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;
15 declare_clippy_lint! {
16 /// **What it does:** Checks for calls of `unwrap[_err]()` that cannot fail.
18 /// **Why is this bad?** Using `if let` or `match` is more idiomatic.
20 /// **Known problems:** None
24 /// # let option = Some(0);
25 /// # fn do_something_with(_x: usize) {}
26 /// if option.is_some() {
27 /// do_something_with(option.unwrap())
34 /// # let option = Some(0);
35 /// # fn do_something_with(_x: usize) {}
36 /// if let Some(value) = option {
37 /// do_something_with(value)
40 pub UNNECESSARY_UNWRAP,
42 "checks for calls of `unwrap[_err]()` that cannot fail"
45 declare_clippy_lint! {
46 /// **What it does:** Checks for calls of `unwrap[_err]()` that will always fail.
48 /// **Why is this bad?** If panicking is desired, an explicit `panic!()` should be used.
50 /// **Known problems:** This lint only checks `if` conditions not assignments.
51 /// So something like `let x: Option<()> = None; x.unwrap();` will not be recognized.
55 /// # let option = Some(0);
56 /// # fn do_something_with(_x: usize) {}
57 /// if option.is_none() {
58 /// do_something_with(option.unwrap())
62 /// This code will always panic. The if condition should probably be inverted.
65 "checks for calls of `unwrap[_err]()` that will always fail"
68 /// Visitor that keeps track of which variables are unwrappable.
69 struct UnwrappableVariablesVisitor<'a, 'tcx> {
70 unwrappables: Vec<UnwrapInfo<'tcx>>,
71 cx: &'a LateContext<'tcx>,
73 /// Contains information about whether a variable can be unwrapped.
74 #[derive(Copy, Clone, Debug)]
75 struct UnwrapInfo<'tcx> {
76 /// The variable that is checked
77 ident: &'tcx Path<'tcx>,
78 /// The check, like `x.is_ok()`
79 check: &'tcx Expr<'tcx>,
80 /// The branch where the check takes place, like `if x.is_ok() { .. }`
81 branch: &'tcx Expr<'tcx>,
82 /// Whether `is_some()` or `is_ok()` was called (as opposed to `is_err()` or `is_none()`).
86 /// Collects the information about unwrappable variables from an if condition
87 /// The `invert` argument tells us whether the condition is negated.
88 fn collect_unwrap_info<'tcx>(
89 cx: &LateContext<'tcx>,
91 branch: &'tcx Expr<'_>,
93 ) -> Vec<UnwrapInfo<'tcx>> {
94 fn is_relevant_option_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
95 is_type_diagnostic_item(cx, ty, sym!(option_type)) && ["is_some", "is_none"].contains(&method_name)
98 fn is_relevant_result_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
99 is_type_diagnostic_item(cx, ty, sym!(result_type)) && ["is_ok", "is_err"].contains(&method_name)
102 if let ExprKind::Binary(op, left, right) = &expr.kind {
103 match (invert, op.node) {
104 (false, BinOpKind::And | BinOpKind::BitAnd) | (true, BinOpKind::Or | BinOpKind::BitOr) => {
105 let mut unwrap_info = collect_unwrap_info(cx, left, branch, invert);
106 unwrap_info.append(&mut collect_unwrap_info(cx, right, branch, invert));
111 } else if let ExprKind::Unary(UnOp::UnNot, expr) = &expr.kind {
112 return collect_unwrap_info(cx, expr, branch, !invert);
115 if let ExprKind::MethodCall(method_name, _, args, _) = &expr.kind;
116 if let ExprKind::Path(QPath::Resolved(None, path)) = &args[0].kind;
117 let ty = cx.typeck_results().expr_ty(&args[0]);
118 let name = method_name.ident.as_str();
119 if is_relevant_option_call(cx, ty, &name) || is_relevant_result_call(cx, ty, &name);
121 assert!(args.len() == 1);
122 let unwrappable = match name.as_ref() {
123 "is_some" | "is_ok" => true,
124 "is_err" | "is_none" => false,
127 let safe_to_unwrap = unwrappable != invert;
128 return vec![UnwrapInfo { ident: path, check: expr, branch, safe_to_unwrap }];
135 impl<'a, 'tcx> UnwrappableVariablesVisitor<'a, 'tcx> {
136 fn visit_branch(&mut self, cond: &'tcx Expr<'_>, branch: &'tcx Expr<'_>, else_branch: bool) {
137 let prev_len = self.unwrappables.len();
138 for unwrap_info in collect_unwrap_info(self.cx, cond, branch, else_branch) {
139 if is_potentially_mutated(unwrap_info.ident, cond, self.cx)
140 || is_potentially_mutated(unwrap_info.ident, branch, self.cx)
142 // if the variable is mutated, we don't know whether it can be unwrapped:
145 self.unwrappables.push(unwrap_info);
147 walk_expr(self, branch);
148 self.unwrappables.truncate(prev_len);
152 impl<'a, 'tcx> Visitor<'tcx> for UnwrappableVariablesVisitor<'a, 'tcx> {
153 type Map = Map<'tcx>;
155 fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
156 // Shouldn't lint when `expr` is in macro.
157 if in_external_macro(self.cx.tcx.sess, expr.span) {
160 if let Some((cond, then, els)) = if_block(&expr) {
161 walk_expr(self, cond);
162 self.visit_branch(cond, then, false);
163 if let Some(els) = els {
164 self.visit_branch(cond, els, true);
167 // find `unwrap[_err]()` calls:
169 if let ExprKind::MethodCall(ref method_name, _, ref args, _) = expr.kind;
170 if let ExprKind::Path(QPath::Resolved(None, ref path)) = args[0].kind;
171 if [sym!(unwrap), sym!(unwrap_err)].contains(&method_name.ident.name);
172 let call_to_unwrap = method_name.ident.name == sym!(unwrap);
173 if let Some(unwrappable) = self.unwrappables.iter()
174 .find(|u| u.ident.res == path.res);
175 // Span contexts should not differ with the conditional branch
176 if !differing_macro_contexts(unwrappable.branch.span, expr.span);
177 if !differing_macro_contexts(unwrappable.branch.span, unwrappable.check.span);
179 if call_to_unwrap == unwrappable.safe_to_unwrap {
184 &format!("You checked before that `{}()` cannot fail. \
185 Instead of checking and unwrapping, it's better to use `if let` or `match`.",
186 method_name.ident.name),
187 |diag| { diag.span_label(unwrappable.check.span, "the check is happening here"); },
194 &format!("This call to `{}()` will always panic.",
195 method_name.ident.name),
196 |diag| { diag.span_label(unwrappable.check.span, "because of this check"); },
201 walk_expr(self, expr);
205 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
206 NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
210 declare_lint_pass!(Unwrap => [PANICKING_UNWRAP, UNNECESSARY_UNWRAP]);
212 impl<'tcx> LateLintPass<'tcx> for Unwrap {
215 cx: &LateContext<'tcx>,
217 decl: &'tcx FnDecl<'_>,
218 body: &'tcx Body<'_>,
222 if span.from_expansion() {
226 let mut v = UnwrappableVariablesVisitor {
228 unwrappables: Vec::new(),
231 walk_fn(&mut v, kind, decl, body.id(), span, fn_id);