1 use clippy_utils::diagnostics::span_lint_and_then;
2 use clippy_utils::higher;
3 use clippy_utils::ty::is_type_diagnostic_item;
4 use clippy_utils::{differing_macro_contexts, 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! {
18 /// Checks for calls of `unwrap[_err]()` that cannot fail.
20 /// ### Why is this bad?
21 /// Using `if let` or `match` is more idiomatic.
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! {
48 /// Checks for calls of `unwrap[_err]()` that will always fail.
50 /// ### Why is this bad?
51 /// If panicking is desired, an explicit `panic!()` should be used.
53 /// ### Known problems
54 /// This lint only checks `if` conditions not assignments.
55 /// So something like `let x: Option<()> = None; x.unwrap();` will not be recognized.
59 /// # let option = Some(0);
60 /// # fn do_something_with(_x: usize) {}
61 /// if option.is_none() {
62 /// do_something_with(option.unwrap())
66 /// This code will always panic. The if condition should probably be inverted.
69 "checks for calls of `unwrap[_err]()` that will always fail"
72 /// Visitor that keeps track of which variables are unwrappable.
73 struct UnwrappableVariablesVisitor<'a, 'tcx> {
74 unwrappables: Vec<UnwrapInfo<'tcx>>,
75 cx: &'a LateContext<'tcx>,
77 /// Contains information about whether a variable can be unwrapped.
78 #[derive(Copy, Clone, Debug)]
79 struct UnwrapInfo<'tcx> {
80 /// The variable that is checked
81 ident: &'tcx Path<'tcx>,
82 /// The check, like `x.is_ok()`
83 check: &'tcx Expr<'tcx>,
84 /// The branch where the check takes place, like `if x.is_ok() { .. }`
85 branch: &'tcx Expr<'tcx>,
86 /// Whether `is_some()` or `is_ok()` was called (as opposed to `is_err()` or `is_none()`).
90 /// Collects the information about unwrappable variables from an if condition
91 /// The `invert` argument tells us whether the condition is negated.
92 fn collect_unwrap_info<'tcx>(
93 cx: &LateContext<'tcx>,
95 branch: &'tcx Expr<'_>,
97 ) -> Vec<UnwrapInfo<'tcx>> {
98 fn is_relevant_option_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
99 is_type_diagnostic_item(cx, ty, sym::option_type) && ["is_some", "is_none"].contains(&method_name)
102 fn is_relevant_result_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
103 is_type_diagnostic_item(cx, ty, sym::result_type) && ["is_ok", "is_err"].contains(&method_name)
106 if let ExprKind::Binary(op, left, right) = &expr.kind {
107 match (invert, op.node) {
108 (false, BinOpKind::And | BinOpKind::BitAnd) | (true, BinOpKind::Or | BinOpKind::BitOr) => {
109 let mut unwrap_info = collect_unwrap_info(cx, left, branch, invert);
110 unwrap_info.append(&mut collect_unwrap_info(cx, right, branch, invert));
115 } else if let ExprKind::Unary(UnOp::Not, expr) = &expr.kind {
116 return collect_unwrap_info(cx, expr, branch, !invert);
119 if let ExprKind::MethodCall(method_name, _, args, _) = &expr.kind;
120 if let ExprKind::Path(QPath::Resolved(None, path)) = &args[0].kind;
121 let ty = cx.typeck_results().expr_ty(&args[0]);
122 let name = method_name.ident.as_str();
123 if is_relevant_option_call(cx, ty, &name) || is_relevant_result_call(cx, ty, &name);
125 assert!(args.len() == 1);
126 let unwrappable = match name.as_ref() {
127 "is_some" | "is_ok" => true,
128 "is_err" | "is_none" => false,
131 let safe_to_unwrap = unwrappable != invert;
132 return vec![UnwrapInfo { ident: path, check: expr, branch, safe_to_unwrap }];
139 impl<'a, 'tcx> UnwrappableVariablesVisitor<'a, 'tcx> {
140 fn visit_branch(&mut self, cond: &'tcx Expr<'_>, branch: &'tcx Expr<'_>, else_branch: bool) {
141 let prev_len = self.unwrappables.len();
142 for unwrap_info in collect_unwrap_info(self.cx, cond, branch, else_branch) {
143 if is_potentially_mutated(unwrap_info.ident, cond, self.cx)
144 || is_potentially_mutated(unwrap_info.ident, branch, self.cx)
146 // if the variable is mutated, we don't know whether it can be unwrapped:
149 self.unwrappables.push(unwrap_info);
151 walk_expr(self, branch);
152 self.unwrappables.truncate(prev_len);
156 impl<'a, 'tcx> Visitor<'tcx> for UnwrappableVariablesVisitor<'a, 'tcx> {
157 type Map = Map<'tcx>;
159 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
160 // Shouldn't lint when `expr` is in macro.
161 if in_external_macro(self.cx.tcx.sess, expr.span) {
164 if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr) {
165 walk_expr(self, cond);
166 self.visit_branch(cond, then, false);
167 if let Some(else_inner) = r#else {
168 self.visit_branch(cond, else_inner, true);
171 // find `unwrap[_err]()` calls:
173 if let ExprKind::MethodCall(method_name, _, args, _) = expr.kind;
174 if let ExprKind::Path(QPath::Resolved(None, path)) = args[0].kind;
175 if [sym::unwrap, sym!(unwrap_err)].contains(&method_name.ident.name);
176 let call_to_unwrap = method_name.ident.name == sym::unwrap;
177 if let Some(unwrappable) = self.unwrappables.iter()
178 .find(|u| u.ident.res == path.res);
179 // Span contexts should not differ with the conditional branch
180 if !differing_macro_contexts(unwrappable.branch.span, expr.span);
181 if !differing_macro_contexts(unwrappable.branch.span, unwrappable.check.span);
183 if call_to_unwrap == unwrappable.safe_to_unwrap {
188 &format!("you checked before that `{}()` cannot fail, \
189 instead of checking and unwrapping, it's better to use `if let` or `match`",
190 method_name.ident.name),
191 |diag| { diag.span_label(unwrappable.check.span, "the check is happening here"); },
198 &format!("this call to `{}()` will always panic",
199 method_name.ident.name),
200 |diag| { diag.span_label(unwrappable.check.span, "because of this check"); },
205 walk_expr(self, expr);
209 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
210 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
214 declare_lint_pass!(Unwrap => [PANICKING_UNWRAP, UNNECESSARY_UNWRAP]);
216 impl<'tcx> LateLintPass<'tcx> for Unwrap {
219 cx: &LateContext<'tcx>,
221 decl: &'tcx FnDecl<'_>,
222 body: &'tcx Body<'_>,
226 if span.from_expansion() {
230 let mut v = UnwrappableVariablesVisitor {
232 unwrappables: Vec::new(),
235 walk_fn(&mut v, kind, decl, body.id(), span, fn_id);