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 crate::rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
16 use crate::rustc::{declare_tool_lint, lint_array};
17 use if_chain::if_chain;
18 use crate::syntax::ast;
20 use crate::utils::{in_macro, snippet_block, span_lint_and_sugg, span_lint_and_then};
21 use crate::utils::sugg::Sugg;
22 use crate::rustc_errors::Applicability;
24 /// **What it does:** Checks for nested `if` statements which can be collapsed
25 /// by `&&`-combining their conditions and for `else { if ... }` expressions
27 /// can be collapsed to `else if ...`.
29 /// **Why is this bad?** Each `if`-statement adds one level of nesting, which
30 /// makes code look more complex than it really is.
32 /// **Known problems:** None.
53 /// Should be written:
68 declare_clippy_lint! {
71 "`if`s that can be collapsed (e.g. `if x { if y { ... } }` and `else { if x { ... } }`)"
74 #[derive(Copy, Clone)]
75 pub struct CollapsibleIf;
77 impl LintPass for CollapsibleIf {
78 fn get_lints(&self) -> LintArray {
79 lint_array!(COLLAPSIBLE_IF)
83 impl EarlyLintPass for CollapsibleIf {
84 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
85 if !in_macro(expr.span) {
91 fn check_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
93 ast::ExprKind::If(ref check, ref then, ref else_) => if let Some(ref else_) = *else_ {
94 check_collapsible_maybe_if_let(cx, else_);
96 check_collapsible_no_if_let(cx, expr, check, then);
98 ast::ExprKind::IfLet(_, _, _, Some(ref else_)) => {
99 check_collapsible_maybe_if_let(cx, else_);
105 fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, else_: &ast::Expr) {
107 if let ast::ExprKind::Block(ref block, _) = else_.node;
108 if let Some(else_) = expr_block(block);
109 if !in_macro(else_.span);
112 ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => {
113 span_lint_and_sugg(cx,
116 "this `else { if .. }` block can be collapsed",
118 snippet_block(cx, else_.span, "..").into_owned());
126 fn check_collapsible_no_if_let(cx: &EarlyContext<'_>, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
128 if let Some(inner) = expr_block(then);
129 if let ast::ExprKind::If(ref check_inner, ref content, None) = inner.node;
131 if expr.span.ctxt() != inner.span.ctxt() {
134 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this if statement can be collapsed", |db| {
135 let lhs = Sugg::ast(cx, check, "..");
136 let rhs = Sugg::ast(cx, check_inner, "..");
137 db.span_suggestion_with_applicability(
143 snippet_block(cx, content.span, ".."),
145 Applicability::MachineApplicable, // snippet
152 /// If the block contains only one expression, return it.
153 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
154 let mut it = block.stmts.iter();
156 if let (Some(stmt), None) = (it.next(), it.next()) {
158 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),