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1 | use clippy_utils::diagnostics::span_lint_and_then; | |
2 | use clippy_utils::path_to_local; | |
3 | use clippy_utils::source::snippet_opt; | |
4 | use clippy_utils::visitors::{expr_visitor, is_local_used}; | |
5 | use rustc_errors::Applicability; | |
6 | use rustc_hir::intravisit::Visitor; | |
7 | use rustc_hir::{Block, Expr, ExprKind, HirId, Local, LocalSource, MatchSource, Node, Pat, PatKind, Stmt, StmtKind}; | |
8 | use rustc_lint::{LateContext, LateLintPass}; | |
9 | use rustc_session::{declare_lint_pass, declare_tool_lint}; | |
10 | use rustc_span::Span; | |
11 | ||
12 | declare_clippy_lint! { | |
13 | /// ### What it does | |
14 | /// Checks for late initializations that can be replaced by a `let` statement | |
15 | /// with an initializer. | |
16 | /// | |
17 | /// ### Why is this bad? | |
18 | /// Assigning in the `let` statement is less repetitive. | |
19 | /// | |
20 | /// ### Example | |
21 | /// ```rust | |
22 | /// let a; | |
23 | /// a = 1; | |
24 | /// | |
25 | /// let b; | |
26 | /// match 3 { | |
27 | /// 0 => b = "zero", | |
28 | /// 1 => b = "one", | |
29 | /// _ => b = "many", | |
30 | /// } | |
31 | /// | |
32 | /// let c; | |
33 | /// if true { | |
34 | /// c = 1; | |
35 | /// } else { | |
36 | /// c = -1; | |
37 | /// } | |
38 | /// ``` | |
39 | /// Use instead: | |
40 | /// ```rust | |
41 | /// let a = 1; | |
42 | /// | |
43 | /// let b = match 3 { | |
44 | /// 0 => "zero", | |
45 | /// 1 => "one", | |
46 | /// _ => "many", | |
47 | /// }; | |
48 | /// | |
49 | /// let c = if true { | |
50 | /// 1 | |
51 | /// } else { | |
52 | /// -1 | |
53 | /// }; | |
54 | /// ``` | |
55 | #[clippy::version = "1.58.0"] | |
56 | pub NEEDLESS_LATE_INIT, | |
57 | style, | |
58 | "late initializations that can be replaced by a `let` statement with an initializer" | |
59 | } | |
60 | declare_lint_pass!(NeedlessLateInit => [NEEDLESS_LATE_INIT]); | |
61 | ||
62 | fn contains_assign_expr<'tcx>(cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'tcx>) -> bool { | |
63 | let mut seen = false; | |
64 | expr_visitor(cx, |expr| { | |
65 | if let ExprKind::Assign(..) = expr.kind { | |
66 | seen = true; | |
67 | } | |
68 | ||
69 | !seen | |
70 | }) | |
71 | .visit_stmt(stmt); | |
72 | ||
73 | seen | |
74 | } | |
75 | ||
76 | #[derive(Debug)] | |
77 | struct LocalAssign { | |
78 | lhs_id: HirId, | |
79 | lhs_span: Span, | |
80 | rhs_span: Span, | |
81 | span: Span, | |
82 | } | |
83 | ||
84 | impl LocalAssign { | |
85 | fn from_expr(expr: &Expr<'_>, span: Span) -> Option<Self> { | |
86 | if let ExprKind::Assign(lhs, rhs, _) = expr.kind { | |
87 | if lhs.span.from_expansion() { | |
88 | return None; | |
89 | } | |
90 | ||
91 | Some(Self { | |
92 | lhs_id: path_to_local(lhs)?, | |
93 | lhs_span: lhs.span, | |
94 | rhs_span: rhs.span.source_callsite(), | |
95 | span, | |
96 | }) | |
97 | } else { | |
98 | None | |
99 | } | |
100 | } | |
101 | ||
102 | fn new<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>, binding_id: HirId) -> Option<LocalAssign> { | |
103 | let assign = match expr.kind { | |
104 | ExprKind::Block(Block { expr: Some(expr), .. }, _) => Self::from_expr(expr, expr.span), | |
105 | ExprKind::Block(block, _) => { | |
106 | if_chain! { | |
107 | if let Some((last, other_stmts)) = block.stmts.split_last(); | |
108 | if let StmtKind::Expr(expr) | StmtKind::Semi(expr) = last.kind; | |
109 | ||
110 | let assign = Self::from_expr(expr, last.span)?; | |
111 | ||
112 | // avoid visiting if not needed | |
113 | if assign.lhs_id == binding_id; | |
114 | if other_stmts.iter().all(|stmt| !contains_assign_expr(cx, stmt)); | |
115 | ||
116 | then { | |
117 | Some(assign) | |
118 | } else { | |
119 | None | |
120 | } | |
121 | } | |
122 | }, | |
123 | ExprKind::Assign(..) => Self::from_expr(expr, expr.span), | |
124 | _ => None, | |
125 | }?; | |
126 | ||
127 | if assign.lhs_id == binding_id { | |
128 | Some(assign) | |
129 | } else { | |
130 | None | |
131 | } | |
132 | } | |
133 | } | |
134 | ||
135 | fn assignment_suggestions<'tcx>( | |
136 | cx: &LateContext<'tcx>, | |
137 | binding_id: HirId, | |
138 | exprs: impl IntoIterator<Item = &'tcx Expr<'tcx>>, | |
139 | ) -> Option<(Applicability, Vec<(Span, String)>)> { | |
140 | let mut assignments = Vec::new(); | |
141 | ||
142 | for expr in exprs { | |
143 | let ty = cx.typeck_results().expr_ty(expr); | |
144 | ||
145 | if ty.is_never() { | |
146 | continue; | |
147 | } | |
148 | if !ty.is_unit() { | |
149 | return None; | |
150 | } | |
151 | ||
152 | let assign = LocalAssign::new(cx, expr, binding_id)?; | |
153 | ||
154 | assignments.push(assign); | |
155 | } | |
156 | ||
157 | let suggestions = assignments | |
158 | .iter() | |
159 | .map(|assignment| Some((assignment.span.until(assignment.rhs_span), String::new()))) | |
160 | .chain(assignments.iter().map(|assignment| { | |
161 | Some(( | |
162 | assignment.rhs_span.shrink_to_hi().with_hi(assignment.span.hi()), | |
163 | String::new(), | |
164 | )) | |
165 | })) | |
166 | .collect::<Option<Vec<(Span, String)>>>()?; | |
167 | ||
168 | let applicability = if suggestions.len() > 1 { | |
169 | // multiple suggestions don't work with rustfix in multipart_suggest | |
170 | // https://github.com/rust-lang/rustfix/issues/141 | |
171 | Applicability::Unspecified | |
172 | } else { | |
173 | Applicability::MachineApplicable | |
174 | }; | |
175 | Some((applicability, suggestions)) | |
176 | } | |
177 | ||
178 | struct Usage<'tcx> { | |
179 | stmt: &'tcx Stmt<'tcx>, | |
180 | expr: &'tcx Expr<'tcx>, | |
181 | needs_semi: bool, | |
182 | } | |
183 | ||
184 | fn first_usage<'tcx>( | |
185 | cx: &LateContext<'tcx>, | |
186 | binding_id: HirId, | |
187 | local_stmt_id: HirId, | |
188 | block: &'tcx Block<'tcx>, | |
189 | ) -> Option<Usage<'tcx>> { | |
190 | block | |
191 | .stmts | |
192 | .iter() | |
193 | .skip_while(|stmt| stmt.hir_id != local_stmt_id) | |
194 | .skip(1) | |
195 | .find(|&stmt| is_local_used(cx, stmt, binding_id)) | |
196 | .and_then(|stmt| match stmt.kind { | |
197 | StmtKind::Expr(expr) => Some(Usage { | |
198 | stmt, | |
199 | expr, | |
200 | needs_semi: true, | |
201 | }), | |
202 | StmtKind::Semi(expr) => Some(Usage { | |
203 | stmt, | |
204 | expr, | |
205 | needs_semi: false, | |
206 | }), | |
207 | _ => None, | |
208 | }) | |
209 | } | |
210 | ||
211 | fn local_snippet_without_semicolon(cx: &LateContext<'_>, local: &Local<'_>) -> Option<String> { | |
212 | let span = local.span.with_hi(match local.ty { | |
213 | // let <pat>: <ty>; | |
214 | // ~~~~~~~~~~~~~~~ | |
215 | Some(ty) => ty.span.hi(), | |
216 | // let <pat>; | |
217 | // ~~~~~~~~~ | |
218 | None => local.pat.span.hi(), | |
219 | }); | |
220 | ||
221 | snippet_opt(cx, span) | |
222 | } | |
223 | ||
224 | fn check<'tcx>( | |
225 | cx: &LateContext<'tcx>, | |
226 | local: &'tcx Local<'tcx>, | |
227 | local_stmt: &'tcx Stmt<'tcx>, | |
228 | block: &'tcx Block<'tcx>, | |
229 | binding_id: HirId, | |
230 | ) -> Option<()> { | |
231 | let usage = first_usage(cx, binding_id, local_stmt.hir_id, block)?; | |
232 | let binding_name = cx.tcx.hir().opt_name(binding_id)?; | |
233 | let let_snippet = local_snippet_without_semicolon(cx, local)?; | |
234 | ||
235 | match usage.expr.kind { | |
236 | ExprKind::Assign(..) => { | |
237 | let assign = LocalAssign::new(cx, usage.expr, binding_id)?; | |
238 | ||
239 | span_lint_and_then( | |
240 | cx, | |
241 | NEEDLESS_LATE_INIT, | |
242 | local_stmt.span, | |
243 | "unneeded late initalization", | |
244 | |diag| { | |
245 | diag.tool_only_span_suggestion( | |
246 | local_stmt.span, | |
247 | "remove the local", | |
248 | String::new(), | |
249 | Applicability::MachineApplicable, | |
250 | ); | |
251 | ||
252 | diag.span_suggestion( | |
253 | assign.lhs_span, | |
254 | &format!("declare `{}` here", binding_name), | |
255 | let_snippet, | |
256 | Applicability::MachineApplicable, | |
257 | ); | |
258 | }, | |
259 | ); | |
260 | }, | |
261 | ExprKind::If(_, then_expr, Some(else_expr)) => { | |
262 | let (applicability, suggestions) = assignment_suggestions(cx, binding_id, [then_expr, else_expr])?; | |
263 | ||
264 | span_lint_and_then( | |
265 | cx, | |
266 | NEEDLESS_LATE_INIT, | |
267 | local_stmt.span, | |
268 | "unneeded late initalization", | |
269 | |diag| { | |
270 | diag.tool_only_span_suggestion(local_stmt.span, "remove the local", String::new(), applicability); | |
271 | ||
272 | diag.span_suggestion_verbose( | |
273 | usage.stmt.span.shrink_to_lo(), | |
274 | &format!("declare `{}` here", binding_name), | |
275 | format!("{} = ", let_snippet), | |
276 | applicability, | |
277 | ); | |
278 | ||
279 | diag.multipart_suggestion("remove the assignments from the branches", suggestions, applicability); | |
280 | ||
281 | if usage.needs_semi { | |
282 | diag.span_suggestion( | |
283 | usage.stmt.span.shrink_to_hi(), | |
284 | "add a semicolon after the `if` expression", | |
285 | ";".to_string(), | |
286 | applicability, | |
287 | ); | |
288 | } | |
289 | }, | |
290 | ); | |
291 | }, | |
292 | ExprKind::Match(_, arms, MatchSource::Normal) => { | |
293 | let (applicability, suggestions) = assignment_suggestions(cx, binding_id, arms.iter().map(|arm| arm.body))?; | |
294 | ||
295 | span_lint_and_then( | |
296 | cx, | |
297 | NEEDLESS_LATE_INIT, | |
298 | local_stmt.span, | |
299 | "unneeded late initalization", | |
300 | |diag| { | |
301 | diag.tool_only_span_suggestion(local_stmt.span, "remove the local", String::new(), applicability); | |
302 | ||
303 | diag.span_suggestion_verbose( | |
304 | usage.stmt.span.shrink_to_lo(), | |
305 | &format!("declare `{}` here", binding_name), | |
306 | format!("{} = ", let_snippet), | |
307 | applicability, | |
308 | ); | |
309 | ||
310 | diag.multipart_suggestion( | |
311 | "remove the assignments from the `match` arms", | |
312 | suggestions, | |
313 | applicability, | |
314 | ); | |
315 | ||
316 | if usage.needs_semi { | |
317 | diag.span_suggestion( | |
318 | usage.stmt.span.shrink_to_hi(), | |
319 | "add a semicolon after the `match` expression", | |
320 | ";".to_string(), | |
321 | applicability, | |
322 | ); | |
323 | } | |
324 | }, | |
325 | ); | |
326 | }, | |
327 | _ => {}, | |
328 | }; | |
329 | ||
330 | Some(()) | |
331 | } | |
332 | ||
333 | impl LateLintPass<'tcx> for NeedlessLateInit { | |
334 | fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'tcx>) { | |
335 | let mut parents = cx.tcx.hir().parent_iter(local.hir_id); | |
336 | ||
337 | if_chain! { | |
338 | if let Local { | |
339 | init: None, | |
340 | pat: &Pat { | |
341 | kind: PatKind::Binding(_, binding_id, _, None), | |
342 | .. | |
343 | }, | |
344 | source: LocalSource::Normal, | |
345 | .. | |
346 | } = local; | |
347 | if let Some((_, Node::Stmt(local_stmt))) = parents.next(); | |
348 | if let Some((_, Node::Block(block))) = parents.next(); | |
349 | ||
350 | then { | |
351 | check(cx, local, local_stmt, block, binding_id); | |
352 | } | |
353 | } | |
354 | } | |
355 | } |