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
17 use syntax::codemap::Spanned;
20 use utils::{in_macro, snippet, snippet_block, span_lint_and_then};
22 /// **What it does:** This lint checks for nested `if`-statements which can be collapsed by
23 /// `&&`-combining their conditions and for `else { if .. }` expressions that can be collapsed to
26 /// **Why is this bad?** Each `if`-statement adds one level of nesting, which makes code look more complex than it really is.
28 /// **Known problems:** None
30 /// **Example:** `if x { if y { .. } }`
34 "two nested `if`-expressions can be collapsed into one, e.g. `if x { if y { foo() } }` \
35 can be written as `if x && y { foo() }` and an `else { if .. } expression can be collapsed to \
40 pub struct CollapsibleIf;
42 impl LintPass for CollapsibleIf {
43 fn get_lints(&self) -> LintArray {
44 lint_array!(COLLAPSIBLE_IF)
48 impl EarlyLintPass for CollapsibleIf {
49 fn check_expr(&mut self, cx: &EarlyContext, expr: &ast::Expr) {
50 if !in_macro(cx, expr.span) {
56 fn check_if(cx: &EarlyContext, expr: &ast::Expr) {
58 ast::ExprKind::If(ref check, ref then, ref else_) => {
59 if let Some(ref else_) = *else_ {
60 check_collapsible_maybe_if_let(cx, else_);
62 check_collapsible_no_if_let(cx, expr, check, then);
65 ast::ExprKind::IfLet(_, _, _, Some(ref else_)) => {
66 check_collapsible_maybe_if_let(cx, else_);
72 fn check_collapsible_maybe_if_let(cx: &EarlyContext, else_: &ast::Expr) {
74 let ast::ExprKind::Block(ref block) = else_.node,
75 let Some(ref else_) = expr_block(block),
76 !in_macro(cx, else_.span),
79 ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => {
80 span_lint_and_then(cx,
83 "this `else { if .. }` block can be collapsed", |db| {
84 db.span_suggestion(block.span, "try", snippet_block(cx, else_.span, "..").into_owned());
92 fn check_collapsible_no_if_let(
99 let Some(inner) = expr_block(then),
100 let ast::ExprKind::If(ref check_inner, ref content, None) = inner.node,
102 if expr.span.expn_id != inner.span.expn_id {
105 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this if statement can be collapsed", |db| {
106 db.span_suggestion(expr.span,
108 format!("if {} && {} {}",
109 check_to_string(cx, check),
110 check_to_string(cx, check_inner),
111 snippet_block(cx, content.span, "..")));
116 fn requires_brackets(e: &ast::Expr) -> bool {
118 ast::ExprKind::Binary(Spanned { node: n, .. }, _, _) if n == ast::BinOpKind::Eq => false,
123 fn check_to_string(cx: &EarlyContext, e: &ast::Expr) -> Cow<'static, str> {
124 if requires_brackets(e) {
125 format!("({})", snippet(cx, e.span, "..")).into()
127 snippet(cx, e.span, "..")
131 /// If the block contains only one expression, returns it.
132 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
133 let mut it = block.stmts.iter();
135 if let (Some(stmt), None) = (it.next(), it.next()) {
137 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),