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[rustc.git] / src / tools / clippy / clippy_lints / src / fallible_impl_from.rs
1 use rustc::lint::*;
2 use rustc::hir;
3 use rustc::ty;
4 use syntax_pos::Span;
5 use utils::{match_def_path, method_chain_args, span_lint_and_then, walk_ptrs_ty};
6 use utils::paths::{BEGIN_PANIC, BEGIN_PANIC_FMT, FROM_TRAIT, OPTION, RESULT};
7
8 /// **What it does:** Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
9 ///
10 /// **Why is this bad?** `TryFrom` should be used if there's a possibility of failure.
11 ///
12 /// **Known problems:** None.
13 ///
14 /// **Example:**
15 /// ```rust
16 /// struct Foo(i32);
17 /// impl From<String> for Foo {
18 /// fn from(s: String) -> Self {
19 /// Foo(s.parse().unwrap())
20 /// }
21 /// }
22 /// ```
23 declare_lint! {
24 pub FALLIBLE_IMPL_FROM, Allow,
25 "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
26 }
27
28 pub struct FallibleImplFrom;
29
30 impl LintPass for FallibleImplFrom {
31 fn get_lints(&self) -> LintArray {
32 lint_array!(FALLIBLE_IMPL_FROM)
33 }
34 }
35
36 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FallibleImplFrom {
37 fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
38 // check for `impl From<???> for ..`
39 let impl_def_id = cx.tcx.hir.local_def_id(item.id);
40 if_chain! {
41 if let hir::ItemImpl(.., ref impl_items) = item.node;
42 if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id);
43 if match_def_path(cx.tcx, impl_trait_ref.def_id, &FROM_TRAIT);
44 then {
45 lint_impl_body(cx, item.span, impl_items);
46 }
47 }
48 }
49 }
50
51 fn lint_impl_body<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, impl_span: Span, impl_items: &hir::HirVec<hir::ImplItemRef>) {
52 use rustc::hir::*;
53 use rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
54
55 struct FindPanicUnwrap<'a, 'tcx: 'a> {
56 tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
57 tables: &'tcx ty::TypeckTables<'tcx>,
58 result: Vec<Span>,
59 }
60
61 impl<'a, 'tcx: 'a> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
62 fn visit_expr(&mut self, expr: &'tcx Expr) {
63 // check for `begin_panic`
64 if_chain! {
65 if let ExprCall(ref func_expr, _) = expr.node;
66 if let ExprPath(QPath::Resolved(_, ref path)) = func_expr.node;
67 if match_def_path(self.tcx, path.def.def_id(), &BEGIN_PANIC) ||
68 match_def_path(self.tcx, path.def.def_id(), &BEGIN_PANIC_FMT);
69 then {
70 self.result.push(expr.span);
71 }
72 }
73
74 // check for `unwrap`
75 if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
76 let reciever_ty = walk_ptrs_ty(self.tables.expr_ty(&arglists[0][0]));
77 if match_type(self.tcx, reciever_ty, &OPTION) || match_type(self.tcx, reciever_ty, &RESULT) {
78 self.result.push(expr.span);
79 }
80 }
81
82 // and check sub-expressions
83 intravisit::walk_expr(self, expr);
84 }
85
86 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
87 NestedVisitorMap::None
88 }
89 }
90
91 for impl_item in impl_items {
92 if_chain! {
93 if impl_item.name == "from";
94 if let ImplItemKind::Method(_, body_id) =
95 cx.tcx.hir.impl_item(impl_item.id).node;
96 then {
97 // check the body for `begin_panic` or `unwrap`
98 let body = cx.tcx.hir.body(body_id);
99 let impl_item_def_id = cx.tcx.hir.local_def_id(impl_item.id.node_id);
100 let mut fpu = FindPanicUnwrap {
101 tcx: cx.tcx,
102 tables: cx.tcx.typeck_tables_of(impl_item_def_id),
103 result: Vec::new(),
104 };
105 fpu.visit_expr(&body.value);
106
107 // if we've found one, lint
108 if !fpu.result.is_empty() {
109 span_lint_and_then(
110 cx,
111 FALLIBLE_IMPL_FROM,
112 impl_span,
113 "consider implementing `TryFrom` instead",
114 move |db| {
115 db.help(
116 "`From` is intended for infallible conversions only. \
117 Use `TryFrom` if there's a possibility for the conversion to fail.");
118 db.span_note(fpu.result, "potential failure(s)");
119 });
120 }
121 }
122 }
123 }
124 }
125
126 fn match_type(tcx: ty::TyCtxt, ty: ty::Ty, path: &[&str]) -> bool {
127 match ty.sty {
128 ty::TyAdt(adt, _) => match_def_path(tcx, adt.did, path),
129 _ => false,
130 }
131 }