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 if_chain::if_chain;
19 use rustc_errors::Applicability;
20 use rustc_lint::{EarlyContext, EarlyLintPass};
21 use rustc_session::{declare_lint_pass, declare_tool_lint};
23 use crate::utils::sugg::Sugg;
25 declare_clippy_lint! {
26 /// **What it does:** Checks for nested `if` statements which can be collapsed
27 /// by `&&`-combining their conditions.
29 /// **Why is this bad?** Each `if`-statement adds one level of nesting, which
30 /// makes code look more complex than it really is.
32 /// **Known problems:** None.
44 /// Should be written:
53 "nested `if`s that can be collapsed (e.g., `if x { if y { ... } }`"
56 declare_clippy_lint! {
57 /// **What it does:** Checks for collapsible `else { if ... }` expressions
58 /// that can be collapsed to `else if ...`.
60 /// **Why is this bad?** Each `if`-statement adds one level of nesting, which
61 /// makes code look more complex than it really is.
63 /// **Known problems:** None.
77 /// Should be written:
86 pub COLLAPSIBLE_ELSE_IF,
88 "nested `else`-`if` expressions that can be collapsed (e.g., `else { if x { ... } }`)"
91 declare_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF, COLLAPSIBLE_ELSE_IF]);
93 impl EarlyLintPass for CollapsibleIf {
94 fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) {
95 if !expr.span.from_expansion() {
101 fn check_if(cx: &EarlyContext<'_>, expr: &ast::Expr) {
102 if let ast::ExprKind::If(check, then, else_) = &expr.kind {
103 if let Some(else_) = else_ {
104 check_collapsible_maybe_if_let(cx, else_);
105 } else if let ast::ExprKind::Let(..) = check.kind {
106 // Prevent triggering on `if let a = b { if c { .. } }`.
108 check_collapsible_no_if_let(cx, expr, check, then);
113 fn block_starts_with_comment(cx: &EarlyContext<'_>, expr: &ast::Block) -> bool {
114 // We trim all opening braces and whitespaces and then check if the next string is a comment.
115 let trimmed_block_text = snippet_block(cx, expr.span, "..", None)
116 .trim_start_matches(|c: char| c.is_whitespace() || c == '{')
118 trimmed_block_text.starts_with("//") || trimmed_block_text.starts_with("/*")
121 fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, else_: &ast::Expr) {
123 if let ast::ExprKind::Block(ref block, _) = else_.kind;
124 if !block_starts_with_comment(cx, block);
125 if let Some(else_) = expr_block(block);
126 if else_.attrs.is_empty();
127 if !else_.span.from_expansion();
128 if let ast::ExprKind::If(..) = else_.kind;
130 let mut applicability = Applicability::MachineApplicable;
135 "this `else { if .. }` block can be collapsed",
136 "collapse nested if block",
137 snippet_block_with_applicability(cx, else_.span, "..", Some(block.span), &mut applicability).into_owned(),
144 fn check_collapsible_no_if_let(cx: &EarlyContext<'_>, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) {
146 if !block_starts_with_comment(cx, then);
147 if let Some(inner) = expr_block(then);
148 if inner.attrs.is_empty();
149 if let ast::ExprKind::If(ref check_inner, ref content, None) = inner.kind;
150 // Prevent triggering on `if c { if let a = b { .. } }`.
151 if !matches!(check_inner.kind, ast::ExprKind::Let(..));
152 if expr.span.ctxt() == inner.span.ctxt();
154 span_lint_and_then(cx, COLLAPSIBLE_IF, expr.span, "this `if` statement can be collapsed", |diag| {
155 let lhs = Sugg::ast(cx, check, "..");
156 let rhs = Sugg::ast(cx, check_inner, "..");
157 diag.span_suggestion(
159 "collapse nested if block",
163 snippet_block(cx, content.span, "..", Some(expr.span)),
165 Applicability::MachineApplicable, // snippet
172 /// If the block contains only one expression, return it.
173 fn expr_block(block: &ast::Block) -> Option<&ast::Expr> {
174 let mut it = block.stmts.iter();
176 if let (Some(stmt), None) = (it.next(), it.next()) {
178 ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr),