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.
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80
src/collapsible_if.rs
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80
src/collapsible_if.rs
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@ -0,0 +1,80 @@
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//! Checks for if expressions that contain only an if expression.
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//!
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//! For example, the lint would catch:
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//!
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//! ```
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//! if x {
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//! if y {
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//! println!("Hello world");
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//! }
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//! }
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//! ```
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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::def::*;
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use syntax::ast::*;
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use syntax::ptr::P;
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use syntax::codemap::{Span, Spanned};
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use syntax::print::pprust::expr_to_string;
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declare_lint! {
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pub COLLAPSIBLE_IF,
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Warn,
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"Warn on if expressions that can be collapsed"
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}
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#[derive(Copy,Clone)]
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pub struct CollapsibleIf;
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impl LintPass for CollapsibleIf {
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fn get_lints(&self) -> LintArray {
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lint_array!(COLLAPSIBLE_IF)
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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 check, ref then_block, None) = e.node {
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let expr = check_block(then_block);
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let expr = match expr {
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Some(e) => e,
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None => return
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};
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if let ExprIf(ref check_inner, _, None) = expr.node {
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let (check, check_inner) = (check_to_string(check), check_to_string(check_inner));
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cx.span_lint(COLLAPSIBLE_IF, e.span,
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&format!("This if statement can be collapsed. Try: if {} && {}", check, check_inner));
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}
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}
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}
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}
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fn requires_brackets(e: &Expr) -> bool {
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match e.node {
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ExprBinary(Spanned {node: n, ..}, _, _) if n == BiEq => false,
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_ => true
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}
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}
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fn check_to_string(e: &Expr) -> String {
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if requires_brackets(e) {
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format!("({})", expr_to_string(e))
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} else {
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format!("{}", expr_to_string(e))
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}
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}
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fn check_block(b: &Block) -> Option<&P<Expr>> {
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if b.stmts.len() == 1 && b.expr.is_none() {
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let stmt = &b.stmts[0];
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return match stmt.node {
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StmtExpr(ref e, _) => Some(e),
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_ => None
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};
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}
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if let Some(ref e) = b.expr {
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return Some(e);
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}
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None
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}
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@ -25,6 +25,7 @@ pub mod eta_reduction;
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pub mod identity_op;
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pub mod mut_mut;
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pub mod len_zero;
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pub mod collapsible_if;
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#[plugin_registrar]
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pub fn plugin_registrar(reg: &mut Registry) {
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@ -45,6 +46,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
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reg.register_lint_pass(box mut_mut::MutMut as LintPassObject);
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reg.register_lint_pass(box len_zero::LenZero as LintPassObject);
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reg.register_lint_pass(box misc::CmpOwned as LintPassObject);
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reg.register_lint_pass(box collapsible_if::CollapsibleIf as LintPassObject);
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reg.register_lint_group("clippy", vec![types::BOX_VEC, types::LINKEDLIST,
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misc::SINGLE_MATCH, misc::STR_TO_STRING,
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@ -61,5 +63,6 @@ pub fn plugin_registrar(reg: &mut Registry) {
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mut_mut::MUT_MUT,
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len_zero::LEN_ZERO,
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len_zero::LEN_WITHOUT_IS_EMPTY,
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collapsible_if::COLLAPSIBLE_IF,
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]);
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}
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37
tests/compile-fail/collapsible_if.rs
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37
tests/compile-fail/collapsible_if.rs
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@ -0,0 +1,37 @@
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#![feature(plugin)]
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#![plugin(clippy)]
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#[deny(collapsible_if)]
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fn main() {
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let x = "hello";
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let y = "world";
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if x == "hello" { //~ERROR This if statement can be collapsed
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if y == "world" {
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println!("Hello world!");
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}
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}
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if x == "hello" || x == "world" { //~ERROR This if statement can be collapsed
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if y == "world" || y == "hello" {
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println!("Hello world!");
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}
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}
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// Works because any if with an else statement cannot be collapsed.
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if x == "hello" {
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if y == "world" {
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println!("Hello world!");
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}
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} else {
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println!("Not Hello world");
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}
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if x == "hello" {
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if y == "world" {
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println!("Hello world!");
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} else {
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println!("Hello something else");
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}
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}
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}
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