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, 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};
25 declare_clippy_lint! {
27 /// Checks for nested `if` statements which can be collapsed
28 /// by `&&`-combining their conditions.
30 /// ### Why is this bad?
31 /// Each `if`-statement adds one level of nesting, which
32 /// makes code look more complex than it really is.
36 /// # let (x, y) = (true, true);
46 /// # let (x, y) = (true, true);
51 #[clippy::version = "pre 1.29.0"]
54 "nested `if`s that can be collapsed (e.g., `if x { if y { ... } }`"
57 declare_clippy_lint! {
59 /// Checks for collapsible `else { if ... }` expressions
60 /// that can be collapsed to `else if ...`.
62 /// ### Why is this bad?
63 /// Each `if`-statement adds one level of nesting, which
64 /// makes code look more complex than it really is.
78 /// Should be written:
87 #[clippy::version = "1.51.0"]
88 pub COLLAPSIBLE_ELSE_IF,
90 "nested `else`-`if` expressions that can be collapsed (e.g., `else { if x { ... } }`)"
93 declare_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF, COLLAPSIBLE_ELSE_IF]);
95 impl EarlyLintPass for CollapsibleIf {
96 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
97 if !expr.span.from_expansion() {
103 fn check_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
104 if let ast::ExprKind::If(check, then, else_) = &expr.kind {
105 if let Some(else_) = else_ {
106 check_collapsible_maybe_if_let(cx, then.span, else_);
107 } else if let ast::ExprKind::Let(..) = check.kind {
108 // Prevent triggering on `if let a = b { if c { .. } }`.
110 check_collapsible_no_if_let(cx, expr, check, then);
115 fn block_starts_with_comment(cx: &EarlyContext<'_>, expr: &ast::Block) -> bool {
116 // We trim all opening braces and whitespaces and then check if the next string is a comment.
117 let trimmed_block_text = snippet_block(cx, expr.span, "..", None)
118 .trim_start_matches(|c: char| c.is_whitespace() || c == '{')
120 trimmed_block_text.starts_with("//") || trimmed_block_text.starts_with("/*")
123 fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, then_span: Span, else_: &ast::Expr) {
125 if let ast::ExprKind::Block(ref block, _) = else_.kind;
126 if !block_starts_with_comment(cx, block);
127 if let Some(else_) = expr_block(block);
128 if else_.attrs.is_empty();
129 if !else_.span.from_expansion();
130 if let ast::ExprKind::If(..) = else_.kind;
133 // Check that the "else" is followed by whitespace
134 let up_to_else = then_span.between(block.span);
135 let requires_space = if let Some(c) = snippet(cx, up_to_else, "..").chars().last() { !c.is_whitespace() } else { false };
137 let mut applicability = Applicability::MachineApplicable;
142 "this `else { if .. }` block can be collapsed",
143 "collapse nested if block",
146 if requires_space { " " } else { "" },
147 snippet_block_with_applicability(cx, else_.span, "..", Some(block.span), &mut applicability)
155 fn check_collapsible_no_if_let(cx: &EarlyContext<'_>, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
157 if !block_starts_with_comment(cx, then);
158 if let Some(inner) = expr_block(then);
159 if inner.attrs.is_empty();
160 if let ast::ExprKind::If(ref check_inner, ref content, None) = inner.kind;
161 // Prevent triggering on `if c { if let a = b { .. } }`.
162 if !matches!(check_inner.kind, ast::ExprKind::Let(..));
163 if expr.span.ctxt() == inner.span.ctxt();
165 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this `if` statement can be collapsed", |diag| {
166 let lhs = Sugg::ast(cx, check, "..");
167 let rhs = Sugg::ast(cx, check_inner, "..");
168 diag.span_suggestion(
170 "collapse nested if block",
174 snippet_block(cx, content.span, "..", Some(expr.span)),
176 Applicability::MachineApplicable, // snippet
183 /// If the block contains only one expression, return it.
184 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
185 let mut it = block.stmts.iter();
187 if let (Some(stmt), None) = (it.next(), it.next()) {
189 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),