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1 | //! Checks for if expressions that contain only an if expression. |
2 | //! | |
3 | //! For example, the lint would catch: | |
4 | //! | |
5 | //! ```rust,ignore | |
6 | //! if x { | |
7 | //! if y { | |
8 | //! println!("Hello world"); | |
9 | //! } | |
10 | //! } | |
11 | //! ``` | |
12 | //! | |
13 | //! This lint is **warn** by default | |
14 | ||
15 | use if_chain::if_chain; | |
16 | use rustc_ast::ast; | |
17 | use rustc_lint::{EarlyContext, EarlyLintPass}; | |
18 | use rustc_session::{declare_lint_pass, declare_tool_lint}; | |
19 | ||
20 | use crate::utils::sugg::Sugg; | |
21 | use crate::utils::{snippet_block, snippet_block_with_applicability, span_lint_and_sugg, span_lint_and_then}; | |
22 | use rustc_errors::Applicability; | |
23 | ||
24 | declare_clippy_lint! { | |
25 | /// **What it does:** Checks for nested `if` statements which can be collapsed | |
26 | /// by `&&`-combining their conditions. | |
27 | /// | |
28 | /// **Why is this bad?** Each `if`-statement adds one level of nesting, which | |
29 | /// makes code look more complex than it really is. | |
30 | /// | |
31 | /// **Known problems:** None. | |
32 | /// | |
33 | /// **Example:** | |
34 | /// ```rust,ignore | |
35 | /// if x { | |
36 | /// if y { | |
37 | /// … | |
38 | /// } | |
39 | /// } | |
40 | /// | |
41 | /// ``` | |
42 | /// | |
43 | /// Should be written: | |
44 | /// | |
45 | /// ```rust.ignore | |
46 | /// if x && y { | |
47 | /// … | |
48 | /// } | |
49 | /// ``` | |
50 | pub COLLAPSIBLE_IF, | |
51 | style, | |
52 | "nested `if`s that can be collapsed (e.g., `if x { if y { ... } }`" | |
53 | } | |
54 | ||
55 | declare_clippy_lint! { | |
56 | /// **What it does:** Checks for collapsible `else { if ... }` expressions | |
57 | /// that can be collapsed to `else if ...`. | |
58 | /// | |
59 | /// **Why is this bad?** Each `if`-statement adds one level of nesting, which | |
60 | /// makes code look more complex than it really is. | |
61 | /// | |
62 | /// **Known problems:** None. | |
63 | /// | |
64 | /// **Example:** | |
65 | /// ```rust,ignore | |
66 | /// | |
67 | /// if x { | |
68 | /// … | |
69 | /// } else { | |
70 | /// if y { | |
71 | /// … | |
72 | /// } | |
73 | /// } | |
74 | /// ``` | |
75 | /// | |
76 | /// Should be written: | |
77 | /// | |
78 | /// ```rust.ignore | |
79 | /// if x { | |
80 | /// … | |
81 | /// } else if y { | |
82 | /// … | |
83 | /// } | |
84 | /// ``` | |
85 | pub COLLAPSIBLE_ELSE_IF, | |
86 | style, | |
87 | "nested `else`-`if` expressions that can be collapsed (e.g., `else { if x { ... } }`)" | |
88 | } | |
89 | ||
90 | declare_lint_pass!(CollapsibleIf => [COLLAPSIBLE_IF, COLLAPSIBLE_ELSE_IF]); | |
91 | ||
92 | impl EarlyLintPass for CollapsibleIf { | |
93 | fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &ast::Expr) { | |
94 | if !expr.span.from_expansion() { | |
95 | check_if(cx, expr) | |
96 | } | |
97 | } | |
98 | } | |
99 | ||
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 { .. } }`. | |
106 | } else { | |
107 | check_collapsible_no_if_let(cx, expr, check, then); | |
108 | } | |
109 | } | |
110 | } | |
111 | ||
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 == '{') | |
116 | .to_owned(); | |
117 | trimmed_block_text.starts_with("//") || trimmed_block_text.starts_with("/*") | |
118 | } | |
119 | ||
120 | fn check_collapsible_maybe_if_let(cx: &EarlyContext<'_>, else_: &ast::Expr) { | |
121 | if_chain! { | |
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; | |
128 | then { | |
129 | let mut applicability = Applicability::MachineApplicable; | |
130 | span_lint_and_sugg( | |
131 | cx, | |
132 | COLLAPSIBLE_ELSE_IF, | |
133 | block.span, | |
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(), | |
137 | applicability, | |
138 | ); | |
139 | } | |
140 | } | |
141 | } | |
142 | ||
143 | fn check_collapsible_no_if_let(cx: &EarlyContext<'_>, expr: &ast::Expr, check: &ast::Expr, then: &ast::Block) { | |
144 | if_chain! { | |
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(); | |
152 | then { | |
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( | |
157 | expr.span, | |
158 | "collapse nested if block", | |
159 | format!( | |
160 | "if {} {}", | |
161 | lhs.and(&rhs), | |
162 | snippet_block(cx, content.span, "..", Some(expr.span)), | |
163 | ), | |
164 | Applicability::MachineApplicable, // snippet | |
165 | ); | |
166 | }); | |
167 | } | |
168 | } | |
169 | } | |
170 | ||
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(); | |
174 | ||
175 | if let (Some(stmt), None) = (it.next(), it.next()) { | |
176 | match stmt.kind { | |
177 | ast::StmtKind::Expr(ref expr) | ast::StmtKind::Semi(ref expr) => Some(expr), | |
178 | _ => None, | |
179 | } | |
180 | } else { | |
181 | None | |
182 | } | |
183 | } |