64 lines
2.2 KiB
Rust
64 lines
2.2 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::plugin::Registry;
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use rustc::lint::*;
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use rustc::middle::const_eval::lookup_const_by_id;
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use rustc::middle::def::*;
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use syntax::ast::*;
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use syntax::ast_util::{is_comparison_binop, binop_to_string};
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use syntax::ptr::P;
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use syntax::codemap::Span;
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use utils::{de_p, span_lint};
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declare_lint! {
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pub NEEDLESS_BOOL,
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Warn,
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"Warn on needless use of if x { true } else { false } (or vice versa)"
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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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fn check_expr(&mut self, cx: &Context, e: &Expr) {
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if let ExprIf(_, ref then_block, Option::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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(Option::Some(true), Option::Some(true)) => {
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span_lint(cx, NEEDLESS_BOOL, e.span,
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"your if-then-else expression will always return true"); },
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(Option::Some(true), Option::Some(false)) => {
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span_lint(cx, NEEDLESS_BOOL, e.span,
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"you can reduce your if-statement to its predicate"); },
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(Option::Some(false), Option::Some(true)) => {
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span_lint(cx, NEEDLESS_BOOL, e.span,
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"you can reduce your if-statement to '!' + your predicate"); },
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(Option::Some(false), Option::Some(false)) => {
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span_lint(cx, NEEDLESS_BOOL, e.span,
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"your if-then-else expression will always return false"); },
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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().map(de_p).and_then(fetch_bool_expr)
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} else { Option::None }
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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) => if let &LitBool(value) = &lit_ptr.node {
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Option::Some(value) } else { Option::None },
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_ => Option::None
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}
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}
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