rust-clippy/clippy_lints/src/fallible_impl_from.rs

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use crate::utils::paths::{BEGIN_PANIC, BEGIN_PANIC_FMT, FROM_TRAIT, OPTION, RESULT};
use crate::utils::{is_expn_of, method_chain_args, span_lint_and_then, walk_ptrs_ty};
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use if_chain::if_chain;
use rustc::hir;
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
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use rustc::ty::{self, Ty};
use rustc::{declare_tool_lint, lint_array};
use syntax_pos::Span;
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declare_clippy_lint! {
/// **What it does:** Checks for impls of `From<..>` that contain `panic!()` or `unwrap()`
///
/// **Why is this bad?** `TryFrom` should be used if there's a possibility of failure.
///
/// **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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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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}
fn name(&self) -> &'static str {
"FallibleImpleFrom"
}
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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 ..`
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let impl_def_id = cx.tcx.hir().local_def_id_from_hir_id(item.hir_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 cx.match_def_path(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 rustc::hir::intravisit::{self, NestedVisitorMap, Visitor};
use rustc::hir::*;
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struct FindPanicUnwrap<'a, 'tcx: 'a> {
lcx: &'a LateContext<'a, 'tcx>,
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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) = path.def.opt_def_id();
if self.lcx.match_def_path(path_def_id, &BEGIN_PANIC) ||
self.lcx.match_def_path(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]));
if match_type(self.lcx, reciever_ty, &OPTION) || match_type(self.lcx, 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);
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let impl_item_def_id = cx.tcx.hir().local_def_id_from_hir_id(impl_item.id.hir_id);
let mut fpu = FindPanicUnwrap {
lcx: cx,
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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}
}
fn match_type(cx: &LateContext<'_, '_>, ty: Ty<'_>, path: &[&str]) -> bool {
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match ty.sty {
ty::Adt(adt, _) => cx.match_def_path(adt.did, path),
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_ => false,
}
}