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 clippy_utils::diagnostics::{span_lint_and_sugg, span_lint_and_then};
16 use clippy_utils::source::{snippet_block, snippet_block_with_applicability};
17 use clippy_utils::sugg::Sugg;
18 use if_chain::if_chain;
20 use rustc_errors::Applicability;
21 use rustc_lint::{EarlyContext, EarlyLintPass};
22 use rustc_session::{declare_lint_pass, declare_tool_lint};
24 declare_clippy_lint! {
26 /// Checks for nested `if` statements which can be collapsed
27 /// by `&&`-combining their conditions.
29 /// ### Why is this bad?
30 /// Each `if`-statement adds one level of nesting, which
31 /// makes code look more complex than it really is.
43 /// Should be written:
52 "nested `if`s that can be collapsed (e.g., `if x { if y { ... } }`"
55 declare_clippy_lint! {
57 /// Checks for collapsible `else { if ... }` expressions
58 /// that can be collapsed to `else if ...`.
60 /// ### Why is this bad?
61 /// Each `if`-statement adds one level of nesting, which
62 /// makes code look more complex than it really is.
76 /// Should be written:
85 pub COLLAPSIBLE_ELSE_IF,
87 "nested `else`-`if` expressions that can be collapsed (e.g., `else { if x { ... } }`)"
90 declare_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF, COLLAPSIBLE_ELSE_IF]);
92 impl EarlyLintPass for CollapsibleIf {
93 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
94 if !expr.span.from_expansion() {
100 fn check_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
101 if let ast::ExprKind::If(check, then, else_) = &expr.kind {
102 if let Some(else_) = else_ {
103 check_collapsible_maybe_if_let(cx, else_);
104 } else if let ast::ExprKind::Let(..) = check.kind {
105 // Prevent triggering on `if let a = b { if c { .. } }`.
107 check_collapsible_no_if_let(cx, expr, check, then);
112 fn block_starts_with_comment(cx: &EarlyContext<'_>, expr: &ast::Block) -> bool {
113 // We trim all opening braces and whitespaces and then check if the next string is a comment.
114 let trimmed_block_text = snippet_block(cx, expr.span, "..", None)
115 .trim_start_matches(|c: char| c.is_whitespace() || c == '{')
117 trimmed_block_text.starts_with("//") || trimmed_block_text.starts_with("/*")
120 fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, else_: &ast::Expr) {
122 if let ast::ExprKind::Block(ref block, _) = else_.kind;
123 if !block_starts_with_comment(cx, block);
124 if let Some(else_) = expr_block(block);
125 if else_.attrs.is_empty();
126 if !else_.span.from_expansion();
127 if let ast::ExprKind::If(..) = else_.kind;
129 let mut applicability = Applicability::MachineApplicable;
134 "this `else { if .. }` block can be collapsed",
135 "collapse nested if block",
136 snippet_block_with_applicability(cx, else_.span, "..", Some(block.span), &mut applicability).into_owned(),
143 fn check_collapsible_no_if_let(cx: &EarlyContext<'_>, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
145 if !block_starts_with_comment(cx, then);
146 if let Some(inner) = expr_block(then);
147 if inner.attrs.is_empty();
148 if let ast::ExprKind::If(ref check_inner, ref content, None) = inner.kind;
149 // Prevent triggering on `if c { if let a = b { .. } }`.
150 if !matches!(check_inner.kind, ast::ExprKind::Let(..));
151 if expr.span.ctxt() == inner.span.ctxt();
153 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this `if` statement can be collapsed", |diag| {
154 let lhs = Sugg::ast(cx, check, "..");
155 let rhs = Sugg::ast(cx, check_inner, "..");
156 diag.span_suggestion(
158 "collapse nested if block",
162 snippet_block(cx, content.span, "..", Some(expr.span)),
164 Applicability::MachineApplicable, // snippet
171 /// If the block contains only one expression, return it.
172 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
173 let mut it = block.stmts.iter();
175 if let (Some(stmt), None) = (it.next(), it.next()) {
177 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),