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:
50 #[clippy::version = "pre 1.29.0"]
53 "nested `if`s that can be collapsed (e.g., `if x { if y { ... } }`"
56 declare_clippy_lint! {
58 /// Checks for collapsible `else { if ... }` expressions
59 /// that can be collapsed to `else if ...`.
61 /// ### Why is this bad?
62 /// Each `if`-statement adds one level of nesting, which
63 /// makes code look more complex than it really is.
77 /// Should be written:
86 #[clippy::version = "1.51.0"]
87 pub COLLAPSIBLE_ELSE_IF,
89 "nested `else`-`if` expressions that can be collapsed (e.g., `else { if x { ... } }`)"
92 declare_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF, COLLAPSIBLE_ELSE_IF]);
94 impl EarlyLintPass for CollapsibleIf {
95 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
96 if !expr.span.from_expansion() {
102 fn check_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
103 if let ast::ExprKind::If(check, then, else_) = &expr.kind {
104 if let Some(else_) = else_ {
105 check_collapsible_maybe_if_let(cx, else_);
106 } else if let ast::ExprKind::Let(..) = check.kind {
107 // Prevent triggering on `if let a = b { if c { .. } }`.
109 check_collapsible_no_if_let(cx, expr, check, then);
114 fn block_starts_with_comment(cx: &EarlyContext<'_>, expr: &ast::Block) -> bool {
115 // We trim all opening braces and whitespaces and then check if the next string is a comment.
116 let trimmed_block_text = snippet_block(cx, expr.span, "..", None)
117 .trim_start_matches(|c: char| c.is_whitespace() || c == '{')
119 trimmed_block_text.starts_with("//") || trimmed_block_text.starts_with("/*")
122 fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, else_: &ast::Expr) {
124 if let ast::ExprKind::Block(ref block, _) = else_.kind;
125 if !block_starts_with_comment(cx, block);
126 if let Some(else_) = expr_block(block);
127 if else_.attrs.is_empty();
128 if !else_.span.from_expansion();
129 if let ast::ExprKind::If(..) = else_.kind;
131 let mut applicability = Applicability::MachineApplicable;
136 "this `else { if .. }` block can be collapsed",
137 "collapse nested if block",
138 snippet_block_with_applicability(cx, else_.span, "..", Some(block.span), &mut applicability).into_owned(),
145 fn check_collapsible_no_if_let(cx: &EarlyContext<'_>, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
147 if !block_starts_with_comment(cx, then);
148 if let Some(inner) = expr_block(then);
149 if inner.attrs.is_empty();
150 if let ast::ExprKind::If(ref check_inner, ref content, None) = inner.kind;
151 // Prevent triggering on `if c { if let a = b { .. } }`.
152 if !matches!(check_inner.kind, ast::ExprKind::Let(..));
153 if expr.span.ctxt() == inner.span.ctxt();
155 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this `if` statement can be collapsed", |diag| {
156 let lhs = Sugg::ast(cx, check, "..");
157 let rhs = Sugg::ast(cx, check_inner, "..");
158 diag.span_suggestion(
160 "collapse nested if block",
164 snippet_block(cx, content.span, "..", Some(expr.span)),
166 Applicability::MachineApplicable, // snippet
173 /// If the block contains only one expression, return it.
174 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
175 let mut it = block.stmts.iter();
177 if let (Some(stmt), None) = (it.next(), it.next()) {
179 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),