rust-clippy/clippy_lints/src/fallible_impl_from.rs

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// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use crate::rustc::hir;
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use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use crate::rustc::ty;
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use crate::rustc::{declare_tool_lint, lint_array};
use crate::syntax_pos::Span;
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use crate::utils::paths::{BEGIN_PANIC, BEGIN_PANIC_FMT, FROM_TRAIT, OPTION, RESULT};
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use crate::utils::{is_expn_of, match_def_path, method_chain_args, opt_def_id, span_lint_and_then, walk_ptrs_ty};
use if_chain::if_chain;
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/// **What it does:** Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
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///
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/// **Why is this bad?** `TryFrom` should be used if there's a possibility of failure.
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///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// struct Foo(i32);
/// impl From<String> for Foo {
/// fn from(s: String) -> Self {
/// Foo(s.parse().unwrap())
/// }
/// }
/// ```
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declare_clippy_lint! {
pub FALLIBLE_IMPL_FROM,
nursery,
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"Warn on impls of `From<..>` that contain `panic!()` or `unwrap()`"
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}
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pub struct FallibleImplFrom;
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impl LintPass for FallibleImplFrom {
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fn get_lints(&self) -> LintArray {
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lint_array!(FALLIBLE_IMPL_FROM)
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}
}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for FallibleImplFrom {
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fn check_item(&mut self, cx: &LateContext<'a, 'tcx>, item: &'tcx hir::Item) {
// check for `impl From<???> for ..`
let impl_def_id = cx.tcx.hir.local_def_id(item.id);
if_chain! {
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if let hir::ItemKind::Impl(.., ref impl_items) = item.node;
if let Some(impl_trait_ref) = cx.tcx.impl_trait_ref(impl_def_id);
if match_def_path(cx.tcx, impl_trait_ref.def_id, &FROM_TRAIT);
then {
lint_impl_body(cx, item.span, impl_items);
}
}
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}
}
fn lint_impl_body<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, impl_span: Span, impl_items: &hir::HirVec<hir::ImplItemRef>) {
use crate::rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
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use crate::rustc::hir::*;
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struct FindPanicUnwrap<'a, 'tcx: 'a> {
tcx: ty::TyCtxt<'a, 'tcx, 'tcx>,
tables: &'tcx ty::TypeckTables<'tcx>,
result: Vec<Span>,
}
impl<'a, 'tcx: 'a> Visitor<'tcx> for FindPanicUnwrap<'a, 'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr) {
// check for `begin_panic`
if_chain! {
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if let ExprKind::Call(ref func_expr, _) = expr.node;
if let ExprKind::Path(QPath::Resolved(_, ref path)) = func_expr.node;
if let Some(path_def_id) = opt_def_id(path.def);
if match_def_path(self.tcx, path_def_id, &BEGIN_PANIC) ||
match_def_path(self.tcx, path_def_id, &BEGIN_PANIC_FMT);
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if is_expn_of(expr.span, "unreachable").is_none();
then {
self.result.push(expr.span);
}
}
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// check for `unwrap`
if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
let reciever_ty = walk_ptrs_ty(self.tables.expr_ty(&arglists[0][0]));
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if match_type(self.tcx, reciever_ty, &OPTION) || match_type(self.tcx, reciever_ty, &RESULT) {
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self.result.push(expr.span);
}
}
// and check sub-expressions
intravisit::walk_expr(self, expr);
}
fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
NestedVisitorMap::None
}
}
for impl_item in impl_items {
if_chain! {
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if impl_item.ident.name == "from";
if let ImplItemKind::Method(_, body_id) =
cx.tcx.hir.impl_item(impl_item.id).node;
then {
// check the body for `begin_panic` or `unwrap`
let body = cx.tcx.hir.body(body_id);
let impl_item_def_id = cx.tcx.hir.local_def_id(impl_item.id.node_id);
let mut fpu = FindPanicUnwrap {
tcx: cx.tcx,
tables: cx.tcx.typeck_tables_of(impl_item_def_id),
result: Vec::new(),
};
fpu.visit_expr(&body.value);
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// if we've found one, lint
if !fpu.result.is_empty() {
span_lint_and_then(
cx,
FALLIBLE_IMPL_FROM,
impl_span,
"consider implementing `TryFrom` instead",
move |db| {
db.help(
"`From` is intended for infallible conversions only. \
Use `TryFrom` if there's a possibility for the conversion to fail.");
db.span_note(fpu.result, "potential failure(s)");
});
}
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}
}
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}
}
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fn match_type(tcx: ty::TyCtxt<'_, '_, '_>, ty: ty::Ty<'_>, path: &[&str]) -> bool {
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match ty.sty {
ty::Adt(adt, _) => match_def_path(tcx, adt.did, path),
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_ => false,
}
}