Add lint for ifs that could be collapsed

"Collapsible" ifs are ones which contain only a then block, and the then
block consists of an if that only has a then block.
This commit is contained in:
Matthew Hall 2015-05-29 15:07:34 +01:00
parent eb421ca202
commit 7e16822925
3 changed files with 120 additions and 0 deletions

80
src/collapsible_if.rs Normal file
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@ -0,0 +1,80 @@
//! Checks for if expressions that contain only an if expression.
//!
//! For example, the lint would catch:
//!
//! ```
//! if x {
//! if y {
//! println!("Hello world");
//! }
//! }
//! ```
//!
//! This lint is **warn** by default
use rustc::plugin::Registry;
use rustc::lint::*;
use rustc::middle::def::*;
use syntax::ast::*;
use syntax::ptr::P;
use syntax::codemap::{Span, Spanned};
use syntax::print::pprust::expr_to_string;
declare_lint! {
pub COLLAPSIBLE_IF,
Warn,
"Warn on if expressions that can be collapsed"
}
#[derive(Copy,Clone)]
pub struct CollapsibleIf;
impl LintPass for CollapsibleIf {
fn get_lints(&self) -> LintArray {
lint_array!(COLLAPSIBLE_IF)
}
fn check_expr(&mut self, cx: &Context, e: &Expr) {
if let ExprIf(ref check, ref then_block, None) = e.node {
let expr = check_block(then_block);
let expr = match expr {
Some(e) => e,
None => return
};
if let ExprIf(ref check_inner, _, None) = expr.node {
let (check, check_inner) = (check_to_string(check), check_to_string(check_inner));
cx.span_lint(COLLAPSIBLE_IF, e.span,
&format!("This if statement can be collapsed. Try: if {} && {}", check, check_inner));
}
}
}
}
fn requires_brackets(e: &Expr) -> bool {
match e.node {
ExprBinary(Spanned {node: n, ..}, _, _) if n == BiEq => false,
_ => true
}
}
fn check_to_string(e: &Expr) -> String {
if requires_brackets(e) {
format!("({})", expr_to_string(e))
} else {
format!("{}", expr_to_string(e))
}
}
fn check_block(b: &Block) -> Option<&P<Expr>> {
if b.stmts.len() == 1 && b.expr.is_none() {
let stmt = &b.stmts[0];
return match stmt.node {
StmtExpr(ref e, _) => Some(e),
_ => None
};
}
if let Some(ref e) = b.expr {
return Some(e);
}
None
}

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@ -25,6 +25,7 @@ pub mod eta_reduction;
pub mod identity_op;
pub mod mut_mut;
pub mod len_zero;
pub mod collapsible_if;
#[plugin_registrar]
pub fn plugin_registrar(reg: &mut Registry) {
@ -45,6 +46,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
reg.register_lint_pass(box mut_mut::MutMut as LintPassObject);
reg.register_lint_pass(box len_zero::LenZero as LintPassObject);
reg.register_lint_pass(box misc::CmpOwned as LintPassObject);
reg.register_lint_pass(box collapsible_if::CollapsibleIf as LintPassObject);
reg.register_lint_group("clippy", vec![types::BOX_VEC, types::LINKEDLIST,
misc::SINGLE_MATCH, misc::STR_TO_STRING,
@ -61,5 +63,6 @@ pub fn plugin_registrar(reg: &mut Registry) {
mut_mut::MUT_MUT,
len_zero::LEN_ZERO,
len_zero::LEN_WITHOUT_IS_EMPTY,
collapsible_if::COLLAPSIBLE_IF,
]);
}

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@ -0,0 +1,37 @@
#![feature(plugin)]
#![plugin(clippy)]
#[deny(collapsible_if)]
fn main() {
let x = "hello";
let y = "world";
if x == "hello" { //~ERROR This if statement can be collapsed
if y == "world" {
println!("Hello world!");
}
}
if x == "hello" || x == "world" { //~ERROR This if statement can be collapsed
if y == "world" || y == "hello" {
println!("Hello world!");
}
}
// Works because any if with an else statement cannot be collapsed.
if x == "hello" {
if y == "world" {
println!("Hello world!");
}
} else {
println!("Not Hello world");
}
if x == "hello" {
if y == "world" {
println!("Hello world!");
} else {
println!("Hello something else");
}
}
}