2 differing_macro_contexts, higher::if_block, is_type_diagnostic_item, span_lint_and_then,
3 usage::is_potentially_mutated,
5 use if_chain::if_chain;
6 use rustc_hir::intravisit::{walk_expr, walk_fn, FnKind, NestedVisitorMap, Visitor};
7 use rustc_hir::{BinOpKind, Body, Expr, ExprKind, FnDecl, HirId, Path, QPath, UnOp};
8 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_middle::hir::map::Map;
10 use rustc_middle::lint::in_external_macro;
11 use rustc_middle::ty::Ty;
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 use rustc_span::source_map::Span;
16 declare_clippy_lint! {
17 /// **What it does:** Checks for calls of `unwrap[_err]()` that cannot fail.
19 /// **Why is this bad?** Using `if let` or `match` is more idiomatic.
21 /// **Known problems:** None
25 /// # let option = Some(0);
26 /// # fn do_something_with(_x: usize) {}
27 /// if option.is_some() {
28 /// do_something_with(option.unwrap())
35 /// # let option = Some(0);
36 /// # fn do_something_with(_x: usize) {}
37 /// if let Some(value) = option {
38 /// do_something_with(value)
41 pub UNNECESSARY_UNWRAP,
43 "checks for calls of `unwrap[_err]()` that cannot fail"
46 declare_clippy_lint! {
47 /// **What it does:** Checks for calls of `unwrap[_err]()` that will always fail.
49 /// **Why is this bad?** If panicking is desired, an explicit `panic!()` should be used.
51 /// **Known problems:** This lint only checks `if` conditions not assignments.
52 /// So something like `let x: Option<()> = None; x.unwrap();` will not be recognized.
56 /// # let option = Some(0);
57 /// # fn do_something_with(_x: usize) {}
58 /// if option.is_none() {
59 /// do_something_with(option.unwrap())
63 /// This code will always panic. The if condition should probably be inverted.
66 "checks for calls of `unwrap[_err]()` that will always fail"
69 /// Visitor that keeps track of which variables are unwrappable.
70 struct UnwrappableVariablesVisitor<'a, 'tcx> {
71 unwrappables: Vec<UnwrapInfo<'tcx>>,
72 cx: &'a LateContext<'tcx>,
74 /// Contains information about whether a variable can be unwrapped.
75 #[derive(Copy, Clone, Debug)]
76 struct UnwrapInfo<'tcx> {
77 /// The variable that is checked
78 ident: &'tcx Path<'tcx>,
79 /// The check, like `x.is_ok()`
80 check: &'tcx Expr<'tcx>,
81 /// The branch where the check takes place, like `if x.is_ok() { .. }`
82 branch: &'tcx Expr<'tcx>,
83 /// Whether `is_some()` or `is_ok()` was called (as opposed to `is_err()` or `is_none()`).
87 /// Collects the information about unwrappable variables from an if condition
88 /// The `invert` argument tells us whether the condition is negated.
89 fn collect_unwrap_info<'tcx>(
90 cx: &LateContext<'tcx>,
92 branch: &'tcx Expr<'_>,
94 ) -> Vec<UnwrapInfo<'tcx>> {
95 fn is_relevant_option_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
96 is_type_diagnostic_item(cx, ty, sym::option_type) && ["is_some", "is_none"].contains(&method_name)
99 fn is_relevant_result_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
100 is_type_diagnostic_item(cx, ty, sym::result_type) && ["is_ok", "is_err"].contains(&method_name)
103 if let ExprKind::Binary(op, left, right) = &expr.kind {
104 match (invert, op.node) {
105 (false, BinOpKind::And | BinOpKind::BitAnd) | (true, BinOpKind::Or | BinOpKind::BitOr) => {
106 let mut unwrap_info = collect_unwrap_info(cx, left, branch, invert);
107 unwrap_info.append(&mut collect_unwrap_info(cx, right, branch, invert));
112 } else if let ExprKind::Unary(UnOp::UnNot, expr) = &expr.kind {
113 return collect_unwrap_info(cx, expr, branch, !invert);
116 if let ExprKind::MethodCall(method_name, _, args, _) = &expr.kind;
117 if let ExprKind::Path(QPath::Resolved(None, path)) = &args[0].kind;
118 let ty = cx.typeck_results().expr_ty(&args[0]);
119 let name = method_name.ident.as_str();
120 if is_relevant_option_call(cx, ty, &name) || is_relevant_result_call(cx, ty, &name);
122 assert!(args.len() == 1);
123 let unwrappable = match name.as_ref() {
124 "is_some" | "is_ok" => true,
125 "is_err" | "is_none" => false,
128 let safe_to_unwrap = unwrappable != invert;
129 return vec![UnwrapInfo { ident: path, check: expr, branch, safe_to_unwrap }];
136 impl<'a, 'tcx> UnwrappableVariablesVisitor<'a, 'tcx> {
137 fn visit_branch(&mut self, cond: &'tcx Expr<'_>, branch: &'tcx Expr<'_>, else_branch: bool) {
138 let prev_len = self.unwrappables.len();
139 for unwrap_info in collect_unwrap_info(self.cx, cond, branch, else_branch) {
140 if is_potentially_mutated(unwrap_info.ident, cond, self.cx)
141 || is_potentially_mutated(unwrap_info.ident, branch, self.cx)
143 // if the variable is mutated, we don't know whether it can be unwrapped:
146 self.unwrappables.push(unwrap_info);
148 walk_expr(self, branch);
149 self.unwrappables.truncate(prev_len);
153 impl<'a, 'tcx> Visitor<'tcx> for UnwrappableVariablesVisitor<'a, 'tcx> {
154 type Map = Map<'tcx>;
156 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
157 // Shouldn't lint when `expr` is in macro.
158 if in_external_macro(self.cx.tcx.sess, expr.span) {
161 if let Some((cond, then, els)) = if_block(&expr) {
162 walk_expr(self, cond);
163 self.visit_branch(cond, then, false);
164 if let Some(els) = els {
165 self.visit_branch(cond, els, true);
168 // find `unwrap[_err]()` calls:
170 if let ExprKind::MethodCall(ref method_name, _, ref args, _) = expr.kind;
171 if let ExprKind::Path(QPath::Resolved(None, ref path)) = args[0].kind;
172 if [sym::unwrap, sym!(unwrap_err)].contains(&method_name.ident.name);
173 let call_to_unwrap = method_name.ident.name == sym::unwrap;
174 if let Some(unwrappable) = self.unwrappables.iter()
175 .find(|u| u.ident.res == path.res);
176 // Span contexts should not differ with the conditional branch
177 if !differing_macro_contexts(unwrappable.branch.span, expr.span);
178 if !differing_macro_contexts(unwrappable.branch.span, unwrappable.check.span);
180 if call_to_unwrap == unwrappable.safe_to_unwrap {
185 &format!("you checked before that `{}()` cannot fail, \
186 instead of checking and unwrapping, it's better to use `if let` or `match`",
187 method_name.ident.name),
188 |diag| { diag.span_label(unwrappable.check.span, "the check is happening here"); },
195 &format!("this call to `{}()` will always panic",
196 method_name.ident.name),
197 |diag| { diag.span_label(unwrappable.check.span, "because of this check"); },
202 walk_expr(self, expr);
206 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
207 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
211 declare_lint_pass!(Unwrap => [PANICKING_UNWRAP, UNNECESSARY_UNWRAP]);
213 impl<'tcx> LateLintPass<'tcx> for Unwrap {
216 cx: &LateContext<'tcx>,
218 decl: &'tcx FnDecl<'_>,
219 body: &'tcx Body<'_>,
223 if span.from_expansion() {
227 let mut v = UnwrappableVariablesVisitor {
229 unwrappables: Vec::new(),
232 walk_fn(&mut v, kind, decl, body.id(), span, fn_id);