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1 | use crate::utils::{ |
2 | any_parent_is_automatically_derived, contains_name, match_def_path, paths, snippet_with_macro_callsite, | |
3 | }; | |
4 | use crate::utils::{span_lint_and_note, span_lint_and_sugg}; | |
5 | use if_chain::if_chain; | |
6 | use rustc_data_structures::fx::FxHashSet; | |
7 | use rustc_errors::Applicability; | |
8 | use rustc_hir::def::Res; | |
9 | use rustc_hir::{Block, Expr, ExprKind, PatKind, QPath, Stmt, StmtKind}; | |
10 | use rustc_lint::{LateContext, LateLintPass}; | |
11 | use rustc_middle::lint::in_external_macro; | |
12 | use rustc_middle::ty; | |
13 | use rustc_session::{declare_tool_lint, impl_lint_pass}; | |
14 | use rustc_span::symbol::{Ident, Symbol}; | |
15 | use rustc_span::Span; | |
16 | ||
17 | declare_clippy_lint! { | |
18 | /// **What it does:** Checks for literal calls to `Default::default()`. | |
19 | /// | |
20 | /// **Why is this bad?** It's more clear to the reader to use the name of the type whose default is | |
21 | /// being gotten than the generic `Default`. | |
22 | /// | |
23 | /// **Known problems:** None. | |
24 | /// | |
25 | /// **Example:** | |
26 | /// ```rust | |
27 | /// // Bad | |
28 | /// let s: String = Default::default(); | |
29 | /// | |
30 | /// // Good | |
31 | /// let s = String::default(); | |
32 | /// ``` | |
33 | pub DEFAULT_TRAIT_ACCESS, | |
34 | pedantic, | |
35 | "checks for literal calls to `Default::default()`" | |
36 | } | |
37 | ||
38 | declare_clippy_lint! { | |
39 | /// **What it does:** Checks for immediate reassignment of fields initialized | |
40 | /// with Default::default(). | |
41 | /// | |
42 | /// **Why is this bad?**It's more idiomatic to use the [functional update syntax](https://doc.rust-lang.org/reference/expressions/struct-expr.html#functional-update-syntax). | |
43 | /// | |
44 | /// **Known problems:** Assignments to patterns that are of tuple type are not linted. | |
45 | /// | |
46 | /// **Example:** | |
47 | /// Bad: | |
48 | /// ``` | |
49 | /// # #[derive(Default)] | |
50 | /// # struct A { i: i32 } | |
51 | /// let mut a: A = Default::default(); | |
52 | /// a.i = 42; | |
53 | /// ``` | |
54 | /// Use instead: | |
55 | /// ``` | |
56 | /// # #[derive(Default)] | |
57 | /// # struct A { i: i32 } | |
58 | /// let a = A { | |
59 | /// i: 42, | |
60 | /// .. Default::default() | |
61 | /// }; | |
62 | /// ``` | |
63 | pub FIELD_REASSIGN_WITH_DEFAULT, | |
64 | style, | |
65 | "binding initialized with Default should have its fields set in the initializer" | |
66 | } | |
67 | ||
68 | #[derive(Default)] | |
69 | pub struct Default { | |
70 | // Spans linted by `field_reassign_with_default`. | |
71 | reassigned_linted: FxHashSet<Span>, | |
72 | } | |
73 | ||
74 | impl_lint_pass!(Default => [DEFAULT_TRAIT_ACCESS, FIELD_REASSIGN_WITH_DEFAULT]); | |
75 | ||
76 | impl LateLintPass<'_> for Default { | |
77 | fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) { | |
78 | if_chain! { | |
79 | // Avoid cases already linted by `field_reassign_with_default` | |
80 | if !self.reassigned_linted.contains(&expr.span); | |
81 | if let ExprKind::Call(ref path, ..) = expr.kind; | |
82 | if !any_parent_is_automatically_derived(cx.tcx, expr.hir_id); | |
83 | if let ExprKind::Path(ref qpath) = path.kind; | |
84 | if let Some(def_id) = cx.qpath_res(qpath, path.hir_id).opt_def_id(); | |
85 | if match_def_path(cx, def_id, &paths::DEFAULT_TRAIT_METHOD); | |
86 | // Detect and ignore <Foo as Default>::default() because these calls do explicitly name the type. | |
87 | if let QPath::Resolved(None, _path) = qpath; | |
88 | then { | |
89 | let expr_ty = cx.typeck_results().expr_ty(expr); | |
90 | if let ty::Adt(def, ..) = expr_ty.kind() { | |
91 | // TODO: Work out a way to put "whatever the imported way of referencing | |
92 | // this type in this file" rather than a fully-qualified type. | |
93 | let replacement = format!("{}::default()", cx.tcx.def_path_str(def.did)); | |
94 | span_lint_and_sugg( | |
95 | cx, | |
96 | DEFAULT_TRAIT_ACCESS, | |
97 | expr.span, | |
98 | &format!("calling `{}` is more clear than this expression", replacement), | |
99 | "try", | |
100 | replacement, | |
101 | Applicability::Unspecified, // First resolve the TODO above | |
102 | ); | |
103 | } | |
104 | } | |
105 | } | |
106 | } | |
107 | ||
108 | fn check_block<'tcx>(&mut self, cx: &LateContext<'tcx>, block: &Block<'tcx>) { | |
109 | // start from the `let mut _ = _::default();` and look at all the following | |
110 | // statements, see if they re-assign the fields of the binding | |
111 | let stmts_head = match block.stmts { | |
112 | // Skip the last statement since there cannot possibly be any following statements that re-assign fields. | |
113 | [head @ .., _] if !head.is_empty() => head, | |
114 | _ => return, | |
115 | }; | |
116 | for (stmt_idx, stmt) in stmts_head.iter().enumerate() { | |
117 | // find all binding statements like `let mut _ = T::default()` where `T::default()` is the | |
118 | // `default` method of the `Default` trait, and store statement index in current block being | |
119 | // checked and the name of the bound variable | |
120 | let (local, variant, binding_name, binding_type, span) = if_chain! { | |
121 | // only take `let ...` statements | |
122 | if let StmtKind::Local(local) = stmt.kind; | |
123 | if let Some(expr) = local.init; | |
124 | if !any_parent_is_automatically_derived(cx.tcx, expr.hir_id); | |
125 | if !in_external_macro(cx.tcx.sess, expr.span); | |
126 | // only take bindings to identifiers | |
127 | if let PatKind::Binding(_, binding_id, ident, _) = local.pat.kind; | |
128 | // only when assigning `... = Default::default()` | |
129 | if is_expr_default(expr, cx); | |
130 | let binding_type = cx.typeck_results().node_type(binding_id); | |
131 | if let Some(adt) = binding_type.ty_adt_def(); | |
132 | if adt.is_struct(); | |
133 | let variant = adt.non_enum_variant(); | |
134 | if adt.did.is_local() || !variant.is_field_list_non_exhaustive(); | |
135 | let module_did = cx.tcx.parent_module(stmt.hir_id).to_def_id(); | |
136 | if variant | |
137 | .fields | |
138 | .iter() | |
139 | .all(|field| field.vis.is_accessible_from(module_did, cx.tcx)); | |
140 | then { | |
141 | (local, variant, ident.name, binding_type, expr.span) | |
142 | } else { | |
143 | continue; | |
144 | } | |
145 | }; | |
146 | ||
147 | // find all "later statement"'s where the fields of the binding set as | |
148 | // Default::default() get reassigned, unless the reassignment refers to the original binding | |
149 | let mut first_assign = None; | |
150 | let mut assigned_fields = Vec::new(); | |
151 | let mut cancel_lint = false; | |
152 | for consecutive_statement in &block.stmts[stmt_idx + 1..] { | |
153 | // find out if and which field was set by this `consecutive_statement` | |
154 | if let Some((field_ident, assign_rhs)) = field_reassigned_by_stmt(consecutive_statement, binding_name) { | |
155 | // interrupt and cancel lint if assign_rhs references the original binding | |
156 | if contains_name(binding_name, assign_rhs) { | |
157 | cancel_lint = true; | |
158 | break; | |
159 | } | |
160 | ||
161 | // if the field was previously assigned, replace the assignment, otherwise insert the assignment | |
162 | if let Some(prev) = assigned_fields | |
163 | .iter_mut() | |
164 | .find(|(field_name, _)| field_name == &field_ident.name) | |
165 | { | |
166 | *prev = (field_ident.name, assign_rhs); | |
167 | } else { | |
168 | assigned_fields.push((field_ident.name, assign_rhs)); | |
169 | } | |
170 | ||
171 | // also set first instance of error for help message | |
172 | if first_assign.is_none() { | |
173 | first_assign = Some(consecutive_statement); | |
174 | } | |
175 | } | |
176 | // interrupt if no field was assigned, since we only want to look at consecutive statements | |
177 | else { | |
178 | break; | |
179 | } | |
180 | } | |
181 | ||
182 | // if there are incorrectly assigned fields, do a span_lint_and_note to suggest | |
183 | // construction using `Ty { fields, ..Default::default() }` | |
184 | if !assigned_fields.is_empty() && !cancel_lint { | |
185 | // if all fields of the struct are not assigned, add `.. Default::default()` to the suggestion. | |
186 | let ext_with_default = !variant | |
187 | .fields | |
188 | .iter() | |
189 | .all(|field| assigned_fields.iter().any(|(a, _)| a == &field.ident.name)); | |
190 | ||
191 | let field_list = assigned_fields | |
192 | .into_iter() | |
193 | .map(|(field, rhs)| { | |
194 | // extract and store the assigned value for help message | |
195 | let value_snippet = snippet_with_macro_callsite(cx, rhs.span, ".."); | |
196 | format!("{}: {}", field, value_snippet) | |
197 | }) | |
198 | .collect::<Vec<String>>() | |
199 | .join(", "); | |
200 | ||
201 | let sugg = if ext_with_default { | |
202 | if field_list.is_empty() { | |
203 | format!("{}::default()", binding_type) | |
204 | } else { | |
205 | format!("{} {{ {}, ..Default::default() }}", binding_type, field_list) | |
206 | } | |
207 | } else { | |
208 | format!("{} {{ {} }}", binding_type, field_list) | |
209 | }; | |
210 | ||
211 | // span lint once per statement that binds default | |
212 | span_lint_and_note( | |
213 | cx, | |
214 | FIELD_REASSIGN_WITH_DEFAULT, | |
215 | first_assign.unwrap().span, | |
216 | "field assignment outside of initializer for an instance created with Default::default()", | |
217 | Some(local.span), | |
218 | &format!( | |
219 | "consider initializing the variable with `{}` and removing relevant reassignments", | |
220 | sugg | |
221 | ), | |
222 | ); | |
223 | self.reassigned_linted.insert(span); | |
224 | } | |
225 | } | |
226 | } | |
227 | } | |
228 | ||
229 | /// Checks if the given expression is the `default` method belonging to the `Default` trait. | |
230 | fn is_expr_default<'tcx>(expr: &'tcx Expr<'tcx>, cx: &LateContext<'tcx>) -> bool { | |
231 | if_chain! { | |
232 | if let ExprKind::Call(ref fn_expr, _) = &expr.kind; | |
233 | if let ExprKind::Path(qpath) = &fn_expr.kind; | |
234 | if let Res::Def(_, def_id) = cx.qpath_res(qpath, fn_expr.hir_id); | |
235 | then { | |
236 | // right hand side of assignment is `Default::default` | |
237 | match_def_path(cx, def_id, &paths::DEFAULT_TRAIT_METHOD) | |
238 | } else { | |
239 | false | |
240 | } | |
241 | } | |
242 | } | |
243 | ||
244 | /// Returns the reassigned field and the assigning expression (right-hand side of assign). | |
245 | fn field_reassigned_by_stmt<'tcx>(this: &Stmt<'tcx>, binding_name: Symbol) -> Option<(Ident, &'tcx Expr<'tcx>)> { | |
246 | if_chain! { | |
247 | // only take assignments | |
248 | if let StmtKind::Semi(ref later_expr) = this.kind; | |
249 | if let ExprKind::Assign(ref assign_lhs, ref assign_rhs, _) = later_expr.kind; | |
250 | // only take assignments to fields where the left-hand side field is a field of | |
251 | // the same binding as the previous statement | |
252 | if let ExprKind::Field(ref binding, field_ident) = assign_lhs.kind; | |
253 | if let ExprKind::Path(QPath::Resolved(_, path)) = binding.kind; | |
254 | if let Some(second_binding_name) = path.segments.last(); | |
255 | if second_binding_name.ident.name == binding_name; | |
256 | then { | |
257 | Some((field_ident, assign_rhs)) | |
258 | } else { | |
259 | None | |
260 | } | |
261 | } | |
262 | } |