mirror of
https://github.com/rust-lang/rust-clippy
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175 lines
6.6 KiB
Rust
175 lines
6.6 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 rustc::lint::*;
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use rustc_front::hir::*;
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use syntax::ast::Lit_;
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use syntax::codemap::Spanned;
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use utils::{span_lint, span_lint_and_then, snippet};
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/// **What it does:** This lint checks for expressions of the form `if c { true } else { false }` (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 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.
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///
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/// **Example:** `if x { false } else { true }`
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declare_lint! {
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pub NEEDLESS_BOOL,
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Warn,
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"if-statements with plain booleans in the then- and else-clause, e.g. \
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`if p { true } else { false }`"
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}
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/// **What it does:** This lint checks for expressions of the form `x == true` (or vice versa) and 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:** `if x == true { }` could be `if x { }`
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declare_lint! {
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pub BOOL_COMPARISON,
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Warn,
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"comparing a variable to a boolean, e.g. \
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`if x == true`"
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}
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#[derive(Copy,Clone)]
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pub struct NeedlessBool;
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impl LintPass for NeedlessBool {
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fn get_lints(&self) -> LintArray {
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lint_array!(NEEDLESS_BOOL)
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}
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}
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impl LateLintPass for NeedlessBool {
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fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
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if let ExprIf(ref pred, ref then_block, Some(ref else_expr)) = e.node {
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match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
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(Some(true), Some(true)) => {
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span_lint(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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(Some(false), Some(false)) => {
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span_lint(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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(Some(true), Some(false)) => {
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let pred_snip = snippet(cx, pred.span, "..");
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let hint = if pred_snip == ".." {
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"its predicate".into()
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} else {
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format!("`{}`", pred_snip)
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};
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span_lint(cx,
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NEEDLESS_BOOL,
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e.span,
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&format!("you can reduce this if-then-else expression to just {}", hint));
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}
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(Some(false), Some(true)) => {
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let pred_snip = snippet(cx, pred.span, "..");
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let hint = if pred_snip == ".." {
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"`!` and its predicate".into()
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} else {
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format!("`!{}`", pred_snip)
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};
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span_lint(cx,
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NEEDLESS_BOOL,
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e.span,
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&format!("you can reduce this if-then-else expression to just {}", hint));
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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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#[derive(Copy,Clone)]
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pub struct BoolComparison;
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impl LintPass for BoolComparison {
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fn get_lints(&self) -> LintArray {
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lint_array!(BOOL_COMPARISON)
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}
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}
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impl LateLintPass for BoolComparison {
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fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
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if let ExprBinary(Spanned{ node: BiEq, .. }, ref left_side, ref right_side) = e.node {
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match (fetch_bool_expr(left_side), fetch_bool_expr(right_side)) {
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(Some(true), None) => {
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let hint = snippet(cx, right_side.span, "..").into_owned();
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span_lint_and_then(cx,
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BOOL_COMPARISON,
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e.span,
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"equality checks against true are unnecesary",
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|db| {
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db.span_suggestion(e.span, "try simplifying it as shown:", hint);
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});
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}
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(None, Some(true)) => {
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let hint = snippet(cx, left_side.span, "..").into_owned();
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span_lint_and_then(cx,
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BOOL_COMPARISON,
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e.span,
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"equality checks against true are unnecesary",
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|db| {
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db.span_suggestion(e.span, "try simplifying it as shown:", hint);
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});
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}
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(Some(false), None) => {
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let hint = format!("!{}", snippet(cx, right_side.span, ".."));
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span_lint_and_then(cx,
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BOOL_COMPARISON,
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e.span,
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"equality checks against false can be replaced by a negation",
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|db| {
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db.span_suggestion(e.span, "try simplifying it as shown:", hint);
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});
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}
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(None, Some(false)) => {
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let hint = format!("!{}", snippet(cx, left_side.span, ".."));
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span_lint_and_then(cx,
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BOOL_COMPARISON,
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e.span,
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"equality checks against false can be replaced by a negation",
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|db| {
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db.span_suggestion(e.span, "try simplifying it as shown:", hint);
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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 fetch_bool_block(block: &Block) -> Option<bool> {
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if block.stmts.is_empty() {
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block.expr.as_ref().and_then(|e| fetch_bool_expr(e))
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} else {
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None
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}
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}
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fn fetch_bool_expr(expr: &Expr) -> Option<bool> {
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match expr.node {
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ExprBlock(ref block) => fetch_bool_block(block),
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ExprLit(ref lit_ptr) => {
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if let Lit_::LitBool(value) = lit_ptr.node {
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Some(value)
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} else {
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None
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}
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}
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_ => None,
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}
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}
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