1 //! Checks for if expressions that contain only an if expression.
3 //! For example, the lint would catch:
8 //! println!("Hello world");
13 //! This lint is **warn** by default
15 use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
16 use rustc::{declare_tool_lint, lint_array};
17 use if_chain::if_chain;
20 use crate::utils::{in_macro, snippet_block, span_lint_and_sugg, span_lint_and_then};
21 use crate::utils::sugg::Sugg;
23 /// **What it does:** Checks for nested `if` statements which can be collapsed
24 /// by `&&`-combining their conditions and for `else { if ... }` expressions
26 /// can be collapsed to `else if ...`.
28 /// **Why is this bad?** Each `if`-statement adds one level of nesting, which
29 /// makes code look more complex than it really is.
31 /// **Known problems:** None.
52 /// Should be written:
67 declare_clippy_lint! {
70 "`if`s that can be collapsed (e.g. `if x { if y { ... } }` and `else { if x { ... } }`)"
73 #[derive(Copy, Clone)]
74 pub struct CollapsibleIf;
76 impl LintPass for CollapsibleIf {
77 fn get_lints(&self) -> LintArray {
78 lint_array!(COLLAPSIBLE_IF)
82 impl EarlyLintPass for CollapsibleIf {
83 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
84 if !in_macro(expr.span) {
90 fn check_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
92 ast::ExprKind::If(ref check, ref then, ref else_) => if let Some(ref else_) = *else_ {
93 check_collapsible_maybe_if_let(cx, else_);
95 check_collapsible_no_if_let(cx, expr, check, then);
97 ast::ExprKind::IfLet(_, _, _, Some(ref else_)) => {
98 check_collapsible_maybe_if_let(cx, else_);
104 fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, else_: &ast::Expr) {
106 if let ast::ExprKind::Block(ref block, _) = else_.node;
107 if let Some(else_) = expr_block(block);
108 if !in_macro(else_.span);
111 ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => {
112 span_lint_and_sugg(cx,
115 "this `else { if .. }` block can be collapsed",
117 snippet_block(cx, else_.span, "..").into_owned());
125 fn check_collapsible_no_if_let(cx: &EarlyContext<'_>, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
127 if let Some(inner) = expr_block(then);
128 if let ast::ExprKind::If(ref check_inner, ref content, None) = inner.node;
130 if expr.span.ctxt() != inner.span.ctxt() {
133 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this if statement can be collapsed", |db| {
134 let lhs = Sugg::ast(cx, check, "..");
135 let rhs = Sugg::ast(cx, check_inner, "..");
136 db.span_suggestion(expr.span,
140 snippet_block(cx, content.span, "..")));
146 /// If the block contains only one expression, return it.
147 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
148 let mut it = block.stmts.iter();
150 if let (Some(stmt), None) = (it.next(), it.next()) {
152 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),