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};
19 use utils::sugg::Sugg;
21 /// **What it does:** This lint checks for nested `if`-statements which can be collapsed by
22 /// `&&`-combining their conditions and for `else { if .. }` expressions that can be collapsed to
25 /// **Why is this bad?** Each `if`-statement adds one level of nesting, which makes code look more complex than it really is.
27 /// **Known problems:** None
29 /// **Example:** `if x { if y { .. } }`
33 "two nested `if`-expressions can be collapsed into one, e.g. `if x { if y { foo() } }` \
34 can be written as `if x && y { foo() }` and an `else { if .. } expression can be collapsed to \
39 pub struct CollapsibleIf;
41 impl LintPass for CollapsibleIf {
42 fn get_lints(&self) -> LintArray {
43 lint_array!(COLLAPSIBLE_IF)
47 impl EarlyLintPass for CollapsibleIf {
48 fn check_expr(&mut self, cx: &EarlyContext, expr: &ast::Expr) {
49 if !in_macro(cx, expr.span) {
55 fn check_if(cx: &EarlyContext, expr: &ast::Expr) {
57 ast::ExprKind::If(ref check, ref then, ref else_) => {
58 if let Some(ref else_) = *else_ {
59 check_collapsible_maybe_if_let(cx, else_);
61 check_collapsible_no_if_let(cx, expr, check, then);
64 ast::ExprKind::IfLet(_, _, _, Some(ref else_)) => {
65 check_collapsible_maybe_if_let(cx, else_);
71 fn check_collapsible_maybe_if_let(cx: &EarlyContext, else_: &ast::Expr) {
73 let ast::ExprKind::Block(ref block) = else_.node,
74 let Some(ref else_) = expr_block(block),
75 !in_macro(cx, else_.span),
78 ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => {
79 span_lint_and_then(cx,
82 "this `else { if .. }` block can be collapsed", |db| {
83 db.span_suggestion(block.span, "try", snippet_block(cx, else_.span, "..").into_owned());
91 fn check_collapsible_no_if_let(
98 let Some(inner) = expr_block(then),
99 let ast::ExprKind::If(ref check_inner, ref content, None) = inner.node,
101 if expr.span.expn_id != inner.span.expn_id {
104 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this if statement can be collapsed", |db| {
105 let lhs = Sugg::ast(cx, check, "..");
106 let rhs = Sugg::ast(cx, check_inner, "..");
107 db.span_suggestion(expr.span,
111 snippet_block(cx, content.span, "..")));
116 /// If the block contains only one expression, returns it.
117 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
118 let mut it = block.stmts.iter();
120 if let (Some(stmt), None) = (it.next(), it.next()) {
122 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),