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::declare_lint_pass;
17 use rustc::lint::{EarlyContext, EarlyLintPass, LintArray, LintPass};
18 use rustc_session::declare_tool_lint;
21 use crate::utils::sugg::Sugg;
22 use crate::utils::{snippet_block, snippet_block_with_applicability, span_lint_and_sugg, span_lint_and_then};
23 use rustc_errors::Applicability;
25 declare_clippy_lint! {
26 /// **What it does:** Checks for nested `if` statements which can be collapsed
27 /// by `&&`-combining their conditions and for `else { if ... }` expressions
29 /// can be collapsed to `else if ...`.
31 /// **Why is this bad?** Each `if`-statement adds one level of nesting, which
32 /// makes code look more complex than it really is.
34 /// **Known problems:** None.
55 /// Should be written:
72 "`if`s that can be collapsed (e.g., `if x { if y { ... } }` and `else { if x { ... } }`)"
75 declare_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF]);
77 impl EarlyLintPass for CollapsibleIf {
78 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
79 if !expr.span.from_expansion() {
85 fn check_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
86 if let ast::ExprKind::If(check, then, else_) = &expr.kind {
87 if let Some(else_) = else_ {
88 check_collapsible_maybe_if_let(cx, else_);
89 } else if let ast::ExprKind::Let(..) = check.kind {
90 // Prevent triggering on `if let a = b { if c { .. } }`.
92 check_collapsible_no_if_let(cx, expr, check, then);
97 fn block_starts_with_comment(cx: &EarlyContext<'_>, expr: &ast::Block) -> bool {
98 // We trim all opening braces and whitespaces and then check if the next string is a comment.
99 let trimmed_block_text = snippet_block(cx, expr.span, "..")
100 .trim_start_matches(|c: char| c.is_whitespace() || c == '{')
102 trimmed_block_text.starts_with("//") || trimmed_block_text.starts_with("/*")
105 fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, else_: &ast::Expr) {
107 if let ast::ExprKind::Block(ref block, _) = else_.kind;
108 if !block_starts_with_comment(cx, block);
109 if let Some(else_) = expr_block(block);
110 if !else_.span.from_expansion();
111 if let ast::ExprKind::If(..) = else_.kind;
113 let mut applicability = Applicability::MachineApplicable;
118 "this `else { if .. }` block can be collapsed",
120 snippet_block_with_applicability(cx, else_.span, "..", &mut applicability).into_owned(),
127 fn check_collapsible_no_if_let(cx: &EarlyContext<'_>, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
129 if !block_starts_with_comment(cx, then);
130 if let Some(inner) = expr_block(then);
131 if let ast::ExprKind::If(ref check_inner, ref content, None) = inner.kind;
133 if let ast::ExprKind::Let(..) = check_inner.kind {
134 // Prevent triggering on `if c { if let a = b { .. } }`.
138 if expr.span.ctxt() != inner.span.ctxt() {
141 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this if statement can be collapsed", |db| {
142 let lhs = Sugg::ast(cx, check, "..");
143 let rhs = Sugg::ast(cx, check_inner, "..");
150 snippet_block(cx, content.span, ".."),
152 Applicability::MachineApplicable, // snippet
159 /// If the block contains only one expression, return it.
160 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
161 let mut it = block.stmts.iter();
163 if let (Some(stmt), None) = (it.next(), it.next()) {
165 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),