON,
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complexity,
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"comparing a variable to a boolean, e.g., `if x == true` or `if x != true`"
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}
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declare_lint_pass!(NeedlessBool => [NEEDLESS_BOOL]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for NeedlessBool {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
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use self::Expression::*;
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if let Some((ref pred, ref then_block, Some(ref else_expr))) = higher::if_block(&e) {
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let reduce = |ret, not| {
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let mut applicability = Applicability::MachineApplicable;
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let snip = Sugg::hir_with_applicability(cx, pred, "<predicate>", &mut applicability);
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let mut snip = if not { !snip } else { snip };
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if ret {
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snip = snip.make_return();
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}
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if parent_node_is_if_expr(&e, &cx) {
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snip = snip.blockify()
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}
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span_lint_and_sugg(
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cx,
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NEEDLESS_BOOL,
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e.span,
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"this if-then-else expression returns a bool literal",
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"you can reduce it to",
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snip.to_string(),
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applicability,
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);
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};
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if let ExprKind::Block(ref then_block, _) = then_block.kind {
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match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
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(RetBool(true), RetBool(true)) | (Bool(true), Bool(true)) => {
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span_lint(
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cx,
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NEEDLESS_BOOL,
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e.span,
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"this if-then-else expression will always return true",
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);
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},
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(RetBool(false), RetBool(false)) | (Bool(false), Bool(false)) => {
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span_lint(
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cx,
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NEEDLESS_BOOL,
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e.span,
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"this if-then-else expression will always return false",
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);
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},
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(RetBool(true), RetBool(false)) => reduce(true, false),
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(Bool(true), Bool(false)) => reduce(false, false),
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(RetBool(false), RetBool(true)) => reduce(true, true),
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(Bool(false), Bool(true)) => reduce(false, true),
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_ => (),
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}
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} else {
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panic!("IfExpr `then` node is not an `ExprKind::Block`");
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}
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}
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}
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}
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declare_lint_pass!(BoolComparison => [BOOL_COMPARISON]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for BoolComparison {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, e: &'tcx Expr<'_>) {
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if e.span.from_expansion() {
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return;
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}
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if let ExprKind::Binary(Spanned { node, .. }, ..) = e.kind {
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let ignore_case = None::<(fn(_) -> _, &str)>;
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let ignore_no_literal = None::<(fn(_, _) -> _, &str)>;
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match node {
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BinOpKind::Eq => {
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let true_case = Some((|h| h, "equality checks against true are unnecessary"));
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let false_case = Some((
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|h: Sugg<'_>| !h,
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"equality checks against false can be replaced by a negation",
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));
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check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
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},
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BinOpKind::Ne => {
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let true_case = Some((
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|h: Sugg<'_>| !h,
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"inequality checks against true can be replaced by a negation",
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));
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let false_case = Some((|h| h, "inequality checks against false are unnecessary"));
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check_comparison(cx, e, true_case, false_case, true_case, false_case, ignore_no_literal)
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},
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BinOpKind::Lt => check_comparison(
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cx,
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e,
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ignore_case,
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Some((|h| h, "greater than checks against false are unnecessary")),
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Some((
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|h: Sugg<'_>| !h,
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"less than comparison against true can be replaced by a negation",
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)),
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ignore_case,
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Some((
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|l: Sugg<'_>, r: Sugg<'_>| (!l).bit_and(&r),
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"order comparisons between booleans can be simplified",
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)),
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),
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BinOpKind::Gt => check_comparison(
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cx,
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e,
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Some((
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|h: Sugg<'_>| !h,
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"less than comparison against true can be replaced by a negation",
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)),
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ignore_case,
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ignore_case,
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Some((|h| h, "greater than checks against false are unnecessary")),
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Some((
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|l: Sugg<'_>, r: Sugg<'_>| l.bit_and(&(!r)),
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"order comparisons between booleans can be simplified",
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)),
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),
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_ => (),
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}
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}
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}
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}
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fn check_comparison<'a, 'tcx>(
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cx: &LateContext<'a, 'tcx>,
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e: &'tcx Expr<'_>,
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left_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
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left_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
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right_true: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
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right_false: Option<(impl FnOnce(Sugg<'a>) -> Sugg<'a>, &str)>,
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no_literal: Option<(impl FnOnce(Sugg<'a>, Sugg<'a>) -> Sugg<'a>, &str)>,
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) {
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use self::Expression::*;
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if let ExprKind::Binary(_, ref left_side, ref right_side) = e.kind {
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let (l_ty, r_ty) = (cx.tables.expr_ty(left_side), cx.tables.expr_ty(right_side));
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if l_ty.is_bool() && r_ty.is_bool() {
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let mut applicability = Applicability::MachineApplicable;
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match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
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(Bool(true), Other) => left_true.map_or((), |(h, m)| {
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suggest_bool_comparison(cx, e, right_side, applicability, m, h)
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}),
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(Other, Bool(true)) => right_true.map_or((), |(h, m)| {
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suggest_bool_comparison(cx, e, left_side, applicability, m, h)
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}),
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(Bool(false), Other) => left_false.map_or((), |(h, m)| {
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suggest_bool_comparison(cx, e, right_side, applicability, m, h)
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}),
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(Other, Bool(false)) => right_false.map_or((), |(h, m)| {
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suggest_bool_comparison(cx, e, left_side, applicability, m, h)
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}),
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(Other, Other) => no_literal.map_or((), |(h, m)| {
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let left_side = Sugg::hir_with_applicability(cx, left_side, "..", &mut applicability);
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let right_side = Sugg::hir_with_applicability(cx, right_side, "..", &mut applicability);
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span_lint_and_sugg(
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cx,
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BOOL_COMPARISON,
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e.span,
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m,
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"try simplifying it as shown",
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h(left_side, right_side).to_string(),
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applicability,
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)
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}),
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_ => (),
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}
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}
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}
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}
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fn suggest_bool_comparison<'a, 'tcx>(
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cx: &LateContext<'a, 'tcx>,
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e: &'tcx Expr<'_>,
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expr: &Expr<'_>,
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mut applicability: Applicability,
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message: &str,
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conv_hint: impl FnOnce(Sugg<'a>) -> Sugg<'a>,
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) {
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let hint = Sugg::hir_with_applicability(cx, expr, "..", &mut applicability);
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span_lint_and_sugg(
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cx,
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BOOL_COMPARISON,
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e.span,
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message,
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"try simplifying it as shown",
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conv_hint(hint).to_string(),
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applicability,
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);
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}
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enum Expression {
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Bool(bool),
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RetBool(bool),
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Other,
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}
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fn fetch_bool_block(block: &Block<'_>) -> Expression {
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match (&*block.stmts, block.expr.as_ref()) {
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(&[], Some(e)) => fetch_bool_expr(&**e),
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(&[ref e], None) => {
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if let StmtKind::Semi(ref e) = e.kind {
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if let ExprKind::Ret(_) = e.kind {
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fetch_bool_expr(&**e)
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} else {
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Expression::Other
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}
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} else {
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Expression::Other
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}
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},
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_ => Expression::Other,
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}
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}
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fn fetch_bool_expr(expr: &Expr<'_>) -> Expression {
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match expr.kind {
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ExprKind::Block(ref block, _) => fetch_bool_block(block),
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ExprKind::Lit(ref lit_ptr) => {
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if let LitKind::Bool(value) = lit_ptr.node {
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Expression::Bool(value)
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} else {
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Expression::Other
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}
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},
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ExprKind::Ret(Some(ref expr)) => match fetch_bool_expr(expr) {
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Expression::Bool(value) => Expression::RetBool(value),
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_ => Expression::Other,
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},
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_ => Expression::Other,
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}
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}
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