102 lines
3.5 KiB
Rust
102 lines
3.5 KiB
Rust
//! Checks for needless boolean results of if-else expressions
|
|
//!
|
|
//! This lint is **warn** by default
|
|
|
|
use rustc::lint::*;
|
|
use rustc_front::hir::*;
|
|
|
|
use syntax::ast::Lit_::*;
|
|
|
|
use utils::{span_lint, snippet};
|
|
|
|
/// **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. It is `Warn` by default.
|
|
///
|
|
/// **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:** `if x { false } else { true }`
|
|
declare_lint! {
|
|
pub NEEDLESS_BOOL,
|
|
Warn,
|
|
"if-statements with plain booleans in the then- and else-clause, e.g. \
|
|
`if p { true } else { false }`"
|
|
}
|
|
|
|
#[derive(Copy,Clone)]
|
|
pub struct NeedlessBool;
|
|
|
|
impl LintPass for NeedlessBool {
|
|
fn get_lints(&self) -> LintArray {
|
|
lint_array!(NEEDLESS_BOOL)
|
|
}
|
|
}
|
|
|
|
impl LateLintPass for NeedlessBool {
|
|
fn check_expr(&mut self, cx: &LateContext, e: &Expr) {
|
|
if let ExprIf(ref pred, ref then_block, Some(ref else_expr)) = e.node {
|
|
match (fetch_bool_block(then_block), fetch_bool_expr(else_expr)) {
|
|
(Some(true), Some(true)) => {
|
|
span_lint(cx,
|
|
NEEDLESS_BOOL,
|
|
e.span,
|
|
"this if-then-else expression will always return true");
|
|
}
|
|
(Some(false), Some(false)) => {
|
|
span_lint(cx,
|
|
NEEDLESS_BOOL,
|
|
e.span,
|
|
"this if-then-else expression will always return false");
|
|
}
|
|
(Some(true), Some(false)) => {
|
|
let pred_snip = snippet(cx, pred.span, "..");
|
|
let hint = if pred_snip == ".." {
|
|
"its predicate".into()
|
|
} else {
|
|
format!("`{}`", pred_snip)
|
|
};
|
|
span_lint(cx,
|
|
NEEDLESS_BOOL,
|
|
e.span,
|
|
&format!("you can reduce this if-then-else expression to just {}", hint));
|
|
}
|
|
(Some(false), Some(true)) => {
|
|
let pred_snip = snippet(cx, pred.span, "..");
|
|
let hint = if pred_snip == ".." {
|
|
"`!` and its predicate".into()
|
|
} else {
|
|
format!("`!{}`", pred_snip)
|
|
};
|
|
span_lint(cx,
|
|
NEEDLESS_BOOL,
|
|
e.span,
|
|
&format!("you can reduce this if-then-else expression to just {}", hint));
|
|
}
|
|
_ => (),
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
fn fetch_bool_block(block: &Block) -> Option<bool> {
|
|
if block.stmts.is_empty() {
|
|
block.expr.as_ref().and_then(|e| fetch_bool_expr(e))
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
|
|
fn fetch_bool_expr(expr: &Expr) -> Option<bool> {
|
|
match expr.node {
|
|
ExprBlock(ref block) => fetch_bool_block(block),
|
|
ExprLit(ref lit_ptr) => {
|
|
if let LitBool(value) = lit_ptr.node {
|
|
Some(value)
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
_ => None,
|
|
}
|
|
}
|