clippy_lints/src/fallible_impl_from.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10
  11 use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  12 use crate::rustc::{declare_tool_lint, lint_array};
  13 use if_chain::if_chain;
  14 use crate::rustc::hir;
  15 use crate::rustc::ty;
  16 use crate::syntax_pos::Span;
  17 use crate::utils::{match_def_path, method_chain_args, span_lint_and_then, walk_ptrs_ty, is_expn_of, opt_def_id};
  18 use crate::utils::paths::{BEGIN_PANIC, BEGIN_PANIC_FMT, FROM_TRAIT, OPTION, RESULT};
  19
  20 /// **What it does:** Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
  21 ///
  22 /// **Why is this bad?** `TryFrom` should be used if there's a possibility of failure.
  23 ///
  24 /// **Known problems:** None.
  25 ///
  26 /// **Example:**
  27 /// ```rust
  28 /// struct Foo(i32);
  29 /// impl From<String> for Foo {
  30 ///     fn from(s: String) -> Self {
  31 ///         Foo(s.parse().unwrap())
  32 ///     }
  33 /// }
  34 /// ```
  35 declare_clippy_lint! {
  36     pub FALLIBLE_IMPL_FROM,
  37     nursery,
  38     "Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
  39 }
  40
  41 pub struct FallibleImplFrom;
  42
  43 impl LintPass for FallibleImplFrom {
  44     fn get_lints(&self) -> LintArray {
  45         lint_array!(FALLIBLE_IMPL_FROM)
  46     }
  47 }
  48
  49 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FallibleImplFrom {
  50     fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
  51         // check for `impl From<???> for ..`
  52         let impl_def_id = cx.tcx.hir.local_def_id(item.id);
  53         if_chain! {
  54             if let hir::ItemKind::Impl(.., ref impl_items) = item.node;
  55             if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id);
  56             if match_def_path(cx.tcx, impl_trait_ref.def_id, &FROM_TRAIT);
  57             then {
  58                 lint_impl_body(cx, item.span, impl_items);
  59             }
  60         }
  61     }
  62 }
  63
  64 fn lint_impl_body<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, impl_span: Span, impl_items: &hir::HirVec<hir::ImplItemRef>) {
  65     use crate::rustc::hir::*;
  66     use crate::rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
  67
  68     struct FindPanicUnwrap<'a, 'tcx: 'a> {
  69         tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
  70         tables: &'tcx ty::TypeckTables<'tcx>,
  71         result: Vec<Span>,
  72     }
  73
  74     impl<'a, 'tcx: 'a> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
  75         fn visit_expr(&mut self, expr: &'tcx Expr) {
  76             // check for `begin_panic`
  77             if_chain! {
  78                 if let ExprKind::Call(ref func_expr, _) = expr.node;
  79                 if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.node;
  80                 if let Some(path_def_id) = opt_def_id(path.def);
  81                 if match_def_path(self.tcx, path_def_id, &BEGIN_PANIC) ||
  82                     match_def_path(self.tcx, path_def_id, &BEGIN_PANIC_FMT);
  83                 if is_expn_of(expr.span, "unreachable").is_none();
  84                 then {
  85                     self.result.push(expr.span);
  86                 }
  87             }
  88
  89             // check for `unwrap`
  90             if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
  91                 let reciever_ty = walk_ptrs_ty(self.tables.expr_ty(&arglists[0][0]));
  92                 if match_type(self.tcx, reciever_ty, &OPTION) || match_type(self.tcx, reciever_ty, &RESULT) {
  93                     self.result.push(expr.span);
  94                 }
  95             }
  96
  97             // and check sub-expressions
  98             intravisit::walk_expr(self, expr);
  99         }
 100
 101         fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
 102             NestedVisitorMap::None
 103         }
 104     }
 105
 106     for impl_item in impl_items {
 107         if_chain! {
 108             if impl_item.ident.name == "from";
 109             if let ImplItemKind::Method(_, body_id) =
 110                 cx.tcx.hir.impl_item(impl_item.id).node;
 111             then {
 112                 // check the body for `begin_panic` or `unwrap`
 113                 let body = cx.tcx.hir.body(body_id);
 114                 let impl_item_def_id = cx.tcx.hir.local_def_id(impl_item.id.node_id);
 115                 let mut fpu = FindPanicUnwrap {
 116                     tcx: cx.tcx,
 117                     tables: cx.tcx.typeck_tables_of(impl_item_def_id),
 118                     result: Vec::new(),
 119                 };
 120                 fpu.visit_expr(&body.value);
 121
 122                 // if we've found one, lint
 123                 if !fpu.result.is_empty() {
 124                     span_lint_and_then(
 125                         cx,
 126                         FALLIBLE_IMPL_FROM,
 127                         impl_span,
 128                         "consider implementing `TryFrom` instead",
 129                         move |db| {
 130                             db.help(
 131                                 "`From` is intended for infallible conversions only. \
 132                                  Use `TryFrom` if there's a possibility for the conversion to fail.");
 133                             db.span_note(fpu.result, "potential failure(s)");
 134                         });
 135                 }
 136             }
 137         }
 138     }
 139 }
 140
 141 fn match_type(tcx: ty::TyCtxt<'_, '_, '_>, ty: ty::Ty<'_>, path: &[&str]) -> bool {
 142     match ty.sty {
 143         ty::Adt(adt, _) => match_def_path(tcx, adt.did, path),
 144         _ => false,
 145     }
 146 }