rust-clippy/clippy_lints/src/unwrap.rs

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use crate::utils::{
differing_macro_contexts, higher::if_block, is_type_diagnostic_item, span_lint_and_then,
usage::is_potentially_mutated,
};
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use if_chain::if_chain;
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use rustc_hir::intravisit::{walk_expr, walk_fn, FnKind, NestedVisitorMap, Visitor};
use rustc_hir::{BinOpKind, Body, Expr, ExprKind, FnDecl, HirId, Path, QPath, UnOp};
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use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::hir::map::Map;
use rustc_middle::lint::in_external_macro;
use rustc_middle::ty::Ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
declare_clippy_lint! {
/// **What it does:** Checks for calls of `unwrap[_err]()` that cannot fail.
///
/// **Why is this bad?** Using `if let` or `match` is more idiomatic.
///
/// **Known problems:** None
///
/// **Example:**
/// ```rust
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/// # let option = Some(0);
/// # fn do_something_with(_x: usize) {}
/// if option.is_some() {
/// do_something_with(option.unwrap())
/// }
/// ```
///
/// Could be written:
///
/// ```rust
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/// # let option = Some(0);
/// # fn do_something_with(_x: usize) {}
/// if let Some(value) = option {
/// do_something_with(value)
/// }
/// ```
pub UNNECESSARY_UNWRAP,
complexity,
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"checks for calls of `unwrap[_err]()` that cannot fail"
}
declare_clippy_lint! {
/// **What it does:** Checks for calls of `unwrap[_err]()` that will always fail.
///
/// **Why is this bad?** If panicking is desired, an explicit `panic!()` should be used.
///
/// **Known problems:** This lint only checks `if` conditions not assignments.
/// So something like `let x: Option<()> = None; x.unwrap();` will not be recognized.
///
/// **Example:**
/// ```rust
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/// # let option = Some(0);
/// # fn do_something_with(_x: usize) {}
/// if option.is_none() {
/// do_something_with(option.unwrap())
/// }
/// ```
///
/// This code will always panic. The if condition should probably be inverted.
pub PANICKING_UNWRAP,
correctness,
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"checks for calls of `unwrap[_err]()` that will always fail"
}
/// Visitor that keeps track of which variables are unwrappable.
struct UnwrappableVariablesVisitor<'a, 'tcx> {
unwrappables: Vec<UnwrapInfo<'tcx>>,
cx: &'a LateContext<'tcx>,
}
/// Contains information about whether a variable can be unwrapped.
#[derive(Copy, Clone, Debug)]
struct UnwrapInfo<'tcx> {
/// The variable that is checked
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ident: &'tcx Path<'tcx>,
/// The check, like `x.is_ok()`
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check: &'tcx Expr<'tcx>,
/// The branch where the check takes place, like `if x.is_ok() { .. }`
branch: &'tcx Expr<'tcx>,
/// Whether `is_some()` or `is_ok()` was called (as opposed to `is_err()` or `is_none()`).
safe_to_unwrap: bool,
}
/// Collects the information about unwrappable variables from an if condition
/// The `invert` argument tells us whether the condition is negated.
fn collect_unwrap_info<'tcx>(
cx: &LateContext<'tcx>,
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expr: &'tcx Expr<'_>,
branch: &'tcx Expr<'_>,
invert: bool,
) -> Vec<UnwrapInfo<'tcx>> {
fn is_relevant_option_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
is_type_diagnostic_item(cx, ty, sym!(option_type)) && ["is_some", "is_none"].contains(&method_name)
}
fn is_relevant_result_call(cx: &LateContext<'_>, ty: Ty<'_>, method_name: &str) -> bool {
is_type_diagnostic_item(cx, ty, sym!(result_type)) && ["is_ok", "is_err"].contains(&method_name)
}
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if let ExprKind::Binary(op, left, right) = &expr.kind {
match (invert, op.node) {
(false, BinOpKind::And | BinOpKind::BitAnd) | (true, BinOpKind::Or | BinOpKind::BitOr) => {
let mut unwrap_info = collect_unwrap_info(cx, left, branch, invert);
unwrap_info.append(&mut collect_unwrap_info(cx, right, branch, invert));
return unwrap_info;
},
_ => (),
}
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} else if let ExprKind::Unary(UnOp::UnNot, expr) = &expr.kind {
return collect_unwrap_info(cx, expr, branch, !invert);
} else {
if_chain! {
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if let ExprKind::MethodCall(method_name, _, args, _) = &expr.kind;
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if let ExprKind::Path(QPath::Resolved(None, path)) = &args[0].kind;
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let ty = cx.typeck_results().expr_ty(&args[0]);
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let name = method_name.ident.as_str();
if is_relevant_option_call(cx, ty, &name) || is_relevant_result_call(cx, ty, &name);
then {
assert!(args.len() == 1);
let unwrappable = match name.as_ref() {
"is_some" | "is_ok" => true,
"is_err" | "is_none" => false,
_ => unreachable!(),
};
let safe_to_unwrap = unwrappable != invert;
return vec![UnwrapInfo { ident: path, check: expr, branch, safe_to_unwrap }];
}
}
}
Vec::new()
}
impl<'a, 'tcx> UnwrappableVariablesVisitor<'a, 'tcx> {
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fn visit_branch(&mut self, cond: &'tcx Expr<'_>, branch: &'tcx Expr<'_>, else_branch: bool) {
let prev_len = self.unwrappables.len();
for unwrap_info in collect_unwrap_info(self.cx, cond, branch, else_branch) {
if is_potentially_mutated(unwrap_info.ident, cond, self.cx)
|| is_potentially_mutated(unwrap_info.ident, branch, self.cx)
{
// if the variable is mutated, we don't know whether it can be unwrapped:
continue;
}
self.unwrappables.push(unwrap_info);
}
walk_expr(self, branch);
self.unwrappables.truncate(prev_len);
}
}
impl<'a, 'tcx> Visitor<'tcx> for UnwrappableVariablesVisitor<'a, 'tcx> {
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type Map = Map<'tcx>;
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fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
// Shouldn't lint when `expr` is in macro.
if in_external_macro(self.cx.tcx.sess, expr.span) {
return;
}
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if let Some((cond, then, els)) = if_block(&expr) {
walk_expr(self, cond);
self.visit_branch(cond, then, false);
if let Some(els) = els {
self.visit_branch(cond, els, true);
}
} else {
// find `unwrap[_err]()` calls:
if_chain! {
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if let ExprKind::MethodCall(ref method_name, _, ref args, _) = expr.kind;
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if let ExprKind::Path(QPath::Resolved(None, ref path)) = args[0].kind;
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if [sym!(unwrap), sym!(unwrap_err)].contains(&method_name.ident.name);
let call_to_unwrap = method_name.ident.name == sym!(unwrap);
if let Some(unwrappable) = self.unwrappables.iter()
.find(|u| u.ident.res == path.res);
// Span contexts should not differ with the conditional branch
if !differing_macro_contexts(unwrappable.branch.span, expr.span);
if !differing_macro_contexts(unwrappable.branch.span, unwrappable.check.span);
then {
if call_to_unwrap == unwrappable.safe_to_unwrap {
span_lint_and_then(
self.cx,
UNNECESSARY_UNWRAP,
expr.span,
&format!("you checked before that `{}()` cannot fail. \
Instead of checking and unwrapping, it's better to use `if let` or `match`",
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method_name.ident.name),
|diag| { diag.span_label(unwrappable.check.span, "the check is happening here"); },
);
} else {
span_lint_and_then(
self.cx,
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PANICKING_UNWRAP,
expr.span,
&format!("this call to `{}()` will always panic",
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method_name.ident.name),
|diag| { diag.span_label(unwrappable.check.span, "because of this check"); },
);
}
}
}
walk_expr(self, expr);
}
}
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
}
}
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declare_lint_pass!(Unwrap => [PANICKING_UNWRAP, UNNECESSARY_UNWRAP]);
impl<'tcx> LateLintPass<'tcx> for Unwrap {
fn check_fn(
&mut self,
cx: &LateContext<'tcx>,
kind: FnKind<'tcx>,
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decl: &'tcx FnDecl<'_>,
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body: &'tcx Body<'_>,
span: Span,
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fn_id: HirId,
) {
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if span.from_expansion() {
return;
}
let mut v = UnwrappableVariablesVisitor {
cx,
unwrappables: Vec::new(),
};
walk_fn(&mut v, kind, decl, body.id(), span, fn_id);
}
}