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 if_chain::if_chain;
16 use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
17 use rustc::{declare_lint_pass, declare_tool_lint};
20 use crate::utils::sugg::Sugg;
21 use crate::utils::{in_macro, snippet_block, snippet_block_with_applicability, span_lint_and_sugg, span_lint_and_then};
22 use rustc_errors::Applicability;
24 declare_clippy_lint! {
25 /// **What it does:** Checks for nested `if` statements which can be collapsed
26 /// by `&&`-combining their conditions and for `else { if ... }` expressions
28 /// can be collapsed to `else if ...`.
30 /// **Why is this bad?** Each `if`-statement adds one level of nesting, which
31 /// makes code look more complex than it really is.
33 /// **Known problems:** None.
54 /// Should be written:
71 "`if`s that can be collapsed (e.g., `if x { if y { ... } }` and `else { if x { ... } }`)"
74 declare_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF]);
76 impl EarlyLintPass for CollapsibleIf {
77 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
78 if !in_macro(expr.span) {
84 fn check_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
86 ast::ExprKind::If(ref check, ref then, ref else_) => {
87 if let Some(ref else_) = *else_ {
88 check_collapsible_maybe_if_let(cx, else_);
90 check_collapsible_no_if_let(cx, expr, check, then);
93 ast::ExprKind::IfLet(_, _, _, Some(ref else_)) => {
94 check_collapsible_maybe_if_let(cx, else_);
100 fn block_starts_with_comment(cx: &EarlyContext<'_>, expr: &ast::Block) -> bool {
101 // We trim all opening braces and whitespaces and then check if the next string is a comment.
102 let trimmed_block_text = snippet_block(cx, expr.span, "..")
103 .trim_start_matches(|c: char| c.is_whitespace() || c == '{')
105 trimmed_block_text.starts_with("//") || trimmed_block_text.starts_with("/*")
108 fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, else_: &ast::Expr) {
110 if let ast::ExprKind::Block(ref block, _) = else_.node;
111 if !block_starts_with_comment(cx, block);
112 if let Some(else_) = expr_block(block);
113 if !in_macro(else_.span);
116 ast::ExprKind::If(..) | ast::ExprKind::IfLet(..) => {
117 let mut applicability = Applicability::MachineApplicable;
122 "this `else { if .. }` block can be collapsed",
124 snippet_block_with_applicability(cx, else_.span, "..", &mut applicability).into_owned(),
134 fn check_collapsible_no_if_let(cx: &EarlyContext<'_>, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
136 if !block_starts_with_comment(cx, then);
137 if let Some(inner) = expr_block(then);
138 if let ast::ExprKind::If(ref check_inner, ref content, None) = inner.node;
140 if expr.span.ctxt() != inner.span.ctxt() {
143 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this if statement can be collapsed", |db| {
144 let lhs = Sugg::ast(cx, check, "..");
145 let rhs = Sugg::ast(cx, check_inner, "..");
152 snippet_block(cx, content.span, ".."),
154 Applicability::MachineApplicable, // snippet
161 /// If the block contains only one expression, return it.
162 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
163 let mut it = block.stmts.iter();
165 if let (Some(stmt), None) = (it.next(), it.next()) {
167 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),