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
18 use utils::{in_macro, snippet_block, span_lint_and_then, span_lint_and_sugg};
19 use utils::sugg::Sugg;
21 /// **What it does:** Checks for nested `if` statements which can be collapsed
22 /// by `&&`-combining their conditions and for `else { if ... }` expressions
24 /// can be collapsed to `else if ...`.
26 /// **Why is this bad?** Each `if`-statement adds one level of nesting, which
27 /// makes code look more complex than it really is.
29 /// **Known problems:** None.
50 /// Should be written:
68 "`if`s that can be collapsed (e.g. `if x { if y { ... } }` and `else { if x { ... } }`)"
71 #[derive(Copy, Clone)]
72 pub struct CollapsibleIf;
74 impl LintPass for CollapsibleIf {
75 fn get_lints(&self) -> LintArray {
76 lint_array!(COLLAPSIBLE_IF)
80 impl EarlyLintPass for CollapsibleIf {
81 fn check_expr(&mut self, cx: &EarlyContext, expr: &ast::Expr) {
82 if !in_macro(expr.span) {
88 fn check_if(cx: &EarlyContext, expr: &ast::Expr) {
90 ast::ExprKind::If(ref check, ref then, ref else_) => {
91 if let Some(ref else_) = *else_ {
92 check_collapsible_maybe_if_let(cx, else_);
94 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 let ast::ExprKind::Block(ref block) = else_.node,
107 let Some(else_) = expr_block(block),
108 !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());
124 fn check_collapsible_no_if_let(cx: &EarlyContext, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
126 let Some(inner) = expr_block(then),
127 let ast::ExprKind::If(ref check_inner, ref content, None) = inner.node,
129 if expr.span.ctxt != inner.span.ctxt {
132 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this if statement can be collapsed", |db| {
133 let lhs = Sugg::ast(cx, check, "..");
134 let rhs = Sugg::ast(cx, check_inner, "..");
135 db.span_suggestion(expr.span,
139 snippet_block(cx, content.span, "..")));
144 /// If the block contains only one expression, return it.
145 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
146 let mut it = block.stmts.iter();
148 if let (Some(stmt), None) = (it.next(), it.next()) {
150 ast::StmtKind::Expr(ref expr) |
151 ast::StmtKind::Semi(ref expr) => Some(expr),